UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 6-K
REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16
OR 15d-16
UNDER THE SECURITIES EXCHANGE ACT OF 1934
For the month of February 2015
Commission File No. 001-32210
NORTHERN DYNASTY MINERALS LTD.
(Translation of registrant's name into English)
15th Floor – 1040 West Georgia Street
Vancouver, British Columbia, V6E 4H8, Canada
(Address of principal executive offices)
Indicate by check mark whether the registrant files or will
file annual reports under cover Form 20-F or Form 40-F.
Form 20-F [ ] Form 40-F [X]
Indicate by check mark if the registrant is submitting the Form
6-K in paper as permitted by Regulation S-T Rule 101(b)(1): [ ]
Indicate by check mark if the registrant is submitting the
Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): [ ]
Information Concerning Estimates of Measured, Indicated and Inferred Resources
The technical report being furnished herewith as Exhibit 99.1 uses the terms “measured resources”, "indicated resources" and "inferred resources". Northern Dynasty Minerals Ltd. advises investors that although these terms are recognized and required by Canadian regulations (under National Instrument 43-101 Standards of Disclosure for Mineral Projects), the U.S. Securities and Exchange Commission does not recognize them. Investors are cautioned not to assume that any part or all of the mineral deposits in these categories will ever be converted into reserves. In addition, "inferred resources" have a great amount of uncertainty as to their existence, and economic and legal feasibility. It cannot be assumed that all or any part of an inferred resource will ever be upgraded to a higher category. Under Canadian rules, estimates of inferred resources may not form the basis of feasibility or pre-feasibility studies, or economic studies except for Preliminary Economic Assessment as defined under 43-101. Investors are cautioned not to assume that part or all of an inferred resource exists, or is economically or legally mineable.
SUBMITTED HEREWITH
Exhibits
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99.1 |
2014 Technical Report On The Pebble Project, Southwest Alaska, effective date December 31, 2014 |
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99.2 |
Consent under NI 43-101 of Qualified Person – J. David Gaunt, P.Geo., B.C. |
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99.3 |
Consent under NI 43-101 of Qualified Person – James R. Lang, Ph.D., P.Geo., B.C. |
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99.4 |
Consent under NI 43-101 of Qualified Person – Eric D. Titley, P.Geo., B.C. |
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99.5 |
Consent under NI 43-101 of Qualified Person – Ting Lu, P.Eng., M.Sc., B.C. |
SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.
NORTHERN DYNASTY MINERALS LTD. |
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Date: February 11, 2015 |
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/s/ Ronald Thiessen |
_____________________________ |
Ronald Thiessen |
President and CEO |
2014 TECHNICAL REPORT
ON THE
PEBBLE PROJECT, SOUTHWEST ALASKA,
USA
NORTHERN DYNASTY MINERALS LTD.
Effective Date December 31, 2014
Qualified Persons
J. David Gaunt, PGeo.
James Lang,
PGeo.
Eric Titley, PGeo.
Ting Lu, PEng.
Forward Looking Information and Other Cautionary Factors
This technical report includes certain statements that may be
deemed "forward-looking statements". All statements in this technical report,
other than statements of historical facts, in particular metal price assumptions
and especially those that address or estimated resource quantities, grades and
contained metals are forward-looking statements because they are generally made
on the basis of estimation and extrapolation from a limited number of drill
holes and metallurgical studies. Although diamond drill hole core provides
valuable information about the size, shape and geology of an exploration
project, there will always remain a significant degree of uncertainty in
connection with these valuation factors until a deposit has been extensively
drilled on closely spaced centers, which has occurred only in specific areas on
the Pebble Project. Although the Company believes the expectations expressed in
its forward-looking statements are based on reasonable assumptions, such
statements should not be in any way construed as guarantees of the ultimate
size, quality or commercial feasibility of the Pebble Project or of the
Company's future performance. Assumptions used by the Company to develop
forward-looking statements include the following: the Pebble Project will obtain
all required environmental and other permits and all land use and other
licenses, studies and development of the Pebble Project will continue to be
positive, and no geological or technical problems will occur. The likelihood of
future mining at the Pebble Project is subject to a large number of risks and
will require achievement of a number of technical, economic and legal
objectives, including obtaining necessary mining and construction permits,
approvals, licenses and title on a timely basis and delays due to third party
opposition, changes in government policies regarding mining and natural resource
exploration and exploitation, the final outcome of any litigation, completion of
pre-feasibility and final feasibility studies, preparation of all necessary
engineering for open pit and underground workings and processing facilities as
well as receipt of significant additional financing to fund these objectives as
well as funding mine construction. Such funding may not be available to the
Company on acceptable terms or on any terms at all. There is no known ore at the
Pebble Project and there is no assurance that the mineralization at the Pebble
Project will ever be classified as ore. The need for compliance with extensive
environmental and socio-economic rules and practices and the requirement for the
Company to obtain government permitting can cause a delay or even abandonment of
a mineral project. The Company is also subject to the specific risks inherent in
the mining business as well as general economic and business conditions. For
more information on the Company, Investors should review the Company's annual
Form 40-F filing with the United States Securities and Exchange Commission and
its home jurisdiction filings that are available at www.sedar.com.
T A B
L E O F C O N T E N T S |
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LIST OF FIGURES
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Figure
12.1.3 |
Performance
of the Gold Standard CGS-16 in 2008 |
83
|
Figure
12.1.4 |
Comparison
of Gold Duplicate Assay Results for 2004 to 2010 |
85
|
Figure
12.1.5 |
Comparison
of Copper Duplicate Assay Results for 2004 to 2010 |
85
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Figure
13.1.1 |
Testwork
Programs and Reports 2008 to 2010 |
92
|
Figure
13.1.2 |
Subsequent
Testwork Programs and Reports, 2011 to 2013 |
93
|
Figure
13.3.1 |
Bond
Low-Energy Impact Test Results, SGS January 2012 |
98
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Figure
13.3.2 |
JK
Tech/SMC Data Comparison SGS January 2012** |
99
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Figure
13.3.3 |
Pebble
West Rod Mill Data Comparison, SGS January 2012** |
99
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Figure
13.3.4 |
Pebble
West Ball Mill Data Comparison, SGS January 2012** |
100
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Figure
13.3.5 |
MacPherson
Autogenous Grindability Test Results, SGS January 2012 |
100
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Figure
13.4.1 |
Basic
Testwork Flowsheet, SGS 2011 |
103
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Figure
13.4.2 |
Summary
of Locked-Cycle Test Variability Test Results |
103
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Figure
13.4.3 |
Locked-Cycle
Test Results of Bulk Samples, SGS 2012 |
105
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Figure
13.4.4 |
Basic
Testwork Flowsheet, SGS 2011 |
107
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Figure
13.4.5 |
Locked-Cycle
Test Results of Molybdenum Flotation, SGS 2011-2012 |
109
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Figure
13.4.6 |
Molybdenum
Recovery, G&T 2011 |
110
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Figure
13.4.7 |
Pyrite
Flotation Kinetics Test Results |
111
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Figure
13.5.1 |
Bulk
Gold Extraction Kinetics, SGS 2012 |
112
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Figure
13.8.1 |
Rhenium
Grade and Recovery Relationship SGS 2012 |
114
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Figure
13.9.1 |
Projected
Metallurgical Recoveries |
115
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Figure
14.1.1 |
Pebble
Deposit Mineral Resource Estimate 2014 |
116
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Figure
14.2.1 |
Pebble
Deposit Assay Database Descriptive Global Statistics |
117
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Figure
14.2.2 |
Pebble
Deposit Plan View of Drill Holes and Block Model Extent (red rectangle)
|
118
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Figure
14.2.3 |
Pebble
Deposit Metal Domains |
119
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Figure
14.2.4 |
Pebble
Deposit Copper Assay Domain Box-and-Whisker Plots |
120
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Figure
14.2.5 |
Pebble
Deposit Gold Assay Domain Box-and-Whisker Plots |
121
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Figure
14.2.6 |
Pebble
Deposit Molybdenum Assay Box-and-Whisker Plots |
122
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Figure
14.2.7 |
Pebble
Deposit Silver Assay Box-and-Whisker Plots |
123
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Figure
14.2.8 |
Pebble
Deposit Copper Grade Domains |
124
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Figure
14.2.9 |
Pebble
Deposit Capping Values |
125
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Figure
14.2.10 |
Pebble
Deposit Composite Mean Values |
125
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Figure
14.5.1 |
Pebble
Deposit Variogram Parameters |
127
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Figure
14.5.2 |
Pebble
Deposit Search Ellipse Parameters |
128
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Figure
14.6.1 |
Pebble
Deposit 2014 Block Model Parameters |
128
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UNIT MEASURES AND ABBREVIATIONS |
Above mean sea level |
amsl |
Acre |
ac |
Alaska Department of Environmental Conservation |
DEC |
Alaska Department of Fish and Game |
ADFG |
Alaska Department of Natural Resources |
ADNR |
Ampere |
A |
Annum (year) |
a |
Anadromous Waters Catalog |
AWC |
Acid Potential |
AP |
Acid Rock Drainage |
ARD |
Atomic absorption spectroscopy |
AAS |
Billion |
B |
Billion years ago |
Ga |
Brittle-ductile fault |
BDF |
Centimetre |
cm |
Carbon-In-Leach |
CIL |
Clean Water Act |
CWA |
Cubic centimetre |
cm3 |
Cubic feet per minute |
cfm |
Cubic feet per second |
ft3/s |
Cubic foot |
ft3 |
Cubic inch |
in3 |
Cubic metre |
m3 |
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Pebble Project, Southwest Alaska |
UNIT MEASURES AND ABBREVIATIONS |
Day |
d |
Days per week |
d/wk |
Days per year (annum) |
d/a |
Degree |
° |
Degrees Celsius |
°C |
Degrees Fahrenheit |
°F |
U.S. Environmental Protection Agency |
EPA |
Fire Assay |
FA |
Gram |
g |
Grams per litre |
g/L |
Grams per tonne |
g/t |
Gallons per minute |
GPM |
Greater than |
> |
Health, safety and environment |
HSE |
Hectare (10,000 m2) |
ha |
Horsepower |
hp |
Hours |
h |
Hours per day |
h/d |
Hours per week |
h/w |
Hours per year |
h/a |
Inch |
in |
Induced Polarization geophysics |
IP |
Inductively coupled plasma atomic emission spectroscopy |
ICP-AES |
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UNIT MEASURES AND ABBREVIATIONS |
Inductively coupled plasma mass spectrometry |
ICP-MS |
Kaskanak Creek |
KC |
Kilo (thousand) |
k |
Kilogram |
kg |
Kilograms per hour |
kg/h |
Kilograms per square metre |
kg/m2 |
Kilometre |
km |
Kilometres per hour |
km/h |
Kilopascal |
kPa |
Kilotonne |
kt |
Kilowatt |
kW |
Kilowatt hour |
kWh |
Kilowatt hours per tonne (metric ton) |
kWh/t |
Kilowatt hours per year |
kWh/a |
Less than |
< |
Litres |
L |
Litres per minute |
L/m |
Maximum potential acidity |
MPA |
Metal Leaching |
ML |
Metres |
m |
Metres above sea level |
masl |
Millions of years ago |
Ma |
Metric tonne |
t |
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UNIT MEASURES AND ABBREVIATIONS |
Microns |
µm |
Milligram |
mg |
Milligrams per litre |
mg/l |
Millilitre |
mL |
Millimetre |
mm |
Million |
M |
Million tonnes |
Mt |
Minute (plane angle) |
|
Minute (time) |
min |
Month |
mo |
National Environmental Policy Act |
NEPA |
Neutralizing Potential |
NP |
Neutralization potential ratio |
NPR |
North Fork Koktuli |
NFK |
Northern and Southern quartz vein domains |
NQV and SQV |
Ounce |
oz |
Parts per million |
ppm |
Parts per billion |
ppb |
Potentially acid generating |
PAG |
Percent |
% |
Pounds |
lb |
Pounds per square inch |
psi |
Pounds per ton |
lb/ton |
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UNIT MEASURES AND ABBREVIATIONS |
Quality Control/Quality Assurance |
QA/QC |
Qualified Person |
QP |
Quartz Sericite Pyrite |
QSP |
Revolutions per minute |
rpm |
Semi-autogenous grinding |
SAG |
Sulphidize, acidify, recycle and thicken |
SART |
Second (plane angle) |
|
Second (time) |
s |
Square |
cm2 |
Square foot |
ft2 |
Square inch |
in2 |
Square kilometre |
km2 |
Square metre |
m2 |
South Fork Koktuli |
SFK |
Three dimensional |
3D |
Three Dimensional Model |
3DM |
Tonnes |
t |
Thousand tonnes (1,000 kg) |
kt |
Tons (imperial) |
tons |
Total dissolved solids |
TDS |
Upper Talarik Creek |
UTC |
U.S. Army Corps of Engineers |
USACE |
Volt |
V |
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UNIT MEASURES AND ABBREVIATIONS |
Week |
wk |
Year (annum) |
a |
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Pebble Project, Southwest Alaska |
The Pebble deposit was originally discovered in 1989 and was
acquired by Northern Dynasty Minerals Ltd. (Northern Dynasty) in 2001. Since
that time, Northern Dynasty and subsequently the Pebble Limited Partnership (the
Pebble Partnership, in which Northern Dynasty currently owns a 100% interest)
have conducted significant mineral exploration, environmental baseline data
collection, and engineering work on the Pebble Project to advance it towards
development.
Work at Pebble has led to an overall expansion of the Pebble
deposit, as well as the discovery of several other mineralized occurrences along
an extensive northeast-trending mineralized system underlying the property. Over
1 million feet of drilling has been completed on the property, a large
proportion of which has been focused on the Pebble deposit. The previous
estimate of the mineral resources in the Pebble deposit was stated in a
technical report completed in 2011.
In light of more recent stakeholder and regulatory feedback,
Northern Dynasty initiated a comprehensive review of previous analyses of the
Pebble Project in late 2013 and in 2014 commissioned the current technical
report to update information on the mineral resources and metallurgy for the
project.
The Pebble Project is located in southwest Alaska,
approximately 200 miles southwest of Anchorage, 17 miles northwest of the
village of Iliamna, 160 miles northeast of Bristol Bay, and approximately 60
miles west of Cook Inlet (Figure 1.2.1) .
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Pebble Project, Southwest Alaska |
Figure
1.2.1 Property Location Map
Northern Dynasty holds, indirectly through wholly-owned
subsidiaries including Pebble Partnership, a 100% interest in a contiguous block
of 2,402 mineral claims covering approximately 417 square miles (Figure 1.2.1) .
This includes 1,718 claims covering 248.2 square miles (including the Pebble
deposit) held by Pebble Partnership subsidiaries Pebble East Claims Corporation
and Pebble West Claims Corporation; 464 claims covering an area of 116 square
miles held by Pebble Partnership subsidiary Kaskanak LLC Inc. (Kaskanak); and
220 claims covering 52.5 square miles held by Northern Dynasty subsidiary U5
Resources Inc.
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Pebble Project, Southwest Alaska |
Figure
1.3.1
Mineral Claim Map of the Pebble Project
1.4 |
GEOLOGICAL SETTING AND MINERALIZATION |
Pebble is a porphyry-style copper-gold-molybdenum-silver
deposit that comprises the Pebble East and Pebble West zones of approximately
equal size, with slightly lower-grade mineralization in the center of the
deposit where the two zones merge. The Pebble deposit is located at the
intersection of crustal-scale structures that are oriented both parallel and
obliquely to a magmatic arc which was active in the mid-Cretaceous age and which
developed in response to the northward subduction of the Pacific Plate beneath
the Wrangellia Superterrane.
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Pebble Project, Southwest Alaska |
The oldest rock within the Pebble district is the
Jurassic-Cretaceous age Kahlitna flysch, composed of turbiditic clastic
sedimentary rocks, interbedded basalt flows and associated gabbro intrusions.
During the mid-Cretaceous (99 to 96 Ma), the Kahlitna assemblage was intruded
first by approximately coeval granodiorite and diorite sills and slightly later
by alkalic monzonite intrusions. At approximately 90 Ma, hornblende diorite
porphyry plutons of the Kaskanak batholith were emplaced.
Copper-gold-molybdenum-silver mineralization is related to smaller granodiorite
plutons similar in composition to, and emplaced around the margins of, the
Kaskanak batholith.
The Pebble East and Pebble West zones are coeval hydrothermal
centers within a single magmatic-hydrothermal system. The movement of
mineralizing fluids was constrained by a broadly vertical fracture system acting
in conjunction with a hornfels aquitard that induced extensive lateral fluid
migration. The large size of the deposit, as well as variations in metal grade
and ratios, may be the result of multiple stages of metal introduction and
redistribution.
Mineralization in the Pebble West zone extends from surface to
approximately 3,000 ft depth and is centered on four small granodiorite plutons.
Mineralization is hosted by flysch, diorite and granodiorite sills, and alkalic
intrusions and breccias. The Pebble East zone is of higher grade and extends to
a depth of at least 5,810 ft; mineralization on the eastern side of the zone was
later dropped 1,970 to 2,950 ft by normal faults which bound the
northeast-trending East Graben. East zone mineralization is hosted by a
granodiorite pluton and adjacent granodiorite sills and flysch. The East and
West zone granodiorite plutons merge with depth.
Mineralization at Pebble is predominantly hypogene, although
the Pebble West zone contains a thin zone of variably developed supergene
mineralization overlain by a leached cap. Disseminated and vein-hosted
copper-gold-molybdenum-silver mineralization, dominated by chalcopyrite and
locally accompanied by bornite, is associated with early potassic alteration in
the shallow part of the Pebble East zone and with early sodic-potassic
alteration in the West zone and deeper portions of the Pebble East zone.
High-grade copper-gold mineralization is associated with younger advanced
argillic alteration that overprinted potassic and sodic-potassic alteration and
was controlled by a syn-hydrothermal, brittle-ductile fault zone located near
the eastern margin of the Pebble East zone. Late quartz veins introduced
additional molybdenum into several parts of the deposit.
The current resource estimate is based on approximately 59,000
assays obtained from 699 drill holes. The resource was estimated by ordinary
kriging and is presented in Figure 1.5.1. The tabulation is based on copper
equivalency (CuEq) that incorporates the contribution of copper, gold and
molybdenum. Although the estimate includes silver, it was not used as part of
the copper equivalency calculation in order to facilitate comparison with
previous estimates which did not consider the silver content or its potential
economic contribution. A base case cut-off of 0.3% CuEq is highlighted.
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Figure
1.5.1
Pebble Resource Estimate 2014
Threshold CuEq % |
CuEq% |
Tonnes |
Cu (%) |
Au (g/t) |
Mo (ppm) |
Ag (g/t) |
Cu Blbs |
Au Moz |
Mo Blbs |
Ag Moz |
Measured |
0.3 |
0.65 |
527,000,000 |
0.33 |
0.35 |
178 |
1.66 |
3.83 |
5.93 |
0.21 |
28.13 |
0.4 |
0.66 |
508,000,000 |
0.34 |
0.36 |
180 |
1.68 |
3.80 |
5.88 |
0.20 |
27.42 |
0.6 |
0.77 |
279,000,000 |
0.40 |
0.42 |
203 |
1.84 |
2.46 |
3.77 |
0.12 |
16.51 |
1.0 |
1.16 |
28,000,000 |
0.62 |
0.62 |
302 |
2.27 |
0.38 |
0.56 |
0.02 |
2.04 |
Indicated |
0.3 |
0.77 |
5,912,000,000 |
0.41 |
0.34 |
245 |
1.66 |
53.42 |
64.62 |
3.20 |
315.50 |
0.4 |
0.82 |
5,173,000,000 |
0.45 |
0.35 |
260 |
1.75 |
51.31 |
58.21 |
2.97 |
291.05 |
0.6 |
0.99 |
3,450,000,000 |
0.55 |
0.41 |
299 |
1.99 |
41.82 |
45.47 |
2.27 |
220.71 |
1.0 |
1.29 |
1,411,000,000 |
0.77 |
0.51 |
343 |
2.42 |
23.95 |
23.14 |
1.07 |
109.79 |
Measured + Indicated |
0.3 |
0.76 |
6,439,000,000 |
0.40 |
0.34 |
240 |
1.66 |
56.76 |
70.38 |
3.40 |
343.63 |
0.4 |
0.81 |
5,681,000,000 |
0.44 |
0.35 |
253 |
1.75 |
55.09 |
63.92 |
3.17 |
319.62 |
0.6 |
0.97 |
3,729,000,000 |
0.54 |
0.41 |
291 |
1.98 |
44.38 |
49.15 |
2.39 |
237.37 |
1.0 |
1.29 |
1,439,000,000 |
0.76 |
0.51 |
342 |
2.42 |
24.11 |
23.60 |
1.08 |
111.97 |
Inferred |
0.3 |
0.54 |
4,460,000,000 |
0.25 |
0.26 |
222 |
1.19 |
24.55 |
37.25 |
2.18 |
170.49 |
0.4 |
0.68 |
2,630,000,000 |
0.33 |
0.30 |
266 |
1.39 |
19.14 |
25.38 |
1.55 |
117.58 |
0.6 |
0.89 |
1,290,000,000 |
0.48 |
0.37 |
291 |
1.79 |
13.66 |
15.35 |
0.83 |
74.28 |
1.0 |
1.20 |
360,000,000 |
0.69 |
0.45 |
377 |
2.27 |
5.41 |
5.14 |
0.30 |
25.94 |
Notes:
These resource estimates have been prepared in accordance with
NI 43-101 and the CIM Definition Standards. Inferred mineral Resources are
considered to be too speculative to allow the application of technical and
economic parameters to support mine planning and evaluation of the economic
viability of the project. Under Canadian rules, estimates of Inferred Mineral
Resources may not form the basis of feasibility or pre-feasibility studies, or
economic studies except for Preliminary Economic Assessments as defined under
43-101. It cannot be assumed that all or any part of the Inferred resources will
ever be upgraded to a higher category.
Copper equivalent calculations use metal prices of $1.85/lb for
copper, $902/oz for gold and $12.50/lb for molybdenum, and recoveries of 85% for
copper 69.6% for gold, and 77.8% for molybdenum in the Pebble West zone and
89.3% for copper, 76.8% for gold, 83.7% for molybdenum in the Pebble East zone.
Contained metal calculations are based on 100% recoveries.
A 0.30% CuEQ cut-off is considered to be appropriate for
porphyry deposit open pit mining operations in the Americas. All mineral
resource estimates, cut-offs and metallurgical recoveries are subject to change
as a consequence of more detailed economic analyses that would be required in
pre-feasibility and feasibility studies.
1.6 |
MINERAL PROCESSING AND METALLURGICAL TESTING |
Metallurgical testwork for the Pebble Project was initiated by
Northern Dynasty in 2003 and continued under the direction of Northern Dynasty
until 2008. From 2008 to 2013, metallurgical testwork progressed under the
direction of the Pebble Partnership.
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Geometallurgical studies were initiated by the Pebble
Partnership in 2008, and continued through 2012. The principal objective of this
work was to quantify significant differences in metal deportment that may result
in variations in metal recoveries during mineral processing. The results of the
geometallurgical studies indicate that the deposit comprises several
geometallurgical (or material type) domains. These domains are defined by
distinct, internally consistent copper and gold deportment characteristics that
correspond spatially with changes in silicate alteration mineralogy.
Metallurgical testwork and associated analytical procedures
were performed by recognized testing facilities with extensive experience with
this analysis, with this type of deposit, and with the Pebble Project. The
samples selected for the comminution, copper/gold/molybdenum bulk flotation, and
copper molybdenum separation testing were representative of the various types
and styles of mineralization present at the Pebble deposit.
The test results on variability samples derived from the 103
lock cycle flotation tests indicate that marketable copper and molybdenum
concentrates can be produced with gold and silver contents that meet or exceed
payable levels in representative smelter contracts. Metal recoveries1
projected in the 2014 technical report are based on the locked-cycle test
(LCT) results of the variability samples, and associated gold leach testwork.
Figure 1.6.1 provides projected overall recoveries, which include the flotation
and gold plant recoveries.
Figure
1.6.1
Projected Metallurgical Recoveries
Domain |
Flotation Recovery to Concentrate |
Gold Plant Recovery |
Overall Recovery
|
|
|
Cu Con |
|
Mo Con |
SART |
Dore |
|
Supergene: |
Cu |
Au |
Ag |
Mo |
Cu |
Au |
Ag |
Cu |
Au |
Ag |
Mo |
Sodic Potassic |
74.7 |
60.4 |
64.1 |
51.2 |
1.5 |
16.0 |
6.0 |
76.2 |
76.4 |
70.2 |
51.2 |
Illite Pyrite |
68.1 |
43.9 |
64.1 |
62.6 |
3.9 |
26.8 |
6.0 |
72.1 |
70.7 |
70.2 |
62.6 |
Hypogene: |
|
|
|
|
|
|
|
|
|
|
|
Illite Pyrite |
86.4 |
43.9 |
64.1 |
73.2 |
1.9 |
26.1 |
6.0 |
88.3 |
70.0 |
70.2 |
73.2 |
Sodic Potassic |
86.2 |
60.4 |
64.1 |
76.6 |
1.4 |
16.7 |
6.0 |
87.6 |
77.1 |
70.2 |
76.6 |
K Silicate |
90.3 |
61.3 |
64.1 |
82.3 |
0.7 |
13.8 |
6.0 |
91.0 |
75.1 |
70.2 |
82.3 |
QP |
94.3 |
65.0 |
64.1 |
80.1 |
1.4 |
14.4 |
6.0 |
95.6 |
79.4 |
70.2 |
80.1 |
Sericite |
86.4 |
39.2 |
64.1 |
73.2 |
1.9 |
26.7 |
6.0 |
88.3 |
65.8 |
70.2 |
73.2 |
QSP |
86.0 |
31.6 |
64.1 |
82.5 |
2.1 |
32.1 |
6.0 |
88.1 |
63.7 |
70.2 |
82.5 |
1.7 |
ENVIRONMENTAL, PERMITTING AND SOCIAL CONDITIONS |
The Pebble deposit is located on state land that has been
specifically designated for mineral exploration and development. The project
area has been the subject of two comprehensive land-use planning exercises
conducted by the Alaska Department of Natural Resources (ADNR), the first in the
1980s and the second completed in 2005. ADNR identified five land parcels
(including Pebble) within the Bristol Bay planning area as having significant
mineral potential, and where the planning intent is to accommodate mineral
exploration and development. These parcels total 2.7% of the total planning area
(ADNR, 2005).
Environmental standards and permitting requirements in Alaska
are stable, objective, rigorous and science-driven. These features are an asset
to projects like Pebble that are being designed to meet U.S. and international
best practice standards of design and performance.
______________________________________________
1Silver
recovery projection based on a data set of 10 LCT samples
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Northern Dynasty began an extensive field study program in 2004
to characterize the existing physical, chemical, biological, and social
environments in the Bristol Bay and Cook Inlet areas where the Pebble Project
might occur. The Pebble Partnership compiled the data for the 2004-2008 study
period into a multi-volume Environmental Baseline Document (PLP, 2012). These
studies have been designed to:
-
Fully characterize the existing biophysical and socioeconomic environment;
-
Support environmental analyses required for effective input into Project
design;
-
Provide a strong foundation for internal environmental and social impact
assessment to support corporate decision-making;
-
Provide the information required for stakeholder consultation and eventual
mine permitting in Alaska; and,
-
Provide a baseline for long-term monitoring of potential changes associated
with mine development.
The baseline study program includes:
|
surface water |
|
wildlife |
|
groundwater |
|
air quality |
|
surface and groundwater quality |
|
cultural resources |
|
geochemistry |
|
subsistence |
|
snow surveys |
|
land use |
|
fish and aquatic resources |
|
recreation |
|
noise |
|
socioeconomics |
|
wetlands |
|
visual aesthetics |
|
trace elements |
|
climate and meteorology |
|
fish habitat stream flow modeling |
|
Iliamna Lake |
|
Marine |
|
|
1.8 |
INTERPRETATION AND CONCLUSIONS
|
Based on the work carried out, this study should be followed by
further technical and economic studies leading to a prefeasibility study.
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1.9.1 Recommended Program
The immediate priority is to maintain the project in good
standing and continue environmental monitoring.
Site operations, property maintenance and sample storage |
$1,811,000 |
-
Annual state rentals are required to maintain the Pebble claims in good standing.
-
Activities to maintain Pebble Partnership’s site facilities and core storage. These include care and maintenance staff, facilities leases, utilities for these facilities, and other associated costs.
Environmental baseline data collection |
$302,000 |
-
A minor environmental base line data collection program is necessary during
2015, as 10 years of data have been acquired.
-
These activities include meteorology and stream flow monitoring, support at
site, and staff to manage the work.
1.9.2 Additional Recommendations
The QPs have recommended two other components of work to
support prefeasibility studies, to be undertaken at a later date as funds become
available.
Additional resource evaluation
-
The deposit remains open in a number of locations, including adjacent to
Hole 6348, which identified high grade mineralization down-dropped on the east
side of the ZG1 graben-bounding fault. The first step would be to complete an
analysis to determine optimal methods for follow up drill testing of this
area.
-
The resource classification must be improved for a NI 43-101 compliant
prefeasibility study. The first step would be to complete a conditional
resource simulation to determine the optimal drill spacing to move inferred
resources to higher classifications.
-
Supplemental geochemical analyses should be undertaken to incorporate
silver and rhenium in the block model estimation.
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Additional metallurgical testwork
-
Additional copper-molybdenum separation testwork is recommended to optimize
metal grade and recovery to the molybdenum concentrate in support of a
prefeasibility study.
-
Ensuring sample numbers for comminution and flotation variability tests for
each respective geometallurgical domain unit reflects the timing and expected
proportions of each contained.
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Pebble Project, Southwest Alaska |
The Pebble property hosts a globally significant deposit of
copper, gold and molybdenum on state lands currently designated for mineral
exploration and development in southwest Alaska.
Alaska was granted statehood in 1959 along with 28% of the
states land base for the explicit purpose of developing land and resources to
support the states government and citizenry. The Alaska State Constitution
states: It is the policy of the State of Alaska
to encourage the development
of its resources by making them available for maximum use consistent with the
public interest. The lands surrounding Pebble within the Bristol Bay Area Plan
were received by the State from the U.S. government as part of the three-way
Cook Inlet Land Exchange of 1976, and were recognized by the State at that time
for their mineral prospectivity.
The Pebble deposit was originally discovered in 1989 and was
acquired by Northern Dynasty Minerals Ltd. (Northern Dynasty) in 2001. Since
that time, Northern Dynasty and subsequently the Pebble Limited Partnership (the
Pebble Partnership)2 have conducted significant mineral exploration,
environmental baseline data collection, and engineering work on the Pebble
Project to advance it towards development.
Northern Dynasty is a mineral exploration and development
company based in Vancouver, Canada, and publicly traded on the Toronto Stock
Exchange under the symbol NDM and on the NYSE MKT exchange under the symbol
NAK. Northern Dynasty is currently the sole owner of the Pebble Partnership
which owns the Pebble Project.
In 2014, Northern Dynasty commissioned a technical report to
update the mineral resources and metallurgy for the project based on work from
2010 to 2013.
2.1 |
TERMS OF REFERENCE AND PURPOSE |
The authors have prepared this technical report for Northern
Dynasty in general accordance with the guidelines provided in National
Instrument (NI) 43-101 Standards of Disclosure for Mineral Projects.
The purpose of this technical report is to integrate a number
of project changes since a 2011 technical report, including an updated resource
estimate based on additional drilling from 2011-2013 and the most recent
metallurgical testwork.
_________________________________________________________________
2 Additional information on the history of the Pebble Partnership and Pebble Project is provided in Section 6.0.
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2.2 |
SOURCES OF INFORMATION AND DATA |
Information and studies from third-party sources for the 2014
Technical Report are included in the references. The authors have reviewed and
used information from these sources under the assumption that the information is
accurate.
The principal units of measure used in this report are U.S.
Standard Units. Exceptions are noted and include the mineral resource estimate,
and other instances dictated by convention. Monetary amounts are in United
States dollars, unless otherwise stated.
The Qualified Persons (QPs) responsible for this technical
report and the dates of their most recent site visits are:
Section |
Report Section |
Company |
Qualified Person &
Professional Accreditation |
Date of
Last Site
Visit |
1.0 |
Summary |
|
All; sign off by discipline |
|
2.0 |
Introduction |
HDSI |
David Gaunt, PGeo |
Sept 2010 |
3.0 |
Reliance on Other Experts |
HDSI |
David Gaunt, PGeo |
|
4.0 |
Property Description and Location |
HDSI |
David Gaunt, PGeo |
|
5.0 |
Accessibility, Climate, Local
Resources, Infrastructure and Physiography |
HDSI |
David Gaunt, PGeo |
|
6.0 |
History |
HDSI |
Eric Titley, PGeo/ David Gaunt,
PGeo/James Lang, PGeo |
|
7.0 |
Geological Setting and
Mineralization |
HDSI |
James Lang, PGeo |
Aug 18-19, 2014 |
8.0 |
Deposit Types |
HDSI |
James Lang, PGeo |
|
9.0 |
Exploration |
HDSI |
James Lang, PGeo |
|
10.0 |
Drilling |
|
Eric Titley, PGeo/ James Lang,
PGeo |
|
11.0 |
Sample Preparation, Analyses and
Security |
HDSI |
Eric Titley, PGeo |
Sept 20, 2011 |
12.0 |
Data Verification |
HDSI |
Eric Titley, PGeo |
|
13.0 |
Mineral Processing and
Metallurgical Testing |
Tetra Tech |
Ting Lu, PEng |
|
14.0 |
Mineral Resource Estimates |
HDSI |
David Gaunt, PGeo |
|
15.0 |
Adjacent Properties |
HDSI |
James Lang, PGeo |
|
16.0 |
Other Relevant Data and
Information |
HDSI |
David Gaunt, PGeo |
|
17.0 |
Interpretation and Conclusions |
|
All; sign off by discipline |
|
18.0 |
Recommendations |
|
All; sign off by discipline |
|
19.0 |
References |
|
All |
|
20.0 |
Certificates |
|
|
|
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3.0 |
RELIANCE ON OTHER EXPERTS |
Standard professional procedures were followed in preparing the
contents of this report. Data used in this report has been verified where
possible and the authors have no reason to believe that the data was not
collected in a professional manner.
A QP has not independently verified the legal status or title
of the claims or exploration permits, and has not investigated the legality of
any of the underlying agreement(s) that may exist concerning the Pebble
property.
In some cases, the QPs are relying on reports, opinions, and
statements from experts who are not QPs for information concerning legal,
environmental, permitting and socio-economic factors relevant to the technical
report.
The following QPs who prepared this report relied on
information provided by a number of experts who are not QPs:
-
David Gaunt, P.Geo., relied on a letter from Trevor Thomas, Northern
Dynastys legal counsel, dated December 31 2014, confirming that title to the
claims comprising the Pebble Project is held in the name of Pebble East Corp.,
Pebble West Corp., and Kaskanak LLC Inc. (subsidiaries of the Pebble
Partnership) and U5 Resources Inc. (a subsidiary of Northern Dynasty) and
these are in good standing. The QP has also relied on Northern Dynasty for
matters relating to permits, surface rights, royalties, agreements and
encumbrances relevant to this report and discussed in Section 4;
-
David Gaunt, P.Geo., relied on a letter from Loretta Ford, P.Ag., Northern
Dynastys VP Environment and Sean Magee, BA, Northern Dynastys VP Public
Affairs, dated December 31 2014 for matters relating to environmental studies,
permitting, and social or community impact discussed in Section 15.
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4.0 |
PROPERTY DESCRIPTION AND LOCATION
|
The Pebble property is located in southwest Alaska,
approximately 200 miles southwest of Anchorage, 17 miles northwest of the
village of Iliamna, 160 miles northeast of Bristol Bay, and approximately 60
miles west of Cook Inlet (Figure 4.1.1) .
The property is centred, approximately, at latitude 59°53′54" N
and longitude 155°17′44" W, and is located on the United States Geological
Survey (USGS) topographic maps Iliamna D6 and D7, in Townships 25 South, Ranges
3338 West, Seward Meridian.
The Pebble Partnership uses the U.S. State Plane Coordinate
System (as Alaska 5005) as the preferred grid, measured in feet.
Figure
4.1.1
Pebble Project Location
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Pebble Project, Southwest Alaska |
Indirectly through wholly-owned subsidiaries (including the
Pebble Partnership), Northern Dynasty holds a 100% interest in a contiguous
block of 2,402 mineral claims covering approximately 417 square miles (Figure
4.2.1), including:
-
1,718 claims covering 248.2 square miles (including the Pebble deposit)
through its Pebble Partnership subsidiaries Pebble East Claims Corporation and
Pebble West Claims Corporation;
-
464 claims covering an area of 116 square miles through the Pebble
Partnership subsidiary Kaskanak LLC Inc. (Kaskanak); and,
-
220 claims covering 52.5 square miles through Northern Dynastys subsidiary
U5 Resources Inc.
Teck Resources Ltd. (Teck) holds a 4% pre-payback net profits
interest (after debt service), followed by a 5% after-payback net profits
interest in any mine production from the Exploration Lands, which are shown in
Figure 4.2.2 and further described in Section 6.0 History.
State mineral claims in Alaska are kept in good standing by
performing annual assessment work or in lieu of assessment work by paying $100
per year per 40 acre (0.06 square mile) mineral claim, and by paying annual
escalating state rentals. All of the claims come due annually on August 31.
However, credit for excess work can be banked for a maximum of five years
afterwards, and can be applied as necessary to continue to hold the claims in
good standing. The Project claims have a variable amount of work credit
available that can be applied in this way. Annual assessment work obligations
for the property total some US$667,700 and annual state rentals for 2015 are
US$990,390.
The details of the mineral claims are provided below in Figure
4.2.3 (ADL refers to the Alaska Department of Lands).
The claim boundaries have not been surveyed.
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Figure
4.2.1
Mineral Claim Map of the Pebble Project
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Pebble Project, Southwest Alaska |
Figure
4.2.2 Mineral Claim Map with Exploration Lands and Resource Lands
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Pebble Project, Southwest Alaska |
Figure
4.2.3 Pebble Mineral Claims
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Northern Dynasty currently does not own surface rights
associated with the mineral claims that comprise the Pebble property. All lands
are held by the State of Alaska, and surface rights may be acquired from the
state government once areas required for mine development have been determined
and permits awarded.
4.4 |
ENVIRONMENTAL LIABILITIES
|
There are no existing material environmental liabilities
associated with the Pebble Project.
Permits necessary for exploration drilling and other field
programs associated with pre-development assessment of the Pebble Project are
applied for each year. There are no activities proposed that require additional
permits.
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5.0 |
ACCESSIBILITY, CLIMATE, LOCAL RESOURCES,
INFRASTRUCTURE AND PHYSIOGRAPHY ACCESSIBILITY
|
The Pebble property is located in southwest Alaska (Figure
4.5.1) .
Figure
4.5.1
Property Location Map
Access to the property is typically via air travel from the
city of Anchorage, which is situated at the northeastern end of Cook Inlet and
is connected to the national road network via Interstate Highway 1 through
Canada to the USA. Anchorage is serviced daily by several regularly scheduled
flights to major airport hubs in the USA.
From Anchorage, there are regular flights to Iliamna through
Iliamna Air Taxi. Charter flights may also be arranged from Anchorage. From
Iliamna, access to the Pebble property is by helicopter.
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Pebble Project, Southwest Alaska |
The climate of the Pebble Project area is transitional; it is
more continental in winter because of frozen water bodies and more maritime in
summer because of the influence of the open water of Iliamna Lake and, to a
lesser extent, the Bering Sea and Cook Inlet. Mean monthly temperatures in the
deposit area range from about 55°F in summer to 2°F in winter. Precipitation
averages approximately 54 inches per year, about one-third of which falls as
snow. The wettest months are August through October.
The climate is sufficiently moderate to allow a well-planned
mineral exploration program to be conducted year-round (Rebagliati, C.M., and
Haslinger, R.J., 2003) at Pebble.
There is a modern airfield at Iliamna, with two paved 4,920 ft
airstrips, that services the communities of Iliamna, Newhalen and Nondalton. The
runways are suitable for DC-6 and Hercules cargo aircraft, and commercial jet
aircraft.
There are paved roads that connect the villages of Iliamna and
Newhalen to the airport and to each other, and a partly paved, partly gravel
road that extends to a proposed Newhalen River crossing near Nondalton. The
property is currently not connected to any of these local communities by road; a
road would be planned as part of the project design.
There is no access road that connects the communities nearest
the Pebble Project to the coast on Cook Inlet. From the coast, at Williamsport
on Iniskin Bay, there is an 18.6 mile state-maintained road that terminates at
the east end of Iliamna Lake, where watercraft and transport barges may be used
to access Iliamna. The route from Williamsport, over land to Pile Bay on Iliamna
Lake, is currently used to transport bulk fuel, equipment and supplies to
communities around the lake during the summer months.
Also during summer, supplies are barged up the Kvichak River,
approximately 43.4 miles southwest of Iliamna, from Kvichak Bay on the North
Pacific Ocean.
A small run-of-river hydroelectric installation on the nearby
Tazamina River provides power for the three communities in the summer months.
Supplemental power generation using diesel generators is required during winter
months.
Iliamna and surrounding communities have a combined population
of just over 400 people. As such, there is limited local commercial
infrastructure except that which services seasonal sports fishing and
hunting.
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The property is situated at approximately 1,000 ft amsl in an
area described as subarctic tundra. It is characterized gently rolling hills and
an absence of permafrost.
From Rebagliati, C.M., and Haslinger, J.M., 2003:
The Pebble property lies 80.5 km (50
miles) west of the Alaska Range in the Nushagak-Big River Hills, an area of
rolling hills and low mountains separated by wide, shallow valleys blanketed
with glacial deposits that contain numerous small, shallow lakes and are cut by
several major meandering streams. The elevation ranges from 250 m (820 ft) amsl
to 841 m (2,758 ft) amsl at Kaskanak Peak, the highest point on the property.
Tundra plant communities (mixtures
of shrub and herbaceous plants) cover the project area. Willow is common only
along streams, and sparse patches of dense alder are confined to better drained
areas where coarse soils have developed. Poorly drained regions underlain by
fine soils support dwarf birch and grasses (Detterman and Reed, 1973).
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Cominco Alaska, a division of Cominco Ltd. now Teck (Cominco
(Teck)), began reconnaissance exploration in the Pebble region in the mid-1980s
and in 1984 discovered the Sharp Mountain gold prospect near the southern margin
of the current property. Gold was discovered in drusy quartz veins of probable
Tertiary age near the peak of Sharp Mountain (anonymous Cominco (Teck) report,
1984). Grab samples of veins in talus ranged from 0.045 oz/ton Au to 9.32 oz/ton
Au and 3.0 oz/ton Ag. No record of further work is available, but similar quartz
veins were encountered in 2004 during surface mapping of the property conducted
by Northern Dynasty. Most of these veins trend north-south and dip steeply.
In 1987, examination and sampling of several prominent
limonitic and hematitic alteration zones yielded anomalous gold concentrations
from the Sill prospect (recognized as a precious-metal, epithermal-vein
occurrence), and the Pebble discovery outcrop (of then-uncertain affinity).
These discoveries were followed by several years of exploration including soil
sampling, geophysical surveys and diamond drilling.
Geophysical surveys were conducted on the property between 1988
and 1997. The surveys were dipole-dipole induced polarization (IP) surveys for a
total of 122 line-km, and were completed by Zonge Geosciences. This work defined
a chargeability anomaly about 31.1 square miles in extent within Cretaceous age
rocks which surround the eastern to southern margins of the Kaskanak batholith.
The anomaly measures about 13 miles north-south and up to 6.3 miles east-west;
the western margin of the anomaly overlaps the contact of the Kaskanak
batholith, whereas to the east the anomaly is masked by Late Cretaceous to
Eocene cover sequences. The broader anomaly was found to contain 11 distinct
centres with stronger chargeability, many of which were later demonstrated to be
coincident with extensive copper, gold and molybdenum soil geochemical
anomalies. All known zones of mineralization of Cretaceous age on the Pebble
property occur within the broad IP anomaly.
Diamond drilling was first conducted on the property during the
1988 exploration program which included 24 diamond drill holes at the Sill
epithermal gold prospect (Figure 6.1.1), soil sampling, geological mapping, two
diamond drill holes at the Pebble target (Figure 6.1.2) and three holes
totalling 893 ft on a target (later named the 25 Gold Zone by Northern Dynasty)
located 3.7 miles south of the Pebble deposit.
Drilling at the Sill prospect intersected mineralization with
gold grades that justified further exploration, but the initial Pebble drill
holes yielded only modest encouragement. In 1989, an expanded soil-sampling
program, the initial stages of the induced polarization (IP) surveys described
above and nine diamond drill holes were completed at the Pebble target, 15
diamond drill holes were completed at the Sill prospect and three diamond drill
holes were completed elsewhere on the property. Although limited in scope, the
IP survey at Pebble displayed response characteristics of a large
porphyry-copper system. Subsequent drilling by Cominco (Teck) intersected
significant intervals of porphyry-style gold, copper and molybdenum
mineralization, validating this interpretation.
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Figure
6.1.1
Cominco (Teck) Drilling on the Sill Prospect to the End of 1997
Year |
No. of Drill Holes |
Feet |
Metres |
1988 |
24 |
7,048 |
2,148 |
1989 |
15 |
3,398 |
1,036 |
Total |
39 |
10,446 |
3,184 |
Figure
6.1.2 Cominco (Teck) Drilling on the Pebble Deposit to the End of 1997
Year |
No. of Drill Holes |
Feet |
Metres |
1988 |
2 |
554 |
169 |
1989 |
9 |
3,131 |
954 |
1990 |
25 |
10,021 |
3,054 |
1991 |
48 |
28,129 |
8,574 |
1992 |
14 |
6,609 |
2,014 |
1997 |
20 |
14,696 |
4,479 |
Total |
118 |
63,140 |
19,245 |
When it became apparent that a significant copper-gold porphyry
deposit had been discovered at Pebble, exploration was accelerated. In 1990 and
1991, 25 and 48 diamond drill holes, respectively, were completed. In 1991,
baseline environmental and engineering studies were initiated and weather
stations were established. A preliminary economic evaluation was undertaken by
Cominco (Teck) in 1991, and was updated in 1992 on the basis of 14 new diamond
drill holes. In 1993, an IP survey and a four-hole diamond-drill program were
completed at the target that was later named the 25 Gold Zone. In 1997, Cominco
(Teck) completed an IP survey, geochemical sampling, geological mapping and 20
diamond drillholes within and near the Pebble deposit (Figure 6.1.3) .
From 1988 to 1995, Cominco (Teck) undertook several soil
geochemical surveys on the property and collected a total of 7,337 samples
(Bouley et al., 1995).
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Figure
6.1.3
Total Cominco (Teck) Drilling on the Property to the End of 1997
Year |
No. of Drill Holes |
Feet |
Metres |
1988 |
26 |
7,602 |
2,317 |
1989 |
27 |
7,422 |
2,262 |
1990 |
25 |
10,021 |
3,054 |
1991 |
48 |
28,129 |
8,574 |
1992 |
14 |
6,609 |
2,014 |
1993 |
4 |
1,263 |
385 |
1997 |
20 |
14,696 |
4,479 |
Total |
164 |
75,741 |
23,086 |
6.2 |
HISTORICAL SAMPLE PREPARATION AND ANALYSIS
|
6.2.1
Sample Preparation
Cominco (Teck) drilled 125 holes in the Pebble area between
1988 and 1997 for a total of 65,295.5 ft. These holes include 118 holes drilled
in what later became known as Pebble West and seven holes drilled elsewhere on
the property. Of the Pebble West holes, 94 were drilled vertically and 20 were
inclined from −45° to −70° at various orientations. Cominco (Teck) also
completed 39 drill holes on the Sill prospect for a total of 10,445.5 ft in 1988
and 1989.
Cominco (Teck) drill core was transported from the drill site
by helicopter to a logging and sampling site in the village of lIiamna. The core
from within the Pebble deposit was typically sampled on 10 ft intervals and most
core from Cretaceous age units was sampled. Samples from the Sill and other
areas were typically 5 ft in length, with shorter samples in areas of vein
mineralization. Samples consisted of mechanically-split drill core. The samples
were transported by air charter to Anchorage and by air freight to Vancouver,
BC. All coarse rejects from 1988 through 1997 and all pulps from 1988 and most
from 1989 have been discarded. The remaining pulps were later shipped by
Northern Dynasty to a secure warehouse at Langley, BC, for long-term storage.
Cominco (Teck) systematically assayed for gold in the
Cretaceous intersections from all drill holes completed on the property from
1988 through 1997. Copper analysis was added when the Pebble porphyry discovery
hole was drilled in 1989, and single element copper analysis continued for all
Cretaceous intersections in 1989. Selective single element molybdenum assays and
single element silver analyses were added to some holes in 1989. In 1990,
Cominco (Teck) added multi-element analysis to the analytical protocol, which
included the determination of copper, molybdenum, silver and 29 additional
elements. In 1991 and 1992, some sections of core were analyzed using the
multi-element analysis and some were analyzed using single element copper
analysis. Only four holes were drilled by Cominco (Teck) in 1993, on targets
well south of the Pebble deposit, and these were only assayed for gold and
copper. No drilling was completed from 1994 to 1996. Drill holes completed in
1997 were analyzed with a multi-element package.
6.2.2
Sample Analysis
Cominco (Teck) samples collected prior to the 1997 program were
prepared and analyzed by ALS Minerals (ALS) Laboratories in North Vancouver, BC.
The core samples were processed by drying, weighing, crushing to 70% passing 10 mesh and then splitting to a 250 g sub-sample and a
coarse reject; the 250 g sub-sample was pulverized to 85% passing 200 mesh.
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During the 1997 program, drill core samples were prepared by
ALS Laboratories in Anchorage. A 250 g pulp sample was then submitted to Cominco
Exploration and Research Laboratory in Vancouver, BC, for copper analysis using
an aqua regia (AR) digestion with inductively coupled plasma atomic emission
spectroscopy (ICP-AES) finish. Gold was analyzed using fire assay (FA) on a one
assay-ton sample with atomic absorption spectroscopy (AAS) finish. Trace
elements also were analyzed by AR digestion and ICP-AES finish. One blind
standard was inserted for every 20 samples analyzed. One duplicate sample was
taken for every 10 samples analyzed.
Cominco (Teck) analyzed a total of 6,311 core samples from 125
drill holes on the property. On the Sill prospect, a total of 676 samples were
analyzed from 39 drill holes.
6.3 |
HISTORICAL RESOURCE ESTIMATES |
Cominco (Teck) prepared several resource estimates on the
Pebble deposit during the 1990s, employing block models estimated with either
kriging or inverse distance (ID) weighting. The cut-off grade used was 0.3% CuEq
based on metal prices of $1.00/lb of copper and $375/oz of gold. These estimates
are summarized in Figure 6.3.1.
Figure
6.3.1 Cominco (Teck) Resource Estimates
Year |
Tonnage (million) |
Cu (%) |
Au (oz/ton) |
1990 |
200 |
0.35 |
0.01 |
1991 |
500 |
0.35 |
0.01 |
1992 |
460 |
0.40 |
0.01 |
2000 |
1,000 |
0.30 |
0.01 |
These historical estimates are considered both relevant and
reliable, as the methodology was consistent with industry standards at the time
of estimation. The historical estimates are classified as Inferred. However, no
QP has done sufficient work to evaluate these historical estimates and Northern
Dynasty is not treating the historical estimates as current Mineral Resources.
More recent estimates are described in Section 14.0.
The following summary of historical property agreements is
taken from Rebagliati et al (2010).
In October 2001, Northern Dynasty
acquired, through its Alaskan subsidiary, a two-part Pebble Property purchase
option previously secured by Hunter Dickinson Group Inc. (HDGI) from an Alaskan
subsidiary of Teck Cominco Limited, now Teck Resources Limited (Teck). In
particular, HDGI assigned this two-part option (the Teck Option) as 80% to
Northern Dynasty while retaining 20% thereof. The first part of the Teck Option
permitted Northern Dynasty to purchase (through its Alaskan subsidiary) 80% of
the previously drilled portions of the Pebble Property on which the majority of
the then known copper mineralization occurred (the Resource Lands
Option). Northern Dynasty could exercise the Resource Lands Option through the
payment of cash and shares aggregating US$10 million prior to November 30, 2004.
The second part of the Teck Option permitted Northern Dynasty to earn a 50%
interest in the exploration area outside of the Resource Lands (the Exploration
Lands Option). Northern Dynasty could exercise the Explorations Lands Option by
doing some 18,288 m (60,000 ft) of exploration drilling by November 30, 2004,
which it completed on time. The HDGI assignment of the Teck Option also allowed
Northern Dynasty to purchase the other 20% of the Teck Option retained by HDGI
for its fair value.
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In November 2004, Northern Dynasty
exercised the Resource Lands Option and acquired 80% of the Resource Lands. In
February 2005, Teck elected to sell its residual 50% interest in the Exploration
Lands to Northern Dynasty for US$4 million. Teck still retains a 4% pre-payback
advance net profits royalty interest (after debt service) and 5% after-payback
net profits interest royalty in any mine production from the Exploration Lands
portion of the Pebble property.
In June 2006, Northern Dynasty
acquired, through its Alaska subsidiaries, the remaining HDGI 20% interest in
the Resource Lands and Exploration Lands by acquiring HDGI from its shareholders
and through its various subsidiaries had thereby acquired an aggregate 100%
interest in the Pebble Property, subject only to the Teck net-profits royalties
on the Exploration Lands described above [see Section 4. At that time,
Northern Dynasty operated the Pebble Property through a general Alaskan
partnership with one of its subsidiaries.
In July 2007, the Pebble Partnership was created and an
indirect wholly-owned subsidiary of Anglo American plc (Anglo American)
subscribed for 50% of the Pebble Partnership's equity effective July 31, 2007.
Each of Northern Dynasty and Anglo American effectively had equal control and
management rights in the Pebble Partnership and its general partner, Pebble
Mines Corp. through respective wholly-owned affiliates. The Pebble Partnership's
assets include the shares of two Alaskan subsidiaries, which hold registered
title to the claims (see Section 4.0 for details). To maintain a 50% interest in
the Pebble Partnership, Anglo American was required to make staged cash
investments into the Pebble Partnership, aggregating $1.5 billion, towards
comprehensive exploration, engineering, environmental and socioeconomic programs
and, if warranted, development of the Pebble Project. On September 15, 2013,
Anglo gave Northern Dynasty a 60-day notice of withdrawal from the Pebble
Project. In December 2013, Northern Dynasty exercised its right to acquire Anglo
Americans interest in the Pebble Partnership and now holds a 100% interest in
the Pebble Partnership.
On June 29, 2010, Northern Dynasty entered into an agreement
with Liberty Star Uranium and Metals Corp. and its subsidiary, Big Chunk Corp.
(together, "Liberty Star"), pursuant to which Liberty Star sold 23.8 square
miles of claims (the 95 "Purchased Claims") to a U.S. subsidiary of Northern
Dynasty in consideration for both a $1 million cash payment and a secured
convertible loan from Northern Dynasty in the amount of $3 million. The parties
agreed, through various amendments to the original agreement, to increase the
principal amount of the Loan by $730,174. Northern Dynasty later agreed to
accept transfer of 199 claims (the Settlement Claims) located north of the
ground held 100% by the Pebble Partnership in settlement of the Loan. These
claims are now held by Northern Dynastys subsidiary U5 Resources Inc. The
current size of this property is described in section 4.1.
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On January 31, 2012, the Pebble Partnership entered into a
Limited Liability Company Agreement with Full Metal Minerals (USA) Inc.
(FMMUSA), a wholly-owned subsidiary of Full Metal Minerals Corp., to form
Kaskanak Copper LLC (the LLC). Under the agreement, the Pebble Partnership could
earn a 60% interest in the LLC, which indirectly owned 100% of the Kaskanak
claims, by incurring exploration expenditures of at least US$3 million and
making annual payments of $50,000 to FMMUSA over a period ending on December 31,
2013. On May 8, 2013,
the Pebble Partnership purchased FMMUSA’s entire ownership interest in the LLC for a cash consideration of $750,000. As a result, the Pebble Partnership gained a 100% ownership interest in the LLC, the indirect owner of a 100% interest in
a group of 542 claims located south and west of other ground held by the Pebble Partnership. The current size of this property is described in section 4.1.
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7.0 |
GEOLOGICAL SETTING AND MINERALIZATION
|
The tectonic and magmatic history of southwest Alaska is
complex (Decker et al., 1994; Plafker and Berg, 1994). It includes formation of
foreland sedimentary basins between tectonostratigraphic terranes, amalgamation
of these terranes and their translation along crustal-scale strike-slip faults,
and episodic magmatism and formation of related mineral occurrences. The
overview presented here is based largely on Goldfarb et al. (2013).
The allochthonous Wrangellia superterrane comprises the
amalgamated Wrangellia, Alexander and Peninsular oceanic arc terranes that
approached North America from the southwest in the early Mesozoic. West-dipping
subduction beneath the superterrane formed the Late Triassic to Early Jurassic
Talkeetna oceanic arc, which is now preserved in the Peninsular terrane east of
Pebble (Figure 7.2.1) . Several foreland sedimentary basins dominated by
Jurassic to Cretaceous flysch, including the Kahiltna basin that hosts the
Pebble deposit (Kalbas et al., 2007), formed between Wrangellia and pericratonic
terranes and previously amalgamated allochthonous terranes of the Intermontane
belt (Wallace et al., 1989; McClelland et al., 1992). Basin closure occurred as
Wrangellia accreted to North America by the late Early Cretaceous (Detterman and
Reed, 1980; Hampton et al., 2010). Between approximately 115 to 110 Ma and 97 to
90 Ma, the strata in the foreland basins were folded, complexly faulted and
subjected to low-grade regional metamorphism (Bouley et al., 1995; Goldfarb et
al., 2013). Intrusions at Pebble are undeformed (Goldfarb et al., 2013) and were
probably emplaced during a period when at least local extension occurred across
southwest Alaska in the mid-Cretaceous (e.g. Pavlis et al., 1993). The relative
importance of extensional versus compressional structures to the formation of
the Pebble deposit is not well constrained, although a syn-hydrothermal
compressional fault has been recognized within the deposit.
Since the early Late Cretaceous, deformation in southwest
Alaska has occurred mostly on major dextral strike-slip faults, broadly parallel
to the continental margin (Figure 7.2.1) . The major Denali fault in central
Alaska forms the contact between the Intermontane Belt and the collapsed flysch
basins. Smaller, subparallel faults are located south of the Denali fault, and
the Pebble district is located between what are probably terminal strands of the
Lake Clark fault zone (Figure 7.2.1; Shah et al., 2009). The Lake Clark fault
zone marks the poorly defined boundary between the Peninsular terrane to the
southeast and the Kahiltna terrane, which hosts Pebble, to the northwest (Figure
7.2.1) . Haeussler and Saltus (2005) propose about 16.1 miles of dextral offset
along the Lake Clark fault zone, most of which is interpreted to have occurred
prior to approximately 38 to 36 million years ago. Recent field studies of
geomorphology along the Lake Clark fault indicate that this structure has not
experienced seismic activity for at least the last 10,000 years (Haeussler and
Saltus, 2005, 2011; Koehler, 2010; Koehler and Reger, 2011). Other sub-parallel
strike-slip faults also form terrane boundaries in the region, including the
Mulchatna and Bruin Bay faults (Figure 7.2.1) . Goldfarb et al. (2013) propose
that most or all movement on these smaller structures occurred during oroclinal
bending in the Tertiary, after formation of the Pebble deposit.
The initiation of magmatism and metallogenesis in the Pebble
district approximately coincides with the onset of dextral transpression during
basin collapse (Goldfarb et al., 2013). Alkalic to subalkalic intrusions were
emplaced between approximately 100 and 88 Ma (Bouley et al., 1995; Amato et al.,
2007; Hart et al., 2010; Lang et al., 2013). Alaska-type ultramafic complexes
were emplaced at Kemuk, which is enriched in platinum group elements (Iriondo et
al., 2003; Foley et al., 1997), and a mineralogically similar alkalic ultramafic
body, albeit probably emplaced at shallow depths and without known enrichment in platinum group
elements, occurs at Pebble (Bouley et al., 1995). Porphyry Cu-Mo±Au
mineralization is associated dominantly with subalkalic, felsic to intermediate
intrusions formed between 97 and 90 Ma, and includes deposits at Pebble, Neacola
(Reed and Lanphere, 1973; Young et al., 1997;Figure 7.2.1) and possibly the
undated Iliamna prospect (Figure 7.2.1) . Late Cretaceous intermediate to felsic
intrusions are subalkalic and were emplaced between 75 and 60 Ma (e.g., Couture
and Siddorn, 2007; Goldfarb et al., 2013). Porphyry Cu-Au±Mo and/or reduced
intrusion-related gold mineralization associated with these rocks formed at the
Whistler deposit (reported in Couture and Siddorn, 2007), located about 93.2
miles northeast of Pebble, at Kijik River, the Bonanza Hills (Anderson et al.,
2013) and Shotgun (Rombach and Newberry, 2001; Figure 7.2.1) . Late Cretaceous
to Tertiary intrusions and voluminous volcanic rocks cover much of the Kahiltna
terrane and are associated with epithermal precious metal mineralization
(Bundtzen and Miller, 1997). Igneous rocks of the mid-Cretaceous, Late
Cretaceous, and Eocene magmatic suites are present within the Pebble district.
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7.2.1
Kahiltna Flysch
The oldest rock type in the Pebble district is the Kahiltna
flysch, which comprises basinal turbidites, interbedded basalt flows and lesser
breccias, and minor gabbroid intrusions. The Kahiltna flysch forms a
northeast-trending belt about 250 miles long, which has experienced multiple
stages of igneous and hydrothermal activity (Figure 7.2.1; Goldfarb, 1997; Young
et al., 1997). The flysch in the vicinity of Pebble is at least 99 to 96 million
years old, based on the maximum age of cross-cutting intrusions. Sediments were
predominately derived from intermediate igneous source rocks and consist of
siltstone, mudstone, subordinate wacke and rare, thin, lensoidal beds of
matrix-supported pebble conglomerate (Figure 7.2.2A) . Bedding ranges from
laminar to thick and is commonly poorly defined. Bouma sequences (Bouley et al.,
1995), graded beds and load casts demonstrate that the stratigraphy is
normal-facing.
The flysch locally contains thick layers of basalt flows,
lesser breccias and minor mafic volcaniclastic rocks located mostly in the
southwest and northern parts of the district. Undated gabbros cut the flysch and
volcanic rocks in several areas and are interpreted to be related either to the
basaltic volcanic rocks within the flysch or to younger diorite sills.
7.2.2 Diorite and Granodiorite Sills
Diorite and granodiorite sills intruded the Kahiltna flysch at
about 96 Ma (Figure 7.2.1) . These two rock types are interpreted to be
approximately coeval, based on the similarity in their distribution and style of
occurrence; they are only well documented within the Pebble deposit.
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Figure
7.2.1
Location of the Pebble Deposit and Regional Geological Setting of Southwest
Alaska
Note:
Modified slightly from Anderson et al., 2013. Dashed lines separate terranes:
KB=Kuskokwim Basin; TT=Togiak Terrane; PT=Peninsular Terrane; FT=Farewell
Terrane; CzC=Cenozoic cover. Filled circles are the locations of mineral
deposits discussed in this text. Major dextral strike-slip faults are indicated
by solid lines.
Diorite sills are laterally extensive and range from less than
10 ft to greater than 300 ft in thickness. They are most common as stacked
sheets in the western part of the Pebble deposit. The sills are medium-grained
and weakly porphyritic, with common plagioclase and hornblende and minor
pyroxene set in a very fine-grained groundmass of plagioclase and hornblende
(Figure 7.2.2B) .
Three laterally continuous granodiorite sills occur within the
Pebble deposit. They are up to 1,000 ft thick, with the thickest portions in the
northeast part of the deposit. The sills range from fine- to medium-grained,
with common plagioclase and hornblende as well as minor amounts of apatite, in a
very fine-grained groundmass of potassium feldspar and quartz with minor to
accessory magnetite, apatite and zircon (Figure 7.2.2C) .
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7.2.3 Alkalic Intrusions and Associated Breccias
A complex suite of alkalic porphyry intrusions (including
quartz-free biotite pyroxenite, syenomonzonite, monzonite and monzodiorite) and
associated breccias extends south from the southwest quadrant of the Pebble
deposit (Schrader, 2001; Hart et al., 2010; Goldfarb et al., 2013). Isotopic
dates on diorite and granodiorite sills, biotite pyroxenite and alkalic
intrusions indicate that they are approximately coeval and were emplaced between
99 and 96 Ma (Schrader, 2001). Early intrusions are medium-grained, biotite
monzonite porphyries (Figure 7.2.2D) that commonly contain scattered potassium
feldspar megacrysts up to several centimetres in size. Later intrusions are
fine-grained porphyritic biotite monzodiorite (Figure 7.2.2E) . All intrusive
phases contain angular to subrounded xenoliths of flysch, diorite and, in the
younger monzodiorite phase, xenoliths of older alkalic intrusions. Many of the
intrusions grade into breccias.
Breccias in the alkalic complex are complicated. Subordinate
intrusion breccias have angular to subangular fragments in a cement of the later
porphyritic biotite monzodiorite intrusion. Fragments of diorite sills, early
alkalic biotite monzonite porphyry intrusions and flysch are most common. The
breccia matrix dominantly consists of a rock flour composed of subangular to
subrounded fragments of these same rock types (Figure 7.2.2F) . Hydrothermal
cement is absent, and fragments range from a few millimetres to tens of metres
in size. Locally, intersections of diorite and granodiorite sills within the
breccia bodies may correlate laterally with undisturbed sills. Due to the
internal complexity of the alkalic rocks within the deposit, the complex is
modeled as a single unit, loosely interpreted as a megabreccia.
7.2.4
Hornblende Granodiorite Porphyry Intrusions
Granodiorite intrusions include the Kaskanak batholith and
numerous smaller bodies, mostly within or proximal to zones of porphyry-style
mineralization around the margins of the batholith. All isotopic dates on these
rocks are approximately 90 Ma (Bouley et al., 1995; Lang et al., 2013). The
Kaskanak batholith is dominantly a medium-grained hornblende granodiorite
porphyry, with minor equigranular hornblende quartz monzonite. Granodiorite
intrusions spatially associated with porphyry-style mineralization throughout
the Pebble district are all mineralogically and texturally similar to the main
phase of the Kaskanak batholith (Figure 7.2.2G) . All of these intrusions are
characterized by common hornblende, plagioclase and minor quartz and titanite,
set in a fine-grained groundmass of quartz, plagioclase, potassium feldspar,
apatite, zircon and magnetite. Megacrysts of potassium feldspar are up to 0.6 in
in size, increase in both size and concentration with depth (from less than 2%
to greater than 5%) and poikilitically enclose plagioclase and hornblende
phenocrysts.
7.2.5 Volcanic-Sedimentary cover sequence
Cretaceous rock types 90 Ma or older are unconformably overlain
by well-bedded sedimentary and volcanic rocks (Figure 7.2.2H), informally called
the cover sequence. The cover sequence is up to 2,200 ft thick over the eastern
edge of the Pebble deposit, and basalt flows with lesser interbeds of clastic
sedimentary rocks are up to 6,400 ft thick within the East Graben. The sequence
occurs mostly on, and thickens toward, the east side of the district, with
additional exposures overlying and to the west and south of the Kaskanak
batholith. Sedimentary rock types are normal-facing but have been tilted about
20o east, and include pebble to boulder conglomerate, wacke,
siltstone and mudstone. Plant fossils are common in wacke, and coal-bearing
seams up to approximately 1.5 ft thick have been intersected by drilling.
Volcanic to sub-volcanic rocks include basalt flows and mafic dykes and sills.
Volcaniclastic rocks are abundant and contain angular fragments ranging from
basalt to rhyolite within a matrix of comminuted volcanic material. The cover
sequence is cut by minor narrow, dykes and sills of felsic to intermediate
composition, as well as by 65 Ma hornblende monzonite porphyry intrusions (Lang
et al., 2013).
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7.2.6 Hornblende Monzonite Porphyry Intrusions
Two porphyry intrusions of hornblende monzonite, up to 820 ft
thick, cut basalts within the East Graben and have been dated at 65 Ma (Lang et
al., 2013). They are medium-grained and porphyritic, with common plagioclase and
lesser hornblende set in a fine-grained groundmass of potassium feldspar,
plagioclase and minor magnetite. These intrusions are not hydrothermally
altered.
7.2.7 Eocene Volcanic Rocks and Intrusions
Volcanic and sub-volcanic intrusive rocks on the east side of
the district are dated at 46 to 48 Ma (Bouley et al., 1995; Lang et al., 2013).
These rocks are mostly exposed on Koktuli Mountain east of the deposit, and
limited drill intersections suggest they may be common in the southeast part of
the district below glacial cover. Rock types include felsic dykes, brecciated
rhyolite flows, fine-grained, equigranular to porphyritic biotite-bearing
hornblende latite intrusions and coarse-grained hornblende monzonite porphyry.
7.2.8 Glacial Sediments
Unconsolidated glacial sediments of Pleistocene to recent age
cover all but the tops of the highest hills (Detterman and Reed, 1973; Hamilton
and Klieforth, 2010). The sediments are typically less than 100 ft thick, but
drill intersections range up to 525 ft in the wide valley in the southeast part
of the district. Ice flow directions over the deposit were to the
south-southwest, and the glaciers had retreated by about 11 Ka (Detterman and
Reed, 1973; Hamilton and Klieforth, 2010).
7.2.9 District Structure
The structural history of the district outside of the Pebble
deposit is poorly understood due to a paucity of outcrop and marker horizons.
The Kahiltna flysch exhibits shallow to moderate dips to the east, south and
southeast, which may reflect doming around the margins of the Kaskanak
batholith. Folds in the flysch are open, and most inter-limb angles are less
than 20°. Folding and related deformation predate hydrothermal activity at
Pebble (Bouley et al., 1995; Goldfarb et al., 2013).
Faults are abundant throughout the Pebble district. The
significant northeast-trending, syn-hydrothermal brittle-ductile fault zone
(BDF) is described later in this section. Most faults are brittle normal or
normal-oblique structures that cut all rock types in the district and, in many
cases, have been inferred from discontinuities in airborne magnetic and
electromagnetic data. The most prominent faults strike north-northeast and
northwest, with fewer striking east. The most important of these faults bound
the northeast-trending East Graben, which down-drops high-grade mineralization
on the east side of the Pebble deposit. Brittle faults cut Eocene rock types,
but precursor structures may have been periodically active since the
mid-Cretaceous (L. Rankin, pers. comm., 2011). There is no geological evidence
to suggest that these faults have been recently active.
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Figure
7.2.2
Rock Types in the Pebble District
Notes:
A: Kahiltna flysch with interbedded siltstone and
wacke affected by biotite-rich potassic alteration.
B: Diorite sill cut by
magnetite-rich veins with intense biotite-rich potassic alteration.
C:
Granodiorite sill with crowded porphyritic texture and pervasive potassic
alteration.
D: Biotite monzonite porphyry member of the alkalic suite.
E:
Late biotite monzodiorite porphyry member of the alkalic suite with angular
xenoliths of flysch.
F: Diatreme breccia from the alkalic suite with
polylithic fragments in a matrix of rock flour.
G: Pebble East zone
granodiorite porphyry pluton with relict hornblende phenocrysts selectively
altered to biotite.
H: Sharp contact between mineralized granodiorite sill
and overlying basal conglomerate of the cover sequence at the top of the Pebble
East zone.
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The characteristics of the Pebble deposit are shown in plan
view in Figure 7.3.1 and Figure 7.3.2, and in cross-section in Figure 7.3.3
toFigure 7.3.5. Geological interpretation of the Pebble deposit is based almost
entirely on diamond drill intersections.
7.3.1 Rock Types
The deposit is hosted by Kahiltna flysch, diorite and
granodiorite sills, alkalic intrusions and breccias, and granodiorite stocks
(Figure 7.3.1 and Figure 7.3.3) . Within the deposit, the Kahiltna flysch is a
well-bedded siltstone with less than 10% coarser-grained, more massive wacke
interbeds; basalt and gabbro are absent. Bedding within the flysch typically
dips less than 25o to the east. The flysch was intruded by diorite
sills, granodiorite sills and rocks of the alkalic suite prior to hydrothermal
activity. The diorite sills are found only in the western half of the deposit
(Figure 7.3.3), whereas some granodiorite sills extend across the entire
deposit. Intrusions and breccias of the alkalic suite occupy the southwest
quadrant of the deposit (Figure 7.3.1) .
The deposit is centered on a group of five hornblende
granodiorite porphyry intrusions, including the larger Pebble East zone pluton
and four smaller bodies in the Pebble West zone. The north contact of the Pebble
East zone pluton is close to vertical, and its upper contact dips shallowly to
the west; it remains undelineated to the south, and has been dropped into the
East Graben by the ZG1 fault. Contacts of stocks in the Pebble West zone dip
steeply to moderately outward. Recent deep drilling suggests that the
granodiorite intrusions coalesce at depths greater than 3,280 ft. Dykes and
sills of hornblende granodiorite porphyry are uncommon and are found mostly in
host rocks above and adjacent to the Pebble East zone pluton.
The Pebble East zone is entirely concealed by the
east-thickening cover sequence. The contact between the flysch and the cover
sequence ranges from sharp and undisturbed to structurally disrupted with
slippage along the contact. The lower half of the sequence comprises a thick
basal conglomerate with well-rounded cobbles and boulders of intrusive and
volcanic rock types of unknown provenance, overlain by complex, interlayered,
discontinuous lenses of pebble conglomerate, wacke, siltstone, and mudstone. The
upper half of the sequence comprises volcanic and volcaniclastic rocks (Figure
7.3.3) dominated by basalt or andesite and intruded by minor felsic to
intermediate sills. The cover sequence within the East Graben ranges from
approximately 4,265 ft thick north of the ZE fault to a thickness of up to 6,400
ft to the south. The graben is filled by basalt flows and lesser sedimentary
rocks.
Eocene rocks are rare within and proximal to the Pebble
deposit. Where thus far encountered, they comprise narrow felsic dykes, a pink
hornblende monzonite intrusion intersected at depth in the central part of the
East Graben, and a rhyolite flow breccia at the top of the East Graben, south of
the ZE fault.
7.3.2
Structure
Within the western part of the Pebble deposit, the Kahiltna
flysch occurs as an open, M-shaped anticline with axes that plunge shallowly to
the east-southeast (Rebagliati and Payne, 2006). Diorite sills are commonly
thicker near the hinges of the folds. Folding did not affect the cover sequence.
A brittle-ductile fault zone (BDF) has been identified on the
east side of the Pebble deposit (Figure 7.3.1) where it manifests a zone of
deformation defined by distributed cataclastic seams and healed breccias. It
strikes north-northeast, extends at least 1.86 miles along strike, is up to 650
ft wide and is vertical to steeply west-dipping. The BDF is truncated on the
east by the ZG1 fault (Figure 7.3.3) and does not penetrate the cover sequence.
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Displacement appears to have been dextral-oblique/reverse (S. Goodman, pers. comm., 2008), and correlation of alteration domains across the fault limits post-hydrothermal lateral displacement to less than 1,310 ft. The BDF was active before, during
and after hydrothermal activity. Deformation is most intense in flysch north of the Pebble East Zone pluton but is weaker within the intrusion, suggesting that the BDF was more active before or during emplacement of the stock. Syn-hydrothermal
control on mineralization by the BDF is indicated by the much higher grades of copper and gold and higher vein density within the structural zone compared to adjacent, undeformed host rocks. The characteristics of deformation along the BDF, and its
timing relative to hydrothermal activity at Pebble, support at least a local compressional to transpressional environment during the formation of the deposit. Local deformation of veins indicates some post-hydrothermal movement.
Brittle faults within the Pebble deposit conform to the district-scale patterns described above (Figure 7.3.1) . The ZB, ZC and ZD faults occur in the Pebble West zone and exhibit normal offset of diorite and granodiorite sills of between 50 ft and
300 ft. Normal displacement on the ZJ and ZI faults is not well constrained. The ZA fault has about 100 ft of apparent reverse movement. A minimum of 820 ft of normal displacement occurred across the steeply west-dipping ZF fault, juxtaposing
mineralized sodic-potassic alteration in the east against poorly mineralized, propylitic and quartz-sericite-pyrite alteration to the west. Displacement on the ZE fault increases from around 100 ft on its western end to about 980 ft on the east side
of the deposit. The ZG1 fault forms the western boundary of the East Graben and has well-defined normal displacement of approximately 2,100 ft in the north and 2,900 ft in the south, based on offset of the contact between the deposit and the cover
sequence (Figure 7.3.3) . The ZG2 fault, which is parallel to the ZG1 fault, has between 880 ft and 1,800 ft of normal displacement. The ZH fault and possible parallel structures farther east mark the eastern margin of the East Graben. Many of these
brittle faults localized intermediate to mafic dykes and a date of 84 Ma for an andesite dyke by Schrader (2001) indicates that brittle faults remained active until at least that time.
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Figure
7.3.1
Geology of the Pebble Deposit Showing Section Locations
Note: |
The late Cretaceous cover sequence occurs to the east of
the dark yellow line and has been removed for clarity. |
|
Cross-sections A-A, B-B and C-C are shown in Figure
7.3.3, Figure 7.3.4 and Figure 7.3.5, respectively. |
|
The brittle-ductile fault zone (BDF) is indicated by the
cross-hatched pattern. |
|
The dashed outline of the estimated resources at a 0.3%
CuEq cut-off is used as a reference point for alteration and grade
distribution in Figure 7.3.5. |
|
White areas are either undrilled or rock types below
cover sequence unknown. |
|
See Figure 7.3.3 for geology legend. |
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Figure
7.3.2 Plan View of Alteration and Metal Distribution in the Pebble Deposit
Note: |
Grades are shown as they appear in a previously completed
resource block model (Gaunt et al., 2010), at the contact between the
deposit and the overlying cover sequence, which has been removed. These
grades are not derived from the current resource estimate. |
|
For geological reference, the resource outline matches
that shown in Figure 7.3.1. |
|
A simplified distribution of alteration types is shown on
the map at upper left. NQV and SQV are the northern and southern quartz
vein domains (>50% quartz veins). |
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Figure
7.3.3 Geology, Alteration and Distribution of Metals on Section A-A
Note:
Location of section is shown inFigure 7.3.1, and grade legends in
Figure 7.3.2.
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Figure
7.3.4 Geology, Alteration and Metal Distribution on Section B-B
Note:
Location of section is shown inFigure 7.3.1, and legend for grade
ranges and alteration in Figure 7.3.2.
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Figure
7.3.5 Geology, Alteration and Metal Distribution on Section C-C
Note:
Location of section is shown in Figure 7.3.1, and legend for grade ranges and
alteration in Figure 7.3.2.
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7.4 |
DEPOSIT ALTERATION STYLES |
Alteration styles are summarized below in the order of their
interpreted relative ages.
7.4.1 Pre-hydrothermal Hornfels
Hornfels related to intrusion of the Kaskanak batholith
pre-dates hydrothermal activity and is found in all Cretaceous rock types,
except granodiorite plutons. The hornfels aureole to the batholith is narrow
south of Pebble but extends well east of the batholith in the vicinity of the
deposit, which suggests that the batholith underlies the deposit (which is
supported by magnetic data; Shah et al., 2009; Anderson et al, 2013).
Hornfels-altered rocks are massive and susceptible to brittle fracture, although
the narrow alteration envelopes around veins indicate that permeability was low.
Hornfels in flysch outside the deposit comprises biotite, K-feldspar, albite,
plagioclase and quartz with minor pyrite and other accessory minerals.
7.4.2 Hydrothermal Alteration
Numerous stages of hydrothermal alteration are present,
including: potassic, sodic-potassic, illite±kaolinite, pyrophyllite and sericite
advanced argillic, quartz-illite-pyrite, propylitic, and quartz-sericite-pyrite
assemblages, as well as a variety of vein types. Sericite is defined herein as
fine-grained, crystalline white mica, whereas illite is very fine-grained,
non-crystalline white mica (Harraden et al., 2013). Advanced argillic alteration
follows the naming convention of Meyer and Hemley (1967), although there are
some differences noted in Pebble alteration. Most metals were introduced during
early potassic and sodic-potassic alteration, with significant enhancement of
grade in areas overprinted by younger advanced argillic alteration.
7.4.2.1. EARLY
POTASSIC AND SODIC-POTASSIC ALTERATION
Most copper-gold-molybdenum mineralization coincides with early
potassic and sodic-potassic alteration. Potassic alteration occurs mostly in the
upper part of the Pebble East zone, whereas sodic-potassic alteration occurs in
the Pebble West zone and below potassic alteration in the Pebble East zone.
Sodic-potassic alteration is distinguished from potassic primarily by the
presence of albite and a higher concentration of carbonate minerals (Gregory and
Lang, 2011, 2012). Associated vein types are described below.
Potassic alteration occurs in all rock types and is most
intense in flysch and granodiorite sills near the Pebble East zone pluton,
within the Pebble East zone pluton and in small areas of the Pebble West zone
(Gregory and Lang, 2009). It is weakest in the area between the Pebble East and
Pebble West zone centers. The assemblage includes potassium feldspar, quartz
(both replacing igneous groundmass and locally plagioclase phenocrysts), and
biotite (replacing igneous hornblende and biotite) with trace to minor ankerite
or ferroan dolomite, apatite and rutile. Sulphides include disseminated
chalcopyrite and pyrite with minor molybdenite and bornite (Gregory and Lang,
2009). The proportion of biotite to potassium feldspar correlates with the Fe-Mg
concentration of host rocks and is highest in flysch and diorite sills.
Intrusive rocks in the Pebble West zone are affected by early
sodic-potassic alteration which comprises albite (replacing plagioclase
phenocrysts), biotite (replacing igneous biotite and hornblende), potassium
feldspar (replacing groundmass feldspars) and quartz, accompanied by ankerite,
ferroan dolomite, trace apatite, magnetite and, locally, siderite. The
concentration of carbonate minerals increases with depth. Sulphides include
pyrite and chalcopyrite that decrease in concentration with depth.
Sodic-potassic alteration of sedimentary rocks is pervasive and characterized by fine-grained potassium feldspar accompanied by
minor biotite or by fine-grained potassium feldspar and albite.
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In the Pebble East zone, sodic-potassic alteration occurs below
potassic alteration and is distinguished from similar alteration of the Pebble
West zone by the presence of epidote and calcite. The potassic to sodic-potassic
transition occurs over vertical distances of less than 330 ft. In the Pebble
East zone pluton, cores and rims of zoned plagioclase phenocrysts are replaced
by calcite-epidote and albite, respectively. Hornblende phenocrysts were
replaced by biotite and then by chlorite. Hematitized igneous magnetite is also
present. The igneous groundmass was replaced by fine-grained quartz, potassium
feldspar, and variable albite. Mineralization is weak and decreases with depth,
and includes 2% pyrite and trace to minor chalcopyrite and molybdenite. This
alteration is pervasive in flysch, is absent in granodiorite sills and is
difficult to distinguish from peripheral propylitic alteration.
Potassic alteration overprints sodic-potassic alteration but
the two alteration types are interpreted to be coeval and therefore are treated
as a single alteration event, with the apparent relative timing a consequence of
telescoping and/or changing fluid chemistry during cooling. The paragenetic and
spatial relationship between sodic-potassic alteration in the Pebble East and
Pebble West zones and peripheral propylitic alteration is not established.
7.4.2.1.1.
Vein Types Associated with Early Potassic and Sodic-Potassic Alteration
Four major quartz-sulphide vein types, comprising 80% of all
veins in the deposit, are associated with early potassic and sodic-potassic
alteration and are classified as types A, B, M and C. Each type includes
varieties that broadly correlate with lateral and/or vertical position in the
deposit. The naming conventions, while similar to standard porphyry vein
nomenclature, are not exact equivalents to vein types described from other
deposits (e.g., Gustafson and Hunt, 1975; Clark, 1993; Gustafson and Quiroga,
1995).
Total density of vein types A, B and C across most of the
Pebble deposit is between 5 and 15 vol % (using the criteria of Haynes and
Titley (1980) and not including alteration envelopes). Lower concentrations
occur near the margins of the deposit and at depth below the 0.3% CuEq resource
boundary. Higher concentrations occur within or proximal to the Pebble East zone
pluton and locally proximal to the smaller granodiorite plutons in the Pebble
West zone. Vein density does not correlate consistently with rock type and
patterns extend smoothly across geologic contacts. Measurements in oriented
drill core do not reveal any preferred vein orientations.
On the east side of the Pebble East zone there are two areas
with 50 to 90% quartz veins within a broader zone with greater than 20% quartz
veins. These veins are interpreted to belong to the A1 or B1 vein types. These
high vein density areas probably reflect repeated refracturing and dilation. The
first area is located north of the ZE fault in a broadly cylindrical zone 330 to
1,640 ft wide and extending up to 1,970 ft below the cover sequence. Veins in
this first zone are not deformed and controlling faults have not been
identified. The second area forms a northeast-trending, nearly vertical, tabular
zone that coincides with the extent of brittle-ductile deformation (described
above). This second area is truncated to the east by the ZG1 fault, continues
into the East Graben and is open below depths of 4,920 ft. Veins in this zone
are commonly deformed and locally brecciated and formed along the active BDF or
a precursor structure.
Type A Veins
Type A veins are the oldest of the four types and include
subtypes A1, A2 and A3. A1 is the most common type and occurs mostly within the
upper 2,300 ft of the Pebble East zone pluton. These veins are sinuous to
anastomosing, discontinuous, and typically have diffuse contacts. They contain
quartz, trace to minor potassium feldspar, less than 1 to 2% pyrite, lesser
chalcopyrite, and rare molybdenite. Potassium feldspar alteration envelopes are
commonly narrow, diffuse, and a few millimetres wide. They occur within
zones of pervasive, weakly mineralized potassic alteration.
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A2 veins occur below approximately 3,300 ft in the Pebble East
zone pluton and have characteristics transitional between quartz veins and
pegmatites. They are characterized by potassium feldspar selvages and
coarse-grained cores of euhedral to subhedral quartz. Coarse clots of biotite
are locally present along with trace chalcopyrite, molybdenite and/or pyrite.
The A2 veins are sinuous, discontinuous, irregular, have diffuse contacts and
lack alteration envelopes.
A3 veins are transitional between vein types A1 and B1 and are
most common below 2,500 ft in the Pebble East zone pluton. The A3 veins are
typically anastomosing, less than 0.4 in wide, sinuous to irregular and have
diffuse contacts with prominent potassium feldspar envelopes. They contain
quartz with trace to minor potassium feldspar and biotite, and locally contain
up to 3% pyrite, minor chalcopyrite and rare molybdenite.
Type B Veins
Type B veins cut type A veins and include subtypes B1, B2 and
B3. These are spatially coincident with potassic and sodic-potassic alteration,
are the most widespread veins at Pebble and are most abundant within and
proximal to the Pebble East zone pluton.
B1 veins are the most common subtype and are planar,
continuous, have sharp contacts, and are typically 0.1 to 1.2 in wide. They are
dominated by quartz with trace to minor biotite, potassium feldspar, apatite
and/or rutile. The veins typically comprise 2 to 5% pyrite and chalcopyrite with
minor molybdenite and local bornite. Potassium feldspar (±biotite) alteration
envelopes are ubiquitous, highly variable in width and contain disseminated
chalcopyrite, pyrite and molybdenite.
B2 veins occur below 2,600 ft in the Pebble East zone and
broadly coincide with sodic-potassic alteration. They contain quartz and minor
K-feldspar and have narrow, weak potassium feldspar or biotite alteration
envelopes. B2 veins transition upward into B1 veins and are distinguished from
B1 veins by green chlorite pseudomorphs after coarse aggregates of locally
preserved biotite and by minor calcite and epidote. The veins typically contain
less than 2% pyrite, minor chalcopyrite, and minor molybdenite.
B3 veins are most common in the north-central and south-central
part of the Pebble East zone as well as at depths below 5,600 ft in the lower
grade domain between the Pebble East and Pebble West zones. These veins are
similar to B1 veins but contain molybdenite as the dominant sulphide and have
only sporadic, weak, potassium feldspar alteration envelopes. B3 veins are
planar and can be greater than 3.3 ft in width. B3 veins cut vein types A, B1
and B2 and, locally, C veins; B3 veins are interpreted to represent a late
substage of early alteration which locally introduced significant molybdenum to
the Pebble deposit.
Type M Veins
Type M veins are associated with magnetite-bearing
sodic-potassic alteration within and proximal to diorite sills in the Pebble
West zone. Paragenetically they formed between vein types B1 and C. They are
planar to irregular and are typically 0.4 to 2 in wide. These veins comprise
mostly magnetite and quartz with lesser ankerite and potassium feldspar as well
as greater than 10% chalcopyrite and pyrite with minor molybdenite. The M veins
have narrow potassium feldspar alteration envelopes.
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Type C Veins
Type C veins are the most abundant veins in the deposit, with
the exception of the Pebble East zone pluton. C veins cut A and B veins (except
possibly the B3 subtype), and are contemporaneous with or slightly younger than
M veins. C veins at Pebble are defined according to their relative timing and do
not resemble the C veins defined by Gustafson and Quiroga (1995). The veins
contain mostly quartz, locally abundant ankerite or ferroan dolomite, minor to
trace potassium feldspar, magnetite and biotite, and 10% (locally up to 50%)
sulphides. Sulphides include pyrite and chalcopyrite, variable molybdenite,
trace arsenopyrite and rare bornite. The veins are planar, have sharp contacts,
range from less than 0.4 in to approximately 2 in wide and commonly contain vugs
along their central axis. Alteration envelopes are prominent with similar
mineralogy to the veins and can be up to 10 times the width of the vein in the
more permeable intrusive host rocks. Where the alteration envelopes to several C
veins overlap, drill intersections up to approximately 15 ft in length can grade
up to several percent copper.
7.4.2.2. INTERMEDIATE ILLITE ± KAOLINITE ALTERATION
Illite ± kaolinite alteration is coincident with and overprints
early potassic and sodic-potassic alteration. Alteration intensity is highest at
moderate depths within the Pebble East zone pluton. In these rocks, illite
replaces phenocrysts of plagioclase altered to potassium feldspar and locally
replaces the potassically-altered igneous matrix. This alteration style is
weakest in flysch in the Pebble West zone. Minor pyrite co-precipitated with
illite. Fracture or fault control is rarely apparent. Kaolinite accompanies
illite in alteration of previously sodic-potassic altered areas where it
replaces albite.
7.4.2.3.
LATE ADVANCED ARGILLIC ALTERATION
Advanced argillic alteration occurs only in the East Zone,
where it is associated with the highest grades of copper and gold in the
deposit. Advanced argillic alteration is focused along and adjacent to the BDF.
This alteration comprises a pyrophyllite-quartz-sericite-chalcopyrite-pyrite
zone along the BDF bounded by an upwardly-flaring envelope of
sericite-quartz-pyrite-bornite-digenite-chalcopyrite alteration to the west
(cf., Khashgerel et al., 2009). Advanced argillic alteration is truncated on the
east by the ZG1 fault but continues into the graben. Both sericite and
pyrophyllite-bearing alteration replace previous alteration type; the sericite
alteration is locally replaced by younger quartz-sericite-pyrite alteration.
Pyrophyllite alteration is accompanied by quartz, sericite,
pyrite and chalcopyrite. Pyrite concentration is commonly greater than 5% and is
much higher than in adjacent early potassic alteration. Pyrophyllite alteration
is coincident with but overprints the southern zone of high quartz vein density,
where quartz-sulphide veins within the BDF are commonly deformed. Veins
associated with pyrophyllite alteration are irregular, narrow, massive to
semi-massive, contain pyrite ± chalcopyrite with variable quartz, and lack
alteration envelopes. Pyrophyllite alteration has not been identified in the
northern zone of high quartz vein density.
Pervasive sericite alteration forms an upward-flaring envelope
west of the pyrophyllite alteration. Sericite alteration occurs in the upper
1,000 ft of the deposit on the downthrown southern side of the ZE fault. This
alteration is pervasive and dominated by white sericite that replaces feldspars
previously affected by potassic and illite alteration. Pyrite concentration is
intermediate between pyrophyllite alteration and early potassic alteration and
decreases with depth. Sericite alteration is distinguished by high-sulphidation
hypogene copper minerals represented by various combinations of bornite,
covellite, digenite, tennanite-tetrahedrite, and locally trace enargite. These
minerals commonly replace the rims of chalcopyrite and pyrite precipitated
during early potassic alteration. Minor quartz-rich veins with pyrite are
related to this alteration, are narrow and irregular, and locally have
well-developed envelopes with quartz, sericite, pyrite and high sulphidation
copper minerals.
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7.4.2.4. PROPYLITIC
ALTERATION
Propylitic alteration extends at least 3 miles south of the
deposit and to the limit of drilling 1.4 miles to the north. Weak propylitic
alteration occurs throughout the eastern half of the Kaskanak batholith. This
alteration comprises chlorite, epidote, calcite, quartz, magnetite and pyrite,
minor albite and hematite, and trace chalcopyrite. Sulphide concentration is
less than 3% and is mostly pyrite.
Type H veins occur locally, in low density, throughout
propylitic alteration and contain calcite, hematized magnetite, quartz, albite,
epidote, pyrite and trace to minor chalcopyrite. H veins are planar, less than
0.4 in (1 cm) wide and have alteration envelopes similar in mineralogy and width
to the veins.
Polymetallic type E veins occur locally south of the deposit,
in areas of propylitic and quartz-sericite-pyrite (QSP) alteration. Rarely, E
veins cut sodic-potassic alteration in the Pebble West zone. E veins are planar,
up to tens of centimetres in width, have sharp contacts with host rocks and
locally have weak sericite alteration envelopes. These veins contain quartz,
calcite, pyrite (locally arsenian), sericite, sphalerite, galena, minor
chalcopyrite and trace arsenopyrite, tennantite-tetrahedrite, freibergite,
argentite and native gold.
7.4.2.5.
QUARTZ-SERICITE-PYRITE AND QUARTZ-ILLITE-PYRITE ALTERATION
Although QSP alteration occurs closer to the centre of the
deposit than propylitic alteration, where these alteration styles overlap QSP
overprints propylitic alteration. QSP alteration (equivalent to classic
phyllic alteration) is texture-destructive and forms a halo around the deposit
with alteration fronts that dip steeply outward. This halo extends at least 2.6
miles south of the deposit and 0.9 miles north; it is weakly developed west of
the ZF fault where it partially overprints propylitic alteration. It occurs at
depth in the north part of the East Graben but its full distribution east of the
ZG1 fault is not established. In the Pebble East zone, the transition to
intense, pervasive QSP alteration typically occurs over 50 to 60 ft. Weak QSP
alteration occurs sporadically throughout the Pebble West zone with a more
gradual transition than in the Pebble East zone.
Mineralogy of QSP alteration includes quartz, sericite, 8 to
20% pyrite, minor to trace ankerite, rutile and apatite, and rare pyrrhotite.
Zones are cut by up to 10% pyrite-rich type D veins (Gustafson and Hunt, 1975)
with variable amounts of quartz and trace rutile, chalcopyrite and ankerite. D
veins are planar, have sharp contacts with host rocks and range from less than 1
in to 5 ft in width. Alteration envelopes are typically wider than the veins and
form intense pervasive QSP alteration where they coalesce.
Quartz-illite-pyrite (QIP) alteration partially replaces
potassic and/or sodic-potassic alteration in the upper, central part of the
deposit. QIP alteration is interpreted as a zone of former weak QSP alteration
at the transition between potassic/sodic and potassic alteration, which was
later overprinted by low-temperature illite alteration as the hydrothermal
system waned. QIP alteration is similar to QSP alteration, with illite as the
main phyllosilicate phase (Harraden et al., 2012). Pyrite abundance is typically
5 to 10% in type D veins and associated QIP alteration envelopes. Domains
between alteration envelopes are marked by a decrease in the density of D veins
and their alteration envelopes.
7.4.3
Post-Hydrothermal Alteration
The youngest alteration at Pebble is clay alteration, which is
common within 50 ft of the contact between the cover sequence and Cretaceous
rocks. Young, brittle faults cut the deposit (in particular the ZG1 fault) and
contain or are associated with basalt dikes related to volcanic rocks in the
cover sequence. The faults and dikes are surrounded by narrow alteration zones of epidote, calcite, chlorite, and
pyrite. A very small proportion of mineralization is disrupted by this
alteration.
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7.5 |
DEPOSIT MINERALIZATION STYLES |
Mineralization in the Pebble West zone is mostly hypogene, with
a thin zone of mostly weak supergene mineralization beneath a thin leached cap.
Mineralization in the Pebble East zone is entirely hypogene with no preservation
of leaching or paleo-supergene below the cover sequence.
7.5.1 Supergene Mineralization and Leached Cap
A thin leached cap occurs at the top of the Pebble West zone;
strong leaching is rarely more than 33 ft thick although weak oxidation locally
extends to depths of up to 500 ft along faults. Hypogene pyrite is common and
minor malachite, chrysocolla and native copper are present locally.
Supergene mineralization occurs only in the Pebble West zone
where the cover sequence is absent. Supergene mineralization has an average
thickness of 72 ft but at least traces of supergene minerals locally extend to
depths of 560 ft in strongly fractured zones. In the supergene zone, pyrite is
typically rimmed by chalcocite, covellite and minor bornite; complete
replacement is rare (Gregory and Lang, 2009; Gregory et al., 2012). The
transition to hypogene mineralization is gradational over distances of up to
approximately 100 feet. Supergene processes increased copper grade up to
approximately 50% across narrow intervals.
7.5.2 Hypogene Mineralization
Patterns of metal grades and ratios at Pebble correspond
closely to alteration styles, with only weak or local relationships to host
rock. The deposit has a tabular geometry when the 20° post-hydrothermal tilt is
removed. Copper and gold grades diminish below approximately 1,300 ft depth in
the Pebble West zone but extend much deeper in the Pebble East zone,
particularly within and proximal to the BDF. Laterally, grades decrease
gradually toward the north and south margins of the deposit, where
mineralization is abruptly terminated where overprinted by poorly-mineralized
QSP alteration. Moderate grades with the shortest vertical extent are observed
in the middle of the deposit between the Pebble East and Pebble West zones.
There is a general correspondence between copper and gold grades outside of the
Pebble East zone pluton; within the Pebble East zone pluton, there is a closer
correspondence between copper and molybdenum at low grades of gold, except where
gold-rich advanced argillic alteration is present. On the west side of the
deposit, mineralization extends to the ZF fault, whereas on the east side it was
down-dropped into the East Graben by the ZG1 fault. Molybdenum exhibits a more
diffuse pattern, is open at depth and, in some areas, elevated grade corresponds
with more abundant type B3 veins.
Mineralization was primarily introduced during early potassic
and sodic-potassic alteration. Copper is hosted primarily by chalcopyrite
(Figure 7.5.1), locally co-precipitated with bornite (Figure 7.5.2) and trace
tennantite-tetrahedrite. The pyrite to chalcopyrite ratio is typically close to
one in potassic alteration in the Pebble East zone but is commonly much higher
in the Pebble West zone where sulphide-rich type C and, locally, type D veins
are present. Gold occurs primarily as electrum inclusions in chalcopyrite with
minor amounts hosted by silicate alteration minerals and pyrite, and rarely as
gold telluride inclusions in pyrite (Gregory et al., 2013). Diorite sills with
magnetite-rich alteration and type M veins have relatively high gold
concentrations. Molybdenite occurs in quartz veins and intergrown with
disseminated chalcopyrite.
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Incipient to weak illite±kaolinite alteration had little effect on grade, whereas strong alteration reduced the grade of copper and gold but left molybdenum largely undisturbed. Gold liberated during illite±kaolinite alteration was
reconstituted as high-fineness inclusions (gold grains with less than 10 wt% Ag) in pyrite (Gregory and Lang 2009; Gregory et al., 2013). These patterns are consistent with the effects of illite alteration on grade in many porphyry deposits (e.g.,
Seedorf et al., 2005; Sillitoe, 2010).
Advanced argillic alteration zones have much higher grades of copper and gold but similar molybdenum compared to adjacent early potassic alteration. Pyrophyllite alteration precipitated high concentrations of pyrite and chalcopyrite and both
minerals contain inclusions of high-fineness gold (Gregory et al., 2013). During sericite alteration, bornite, covellite, digenite and trace enargite or tennantite replaced chalcopyrite formed during early potassic alteration and also precipitated
minor additional pyrite (Gregory and Lang, 2009). In general, gold occurs as high-fineness inclusions in later pyrite and high-sulphidation copper minerals, whereas electrum predominates in relict early chalcopyrite (Gregory et al., 2013).
The zone of high quartz vein density along the BDF is typically well-mineralized where it has been overprinted by pyrophyllite alteration. The northern zone of high quartz vein density has average to low grades of copper and gold except in small
areas where higher grades reflect the presence of sericite alteration.
Copper and molybdenum mineralization was largely removed by late QSP alteration. Gold concentrations remain consistent at 0.15 to 0.5 g/t, and locally exceed 1 g/t (Lang et al., 2008). The QIP alteration partially overprints early alteration types
and affected areas retain low copper and molybdenum grades with gold occurring as inclusions in younger stages of pyrite (Gregory et al., 2013).
Grade variation within the cores of the Pebble East and Pebble West zones shows a weak, local relationship to rock type. Higher than average copper and gold grades are spatially related to iron-rich diorite sills, a relationship common in porphyry
deposits (e.g., Ray, Arizona; Phillips et al., 1974). On the margins of the deposit and in the lower grade area between the Pebble East and Pebble West Zones, relatively impermeable flysch affected by pre-hydrothermal hornfels has lower grades than
adjacent, more permeable granodiorite sills.
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Figure
7.5.1 Drill Core Photograph Showing Chalcopyrite Mineralization
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Figure
7.5.2
Drill Core Photograph Showing Chalcopyrite and Bornite Mineralization
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The Pebble deposit is classified as a copper-gold-molybdenum
porphyry deposit. The principal features of porphyry copper deposits, as
summarized recently by John et al. (2010), include:
-
Mineralization defined by copper and other minerals which occur as
disseminations and in veins and breccias which are relatively evenly
distributed throughout their host rocks;
-
Large tonnage amenable to bulk mining methods;
-
Low to moderate copper grades, typically between 0.3% and 2.0%;
-
A genetic relationship to porphyritic intrusions of intermediate
composition that typically formed in convergent-margin tectonic settings;
-
A metal assemblage dominated by various combinations of copper, gold,
molybdenum and silver, but commonly with other associated metals of low
concentration; and,
-
A spatial association with other styles of intrusion-related
mineralization, including skarns, polymetallic replacements and veins, distal
disseminated gold-silver deposits, and intermediate to high-sulphidation
epithermal deposits.
These characteristics correspond closely to the principal
features of the Pebble deposit as described in Section 7.0 of this report. This
report focuses exclusively on the Pebble porphyry deposit; other deposits of
intrusion-related skarn, vein and porphyry style mineralization have been
encountered elsewhere on the Pebble property but have not been the subject of
detailed exploration or delineation.
Pebble has one of the largest metal endowments of any
gold-bearing porphyry deposit currently known. Comparison of the current Pebble
resource to other major gold-bearing porphyry deposits shows that it ranks at or
near the top in terms of both contained copper (Figure 8.1.1) and gold (Figure
8.1.2) . In fact, Pebble is both the largest known undeveloped copper resource
and the largest known undeveloped gold resource in the world today. The basis of
this estimation of metal endowment in the Pebble deposit is fully described in
Section 14.0 of this report.
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Figure
8.1.1
Pebble Deposit Rank by Contained Copper
Figure
8.1.2 Pebble Deposit Rank by Contained Gold
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Geological, geochemical and geophysical surveys were conducted
in the Pebble Project area from 2001 to 2007 by Northern Dynasty and since
mid-2007 by the Pebble Partnership. The types of historical surveys and their
results are summarized below. More detailed descriptions of historical
exploration programs and results may be found in Rebagliati and Haslinger
(2003), Haslinger et al. (2004), Rebagliati and Payne (2006 and 2007),
Rebagliati and Lang (2009) and Rebagliati et al. (2005, 2008, 2009 and 2010).
9.1.1 Geological Mapping
Between 2001 and 2006, the entire Pebble property was mapped
for rock type, structure and alteration at a scale of 1:10,000. This work
provided an important geological framework for interpretation of other
exploration data and drilling programs. A geological map of the Pebble deposit
was also constructed but, due to a paucity of outcrop, was based solely on
drillhole information. The content and interpretation of district and deposit
scale geological maps have not changed materially from the information presented
by Rebagliati et al. (2009 and 2010).
9.1.2
Geophysical Surveys
In 2001, dipole-dipole IP surveys totalling 19.3 line-mi were
completed by Zonge Geosciences for Northern Dynasty, following up on and
augmenting similar surveys completed by Cominco (Teck).
During 2002, a ground magnetometer survey totalling 11.6
line-mi was completed at Pebble. The survey was conducted by MPX Geophysics
Ltd., based in Richmond Hill, Ontario. The principal objective of this survey
was to obtain a higher resolution map of magnetic patterns than was available
from existing regional government magnetic maps. The focus of this work was the
area surrounding mineralization in the 37 Skarn zone in the southern part of the
Pebble district. A helicopter-based airborne magnetic survey was flown over the
entire Pebble property in 2007. A total of 1,456.5 line-mi were flown at 656 ft
line spacing, covering an area of 164.5 square miles. The survey lines were
flown at a nominal mean terrain clearance of 196.8 ft along flight lines
oriented 135° at a line spacing of 656 ft, with tie lines oriented 045° at a
spacing of 1.24 miles. Immediately over the Pebble deposit, an area of 14.4
square miles was surveyed at a 328 ft line spacing for a total of 212.5 line-mi,
without additional tie lines.
During 2007, a limited magnetotelluric survey was completed by
GSY-USA Inc., the U.S. subsidiary of Geosystem SRL of Milan, Italy, under the
supervision of Northern Dynasty geologists. The survey focused on the area of
drilling in the Pebble East zone and comprised 196 stations on nine east-west
lines and one north-south line, at a nominal station spacing of 656 ft.
Interpretation, including 3D inversion, was completed by Mr. Donald Hinks of Rio
Tinto Zinc.
In July 2009, Spectrem Air Limited, an Anglo
American-affiliated company based in South Africa, completed an airborne
electromagnetic, magnetic and radiometric survey over the Pebble area. A total
of 2,386 line-mi were surveyed in two flight block configurations:
- a regional block covering an area of about 18.6 x 7.5 miles at a line
spacing of 0.95 miles; and,
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- a more detailed block which covered the Pebble property using a line
spacing of 820 ft.
The orientation of flight lines was 135° for both surveys, with
additional tie-lines flown orthogonally. The objectives of this work included
provision of geophysical constraints for structural and geological
interpretation in areas with significant glacial cover.
Between the second half of 2009 and mid-2010, a total of 120.5
line-mi of IP chargeability and resistivity data were collected by Zonge
Engineering and Research Organization Inc. (Zonge Engineering) for the Pebble
Partnership. This survey was conducted in the southern and northern parts of the
property and used a line spacing of about 0.5 miles; the objective of this
survey was to extend the area of IP coverage completed prior to 2001 by Cominco
(Teck) and during 2001 by Northern Dynasty.
During 2010, an airborne electromagnetic (EM) and magnetometer
geophysical survey was completed on the Pebble property totalling 4,009 line-mi.
This survey was conducted by Geotech Ltd. of Aurora, Ontario.
The USGS collected gravity data from 136 stations distributed
over an area of approximately 2,317 square miles during 2008 and 2009.
9.1.3 Geochemical Surveys
Between 2001 and 2003, Northern Dynasty collected 1,026 soil
samples (Rebagliati and Lang, 2009). Typical sample spacing in the central part
of the large geochemical grid was 100 ft to 250 ft along lines spaced 122 to 400
ft to 750 ft apart; samples were more widely spaced near the north, west and
southwest margins of the grid.
These sampling programs outlined high-contrast, coincident
anomalies in gold, copper, molybdenum and other metals in an area that measures
at least 5.6 miles north-south by up to 2.5 miles east-west, with strong but
smaller anomalies in several outlying zones. All soil geochemical anomalies lie
within the IP chargeability anomaly described above. Three very limited
surficial geochemical surveys were completed by the Pebble Partnership in 2010
and 2011; no significant geochemical anomalies were identified. A total of 126
samples, comprising 113 till and 13 soil samples, were collected on the KAS
claims located in the southern end of the property; samples were on lines spaced
approximately 8,000 ft apart with a sample spacing of approximately 1,300 ft. A
total of 109 soil samples were collected from two small areas located
approximately 11 miles to the west-northwest and 15 miles west of the Pebble
deposit; samples were spaced approximately 330 ft apart on lines that were
irregularly spaced to accommodate terrain features.
Additional surveys were completed between 2007 and 2012 by
researchers from the USGS and the University of Alaska Anchorage (see summary in
Kelley et al., 2013 and contained references). The types of surveys that were
completed by these groups include: (1) hydrogeochemical surveys in several parts
of the Pebble property which obtained multi-element inductively coupled plasma
mass spectrometry (ICP-MS) data from samples of surface waters; (2)
determination of copper isotope ratios in surface waters; (4) heavy indicator
mineral analyses of glacial till; and (4) orientation surveys which utilized a
variety of weak extraction geochemical techniques. The results of these surveys
were largely consistent with the results obtained by earlier soil sampling
programs.
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10.1 |
LOCATION OF ALL DRILL HOLES |
Extensive drilling totaling 1,042,218 ft has been
completed in 1,355 holes on the Pebble Project. These drill campaigns took place
during 19 of the 26 years between 1988 and 2013. The spatial distribution and
type of holes drilled is illustrated in Figure 10.1.1.
Figure
10.1.1
Location of all Drill Holes
Drilling completed by Cominco (Teck) (1988 to 1997) is
described briefly in Section 6.0 and will not be discussed further here.
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All drill hole collars have been surveyed using a differential
global positioning system (GPS). A digital terrain model for the site was
generated by photogrammetric methods in 2004. All post-Cominco (Teck) drill
holes have been surveyed downhole, typically using a single shot magnetic
gravimetric tool. A total of 989 holes were drilled vertically (-90°) and 192
were inclined from -42° to -85° at various azimuths.
10.2 |
SUMMARY OF DRILLING 2001 TO 2013 |
The Pebble deposit has been drilled extensively (Figure 10.2.1)
. Drilling statistics and a summary of drilling by various categories to the end
of the 2013 exploration program are compiled in Figure 10.2.2. This includes
seven drill holes completed by FMMUSA, drilled by Peak Exploration (USA) Corp.
in the area in 2008; these holes were drilled on claims that are now part of the
Pebble property and have been added to the Pebble dataset. Detailed descriptions
of the programs and results for 2009 and preceding years may be found in
technical reports by Rebagliati and Haslinger (2003 and 2004), Haslinger et al.
(2004), Rebagliati and Payne (2005, 2006 and 2007), and Rebagliati et al. (2008,
2009 and 2010).
Most of the footage on the Pebble Project was drilled using
diamond core drills. Only 18,716 ft was percussion-drilled from 222 rotary drill
holes. Many of the cored holes were advanced through overburden, using a tricone
bit with no core recovery. These overburden lengths are included in the core
drilling total.
Since early 2004, all Pebble drill core has been geotechnically
logged on a drill run basis. Over 69,000 measurements were made for a variety of
geotechnical parameters on 735,000 ft of core drilling. Recovery is generally
very good and averages 98.5% overall; two-thirds of all measured intervals have
100% core recovery. Additionally, all Pebble drill core from the 2001 through
2013 drill programs was photographed in a digital format.
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Figure
10.2.1
Location of Drill holes Pebble Deposit
Figure
10.2.2
Summary of Drilling to December 2013
|
No. of Holes |
Feet |
Metres |
By Operator |
Cominco (Teck)1 |
164 |
75,741.0 |
23,086 |
Northern Dynasty |
578 |
495,069.5 |
150,897 |
Pebble Partnership2 |
606 |
465,957.7 |
142,024 |
FMMUSA |
7 |
5,450.0 |
1,661 |
Total |
1,355 |
1,042,218.2 |
317,668 |
By Type |
Core1,5 |
1,132 |
1,023,297.6 |
311,901 |
Percussion6 |
223 |
18,920.6 |
5,767 |
Total |
1,355 |
1,042,218.2 |
317,668 |
By Year |
19881 |
26 |
7,601.5 |
2,317 |
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|
No. of Holes |
Feet |
Metres |
19891 |
27 |
7,422.0 |
2,262 |
1990 |
25 |
10,021.0 |
3,054 |
1991 |
48 |
28,129.0 |
8,574 |
1992 |
14 |
6,609.0 |
2,014 |
1993 |
4 |
1,263.0 |
385 |
1997 |
20 |
14,695.5 |
4,479 |
2002 |
68 |
37,236.8 |
11,350 |
2003 |
67 |
71,226.6 |
21,710 |
2004 |
267 |
165,567.7 |
50,465 |
2005 |
114 |
81,978.5 |
24,987 |
20063 |
48 |
72,826.9 |
22,198 |
20074 |
92 |
167,666.9 |
51,105 |
20085 |
241 |
184,726.4 |
56,305 |
2009 |
33 |
34,947.5 |
10,652 |
2010 |
66 |
57,582.0 |
17,551 |
2011 |
85 |
50,767.7 |
15,474 |
2012 |
81 |
35,760.2 |
10,900 |
2013 |
29 |
6,190.0 |
1,887 |
Total |
1,355 |
1,042,218.2 |
317,668 |
By Area |
East |
141 |
446,379.3 |
136,056 |
West |
443 |
351,986.7 |
107,286 |
Main7 |
101 |
10,674.7 |
3,254 |
NW |
203 |
45,948.4 |
14,005 |
North |
46 |
25,695.9 |
7,832 |
NE |
10 |
1,097.0 |
334 |
South |
98 |
50,262.5 |
15,320 |
25 Zone |
8 |
4,047.0 |
1,234 |
37 Zone |
7 |
4,252.0 |
1,296 |
38 Zone |
20 |
14,221.5 |
4,335 |
52 Zone |
5 |
2,534.0 |
772 |
308 Zone |
1 |
879.0 |
268 |
Eastern |
21 |
3,105.0 |
946 |
Southern |
153 |
60,442.4 |
18,423 |
SW |
51 |
9,337.8 |
2,846 |
Sill |
39 |
10,445.5 |
3,184 |
Cook Inlet |
8 |
909.5 |
277 |
Total |
1,355 |
1,042,218.2 |
317,668 |
Notes:
1. Includes holes drilled on the Sill
prospect.
2. Holes started by Northern Dynasty and finished by the
Pebble Partnership are included as the Pebble Partnership.
3.
Drillholes counted in the year in which they were completed.
4. Wedged
holes are counted as a single hole including full length of all wedges
drilled.
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5. Includes FMMUSA drillholes; data acquired in
2010.
6. Shallow (<15 ft) auger holes not included.
7.
Comprises holes drilled entirely in Tertiary cover rocks within the Pebble West
and Pebble East areas.
Some numbers may not sum exactly due to
rounding.
The drill hole database includes drill holes completed up until
2013; the drilling completed in 2013 is outside the area of the resource
estimate. Highlights of drilling completed by Northern Dynasty and the Pebble
Partnership between 2001 and 2013 include:
-
Northern Dynasty drilled 68 holes for a total of 37,237 ft during 2002. The
objective of this work was to test the strongest IP chargeability and
multi-element geochemical anomalies outside of the Pebble deposit, as known at
that time, but within the larger and broader IP chargeability anomaly
described above. This program discovered the 38 Zone porphyry
copper-gold-molybdenum deposit, the 52 Zone porphyry copper occurrence, the 37
Zone gold-copper skarn deposit, the 25 Zone gold deposit, and several small
occurrences in which gold values exceeded 3.0 g/t.
-
In 2003, Northern Dynasty drilled 67 holes for a total of 71,227 ft, mainly
within and adjacent to the Pebble West zone to determine continuity of
mineralization and to identify and extend higher grade zones. Most holes were
drilled to the zero meter elevation above mean sea level and were 900 to 1,200
ft in length. Eight holes for a total of 5,804 ft were drilled outside the
Pebble deposit to test for extensions and new mineralization at four other
zones on the property, including the 38 Zone porphyry copper-gold- molybdenum
deposit and the 37 Zone gold-copper skarn deposit.
-
Drilling by Northern Dynasty in 2004 totalled 165,481 ft in 266 holes. Of
this total, 131,211 ft were drilled in 147 exploration holes in the Pebble
deposit; one exploration hole 879 ft in length was completed in the southern
part of the property that discovered the 308 Zone porphyry
copper-gold-molybdenum deposit. Additional drilling included 21,335 ft in 26
metallurgical holes in Pebble West zone, 9,127 ft in 54 geotechnical holes and
3,334 ft in 39 water monitoring holes, of which 33 holes for a total of 2,638
ft were percussion holes. During the 2004 drilling program, Northern Dynasty
identified a significant new porphyry centre on the eastern side of the Pebble
deposit (the Pebble East zone) beneath the cover sequence (as described in
Section 7).
-
In 2005, Northern Dynasty drilled 81,979 ft in 114 holes. Of these drill
holes, 13 for a total of 12,198 ft were drilled mainly for engineering and
metallurgical purposes in the Pebble West zone. Seventeen drill holes for a
total of 60,696 ft were drilled in the Pebble East zone. The results confirmed
the presence of the Pebble East zone and further demonstrated that it was of
large size and contained higher grades of copper, gold and molybdenum than the
Pebble West zone. The Pebble East zone remained completely open at the end of
2005. A further 13 holes for a total of 2,986 ft were cored for engineering
purposes outside the Pebble deposit area. An additional 6,099 ft of drilling
was completed in 71 non-core water monitoring wells.
-
Drilling during 2006 focused on further expansion of the Pebble East zone.
Drilling comprised 72,827 ft in 48 holes. Twenty of these holes were drilled
in the Pebble East zone, including 17 exploration holes and three engineering
holes for a total of 68,504 ft. The Pebble East zone again remained fully open
at the conclusion of the 2006 drilling program. In addition, 2,710 ft were
drilled in 14 engineering core holes and 1,612 ft were drilled in 14
monitoring well percussion holes elsewhere on the property.
-
Drilling in 2007 continued to focus on the Pebble East zone. A total of
151,306 ft of delineation drilling in 34 holes extended Pebble East to the
northeast, northwest, south and southeast; the zone nonetheless remained open
in these directions, as well as to the east in the East Graben. Additional
drilling included
10,167 ft in nine metallurgical holes in
Pebble West, along with 4,367 ft in 26 engineering holes and 1,824 ft in 23
percussion holes for monitoring wells across the property.
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- In 2008, 234 holes were drilled totalling 179,275 ft, the most extensive
drilling on the project in any year to date. A total of 136,266 ft of
delineation and infill drilling, including six oriented holes, was completed
in 31 holes in Pebble East. This drilling further expanded the Pebble East
zone. Fifteen metallurgical holes for a total of 14,511 ft were drilled in the
Pebble West zone. One 2,949 ft infill/geotechnical hole was drilled in the
Pebble West zone. Geotechnical drilling elsewhere on the property included 105
core holes for a total of 18,806 ft. Hydrogeology and geotechnical drilling
outside of the Pebble deposit accounted for 82 percussion holes for a total of
6,745 ft. In 2010, the Pebble Partnership acquired the data for seven holes
totalling 5,450 ft drilled by FMMUSA in 2008. These drill holes are located
near the Property on land that is now controlled by the Pebble Partnership and
provided information on the regional geology.
- The Pebble Partnership drilled 34,948 ft in 33 core drill holes in 2009.
Five delineation holes were completed for 6,076 ft around the margins of
Pebble West and 21 exploration holes for a total of 22,018 ft were drilled
elsewhere on the property. In addition, seven geotechnical core holes were
drilled for a total of 6,854 ft.
- In 2010, the Pebble Partnership drilled 57,582 ft in 66 core holes.
Forty-eight exploration holes totalling 54,208 ft were drilled over a broad
area of the property outside the Pebble deposit. An additional 3,374 ft were
drilled in 18 geotechnical holes within the deposit area and to the west.
- In 2011, the Pebble Partnership drilled 50,768 ft in 85 core holes. Eleven
holes were drilled in the deposit area totalling 33,978 ft. Of these, two
holes were drilled in Pebble East for metallurgical and hydrogeological
purposes. The other nine holes in the deposit area were drilled for further
delineation of Pebble West and the area immediately to the south. These
results indicated the potential for resource expansion to depth in the Pebble
West zone. Six holes totalling 8,780 ft were also drilled outside the Pebble
deposit area to the west and south. In addition, 8,010.2 ft was drilled in 68
geotechnical holes within and to the north, west and south of the deposit.
- The Pebble Partnership drilled 35,760 ft in 81 core holes in 2012. Eleven
h0les totalling 13,754 ft were drilled in the southern and western parts of
the Pebble West zone. The results show potential for lateral resource
expansion in this area and further delineation drilling is warranted. Six
holes totalling 6,585 ft. were drilled to test exploration targets to the
south on the Kaskanak claim block, to the northwest and south of Pebble, and
on the KAS claim block further south. An additional 64 geotechnical and
hydrogeological holes were drilled totalling 15,422 ft. Of this drilling, 41
holes were within the deposit area and 15 geotechnical holes were drilled at
sites near the deposit, and eight geotechnical holes were completed near Cook
Inlet.
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-
The Pebble Partnership drilled 6,190 ft in 29 core holes for geotechnical
purposes in 2013 at sites west, south and southwest of the deposit area.
-
No holes were drilled in 2014.
A re-survey program of holes drilled at Pebble from 1988 to
2009 was conducted during the 2008 and 2009 field seasons. For consistency
throughout the project, the resurvey program referenced the control network
established by R&M Consultants in the U.S. State Plane Coordinate System
Alaska Zone 5 NAVD88 Geoid99. The resurvey information was applied to the drill
collar coordinates in the database in late 2009.
In 2009 and 2013, the survey locations, hole lengths, naming
conventions and numbering designations of the Pebble drill holes were reviewed.
This exercise confirmed that several shallow, non-cored, overburden drill holes
described in some engineering and environmental reports were essentially the
near-surface pre-collars of existing bedrock diamond drill holes. As these
pre-collar and bedrock holes have redundant traces, the geologic information was
combined into a single trace in the same manner as the wedged holes. In
addition, a number of very shallow (less than 15 ft), small diameter,
water-monitoring auger holes were removed from the exploration drill hole
database, as they did not provide any geological or geochemical information.
10.3 |
BULK DENSITY RESULTS |
Bulk density measurements were collected from drill core
samples, as described in Section 11.4. A summary of all bulk density results is
provided in Figure 10.3.1.
Figure 10.3.2 shows a summary of bulk density drill holes used
in the current mineral resource estimate.
Figure 10.3.1
S ummary of
All Bulk Density Results
Age |
No. of Measurements |
Density Mean |
Density Median |
Quaternary |
34 |
2.60 |
2.61 |
Tertiary |
2,703 |
2.57 |
2.57 |
Cretaceous |
8,671 |
2.66 |
2.64 |
All |
11,775 |
2.63 |
2.62 |
Figure
10.3.2 Summary
of Bulk Density Results Used for Resource Estimation
Age |
No. of Measurements |
Density Mean |
Density Median |
Tertiary |
3,026 |
2.56 |
2.57 |
Cretaceous |
8,130 |
2.64 |
2.62 |
All |
11,185 |
2.62 |
2.61 |
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11.0 |
SAMPLE PREPARATION, ANALYSES, AND SECURITY
|
11.1 |
SAMPLING METHOD AND APPROACH |
The Pebble deposit has been explored by extensive core
drilling, with 80,859 samples taken from drillcore for assay analysis. Nearly
all potentially mineralized Cretaceous core drilled and recovered has been
sampled by halving in 10 ft lengths. Similarly, all core recovered from the Late
Cretaceous to Early Tertiary cover sequence (referred to as Tertiary3
here and in Sections 12.0 and 13.0) has also been sampled, typically on 20 ft
sample lengths, with some shorter sample intervals in areas of geologic
interest. Unconsolidated overburden material, where it exists, is generally not
recovered by core drilling and therefore not usually sampled.
Rock chips from the 222 rotary percussion holes were generally
not sampled for assay analysis, as the holes were drilled for monitoring wells
and environmental purposes. Only 35 samples were taken from the drill chips of
26 rotary percussion holes outside the Pebble deposit area, which were drilled
for condemnation purposes.
For details of the main rock units in the Pebble deposit and
mineralization, see Section 7.0. Summaries of relevant sample composites are
obtained in technical reports by Rebagliati and Haslinger (2003 and 2004),
Haslinger et al. (2004), Rebagliati and Payne (2005, 2006 and 2007), and
Rebagliati et al. (2008). Sampling methods and procedures for drill holes
completed by Cominco (Teck) are described in these earlier reports, and will not
be discussed further here.
Half cores remaining after sampling were replaced in the
original core boxes and stored at Iliamna, AK in a secure compound. Later
geological, metallurgical and environmental sampling took place on a small
portion of this remaining core. Crushed reject samples from the 2006 through
2013 analytical programs are stored in locked containers at Delta Junction, AK.
Drill core assay pulps from the 1989 through 2013 programs are stored at a
secure warehouse in Langley, BC.
11.1.1
Northern Dynasty 2002 Drilling
In 2002, 68 drill holes were completed by Quest America
Drilling Inc. (Quest). All holes were NQ2 diameter (2 inches/5.08 cm). The core
was boxed at the rig and transported daily by helicopter to the secure logging
facility in Iliamna. A total of 2,467 core samples, averaging 10 ft long, were
collected by Northern Dynasty personnel. Sampling was performed by mechanically
splitting the core in half lengthwise.
11.1.2
Northern Dynasty 2003 Drilling
In 2003, drilling was completed by contractor Quest. All core
was NQ2 diameter. The core was boxed at the rig and transported daily by
helicopter to the secure logging facility at the village of Iliamna. Samples
averaged 10 ft long.
_________________________________________________
3Tertiary
in usage throughout this section is a collective reference to all unmineralized
rocks of the cover sequence that directly overlies the Pebble deposit.
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Sampling was performed by mechanically splitting the core in
half lengthwise. Coarse rejects were stored at SGS Mineral Services in
Fairbanks, Alaska, until early 2005, and then discarded.
11.1.3
Northern Dynasty 2004 Drilling
Most of the 2004 drilling was also completed by Quest, with
some footage drilled by Boart Longyear Company (Boart Longyear) and Midnight Sun
Drilling Co. Ltd. Core diameters included NQ2, HQ (2.5 in/6.35 cm diameter) and
PQ (3.3 in/8.31 cm diameter). Thirty-three rotary percussion water well,
engineering and environmental holes were also completed. The 2004 drilling
program included 26 larger diameter (PQ and HQ) holes for metallurgical testing.
The core was boxed at the rig and transported daily by helicopter to the secure
logging facility in the village of Iliamna. A total of 12,865 Cretaceous
(syn-mineralization) samples averaging 10 ft long were taken in 2004; 10,893
samples were mechanically split half-core samples and 1,972 samples were of the
metallurgical type. The metallurgical samples were taken by sawing an off-centre
slice representing 20% of the core volume, which was submitted for assay
analysis. The remaining 80% was used for metallurgical purposes. No intact drill
core remains after this type of metallurgical sampling, only assay reject and
pulp samples. In addition, 904 Tertiary (post-mineralization) samples averaging
15 ft long were taken for trace element analysis. Tertiary samples were
collected by mechanically splitting the core in half lengthwise. The average
core recovery for all samples taken in 2004 was 97.6% .
11.1.4 Northern
Dynasty 2005 Drilling
In 2005, drilling was again completed by contractor Quest. Core
diameters included NQ2, HQ and PQ core. The core was boxed at the rig and
transported daily by helicopter to the secure logging facility in the village of
Iliamna. A total of 4,378 Cretaceous samples and 1,435 Tertiary samples were
collected. Of the Cretaceous samples, 3,541 were taken by sawing the core in
half lengthwise. The remaining 837 Cretaceous samples and all Tertiary samples
were from metallurgical holes, and were sampled using the 20% off-centre saw
method described in Section 11.1.3. Cretaceous samples averaged 10 ft long and
Tertiary samples averaged 20 ft long. The average core recovery for all 2005
core holes was 98.4% . In addition to the core drilling, a total of 6,100 ft was
drilled in 71 rotary percussion holes by Foundex Pacific Inc. (Foundex) for
water monitoring purposes. No samples were collected or analyzed from these
holes.
11.1.5 Northern
Dynasty 2006 Drilling
The drilling contractors in 2006 were American Recon Inc.
(American Recon) and Boart Longyear. Drill holes were NQ2 and HQ in diameter. A
total of 13 shallow rotary percussion holes were also completed for
environmental purposes by Foundex. The core was boxed at the rig and transported
daily by helicopter to the secure logging facility at Iliamna. The 2,759
Cretaceous samples collected averaged 10 ft long and the 1,847 Tertiary samples
averaged 20 ft long. The Cretaceous samples were collected by sawing the core in
half lengthwise, and the Tertiary samples were collected by the 20% off-centre
saw method described in Section 11.1.3. Average core recovery in 2006 was 98.7%
.
11.1.6 Northern
Dynasty and Pebble Partnership 2007 Drilling
The drilling contractors used in 2007 were American Recon,
Quest and Boart Longyear. Drill holes were NQ2 and HQ in diameter, and were
drilled for geological and metallurgical purposes. Additional drilling was
completed by Foundex to establish monitoring wells, but core was not recovered
from these holes. Several holes included wedges; in cases where the wedged hole
successfully extended beyond the total depth of the parent hole, they were
treated as extensions of their parent holes and overlapping information was
ignored. The core was boxed at the rig and transported daily by helicopter to
the secure logging facility at Iliamna. A total of 12,664 samples were taken
from the 72 drill holes. The 9,485 Cretaceous samples averaged 10 ft
long, and the 3,179 Tertiary samples averaged 20 ft long. The Cretaceous samples
were collected by sawing the core in half lengthwise, and the Tertiary samples
were collected by the 20% off-centre saw method described in Section 11.1.3. The
average core recovery for 2007 drill holes was 99.7% .
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11.1.7 Pebble
Partnership 2008 Drilling
The drilling contractors used in 2008 were American Recon,
Boart Longyear and Foundex. Drill holes were NQ, HQ and PQ in diameter, and were
drilled for delineation, geotechnical and metallurgical purposes. The core was
boxed at the rig and transported daily by helicopter to the secure logging
facility at Iliamna. The large 1.7 to 2.2 lb Cretaceous rock assay pulps and the
0.5 lb Tertiary waste rock pulps from these years are stored in a secure
warehouse at Langley, BC. A total of 12,701 samples were taken in 2008 by the
Pebble Partnership. The 9,312 Cretaceous samples averaged 10 ft long and the
3,389 Tertiary samples averaged 20 ft long. The Cretaceous samples were
collected by sawing the core in half lengthwise. The Tertiary samples and assay
samples from metallurgical holes were collected using the 20% off-centre saw
method described in Section 11.1.3. The remaining 80% of the core from the
Cretaceous portions of the metallurgical holes were used for metallurgical
testing.
11.1.8
FMMUSA 2008 Drilling
In 2010, the Pebble Partnership acquired the data for seven
holes with 414 samples drilled by FMMUSA in 2008. These drill holes are located
near the Property on land that is now controlled by the Pebble Partnership, and
provided information on the regional geology.
11.1.9
Pebble Partnership 2009 Drilling
The drilling contractor used for 2009 drilling was American
Recon. Drill holes were NQ, HQ and PQ in diameter. The core was boxed at the rig
and transported daily by helicopter to the secure logging facility at Iliamna. A
total of 2,835 mainstream samples (including duplicate samples) were collected
in 2009. The 2,555 Cretaceous samples averaged 10 ft long and the 280 Tertiary
samples averaged 20 ft long. The Cretaceous samples were collected by sawing the
core in half lengthwise. Tertiary samples were collected using the 20%
off-centre saw method described in Section 11.1.3.
11.1.10
Pebble Partnership 2010 Drilling
Drilling contractors used for 2010 drilling were American Recon
and Foundex. Drill holes were NQ and HQ in diameter. The core was boxed at the
rig and transported daily by helicopter to the secure logging facility at
Iliamna. A total of 4,714 mainstream samples were taken in 2010. The 4,463
Cretaceous samples and the 251 Tertiary samples averaged 10 ft long. All samples
were taken by sawing the core in half lengthwise.
11.1.11 Pebble
Partnership 2011 Drilling
Drill contractors American Recon, Quest and Foundex completed
85 holes in 2011. The hole numbering sequences are 11526 through 11542 for 17
district exploration holes and GH11-229 through GH11-296 for 68 geotechnical
holes. Most of these holes were drilled vertically except for 11526, 11528,
11530, 11532, 11533 and 11539, which were inclined at -80°, and 11529, drilled
at -75°. Among 68 geotechnical holes, 43 were sonic drilling. A total of 4,281
mainstream samples were taken. The 3,674 Cretaceous samples averaged 10 ft in
length and the 607 Tertiary samples averaged 20 ft in length. Cretaceous samples
were taken by sawing the core in half lengthwise. Tertiary samples were taken by
the 20% off-centre saw-cut method described above.
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11.1.12 Pebble
Partnership 2012 Drilling
Drill contractors Quest and Foundex completed 81 holes in 2012.
The hole numbering sequences are 12543 through 12562 for 20 exploration,
delineation and hydrological holes, and GH12-297 through GH12-357S for 61
geotechnical holes. Most of 12-series holes were drilled with dips of -65° to
-80°, and azimuths of 90° to 270° except for 12546, 12554, 12558, 12559, 12561
and 12562, which were drilled vertically. All GH-series holes were drilled
vertically. Among 61 geotechnical holes, 31 were completed by sonic drilling. Of
the 81 holes, 14 h0les were drilled in the southern and western parts of the
Pebble West zone; 6 holes were drilled in the broader claim area to test
exploration targets to the south on the Kaskanak claim block to the northwest
and south and the KAS claim block further south; and the 61 geotechnical and
hydrogeological holes were drilled in the deposit area (45 holes), in Site A (8
holes) and in the area 50 miles to the southeast near Cook Inlet (8 holes). A
total of 2,681 core samples (2,537 Cretaceous samples and the 144 Tertiary
samples) were taken in 2012. The Cretaceous samples averaged 10 feet in length
and were taken by sawing the core in half lengthwise. Tertiary samples averaged
20 ft in length and were taken by the 20% off-centre cut method.
11.1.13 Pebble
Partnership 2013 Drilling
Drill contractor Foundex completed vertical drilling in 37
holes at sites near the deposit in 2013. These holes numbered GH13-358 through
GH13-383 were drilled PQ and HQ size for geotechnical and hydrogeological
purposes. A total of 523 samples were taken: 1 from Quaternary, 124 from
Tertiary and 398 from Cretaceous strata. The Cretaceous and Quaternary samples
average 10 feet in length and were taken by sawing the core in half lengthwise.
The Tertiary samples average 15 feet in length and were taken by the 20%
off-centre cut method.
Essentially, all of the potentially mineralized Cretaceous rock
recovered by drilling on the Pebble Project is subject to sample preparation and
assay analysis for copper, gold, molybdenum and a number of other elements.
Similarly, all Late Cretaceous to Early Tertiary cover sequence (Tertiary) rock
cored and recovered during the drill program is also subject to sample
preparation and geochemical analysis by multi-element methods. Since 2007, all
sampling at Pebble has been undertaken by employees or contractors under the
supervision of a QP. The QP believes these processes are acceptable for use in
geological and resource modelling for the Pebble deposit.
11.2.1
2002 Sample Preparation
In 2002, the samples were prepared at the Fairbanks laboratory
of ALS, which has been certified under an International Organization for
Standardization (ISO) 9001 since 1999. The sample bags were verified against the
numbers listed on the shipment notice. The entire sample of half-core was dried,
weighed and crushed to 70% passing 10 mesh (2 mm), then a 250 g split was taken
and pulverized to 85% passing 200 mesh (75 µm). The pulp was split, and
approximately 125 g were shipped by commercial airfreight for analysis at the
ALS laboratory in North Vancouver. The remaining pulps were shipped to a secure
warehouse at Langley for long-term storage. The coarse rejects were held for
several months at the Fairbanks laboratory until all quality assurance/quality
control (QA/QC) measures were completed and were then discarded.
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11.2.2 2003
Sample Preparation
The 2003 samples were prepared at the SGS Mineral Services
(SGS) sample preparation laboratory in Fairbanks. After verification of the
sample bag numbers against the shipment notice, the entire sample of half-core
was dried, weighed and crushed to 75% passing 10 mesh (2 mm). A 400 g split was
taken and pulverized to 95% passing 200 mesh (75 µm), and the pulp was shipped
by commercial airfreight to the SGS laboratories in either Toronto, ON, or
Rouyn, QC. The assay pulps were returned for storage at the Langley warehouse.
Coarse rejects were held for several months at the Fairbanks laboratory until
all QA/QC measures were completed and were then discarded.
11.2.3 2004-2013
Sample Preparation
For the 2004 through 2013 drill programs, the ALS sample
preparation laboratory in Fairbanks performed the sample preparation work. The
laboratory received the half-core Cretaceous samples and the off-centre saw
splits from the Tertiary samples and metallurgical holes, verified the sample
numbers against the sample shipment notice and performed the sample drying,
weighing, crushing and splitting. ALS of North Vancouver pulverized the samples
from 2004 through 2006 (as described for 2002 samples), and ALS Fairbanks
pulverized the samples from 2007 through 2013.
11.3.1
2002 Sample Analysis
Analytical work for the 2002 drilling program was completed by
ALS of North Vancouver, BC, an ISO 9002 certified laboratory. All samples were
analyzed by fire assay (FA) for gold, and a standard multi-element geochemical
package was used for additional elements including copper and molybdenum. In
addition, several drill holes exhibiting copper-gold porphyry-style
mineralization were subjected to copper assay level determinations. A few
molybdenum assay level determinations were also performed. Gold concentration
was determined by 30 g FA fusion with lead as a collector and an atomic
absorption spectrometry (AAS) finish. The four samples that returned gold
results greater than 10,000 ppb (10 g/t), were re-analyzed by one assay ton FA
fusion with a gravimetric finish.
All samples were subject to multi-element analysis for 34
elements, including copper and molybdenum, by aqua regia digestion with an
ICP-AES finish. A total of 1,822 samples from 31 drill holes exhibiting porphyry
style copper-gold mineralization were assayed for copper by four-acid (total)
digestion with an AAS finish to the ppm level. For copper assays greater than
10,000 ppm, another total digestion with an AAS finish analysis was performed to
the percent level. A further 61 samples from one drill hole were assayed for
molybdenum by four-acid digestion with an AAS finish to the ppm level.
11.3.2 2003
Sample Analysis
Analytical work for the 2003 drilling program was completed by
SGS Canada Inc. of Toronto, ON, an ISO 9002 registered, ISO 17025 accredited
laboratory. All samples were analyzed by FA for gold, and a standard
multi-element geochemical package was used for additional elements including
copper and molybdenum. Gold analyses were completed at SGS Rouyn, QC, by one
assay ton (30 g) lead-collection FA fusion with AAS finish, with results
reported in ppb. Ten samples that returned gold results greater than 2,000 ppb
(2 g/t) were re-analyzed by 30 g FA fusion with a gravimetric finish, with
results reported in grams per tonne. Copper assays were completed at SGS Toronto, ON. Samples were fused with sodium peroxide, digested
in dilute nitric acid and the solution analyzed by ICP-AES, with results
reported to the percent level.
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All samples were subject to multi-element analysis for 33
elements including copper, molybdenum and sulphur by aqua regia digestion with
an ICP-AES finish at SGS Toronto. In addition, 30 samples were analyzed for
whole-rock geochemical analysis by lithium metaborate fusion with an x-ray
fluorescence (XRF) finish. All duplicates were analyzed at ALS laboratory in
North Vancouver, BC.
11.3.3 2004-2013
Sample Analysis
Analytical work in 2002, and from 2004 to 2013 was completed by
ALS of North Vancouver. Total copper and molybdenum concentration was determined
by an intermediate-grade multi-element analytical method. A four-acid digestion
was followed by ICP-AES finish (ALS code ME-ICP61a). The same multi-element
method was used to determine 31 additional elements including sulphur. In 2004
and 2005, approximately one sample in 10 was also analyzed for copper by a
high-grade, four-acid digestion method with AAS finish (ALS code Cu-AA62).
Beginning in 2004 for Tertiary rocks and 2007 for Cretaceous
rocks, samples were analyzed for 47 elements by four-acid digestion followed by
ICP-AES and inductively coupled plasmamass spectroscopy finish (ICP-MS) and for
mercury by aqua regia digestion cold vapour AAS (ALS code ME-MS61m). Gold
content was determined by 30 g lead collection FA fusion with AAS finish (ALS
code Au-AA23). A total of 10 samples from this period returned gold values
greater than 10 ppm; they were re-analyzed by 30 g FA fusion with a gravimetric
finish (ALS code Au-GRA21), with results reported in ppm. From drill hole number
7371 onward, gold, platinum and palladium concentrations were determined by 30 g
FA fusion with ICP-AES finish (ALS code PGM-ICP23).
A total of 13,371 samples were subject to copper speciation
analyses that included: oxide copper analysis by citric acid leach AAS finish;
non-sulphide copper analysis by 10% sulphuric acid leach AAS finish and cyanide
leachable copper on the sample residue of the sulphuric acid leach by cyanide
leach AAS finish (ALS codes Cu-AA04, Cu-AA05 and Cu-AA17). A total of 222
samples from a drill hole in Pebble East were analyzed for precious metals (ALS
code Au-SCR21 modified to include platinum and palladium). A 1,000 g pulp sample
was screened at 100 µm (Tyler 150 mesh) and the entire plus fraction was weighed
and analyzed by FA ICP finish and two 30 g minus fractions.
All duplicates since 2004 have been analyzed at Acme Analytical
Laboratories (Acme) in Vancouver, BC, using similar methods to those at ALS.
Acme code Group 7TD, a four-acid digestion with ICP-AES finish, was used to
determine total concentrations for copper, molybdenum and 20 additional
elements. In 2010, 115 till samples were also analyzed at Acme in Vancouver. The
samples were dried and sieved to 230 mesh (63 µm), and a 15 g sub-sample was
digested in aqua regia and analyzed by ICP-MS (Acme code 1F05).
Check assays for gold were determined by Acme code Group 3B, a
30 g FA fusion with ICP-AES finish.
Figure 11.4.1 illustrates the sampling and analytical flowchart
for the 2010 through 2013 drill programs.
11.4 |
BULK DENSITY DETERMINATIONS |
Density measurements were made at 100 ft intervals within
continuous rock units, and at least once in each rock unit less than 100 ft
wide. Rocks chosen for analysis were typical of the surrounding rock. Where the
sample interval occurred in a section of missing core, or poorly consolidated
material unsuitable for measurement, the nearest intact piece of core was
measured instead.
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Core samples free of visible moisture were selected; they
ranged from 3 to 12 in long, and averaged 11.8 in. The samples were dried,
weighed in air on a digital scale (capacity 4.4 lb) and the mass in air (MA)
recorded to the nearest 0.1 g. Then, the sample was suspended in water below the
scale and its weight in water (Mw) entered into the same table. Calculation of
the density was conducted using the following formula:
Density = MA ⁄ (MA Mw)
Core-sized pieces of aluminum were used as density standards at
site starting in 2008. A total of 9,951 density measurements of Tertiary and
Cretaceous rocks were taken using a water immersion method on whole and half
drill core samples at the Iliamna core logging facility.
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Figure
11.4.1 Pebble
Project 2010 to 2013 Drill Core Sampling and Analytical Flow Chart
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The QP has reviewed the data verification procedures followed
by the Pebble Partnership and by third parties on behalf of the Pebble
Partnership, and believes these procedures are consistent with industry best
practices and acceptable for use in geological and resource modelling.
12.1 |
QUALITY ASSURANCE AND QUALITY CONTROL |
Northern Dynasty maintained an effective QA/QC program
consistent with industry best practices, which has continued from 2007 to 2013
under the Pebble Partnership. This program is in addition to the QA/QC
procedures used internally by the analytical laboratories. The QA/QC program has
also been subject to independent review by Analytical Laboratory Consultants Ltd
(ALC, 2004 to 2007) and Nicholson Analytical Consulting (NAC, 2008 to 2012). The
analytical consultants provide ongoing monitoring, including facility inspection
and timely reporting of the performance of standards, blanks and duplicates in
the sampling and analytical program. The results of this program indicate that
analytical results are of a high quality, suitable for use in detailed modelling
and resource evaluation studies.
Figure 12.1.1 describes the QA/QC sample types used in the
program. The performance of the copper-gold standard CGS-16 is illustrated in
and Figure 12.1.3. A comparison of the matched-pair duplicate assay results of
ALS and Acme for 2004 through 2010 is provided in Figure 12.1.4 and Figure
12.1.5.
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Figure 12.1.1 |
QA/QC Sample Types Used |
QC
Code |
Sample Type |
Description |
Percent of
Total |
MS |
Regular Mainstream |
|
Regular samples submitted for preparation and
analysis at the primary laboratory. |
90% |
ST |
Standard (Certified Reference Material) |
|
Mineralized material in pulverized form with a
known concentration and distribution of element(s) of interest. |
5% or |
|
|
|
Randomly inserted using pre-numbered sample tags. |
1 in 20 |
DP |
Duplicate or Replicate |
|
An additional split taken from the remaining pulp
reject, coarse reject, ¼ core or ½ core remainder. |
5% or |
|
|
|
Random selection using pre-numbered sample tags. |
1 in 20 |
SD |
Standard Duplicate |
|
Standard reference sample submitted with duplicates
and replicates to the check laboratory. |
<1% |
BL |
Blank |
|
Sample containing negligible or background amounts
of elements of interest, to test for contamination. |
1% |
Figure
12.1.2 Performance
of the Copper Standard CGS-16 in 2008
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Figure
12.1.3 Performance
of the Gold Standard CGS-16 in 2008
12.1.1
Standards
Standard reference materials were inserted into the Cretaceous
sample stream (approximately 1 sample for every 20 samples) after sample
preparation as anonymous (blind), consecutively-numbered pulps. These standards
are in addition to internal standards routinely analyzed by the analytical
laboratories. Standards were inserted in the field by the use of sample tags, on
which the "ST" designation for "Standard" was pre-marked. For the Tertiary waste
rock analytical program, coarse blanks were inserted at the sample tags
positions marked as ST until late 2008 and, since then a commercial pulp blank
has been used.
Standard performance was monitored by charting the analytical
results over time against the concentration of the control elements. The results
are compared with the expected value and range, as determined by round-robin
analysis. A total of 32 different standard reference materials were used to
monitor the assay results from 1997 through 2013. Copper and gold standards were
inserted during the 2002 through 2013 programs. Molybdenum standards were added
in September 2008.
In December 2007, several tons of coarse reject samples from
Pebble East and Pebble West were pulled from storage and shipped to Ore Research
& Exploration Pty Ltd in Melbourne, Australia, for the production of ten
matrix-matched certified reference materials. These standards (Pebble
Partnership-1 through Pebble Partnership-10) became available in late 2009 and
have been used to monitor the Pebble analytical results since that time. Nine of
the standards from Cretaceous rock are certified for gold, copper, molybdenum,
silver and arsenic. One standard (Pebble Partnership-2) is from Tertiary rock
and is certified for copper, molybdenum, arsenic, silver and mercury.
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A standard determination outside the control limits indicates a
control failure. The control limits used are as follows:
When a control failure occurred, the laboratory was notified
and the affected range of samples re-analyzed. By the end of the program, no
sample intervals had outstanding QA/QC issues. The standard monitoring program
provides a good indication of the overall accuracy of the analytical results.
12.1.2
Duplicates
Random duplicate samples were selected and tagged in the field
by the use of sample tags on which the DP designation for duplicate was
pre-marked. From 2004 onward, samples to be duplicated were split by ALS at
Fairbanks and submitted to Acme in Vancouver for pulverization.
The original samples were assayed by ALS of North Vancouver and
the corresponding duplicate samples were assayed by Acme of Vancouver. The
approximately 2,000 coarse reject, inter-laboratory duplicate assay results from
2004 to 2010 match well; the correlation coefficients are 0.96 for gold, 0.98
for copper and 0.98 for molybdenum. In 2011 and 2013, the duplicate analyses
rate of 1 in 20 samples was continued and the number of duplicate samples
analyzed was doubled. The protocol was modified so that every 20th
sample analyzed within the regular sample stream was an in-line,
intra-laboratory coarse reject duplicate (a prep-rep duplicate). In addition
to this, the original pulp of this sample was sent to Acme in Vancouver for
inter-laboratory check assaying when final QA/QC on the original samples was
completed.
Figure 12.1.4 and Figure 12.1.5 provide a comparison of the
matched-pair duplicate assay results of ALS and Acme for 2004 through 2010.
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12.1.3 Blanks
A total of 1,362 field blanks have been inserted since 2004 to
test for contamination. This is in addition to the analytical blanks routinely
inserted with the samples by the assay laboratories as a part of their internal
quality control procedures. In 2004, coarse landscape dolomite was inserted as a
blank material. This material was replaced by gravel landscape material between
2005 and late 2008. In late 2008, the gravel blank was replaced by a quarried
grey granitic landscape rock. This material has a lithological matrix similar to
the Pebble Cretaceous host rocks.
About 1 lb of the blank was placed in a sample bag, given a
sequential sample number in the sequence and randomly inserted one to six times
per drill hole after the regular core samples were split at Iliamna. These blank
samples were processed in sample number order along with the regular samples.
Of the blanks inserted, 444 were included in the Tertiary waste
rock sample program in the position marked for the standard. In late 2008, a
commercial precious metals pulp blank was inserted with the Tertiary waste rock
samples. In late 2009, the use of matrix-matched Tertiary standard PLP-2 was
initiated.
The majority of assay results for the blanks report at or below
the detection limit. The maximum values reported in the current results are gold
(0.028 g/t) and copper (0.057%) . No significant contamination occurred during
sample preparation, with a few minor exceptions, likely due to cross-sample
mixing errors during crushing.
12.1.4 QA/QC
on Other Elements
The four-acid digestion ICP-AES 33 multi-element analytical
method employed from 2004 through 2013 is optimized for copper and molybdenum
analysis. The copper and molybdenum assays were monitored by internal laboratory
and external standards.
The lower detection limits of the suite of elements analyzed
are as follows: copper (10 ppm), gold (0.001 ppm), molybdenum (0.05 ppm), silver
(0.01 ppm), aluminum (0.01%), arsenic (0.2 ppm), barium (10 ppm), beryllium
(0.05 ppm), bismuth (0.01 ppm), calcium (0.01%), cadmium (0.02 ppm), cerium
(0.01 ppm) cobalt (0.1 ppm), chromium (1 ppm), cesium (0.05 ppm), iron (0.01%),
gallium (0.05 ppm), germanium (0.05 ppm), hafnium (0.1 ppm), mercury (0.01 ppm),
indium (0.005 ppm), potassium (0.01%), lanthanum (0.5 ppm), lithium (0.2 ppm),
magnesium (0.01%), manganese (5 ppm), sodium (0.01%), niobium (0.1 ppm), nickel
(0.2 ppm), phosphorus (10 ppm), lead (0.5 ppm), palladium (0.001 ppm), platinum
(0.005 ppm), rubidium (0.1 ppm), rhenium (0.002 ppm), sulphur (0.01%), antimony
(0.05 ppm), scandium (0.1 ppm), selenium (1 ppm), tin (0.2 ppm), strontium (0.2
ppm), tantalum (0.05 ppm), tellurium (0.05 ppm), thorium (0.2 ppm), titanium
(0.005%), thallium (0.02 ppm), uranium (0.1 ppm), vanadium (1 ppm), tungsten
(0.1 ppm), yttrium (0.1 ppm), zinc (2 ppm) and zirconium (0.5 ppm).
Parallel to this method (as described in Section 11.0), an
ICP-MS 48 multi-element method was also used to determine the same 25 elements
above and 23 additional elements. The ICP-MS method gives lower detection limits
for most of the elements.
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12.2 |
BULK DENSITY VALIDATION |
The bulk density data were reviewed prior to the July 2008
resource estimation. The following types of errors were noted: entry errors,
standards labelled as regular samples, incorrectly calculated density values
based on the mass in air and mass in water values entered and extremely high or
low-density values without appropriate explanation. These errors were
investigated and corrected prior to including the data for resource
estimation.
Two other possible sources of error in the measurements were
identified: the presence of moisture in the mass in air measurement for some
samples, and the presence of porosity and permeability of the bulk rock mass not
determinable by the method. The former will result in measurements that are
somewhat overstated, and the latter in measurements that are understated in
terms of the dry in situ bulk density.
It is recommended that additional drying and wax coating tests
be performed by an external laboratory under controlled conditions on a variety
of samples already tested by the water immersion method. In addition, several
samples of cut cylinders of core should be included with these tests, the
dimensions of which can be accurately measured so that their volumes can be
calculated directly. It is also recommended that the bulk in situ porosity and
permeability of the rock mass be determined by geotechnical testing.
In 1988, Cominco (Teck) established a survey control network
including the Pebble Beach base monument in the deposit area using U.S.
State Plane Coordinate System Alaska Zone 5. This monument was tied to the NGS
State Monuments Koktuli, PIG and RAP at Iliamna and formed the base for
subsequent drill collar surveys. In 2004, air photo panels and a control network
were established using NAD 83 US State Plane Coordinate System Alaska Zone 5
with elevations corrected to NAVD88 based on Geoid99.
In 2005, differences between the elevations of surveyed drill
collars in the deposit area and the digital elevation model (DEM) topography
were observed. In early 2008, a re-survey program was initiated to investigate
and resolve these discrepancies. A consistent error was identified in the collar
coordinates from some years, and questions arose as to whether drill collars had
been surveyed to the top of the drill casing or to ground level. In September
2008, two new control points - Pebble 1 and Pebble 2 - were established by
R&M Consultants Inc. of Anchorage in the deposit area; they tied these two
points and the Pebble Beach monument into the 2004 control network and an x, y,
z linear coordinate correction was applied to resolve previously observed drill
hole elevation discrepancies.
Subsequently, during the 2008 and 2009 field seasons, all holes
drilled at the Pebble Project since inception in 1988 were re-surveyed using a
real time kinematic (RTK) GPS, referencing the coordinates of the Pebble
Beach monument as established by the 2008 re-survey to gain a complete set
of consistently acquired collar survey data. The majority of the drill holes
were marked with a wooden post and an aluminum tag. In cases where the post was
missing, the original coordinates were used to find evidence of the drill hole.
Any hole missing a drill post was re-marked, and this was noted in the database.
The resurveys were taken to the top of tundra over the centre of the drill hole.
Where a drill hole could not be located, the resurveyed coordinate was taken at
the original drill collar coordinates and the elevation re-established in the
new system.
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All post Cominco (Teck) holes were surveyed by single shot
magnetic methods. In 2008, several angle holes were also surveyed by a
non-magnetic gyroscopic tool.
All drill logs collected on the Pebble Project have been
compiled in a Microsoft® SQL Server database. Drill hole logs have been entered
into notebook computers running the Microsoft® Access data entry module for the
Pebble Project at the core shack in Iliamna. During drilling programs, the core
logging computers are synchronized on a daily basis with the site master
database on the file server in the Iliamna geology office. Core photographs are
also transferred to the file server in the Iliamna geology office on a daily
basis. In the geology office, the logs are printed, reviewed and validated, and
initial corrections made.
The site data is transmitted on a weekly basis to the Vancouver
office, where the logging data are imported into the Project master database and
merged with digital assay results provided by the analytical laboratories. After
importing, a further printing, validation and verification step follows. Any
errors noted are submitted to the Iliamna office for correction. If analytical
re-runs are required, the relevant laboratories are notified and corrections are
made to the corresponding results within the project master database. Parallel
to this, the independent QA/QC consultant compiles sample log data from the site
with assay data received directly from the laboratories as part of the ongoing
monitoring process. Compiled data are exported to the site entry database, to
resource estimators, and to other users as required.
12.4.1
Error Detection Processes
Error detection within the data entry module is used in the
core shack and the Iliamna geology office as part of the data verification
process. This process standardizes and documents the data entry, restricts data
which can be entered and processed, and enables corrections to be made at an
early stage. Users are prompted to make selections from pick-lists, when
appropriate, and other entries are restricted to reasonable ranges of input. In
other instances, information must be entered and certain steps completed prior
to advancing to the next step. After the logs have been entered, they are
reviewed and validated by the logger and a copy printed out for the site files.
Site data are transmitted to the Pebble database compilation
group on a weekly basis. Software validation routines are run to identify
several types of errors. The compiled data from the header, survey, assay,
geology and geotechnical tables are validated for missing, overlapping or
duplicated intervals or sample numbers, and for matching drill hole lengths in
each table. Drill hole collars and traces are viewed on plan view and in section
by a geologist as a visual check on the validity of the collar and survey
information.
As the analytical data are returned from the laboratory, they
are merged with the sample logs and then printed out, and the gold, copper,
molybdenum and silver values of the regular samples and QA/QC samples are
reviewed. Particular attention is paid to standards that have failed QA/QC as
they are targeted for immediate review; re-runs are requested from the
analytical laboratory if necessary.
12.4.2
Analysis Hierarchies
The first valid QA/QC-passed analytical result received from
the primary laboratory has the highest priority in the analytical hierarchy. If
the same analytical method is used more than once, no averaging is done. If different analytical methods are employed on the same sample,
the most appropriate combination of digestion and analytical method is selected
and used.
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For gold analysis, FA determined by gravimetric finish
supersedes results by AAS or ICP finish, particularly where the AAS or ICP
results are designated as over limits. For copper analysis done on Cretaceous
rocks after 2004, ALS intermediate grade multi-element analytical method (code
ME-ICP61a) supersedes copper by low grade multi-element method (code ME-MS61m).
In the case of all other elements, including molybdenum, silver
and sulphur analyses from 2007 through 2013, the low grade multi-element method
(code ME-MS61m) supersedes the intermediate grade multi-element method (code
ME-ICP61a), unless the low grade method results are greater than the upper
detection limit. In that case, the intermediate grade method result prevails.
12.4.3
Wedges
Some long holes, particularly in Pebble East, were
intentionally wedged. This was undertaken when drilling conditions in the parent
hole deteriorated to such an extent that continuation to target depth was
impractical. For consistency of sample support for geological and resource
modelling, mother hole/wedge hole combinations are represented by singular
linear traces in the database. In treating the wedged portion of a hole that
successfully extends beyond its parent hole, the following approach was used.
The wedged portion of the hole was treated as a continuation of the mother hole
from the point where the wedge starts. The information from the mother hole and
the wedge was blended onto a string that follows the mother hole to the wedge
point, and then follows the wedge (and the wedge surveys) to the end of the
hole. The best available information from the two hole strings was combined to
produce one linear drill hole trace.
12.4.4 Control
of QA/QC
Data are made available to the technical team for immediate use
after the error trapping and initial review process is complete. However, at the
time the data is made available, validation, verification and analytical QA/QC
may still be in progress on recently-generated information. At the time the
drill data was exported from the primary database for use in the current
resource estimate, the results had been validated and all assay results had
passed analytical QA/QC.
12.5 |
VERIFICATION OF DRILLING DATA |
The 1997 and prior Cominco (Teck) data were validated by
Northern Dynasty in 2003 using:
-
the digital data and printed information;
-
digital assay results obtained directly from ALS and Cominco Exploration
Research laboratories, where available; and
-
selected re-analysis of the original assay pulps.
Most of the pre-2002 data in the current database is derived
from a digital compilation created by Cominco (Teck) in 1999. Twenty-eight gold
results from 1988 and 1989 holes, which existed only on hand-written drill logs,
were added to the database. Although a complete set of original information does
not exist for all the
historical holes and, in particular, the printed assay certificates were not found, the digital data appear to be of good quality. The data compiled by Cominco (Teck) matches the digital analytical data received directly from the laboratories, with
few exceptions. Most differences appear to be due to separately reported over-limits and re-runs. The small number of errors identified in the Cominco (Teck) data, including mismatched assay data, conversion errors, unapplied over-limits and
typographical errors were corrected.
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The 2002 analytical data were also verified and validated. A few errors were identified and corrected. When the 2003 digital data were verified against the assay certificates, some differences with the printed certificates were identified. In 2003,
the analytical results were provided by SGS in a digital format that included SGS internal standards, duplicates and blanks. These digital results differed from the values on the corresponding printed certificates in two ways: digits in excess of
three significant figures were recorded, and results were not trimmed to the upper detection limit value. As a result, sixteen 2003 gold assays over 2,000 ppb had incorrect values assigned to them in the database. This was corrected by applying the
correct FA over-limit re-run result to these samples in the database. No over-limits existed in the 2003 copper results so there were no errors with this element. The lone over-limit molybdenum value was left untrimmed, because this result was
substantiated by an ALS check assay. Results from 2003 for elements other than gold, copper and molybdenum were left untrimmed in the database.
Norwest Corporation reported on additional data verification done in conjunction with the resource estimate in a technical report dated the February 20, 2004. “Norwest received, from Northern Dynasty, the initial Pebble drill hole database
in the form of an assay, collar, downhole survey and geology file. An audit was undertaken of 5% of the data within these files. Digital files were compared to original assay certificates and survey records. It was determined that the downhole
survey file had an unacceptable number of errors. The assay file had an error rate of approximately 1.2% . This was considered acceptable for this level of study.” These errors were investigated and subsequently corrected by Northern
Dynasty.
The ongoing error-trapping and verification process for drill hole data collected from 2004 to 2013 is described in Section 12.4. Typically, validation and verification work for each year was completed by January of the following year, although some
QA/QC issues took longer to resolve. Work at the Iliamna office consisted mostly of validating the site data entry and resolving errors that were identified. Additional validation and verification work was performed in the Vancouver office. This
consisted of checking the site data tables for missing, overlapping, unacceptable and mismatching entries, and reviewing the analytical QA/QC results. During verification of the 2004 data, a low number of errors were recorded. Erroneously labelled
standards in the sample log were the main source of error. Digital values not matching the analytical certificates were the next area of concern. In this case, the digital data were usually correct, as the certificates had been superseded by new
results from QA/QC re-runs.
In addition to typical database validation procedures, the copper, gold and molybdenum data included in Northern Dynasty news releases were manually verified against the results on the ALS analytical certificates.
A significant amount of due diligence and analytical QA/QC for copper, gold and molybdenum has been completed on the samples that were used in the current mineral resource estimate. This verification and validation work performed on the digital
database provides confidence that it is of good quality and acceptable for use in geological and resource modelling of the Pebble deposit.
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13.0 |
MINERAL PROCESSING AND METALLURGICAL TESTING
|
13.1 |
TEST PROGRAMS 2003 TO 2013 |
Metallurgical testwork for the Pebble Project was initiated by
Northern Dynasty in 2003, and continued under the direction of Northern Dynasty
until 2008. From 2008 to 2013, metallurgical testwork progressed under the
direction of the Pebble Partnership. Tetra Techs current review focuses on
relevant testwork conducted up until 2013.
13.1.1
2003 to 2005 Testwork Summary
The first series of metallurgical testwork was conducted to
develop a baseline flowsheet and was performed by different laboratories.
Vancouver based Process Research Associates Ltd (PRA) testwork was preliminary
in nature, followed by testwork completed in Kamloops by G&T Metallurgical
Services Ltd. (G&T). Subsequently, a comprehensive test program was
completed at SGS Lakefield (SGS) laboratories located in Lakefield, ON. The
basic flowsheet from PRA was optimized by testing on primary grind size, regrind
size, flotation and gold leaching. In addition, comminution data were obtained
from samples covering all of the lithology and alteration combinations in the
mineral resource. A few miscellaneous tests were also performed including
settling and filtration and concentrates properties. The SGS test results
demonstrated that marketable concentrate over 26% copper could be obtained and
production of molybdenum as a separate concentrate and gold doré by leaching
were viable.
13.1.2
2006 to 2010 Testwork Summary
The second series of metallurgical testwork, conducted between
2006 and 2010, was performed primarily by SGS and covered comminution, gravity
separation, flotation, leaching, settling tests and other miscellaneous testwork
as listed in Figure 13.1.1. The main purpose of the testwork was to optimize the
process flowsheet to incorporate supergene mineralization from the western
portion of the Pebble deposit and explore the performance variability of
composite samples from Pebble West zone and Pebble East zone mineralization.
The major observations from the second testwork campaign are
summarized as follows:
-
Bulk flotation testwork was intended to optimize the flowsheet to treat the
supergene and transition zones in Pebble West. Most samples achieved the 26%
copper concentrate target, in the variability tests and the locked cycle
tests.
-
Copper-molybdenum locked cycle separation tests demonstrated, of the
circuit feed, more than 99% of the copper was recovered to copper concentrate
and 92.6 to 98.4% of the molybdenum was recovered to molybdenum concentrate.
-
The molybdenum concentrate was found to contain significant rhenium, with
grades ranging from 960 to 1,100 g/t, and the copper content observed was
between 1.8% and 5.9%.
-
Gravity recoverable gold (GRG) was determined to optimize gravity gold
recovery. The obtained recovery was similar to 2008 testwork.
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-
Pyrite flotation was conducted with pyrite concentrate subjected to gold
leaching tests. The average gold extraction was 55% by leaching for 48 hours.
-
Other metallurgical testwork conducted in this period included tailings
thickening, regrinding jar tests, and copper concentrate thickening and
filtration.
Figure
13.1.1 Testwork
Programs and Reports 2008 to 2010
Test Program |
Laboratory |
Report Date |
Metal Recoveries Related Programs:
Comminution/Flotation/Leaching Tests |
|
|
Screen Analysis Data on Rod Mill Feed |
Phillips Enterprises, LLC |
Apr 17, 2008 |
Rod Mill Grindability Test Data |
Phillips Enterprises, LLC |
Apr 18, 2008 |
Screen Analysis Data on Rod Mill Product |
Phillips Enterprises, LLC |
May 13, 2008 |
Bond Abrasion Test Data |
Phillips Enterprises, LLC |
Apr 22, 2008 |
Ball Mill Grindability Test Data |
Phillips Enterprises, LLC |
Jun 6, 2008 |
Screen Analysis Data on Ball Mill Feed |
Phillips Enterprises, LLC |
Jun 10, 2008 |
Screen Analysis Data on Ball Mil Product |
Phillips Enterprises, LLC |
Jun 24, 2008 |
Mail to the Pebble Partnership c/o Mr. Alex Doll, Final
Report of Comminution QA/QC Testing |
Phillips Enterprises, LLC |
Jul 18, 2008 |
Technical Memorandum to Steve Moult of Pebble Partnership,
Grinding Throughput Calculation Procedure for Mine Production Schedules |
DJB Consultants Inc (DJB) |
Sep 30, 2008 |
E-Mail Transmission, Compare JK SimMet SABC-A and SABC- B
Throughput Prediction to Morrell Total Power Calculation for Selected 2010
SMC Samples; Also Morrell HPGR Predictions |
Contract Support Services |
Jan 21, 2010 |
E-Mail Transmission, Final Report, Pebble LOM Simulations,
Years 1 to 13: SABC-A vs. SABC-B Circuit Options |
Contract Support Services |
Apr 7, 2010 |
E-Mail Transmission, Final Report, Pebble LOM Simulations,
Years 1 to 25: SABC-A vs. SABC-B Circuit Options |
Contract Support Services |
Apr 29, 2010 |
E-Mail Transmission, Summary of Results, Pebble LOM
Simulations: Years 145: SABC-A Revision B, Correct Year 8 Throughput |
Contract Support Services |
Dec 30, 2010 |
E-Mail Transmission, Summary of Results, Pebble LOM
Simulations, Years 145: SABC-B Circuit Option, Comparison with SABC-A |
Contract Support Services |
Dec 30, 2010 |
An Investigation into the Recovery of Copper, Gold, and
Molybdenum by Laboratory Flotation from Pebble Samples. Project 10926-008
Report #1 |
SGS Lakefield |
Jul 6, 2006 |
An Investigation into Copper, Gold, and Molybdenum Recovery
from Pebble East Phase I Composites. Project 11486-003 Report #1 |
SGS Lakefield |
Jun 30, 2009 |
An Investigation into Bulk Flotation of Pebble East and
West Composites, Project 11486-003 Report #2 |
SGS Lakefield |
Jun 26, 2009 |
An Investigation into Aging of Pebble East Phase I Samples.
Project 11486-003 Report #3 |
SGS Lakefield |
Jun 30, 2009 |
Tank Cell e500 Mechanical Testwork |
Outotec |
Mar 11, 2010 |
Copper Sulphide Jar Mill Testing Test Plant Report
#20002007 |
Metso |
Apr 12, 2010 |
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Test Program |
Laboratory |
Report Date |
An Investigation into the Recovery of Copper, Gold, and
Moly from Pebble East and West zones. Project 12072-002 Report #2 |
SGS Lakefield |
Dec 21, 2009, Jan 24, 2010 |
Determination of GRG Content Final Report Revised # T1144 |
COREM |
May 27, 2010 |
Gravity Modelling Report Project # KRTS 20587 |
Knelson Research &
Technology Centre |
Aug 17, 2010 |
Settling Tests |
|
|
Summary of High Rate Thickening Test Results Tailings
Samples |
Outotec |
Apr 2, 2010 |
Outotec Thickener Interpretation and Recommendations for
Test Data Report TH-0493 |
Outotec |
Apr 9, 2010 |
Thickener Test Data Report # TH-0493 |
Outotec |
Apr 9, 2010 |
Thickener Test Data Report # TH-0493_R1 |
Outotec |
Apr 16, 2010 |
Thickener Test Data Report # TH-0497 |
Outotec |
Jun 2, 2010 |
Outotec Thickener Interpretation and Recommendations for
Test Data Report TH-0497 |
Outotec |
Jun 17, 2010 |
Filtration Tests |
|
|
Test Report 12875T1 Pebble Partnership |
Larox |
Mar 8, 2010, Apr 7, 2010 |
Rheology Tests |
|
|
Report of Investigation into The Response of the Pebble
Project Rougher Tailings to Sedimentation and Rheology Testing |
FL Smith |
Mar 2010 |
13.1.3
Testwork Programs 2011 to 2013
The Pebble Partnership continued metallurgical testwork in 2011
and 2012 (Figure 13.1.2) . The major goals of the 2011 and 2012 testwork program
were as follows:
-
Complete QEMSCAN (Quantitative Evaluation of Materials by Scanning Electron
Microscopy) analysis of the variability sample inventory to support
geometallurgical studies;
-
Conduct additional flotation variability tests to ensure samples of each
metallurgical domain type are represented; and,
-
Conduct continuous flotation testwork to generate product for downstream
testwork
-
Provide testwork inputs to support the design of the secondary recovery
gold plant.
Figure
13.1.2
Subsequent Testwork Programs and Reports, 2011 to 2013
Test Program |
Laboratory |
Report Date |
Metal Recoveries Comminution/Flotation/Leaching |
|
|
An Investigation into Ultrafine Grinding of Pilot Plant
Concentrates from the Pebble Deposit |
SGS Lakefield |
Feb 9, 2011 |
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An Investigation into the Grindability Characteristics of a
Single Sample W- 214-215 from the Pebble West zone |
SGS Lakefield |
Apr 6, 2011 |
Continuous Flotation of Five Composites from the Pebble
Deposit |
SGS Lakefield |
Jun 21, 2011 |
Copper Molybdenum Separation Testing on a Pebble Bulk
Concentrate |
G&T Metallurgical Services Ltd. |
Sep 22, 2011 |
An Investigation into the Recovery of Copper, Gold, and
Molybdenum from the Pebble Deposit; Incomplete; Progress Report, Project
12072-003 and -007 |
SGS Lakefield |
Jan 24, 2012 |
Concentrate Quality |
|
|
An Investigation by High Definition Mineralogy into the
Mineralogy Characteristics of Five Concentrate Samples from Five Different
Composites |
SGS Lakefield |
Mar 23, 2011 |
An Investigation into a Deportment Study of Gold in Eight
Samples from the Pebble Gold zone |
SGS Lakefield |
Jun 17, 2011 |
An Investigation by High Definition Mineralogy into the
Mineralogy Characteristics of Eight Products of Three Pilot Plant Samples |
SGS Lakefield |
Jun 23, 2011 |
Filtration |
|
|
Filtration Test Report |
Outotec |
Jun 17, 2011 |
Rheology Tests |
|
|
Grinding Transfer Stream Rheology Testwork Report, Report #
PBL-5172 R02 Rev 0 & Rev 1 |
Paterson & Cooke |
Sep 2011, Oct 2011 |
Bulk Tailings Rheology Testwork Report. Report #
4303207-25-RP-002 |
Paterson & Cooke |
Nov 2011 |
13.2.1
Introduction
Geometallurgical studies were initiated by the Pebble
Partnership in 2008, and continued through 2012. The studies were conducted in
partnership between the Geology and Metallurgy Departments. The principal
objective of this work was to quantify significant differences in metal
deportment that may result in variations in metal recoveries during mineral
processing.
Characterization of the respective geometallurgical domains
within the deposit was based on the acquisition of detailed mineralogical data
determined using QEMSCAN mineral mapping technology. QEMSCAN was used to form
the basis for definition of the geometallurgical domains as follows:
-
To determine the mineralogy of samples;
-
To classify them by alteration assemblage;
-
To assess variations in copper mineral speciation; and,
-
To locate gold inclusions down to 1 µm in diameter and characterize their
size, shape, composition and host mineralogy.
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The results of the geometallurgical studies indicate that the
deposit comprises numerous geometallurgical (or material type) domains. These
domains are defined by distinct, internally consistent copper and gold
deportment characteristics that correspond spatially with changes in silicate
alteration mineralogy. Overall metal deportment reflects characteristics
developed during both initial metal introduction during mineralizing alteration
stages and subsequent redistribution by overprinting alteration types.
Chalcopyrite is the dominant copper mineral in most of the
deposit. Bornite is an important component of advanced argillic alteration.
Supergene enrichment, in the form of chalcocite rims on chalcopyrite occurs in
the near surface portion of the deposit. Molybdenum deportment does not vary
appreciably across the deposit, and occurs as molybdenite associated with both
chalcopyrite and pyrite.
Gold has the most variable deportment characteristics and these
can be related directly to variations in predicted gold recoveries as determined
by metallurgical testwork. Gold occurs mostly as inclusions in chalcopyrite,
pyrite and silicate alteration minerals. The proportion of gold inclusions in
chalcopyrite and silicate alteration minerals relative to inclusions in pyrite
has a positive correlation with higher gold recoveries obtained during
flotation-based mineral process testing.
13.2.2 Description
of Geometallurgical Domains
Hypogene mineralization in the Pebble deposit has been divided
into seven geometallurgical domains that correspond to the seven zones in the
three dimensional alteration model. The most volumetrically significant are the
K-silicate and sodic-potassic domains. The other domains are illite-pyrite, QSP
(quartz-sericite-pyrite), quartz-pyrophyllite, sericite and 8431M domains.
K-silicate
The K-silicate domain is concentrated near the top of the main
granodiorite pluton and its immediate host rocks in the eastern part of the
deposit. Material in this domain is dominated by K-feldspar, quartz and illite
with minor biotite and a chalcopyrite-rich sulphide assemblage (average 2.5 wt%)
accompanied by pyrite (average 3.6 wt%). Sphalerite is a trace component of the
sulphide assemblage in this domain.
Gold occurs dominantly as inclusions in chalcopyrite. This
material type is volumetrically most important in the Pebble East zone and is
predicted to have the best metallurgical response due to low clay and pyrite
concentrations and a close association of gold with chalcopyrite.
NK - sodic-potassic
Material in the NK domain is dominated by K-feldspar, quartz,
albite and biotite with low clay contents that include both illite and
kaolinite, typically in equal amounts. Pyrite (average 3.4 wt%) and chalcopyrite
(average 1.3 wt%) dominate the sulphide assemblage. Siderite (Fe carbonate) is a
component of some material in the southern area of the Pebble West zone. The NK
domain is restricted to the shallow western portion of the Pebble West zone, of
which the upper part contains secondary sulphides, dominantly chalcocite that
rims chalcopyrite.
This domain has a moderate chalcopyrite to pyrite ratio and
gold occurs as inclusions in chalcopyrite and pyrite.
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Illite-pyrite
Samples representing illite-pyrite altered material are dominated by a silicate mineral assemblage of K-feldspar, quartz, illite and biotite. The amount of K-feldspar preserved in the samples varies, and intense illite alteration and pyrite
development are prominent in all samples from this domain. The illite-pyrite domain is high in pyrite (average 9.2 wt%) and low in chalcopyrite (average 1.0 wt%). This assemblage occurs in the eastern part of the Pebble West zone mainly at shallow
levels. Secondary chalcocite occurs in shallow samples on the western edge of the illite-pyrite domain but this effect is not present in the eastern portion of the domain.
Illite-pyrite material has a very high concentration of pyrite and minor chalcopyrite. Gold occurs as inclusions within pyrite. The high clay (illite) and pyrite concentrations and the close gold-pyrite association may lead to mineral processing
challenges.
QSP - quartz-sericite-pyrite
The QSP domain occurs on the far north and south extents of the alteration model, mainly on the eastern side of the deposit. This material is dominated by K-feldspar, quartz and sericite with minor biotite and very high pyrite (average 9.5 wt%) and
lower chalcopyrite (average 1.85 wt%) contents. This material is very similar to the material in the illite-pyrite domain.
Quartz-pyrophyllite
Quartz-pyrophyllite alteration, which occurs in the Pebble East zone is related to a zone of intense quartz veining. The mineralogy of this material is characterized by a quartz-sericite-pyrophyllite assemblage. This domain has the highest pyrite
(average 9.7 wt%) and chalcopyrite (average 3.8 wt%) contents of all the domains. Trace bornite is also present.
Both pyrite and chalcopyrite concentrations are high in this domain, and gold occurs as inclusions in chalcopyrite, pyrite and silicate minerals. This is the highest grade material, but has higher clay (pyrophyllite and sericite) and pyrite
concentrations, along with a more variable gold deportment.
Sericite
Sericite alteration is characterized by quartz and sericite with minor pyrophyllite and variable amounts of K-feldspar. This material occurs in two areas within the Pebble East zone. The main and most intense domain of sericite alteration occurs in
the south, adjacent to the quartz-pyrophyllite domain. A second, weaker domain of sericite alteration occurs in the northern part of the Pebble East Zone in the shallowest part of the zone, below the TK contact. The northern sericite domain has
much higher K-feldspar and lower sericite contents in comparison to the southern sericite domain, which is very sericite-rich. The sulphide assemblage is dominated by pyrite (average 7 to 8 wt%) and chalcopyrite (average 1.5 to 2.9 wt%). Bornite
(accompanied by minor digenite/covellite) content is variable, ranging from absent or trace intergrowths with chalcopyrite to full scale replacement of chalcopyrite by bornite and pyrite. The arsenic sulphides enargite and tennantite are a trace
component of the sulphide assemblage, as is sphalerite. Gold occurs as inclusions in pyrite and chalcopyrite and also in solid solution in bornite and digenite. Some of the highest molybdenite contents are in this domain.
High clay (sericite) and pyrite concentrations and variable gold deportment may have implications for mineral processing but the high-tenor copper sulphides may yield a higher concentrate grade.
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8431M
Drill holes 8431M and 11527 cut across the NK domain in the
center of the Pebble West zone. Samples from these drill holes, however, are
more typical of the core of the K-silicate mineralized system in the Pebble East
zone and are characterized by a K-feldspar-biotite assemblage with minor quartz
and illite. Large zones of K-feldspar-magnetite-pyrite-chalcopyrite-cemented
breccia were encountered in the drill holes. This material, which is limited to
these drill holes, dominantly occurs within a diorite sill and is very high
grade with chalcopyrite content averaging 2.7 wt%, well in excess of other
domains within the Pebble West zone. High molybdenite contents are also observed
in this domain.
Samples from drill hole 8431M have the highest gold recoveries
in the Pebble West zone. The samples are anomalously high in both copper and
gold grade; however, the gold deportment is dominated by pyrite-hosted gold
grains. High gold recovery may be related to the larger than average gold grain
size which may result in liberation during grinding and therefore improved
recovery to the copper concentrate.
Supergene mineralization
A thin, irregular zone of supergene mineralization of variable
thickness covers extensive parts of the Pebble West zone. The zone is
characterized by weak enrichment of chalcocite and covellite that rims primary
chalcopyrite. Supergene mineralization is defined as all material with cyanide
soluble copper above 20%. Two supergene mineralization domains are defined by
the silicate alteration assemblage that has undergone secondary enrichment.
These domains are denoted supergene illite-pyrite and supergene sodic potassic.
Geometallurgy and the resource model
The geometallurgical domains described above correspond
directly with specific domains in the 3D alteration model and are being used to
constrain the geometallurgical parameters in the resource model. Specific
metallurgical recoveries were applied to each geometallurgical domain type,
which is described in section 13.11.2.
13.3.1 Grindability
Comminution testwork was carried out on samples collected
between 2004 and 2010, and summarized in the January 2012 SGS report. These data
are reproduced in Figure 13.3.1 through 4. The testwork completed is considered
to be representative of the deposit. Figure 13.3.1 shows the Bond low-energy
impact test results on Pebble West zone samples. The tests were completed by
Philips Enterprises, LLC under the supervision of SGS.
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Figure
13.3.1 Bond
Low-Energy Impact Test Results, SGS January 2012
|
CWi (kWh/t) |
Rock
Density |
Average |
Minimum |
Maximum |
Average* |
9.9 |
5.3 |
17.8 |
2.52 |
Minimum |
3.7 |
1.6 |
8.1 |
2.38 |
Median |
10.0 |
5.3 |
17.7 |
2.54 |
Maximum |
15.6 |
10.5 |
33.9 |
2.68 |
Note :
*Average of 22 drilling samples from Pebble West zone.
Figure 13.3.2 compares the SAG mill comminution (SMC) test
results, all of which were conducted on Pebble West zone samples.
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Figure
13.3.2 JK
Tech/SMC Data Comparison SGS January 2012**
|
A x b
|
Mineralized Material
Densities
|
Core Years
|
2004
|
2005, 2006 |
2008
|
2004
|
2005, 2006 |
2008
|
Composites
|
-
|
W1 to W177 |
W178 to W394 |
-
|
W1 to W177 |
W178 to W394 |
Years Tested
|
2005
|
2008, 2010, 2011 |
2009, 2010, 2011 |
2005
|
2008, 2010, 2011 |
2009, 2010, 2011 |
Results Available |
47 |
53 |
64 |
47 |
53 |
64 |
Average |
43.5 |
44.0 |
50.1 |
2.59 |
2.60 |
2.60 |
Minimum* |
89.4 |
89.4 |
135.2 |
2.43 |
2.43 |
2.38 |
Median |
42.6 |
43.2 |
45.6 |
2.61 |
2.62 |
2.59 |
Maximum* |
24.0 |
24.0 |
26.1 |
2.76 |
2.76 |
2.90 |
Notes: |
* Minimum and maximum refer to
softest and hardest values for the grindability test. |
|
** Drilled samples are all from
the Pebble West zone. |
The Bond rod mill index (RWi) and Bond ball mill work index
(BWi) are listed in Figure 13.3.3 and, Figure 13.3.4 respectively.
Figure
13.3.3 Pebble
West Rod Mill Data Comparison, SGS January 2012**
|
RWi (kWh/t) |
Core Year |
2004 |
2005, 2006 |
2008 |
2011 |
Composites |
- |
W1 to W177 |
W178 to W394 |
W395 to W445 |
Year Tested |
2005 |
2008, 2010, 2011 |
2009, 2010, 2011 |
2011 |
Results Available |
295 |
47 |
19 |
3 |
Average |
15.6 |
14.4 |
13.0 |
15.3 |
Minimum* |
9.7 |
10.1 |
11.0 |
11.6 |
Median |
15.3 |
14.0 |
12.8 |
12.6 |
Maximum* |
24.3 |
20.4 |
19.5 |
21.7 |
Notes: |
*Minimum and maximum refer to
softest and hardest values for the grindability test. |
|
**Drilled samples are from the
Pebble West zone at a grind particle size of 1.4 mm or 14 mesh. |
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Figure
13.3.4 Pebble
West Ball Mill Data Comparison, SGS January 2012**
|
BWi (kWh/t) |
Core Year |
2004 |
2005, 2006 |
2008 |
2011 |
Composites |
- |
W1 to W177 |
W178 to W394 |
W395 to W445 |
Year Tested |
2005 |
2008, 2010, 2011 |
2009, 2010, 2011 |
2011 |
Results Available |
295 |
57 |
72 |
2 |
Average |
14.2 |
14.0 |
13.4 |
11.7 |
Minimum* |
7.7 |
8.4 |
8.0 |
11.4 |
Median |
14.0 |
13.7 |
12.7 |
11.7 |
Maximum* |
22.1 |
21.7 |
20.4 |
12.1 |
Notes: |
*Minimum and maximum refer to
softest and hardest values for the grindability test. |
|
**Drilled samples are from the
Pebble West zone, at a grind particle size of 0.147 mm or 100 mesh for the
2005 tests, and 0.204 mm/65 mesh for the remaining tests. |
13.3.1.1. MACPHERSON
AUTOGENOUS GRINDABILITY TESTS
Two variable samples from the Pebble West zone were blended and
sent to SGS Lakefield for MacPherson autogenous grindability tests. The test
results are shown in Figure 13.3.5. The composite sample was categorized as
medium with respect to the throughput rate, the specific energy input, and the
final grind. The composite sample is near the median of the Pebble West
distribution for A x b, drop weight index (DWI) and BWi.
Figure
13.3.5 MacPherson
Autogenous Grindability Test Results, SGS January 2012
Sample |
Feed
Rate
(kg/h) |
F80
(µm) |
P80
(µm) |
Gross
Work
Index
(kWh/t) |
Correlated
Work
Index
(kWh/t) |
Gross
Energy
Input
(kWh/t) |
Hardness
Percentile |
W214/215 |
12.4 |
22,176 |
331 |
13.6 |
12.6 |
6.5 |
31 |
Focusing on the on-site production of three final products
(copper concentrate, molybdenum concentrate and doré), metallurgical tests
primarily consisted of:
-
flotation tests to produce a bulk flotation concentrate containing copper,
gold and molybdenum;
-
further separation of copper from molybdenum; and,
-
gold leaching with carbon-in-leach (CIL) of a pyrite flotation concentrate.
Some other tests were also carried out at a preliminary level
to optimize metal recoveries, including GRG tests and sulphidization,
acidification, recycling, and thickening (SART) process tests to recover copper
from leaching circuit residue.
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13.4.1 Recovery
of Bulk Flotation Concentrate Cu/Au/Mo
13.4.1.1. FLOTATION
KINETICS AND PRELIMINARY OPTIMIZATION
In 2011 and 2012 test programs, SGS investigated flotation
kinetic properties. Both rougher flotation and first cleaner flotation were
tested on various samples; pH value, reagent type/dosage/addition points and
pulp density factors were varied in order to determine optimized conditions for
subsequent batch cleaner and locked-cycle tests.
The 2011 program focused on bulk rougher kinetics tests on
composite samples representing supergene and hypogene rock types. The 2012
program included rougher flotation kinetics on the individual variability sample
W182, representing supergene, and four domain composite samples, namely
K-silicate, supergene, sodic potassic and illite-pyrite. Additional first
cleaner kinetics was also investigated on the four domain samples.
The observations from the two programs are summarized as
follows:
|
• |
Rougher pH Level (SGS 2011) |
|
|
|
|
|
|
- |
By increasing pH values of the rougher flotation stage to
about 8.5, metal recoveries to rougher concentrate can be significantly
increased. This was attributed to the low average natural pH value of the
four sample types (i.e., 5.8, 5.7, 7.2 and 6.2). |
|
|
|
|
|
• |
Rougher Reagent Dosage and Addition Points (SGS
2011) |
|
|
|
|
|
|
- |
A rougher flotation collector comparison was made between
using only potassium ethyl xanthate (PEX) as the collector versus PEX with
the promoter (AERO 3894) added. It was observed that metal recoveries
increased for supergene with the addition of AERO 3894; however, metal
recovery increases were not demonstrated for other samples. |
|
|
|
|
|
|
- |
Collector dosages for PEX and AERO 3894 were tested at
27.5 g/t and 45 g/t, respectively. The results indicated that adding 27.5
g/t PEX was sufficient for the first two rougher stages. The optimized
retention time is about 12 minutes for the rougher stage. |
|
|
|
|
|
• |
Rougher Sulphidization (SGS 2012) |
|
|
|
|
|
|
- |
Tests on sample W182 were performed to investigate the
effect in the rougher stage of using sodium hydrosulphide (NaHS) to
achieve a target of a reduction potential (-140 mV measured with
silver/silver cleaner) electrode. There were no observed effects on metal
recoveries to the rougher concentrate. |
|
|
|
|
|
• |
Rougher Pulp Density (SGS 2012) |
|
|
|
|
|
|
- |
Tests on one composite sample indicated that reducing
pulp density from 30 to 25% improved gold and molybdenum recovery
significantly, while copper recovery was
unaffected. |
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|
• |
Flotation Rate (SGS 2011/2012) |
|
|
|
|
|
|
- |
The supergene sample was found to be the slowest to
recover copper, gold and molybdenum in the rougher flotation stage and the
K-silicate sample the fastest. The indicated retention time for rougher
flotation is approximately 12 minutes. At the first cleaner stage, all
samples presented similar flotation rates in terms of copper recovery,
with the molybdenum recovery rate being the slowest. The retention time
indicated by the tests for first cleaner flotation is six
minutes. |
13.4.1.2. FLOTATION
TESTS ON VARIABILITY SAMPLES
SGS has conducted significant flotation testwork since mid-2009
on both the Pebble West and Pebble East zones. The baseline flowsheet is shown
in Figure 13.4.1. The target pH value for the rougher flotation stage was set at
8.5, and the P80 feed particle size was about 200 µm. The regrind
size, reagent dosage and types and pH levels in the cleaner flotation stage were
varied across the testwork in order to determine the optimal copper grade of the
bulk concentrate.
SGS conducted batch cleaner tests on 146 variability samples
from the Pebble West and Pebble East zones. The variability samples represented
the flotation domains as described in Section 13.3.1, and should be considered
representative of the mineralized material. Five of the variable batch cleaner
tests were performed on the low copper grade samples. At an average feed grade
of 0.16% copper, a bulk concentrate containing about 29.3% copper can be
recovered at a 68.1% recovery. This indicates that a saleable concentrate can be
produced from low-grade mineralized material.
SGS also performed locked-cycle tests on 107 variability
samples from the Pebble West and Pebble East zones, the results of which are
summarized in Figure 13.4.2. The average metal recoveries were higher than with
the batch tests, while the metal grades were slightly lower. Three duplicate
locked-cycle tests were performed, with results in a similar range to those
obtained from the variable locked-cycle tests.
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Figure
13.4.1 Basic
Testwork Flowsheet, SGS 2011
Figure
13.4.2 Summary
of Locked-Cycle Test Variability Test Results
Domain |
Feed Properties |
3rd Cl
Average Grade |
3rd Cl
Average Rec |
|
Py |
Cpy |
Py:Cpy |
Cu |
Au |
Mo |
Cu |
Au |
Mo |
Cu |
Au |
Mo |
|
% |
% |
|
% |
gpt |
% |
% |
gpt |
% |
% |
% |
% |
Supergene Illite
Pyrite |
6.8 |
0.8 |
7.0 |
0.33 |
0.4 |
0.011 |
24.1 |
37.7 |
0.8 |
64.3 |
36.0 |
61.0 |
Supergene Sodic
Potassic |
3.3 |
1.0 |
4.0 |
0.48 |
0.42 |
0.016 |
30.7 |
19.6 |
0.8 |
75.4 |
53.8 |
54.7 |
Hypogene Illite
Pyrite |
6.4 |
1.0 |
6.3 |
0.36 |
0.43 |
0.015 |
27.2 |
18.3 |
1.1 |
83.8 |
44.2 |
77.3 |
Hypogene Sodic
Potassic |
3.7 |
1.0 |
4.8 |
0.35 |
0.38 |
0.024 |
27.5 |
19.5 |
1.8 |
84.6 |
55.6 |
79.8 |
Hypogene
K-Silicate |
3.1 |
2.3 |
1.9 |
0.63 |
0.62 |
0.024 |
27.6 |
21.4 |
1.2 |
90.8 |
59.6 |
88.4 |
Hypogene Sericite |
8.3 |
1.9 |
6.1 |
0.66 |
0.36 |
0.031 |
25.1 |
7.6 |
1.3 |
82.5 |
41.9 |
82.0 |
Hypogene
Quartz-sericite-pyrite |
11.8 |
2.2 |
6.9 |
0.58 |
0.33 |
0.036 |
25.7 |
5.7 |
1.6 |
86.0 |
33.0 |
85.6 |
Hypogene Quartz
Pyrophyllite |
18.1 |
5.0 |
3.7 |
1.51 |
0.83 |
0.027 |
30.5 |
11 |
0.5 |
93.6 |
60.9 |
84.5 |
Definitions: cleaner (Cl), pyrite (Py), chalcopyrite (Cpy),
pyrite to chalcopyrite ratio (Py:Cpy), Recovery (Rec)
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13.4.1.3. FLOTATION
TESTS OPTIMIZATION
SGS made a few attempts to improve the copper grade in the
obtained bulk concentrate for samples with high clay and/or pyrite/chalcopyrite
content. SGS observed that:
-
Adding sodium silicate did not appear to have a beneficial impact on the
selectivity of metal recovered to rougher flotation concentrate;
-
Reducing pulp density from 35% to 28% solids improved metal recoveries,
especially with molybdenum;
-
For samples high in pyrite, adding dextrin helped to achieve the desired
26% copper of bulk concentrate copper/gold/molybdenum; however, it was also
noted that extra fuel oil will be required when adding dextrin. SGS also
recommend considering a ratio of sulphur to copper of 10.0 to identify if
dextrin addition is required;
-
The effects of regrind size, and pulp temperature were further investigated
in batch cleaner flotation tests and in the locked-cycle tests. The testwork
was performed by SGS in both 2011 and 2012, resulting in the following major
conclusions: the investigated regrind size P80 of 15 to 58 µm had
little impact on copper recovery or grades, while a finer regrind size
benefitted both gold and molybdenum recovery; and,
-
There was no observed impact from changing the pulp temperature from 5°C to
25°C on metal metallurgical performance.
SGS also compared two other frothers (HP700 and W22 C) with the
primary frother, methyl isobutyl carbinol (MIBC). SGS found that the HP700 froth
bed was less stable than that of the MIBC; W22 C showed better molybdenum
recovery, and a lower dosage produced similar metal recoveries. SGS also
compared the lower cost collector sodium ethyl xanthate (SEX) with PEX, and
concluded that interchanging SEX and PEX had no effect on metal recoveries.
13.4.1.4. FLOTATION
TESTS ON BULK COMPOSITES
As part of SGSs 2011 test program, bulk flotation tests on a
locked-cycle scale were conducted on illite-pyrite, carbonate and supergene
composites. The purpose of this testwork was to produce large quantities of
products that could be used for vendor testwork. It should be noted that the
carbonate composite sample was an early geometallurgical domain type
classification, and was redefined as sodic potassic in later geometallurgical
studies. The locked-cycle test results are shown below in Figure 13.4.3. SGS
observed that the illite-pyrite composite did not reach the target copper grade
of 26%. SGS suspected this may be caused by a low head grade and the presence of
high levels of pyrite and clay minerals.
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Figure
13.4.3
Locked-Cycle Test Results of Bulk Samples, SGS 2012
Composite |
Regrind
Size
P80 µm |
Cu/Mo Concentrate Grade |
Cu/Mo Concentrate Recovery
% |
Cu
% |
Au |
Mo
% |
Cu |
Au |
Mo |
g/t |
oz/ton |
Illite-Pyrite |
28 |
10.4 |
11.2 |
0.327 |
0.20 |
77.0 |
40.3 |
34.9 |
Carbonate |
37 |
28.4 |
10.7 |
0.312 |
1.25 |
79.4 |
43.5 |
59.8 |
Supergene |
38 |
27.1 |
16.0 |
0.467 |
1.64 |
70.6 |
47.3 |
70.0 |
13.4.1.5. FLOTATION
TESTS ON CONTINUOUS COMPOSITES
A small scale continuous flotation plant was utilized on five
composite samples from the Pebble deposit to generate additional quantities of
sample for vendor testwork. The five composites ranged in head grade from 0.28
to 0.57% Cu, from 0.30 to 0.46 g/t Au, and from 0.010 to 0.028% Mo. The main
purpose of this continuous flotation testwork was to generate product for
downstream testwork and to evaluate the implementation of a gravity circuit on a
portion of the feed to the regrind mill.
The pilot plant was completed over a series of day shifts and
continuous runs. Overall, 28 runs were completed: 17 on the commissioning, 3 on
the sodic potassic, 2 on the K-silicate, 3 on the supergene, and 3 on the illite
pyrite composites.
Any further continuous testwork would ideally be completed on a
higher feed rate and a sufficient amount of operation time would be reserved for
reagent optimization. Future testwork should include adequate sample to optimize
Mo recovery by (1) increasing the cleaning circuit retention time and (2)
optimizing reagent dosages. The addition of a Knelson concentrator in the
regrind circuit of a pilot plant this size was challenging due to the amount of
water generated by the Knelson circuit. The additional water generated was
finally managed by inserting a thickener to treat the Knelson tailings stream.
The continuous flotation results for the K-Silicate composite
matched very closely with the locked cycle test results, with the exception that
Mo recoveries were slightly lower. The continuous flotation Cu recovery for the
supergene composite was higher compared to the locked cycle test result. For the
remaining three composites, Cu and gold recoveries were 7% lower, on average.
Except for the supergene composite, Mo losses to the rougher tail were almost
twice as high as in the locked cycle test. Final concentrate Mo recoveries were
almost half the LCT recoveries. The Mo recovery to the final concentrate would
likely improve with longer retention times in the 2nd and 3rd cleaning stages.
One of the main purposes of the pilot plant was to determine
the amount of Au that could be recovered by adding a Knelson concentrator in the
regrind circuit. The Knelson concentrator treated a 33% bleed stream from the
regrind cyclone underflow. The average Au recovery to the Knelson concentrate
ranged from 2.6% for the Supergene composite to 7.5% for the K-silicate
composite. A comparison of metallurgical performance with and without the
Knelson concentrator indicated similar overall Au recoveries to a 26% Cu
concentrate.
13.4.2 Separation
of Molybdenum and Copper
Separation of molybdenum from copper in the bulk flotation
concentrate was tested by SGS in the 2011 and 2012 programs. In addition,
G&T also performed separation tests on one sample.
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13.4.2.1. SGS
SEPARATION WORK, 2011 AND 2012
Preliminary separation tests for molybdenum and copper were
performed on three composite samples, including illite-pyrite, carbonate and
supergene (SGS 2011). The locked-cycle tests in the 2011 program employed a
basic flowsheet, as shown in Figure 13.4.4. The cycle numbers were varied in
order to achieve the target grade of a final molybdenum concentrate.
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Figure
13.4.4 Basic
Testwork Flowsheet, SGS 2011
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The 2011 program results outlined in Figure 13.4.5 show that only the carbonate composite achieved a molybdenum grade of 50%, while the other two composite samples were unable to produce a marketable molybdenum product. Increasing the locked cycles
from 3 to 6 for the illite-pyrite composite produced only a marginal increase in molybdenum grade.
As part of the 2012 testing program, further tests to improve the molybdenum separation were conducted on four domain samples. The commissioning sample, which represented the sodic potassic domain, was used to optimize the flotation conditions
required for copper-molybdenum separation. A series of open cycle and kinetic tests were conducted to establish the conditions for the commissioning composite locked cycle test. Results of the locked cycle tests are provided in Figure 13.4.5.
Locked cycle test results for the latter three composites were found to be below expectation. It should be noted that the locked cycle tests conducted on the illite pyrite, sodic potassic and supergene composites were carried out without the open
cycle tests to confirm conditions (due to their smaller mass compared to the commissioning composite), and by a different flotation operator than previous. Molybdenum head grades of the bulk cleaner concentrates from the three problematic domain
samples were also below typical values achieved in locked cycle tests which may have contributed to the poor results. Further investigation confirmed that major molybdenum loss occurred in the rougher circuit.
Addition of the flotation reagent NaSH in the rougher state was found to be too high, resulting in unacceptable molybdenum depression. Adding a scavenger stage to the rougher flotation resulted in significant improvements in molybdenum recovery of
approximately 15% for the sodic potassic composite, and over 30% for the illite pyrite composite. The scavenger tests were not conducted for the supergene composite due to lack of sample.
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Figure
13.4.5 Locked
-Cycle Test Results of Molybdenum
Flotation, SGS 2011-2012
Composite |
Regrind
Size
P80 µm |
Mo
Concentrate |
Cu
Concentrate |
Grade |
Recovery % |
Grade |
Recovery % |
Cu % |
Au |
Mo % |
Cu |
Au |
Mo |
Cu % |
Au |
Mo % |
Cu |
Au |
Mo |
g/t |
oz/ton |
g/t |
oz/ton |
SGS 2011 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Illite-Pyrite |
28 |
5.93 |
15.4 |
0.500 |
11.6 |
0.7 |
0.9 |
32.3 |
10.5 |
11.1 |
0.324 |
0.015 |
76.3 |
39.4 |
2.6 |
Carbonate |
37 |
1.81 |
3.96 |
0.116 |
49.7 |
0.1 |
0.4 |
55.5 |
29.0 |
10.9 |
0.318 |
0.091 |
79.3 |
43.1 |
4.2 |
Supergene |
38 |
3.46 |
3.84 |
0.112 |
38.7 |
0.4 |
0.5 |
68.9 |
28.1 |
16.5 |
0.482 |
0.027 |
70.2 |
46.8 |
1.1 |
SGS 2012 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Commission |
- |
1.86 |
2.12 |
0.0619 |
48.2 |
0.2 |
0.3 |
92.7 |
21.8 |
11.2 |
0.327 |
0.068 |
99.8 |
99.7 |
7.3 |
Sodic Potassic |
- |
3.01 |
N/A |
N/A |
41.1 |
0.1 |
N/A |
83.6 |
23.3 |
N/A |
N/A |
0.074 |
99.9 |
N/A |
16.4 |
Illite-Pyrite |
- |
3.19 |
N/A |
N/A |
43.5 |
0.02 |
N/A |
79.8 |
23.8 |
N/A |
N/A |
0.14 |
99.8 |
N/A |
20.2 |
Supergene |
- |
2.42 |
N/A |
N/A |
43.8 |
0.1 |
N/A |
86.9 |
29.8 |
N/A |
N/A |
0.078 |
99.9 |
N/A |
13.1 |
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13.4.2.2. G&T SEPARATION WORK
G&T tested molybdenum recovery from bulk flotation
concentrate, using one sample of copper-molybdenum bulk concentrate (G&T
2011). The head analysis indicated that the bulk concentrate had high levels of
pyrite (about 13.2%) and galena (about 0.5%) . Due to the limited sample size,
only two batch cleaner tests were performed on the bulk concentrate sample. A
regrind stage was used in Test 1, while no regrinding was performed in Test 2.
The test results are summarized in Figure 13.4.6.
Test 1 and Test 2 results were 50.6% and 47.6% for molybdenum
grades in the final molybdenum concentrates, and recoveries were 76.2% and 74.7%
molybdenum, respectively. G&T recommended further testing be considered,
including locked-cycle tests and other potential reagent schedules.
Figure
13.4.6
Molybdenum Recovery, G&T 2011
|
Regrind
Size
P80 µm |
Grade |
Recovery %
|
Cu % |
Au |
Mo% |
Cu |
Au |
Mo |
g/t |
oz/ton |
Test 1 |
33 |
- |
- |
- |
- |
- |
- |
- |
Molybdenum Concentrate |
- |
1.45 |
2.36 |
0.0689 |
50.6 |
0.1 |
0.2 |
76.2 |
Molybdenum 3rd Cl Tail |
- |
12.9 |
18.9 |
0.552 |
12.1 |
0.1 |
0.2 |
3.0 |
Molybdenum 2nd Cl Tail |
- |
24.2 |
35.4 |
1.034 |
3.89 |
1.2 |
3.1 |
6.9 |
Molybdenum 1st Cl Tail |
- |
24.3 |
27.7 |
0.809 |
1.47 |
5.3 |
10.4 |
11.3 |
Molybdenum Ro Tail |
- |
26.3 |
14.2 |
0.415 |
0.02 |
93.3 |
86.2 |
2.6 |
Test 2 |
49 |
- |
- |
- |
- |
- |
- |
- |
Molybdenum Concentrate |
- |
2.74 |
3.92 |
0.114 |
47.6 |
0.1 |
0.3 |
74.7 |
Molybdenum 3rd Cl Tail |
- |
14.8 |
21.2 |
0.619 |
8.18 |
0.1 |
0.2 |
1.4 |
Molybdenum 2nd Cl Tail |
- |
21.3 |
38.4 |
1.12 |
5.51 |
0.5 |
1.5 |
4.3 |
Molybdenum 1st Cl Tail |
- |
27.9 |
28.4 |
0.829 |
0.80 |
3.6 |
6.5 |
3.6 |
Molybdenum Ro Tail |
- |
26.0 |
13.9 |
0.406 |
0.12 |
95.8 |
91.5 |
16.0 |
Ro rougher; Cl - cleaner
13.4.3
Pyrite Flotation
A pyrite flotation step was included as part of the locked
cycle variability tests described in Section 13.5.1.2. Pyrite flotation stage
gold recoveries from the initial samples tested were found to be highly
variable, using a four minute laboratory flotation time. In order to optimize
the pyrite flotation metallurgy, SGS performed a series of kinetics tests using
first scavenger tailings generated from four domain composite samples. Results
of the tests are summarized in Figure 13.4.7which shows the optimum laboratory
flotation time occurs at approximately six minutes.
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Figure
13.4.7 Pyrite
Flotation Kinetics Test Results
13.5.1 Gravity
Recovered Gold
Three composite samples, representing illite-pyrite, carbonate
and supergene mineralization types, were tested for gravity recoverable gold
potential in COREMs facility (COREM, 2010). GRG was tested on the regrind
circuit with a target particle size P80 of 25 µm. Using a modified
GRG test, the supergene sample had the highest GRG content of 33%, followed by
illite-pyrite with 29% GRG and carbonate at 23%.
In 2011, four composite samples from the continuous testwork
program were tested for gravity recoverable gold. The K-silicate sample had the
hi9hest GRG potential at 49%, followed by sodic potassic (41%), supergene (33%),
commissioning (26%), and illite pyrite (25%).
13.5.2 Gold
Recovered from CIL Circuit
Leaching testwork was carried out on the pyrite concentrates of
various samples. Initial tests indicated that gold recovery can be significantly
increased by an average of 15% when the pyrite concentrate particle size was
reduced to a P80 (product size of 80% passing) of approximately 10 µm
(SGS 2011).
The pyrite concentrate regrind test was conducted by Xstrata
(SGS 2012). It was shown that the average power consumption is 48.7 kWh/t at a
target P80 of 10 µm, and the average media consumption was 22.2
g/kWh.
Further leaching tests were carried out on the reground pyrite
concentrate on variable samples (SGS 2012). The optimized leaching test
conditions that gave the best gold, copper and silver extraction rates are
summarized below:
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-
Pre-oxidation with oxygen addition to 20 ppm before leaching;
-
Leaching pulp density of 33% solids; and
-
Leaching pH 10.5 to 11.0.
Variability sample leaching tests were performed under the
optimized condition.. The average extraction rates were 72.9% for gold, 72.8%
for silver and 75.5% for copper with a 48-hour leaching period.
Bulk leaching test CN-51 was conducted under the same
conditions with varied composite samples. The leaching kinetic properties are
shown in Figure 13.5.1.
Figure
13.5.1 Bulk
Gold Extraction Kinetics, SGS 2012
Carbon adsorption tests were carried out on commissioning
composite samples as well as K-silicate composite samples. The observations are
summarized as follows:
-
Most leaching can be completed after about 12 hours, but some concentrates
benefited from a longer leach time of 24 to 48 hours; and,
-
The copper loading rate on carbon was higher than with gold or silver,
approximately 20 lb/ton from solution containing 4 to 4.5 g/L copper,
approximately 8 lb/ton from a 1.5 to 2.5 g/L copper solution.
13.6 |
SART PROCESS (SULPHIDIZATION, ACIDIFICATION, RECYCLING, THICKENING) |
SGS tested SART potential to recover the dissolved copper in
the leaching circuit. SART lab tests were performed on both high- and low-copper
pyrite concentrates. For the high-copper sample, the lowest copper concentration in the final solution was lower than 10 ppm from
the original 3,130 ppm, with a copper stage recovery of > 99%. With the
low-copper sample, the concentration of copper dropped from 1,810 ppm to about 3
ppm, with a copper stage recovery of > 99%. The test conditions for the two
optimized results within this test range were:
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-
The addition of sulphuric acid (H2SO4) to reach a pH
value of 4.0; and,
-
The addition of the reagent NaHS at 130% of the stoichiometric ratio.
13.7.1 Concentrate Filtration
Outotec tested the filtration rates and cake moisture on a
copper concentrate sample (Outotec June 2011). Three tests with varied pumping
times were performed at Outotecs laboratory. With a feed solids density of 58
to 60% by weight, the cake moisture for all three tests was less than 9%. The
measured filtration rate was between 569 and 663 kg/m2/h.
13.8 |
QUALITY OF CONCENTRATES |
The results of assays obtained on locked cycle test Cu/Mo
3rd cleaner concentrates indicate that Pebble concentrates will not
be problematic in terms deleterious elements. The assays showed deleterious
elements to be below the penalty trigger for almost all of the 75 samples
tested, with the exception of two supergene samples that exceeded for arsenic,
one sodic potassic sample for antimony, one illite pyrite sample for zinc, and
two illite pyrite and one sodic potassic samples for mercury.
In addition to copper, molybdenum, gold and silver, rhenium was
also identified in the bulk flotation concentrates (SGS, 2012). The rhenium
concentration measured between 0.082 g/t to a high of 3.56 g/t. Rhenium can be
recovered in the molybdenum flotation tests. In test Mo-F13, the rhenium grade
was increased to 26.3 g/t in the molybdenum concentrate. Figure 13.8.1 shows the
rhenium grade and recovery relationship from test Mo-F13.
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Figure
13.8.1
Rhenium Grade and Recovery Relationship SGS 2012
13.9 |
METAL RECOVERY PROJECTION |
Metal recoveries projected in the 2014 technical report are
based on the locked-cycle test results of the variability samples, and
associated gold leach testwork. The analysis can be summarized as follows:
-
After a review of the 103 available samples, eight were excluded from the
analysis 5 of 8 because they were below the 0.20% Cu cut-off grade, and 3 of
8 because they were contaminated by drilling fluid. The remaining 95 samples
were used to determine copper, gold and molybdenum recoveries. Silver recovery
was based on a dataset of 10 samples due to incomplete silver assay data for
the testwork;
-
Locked cycle test recovery distributions were reviewed for each
geometallurgical domain type to determine if domains could be grouped into
similar recovery domains. The outcome of this analysis established seven
recovery domains for copper, six for gold, and seven for molybdenum;
-
Recoveries were determined using the median value of each dataset;
-
Copper-molybdenum separation efficiency was assumed to be 92.7% molybdenum
recovery to the molybdenum concentrate; and,
-
Gold recovery included an incremental 1.0% for the gravity circuit.
Figure 13.9.1 provides projected overall recoveries, which
include the flotation and gold plant recoveries.
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Figure
13.9.1
Projected Metallurgical Recoveries
Domain |
Flotation recovery to Concentrate |
Gold Plant Recovery |
Overall Recovery
|
|
Cu Con |
Mo Con |
SART |
Dore |
Supergene: |
Cu |
Au |
Ag |
Mo |
Cu |
Au |
Ag |
Cu |
Au |
Ag |
Mo |
Sodic Potassic |
74.7 |
60.4 |
64.1 |
51.2 |
1.5 |
16.0 |
6.0 |
76.2 |
76.4 |
70.2 |
51.2 |
Illite Pyrite |
68.1 |
43.9 |
64.1 |
62.6 |
3.9 |
26.8 |
6.0 |
72.1 |
70.7 |
70.2 |
62.6 |
Hypgoene: |
|
|
|
|
|
|
|
|
|
|
|
Illite Pyrite |
86.4 |
43.9 |
64.1 |
73.2 |
1.9 |
26.1 |
6.0 |
88.3 |
70.0 |
70.2 |
73.2 |
Sodic Potassic |
86.2 |
60.4 |
64.1 |
76.6 |
1.4 |
16.7 |
6.0 |
87.6 |
77.1 |
70.2 |
76.6 |
K Silicate |
90.3 |
61.3 |
64.1 |
82.3 |
0.7 |
13.8 |
6.0 |
91.0 |
75.1 |
70.2 |
82.3 |
QP |
94.3 |
65.0 |
64.1 |
80.1 |
1.4 |
14.4 |
6.0 |
95.6 |
79.4 |
70.2 |
80.1 |
Sericite |
86.4 |
39.2 |
64.1 |
73.2 |
1.9 |
26.7 |
6.0 |
88.3 |
65.8 |
70.2 |
73.2 |
QSP |
86.0 |
31.6 |
64.1 |
82.5 |
2.1 |
32.1 |
6.0 |
88.1 |
63.7 |
70.2 |
82.5 |
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14.0 |
MINERAL RESOURCE ESTIMATES |
The current Pebble mineral resource estimate is based on all
core holes in the vicinity of the block extents, completed to the end of 2013.
This dataset includes 4,044 additional assays that were obtained from 53
additional drill holes drilled since the previous estimate was completed. Based
on descriptive statistics, 3D surfaces and wireframe models of domains for each
of the four metals, as well as bulk density were interpreted and used in the
development of search strategies and geostatistical parameters for block
interpolation and resource classification.
The updated Pebble resource estimate is presented in Figure
14.1.1. Tonnes have been rounded to the nearest million. The base case of 0.3%
CuEq, is highlighted by bold type face. Of the total resource, the Measured
category represents approximately 5%, the Indicated category represents 55%, and
the Inferred category represents approximately 40%.
Figure
14.1.1 Pebble
Deposit Mineral Resource Estimate 2014
Threshold CuEq % |
CuEq% |
Tonnes |
Cu (%) |
Au (g/t) |
Mo (ppm) |
Ag (g/t) |
Cu Blbs |
Au Moz |
Mo Blbs |
Ag Moz |
Measured |
0.3 |
0.65 |
527,000,000 |
0.33 |
0.35 |
178 |
1.66 |
3.83 |
5.93 |
0.21 |
28.13 |
0.4 |
0.66 |
508,000,000 |
0.34 |
0.36 |
180 |
1.68 |
3.80 |
5.88 |
0.20 |
27.42 |
0.6 |
0.77 |
279,000,000 |
0.40 |
0.42 |
203 |
1.84 |
2.46 |
3.77 |
0.12 |
16.51 |
1.0 |
1.16 |
28,000,000 |
0.62 |
0.62 |
302 |
2.27 |
0.38 |
0.56 |
0.02 |
2.04 |
Indicated |
0.3 |
0.77 |
5,912,000,000 |
0.41 |
0.34 |
245 |
1.66 |
53.42 |
64.62 |
3.20 |
315.50 |
0.4 |
0.82 |
5,173,000,000 |
0.45 |
0.35 |
260 |
1.75 |
51.31 |
58.21 |
2.97 |
291.05 |
0.6 |
0.99 |
3,450,000,000 |
0.55 |
0.41 |
299 |
1.99 |
41.82 |
45.47 |
2.27 |
220.71 |
1.0 |
1.29 |
1,411,000,000 |
0.77 |
0.51 |
343 |
2.42 |
23.95 |
23.14 |
1.07 |
109.79 |
Measured + Indicated |
0.3 |
0.76 |
6,439,000,000 |
0.40 |
0.34 |
240 |
1.66 |
56.76 |
70.38 |
3.40 |
343.63 |
0.4 |
0.81 |
5,681,000,000 |
0.44 |
0.35 |
253 |
1.75 |
55.09 |
63.92 |
3.17 |
319.62 |
0.6 |
0.97 |
3,729,000,000 |
0.54 |
0.41 |
291 |
1.98 |
44.38 |
49.15 |
2.39 |
237.37 |
1.0 |
1.29 |
1,439,000,000 |
0.76 |
0.51 |
342 |
2.42 |
24.11 |
23.60 |
1.08 |
111.97 |
Inferred |
0.3 |
0.54 |
4,460,000,000 |
0.25 |
0.26 |
222 |
1.19 |
24.55 |
37.25 |
2.18 |
170.49 |
0.4 |
0.68 |
2,630,000,000 |
0.33 |
0.30 |
266 |
1.39 |
19.14 |
25.38 |
1.55 |
117.58 |
0.6 |
0.89 |
1,290,000,000 |
0.48 |
0.37 |
291 |
1.79 |
13.66 |
15.35 |
0.83 |
74.28 |
1.0 |
1.20 |
360,000,000 |
0.69 |
0.45 |
377 |
2.27 |
5.41 |
5.14 |
0.30 |
25.94 |
Notes:
These resource estimates have been prepared in accordance with
NI 43-101 and the CIM Definition Standards. Inferred mineral Resources are
considered to be too speculative to allow the application of technical and
economic parameters to support mine planning and evaluation of the economic
viability of the project. Under Canadian rules, estimates of Inferred Mineral
Resources may not form the basis of feasibility or pre-feasibility studies, or
economic studies except for Preliminary Economic Assessments as defined
under 43-101. It cannot be assumed that all or any part of the Inferred
resources will ever be upgraded to a higher category.
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Copper equivalent calculations use metal prices of $1.85/lb for
copper, $902/oz for gold and $12.50/lb for molybdenum, and recoveries of 85% for
copper 69.6% for gold, and 77.8% for molybdenum in the Pebble West zone and
89.3% for copper, 76.8% for gold, 83.7% for molybdenum in the Pebble East zone.
Contained metal calculations are based on 100% recoveries.
A 0.30% CuEQ cut-off is considered to be appropriate for
porphyry deposit open pit mining operations in the Americas.
All mineral resource estimates, cut-offs and metallurgical
recoveries are subject to change as a consequence of more detailed economic
analyses that would be required in pre-feasibility and feasibility studies.
14.2 |
EXPLORATORY DATA ANALYSIS |
14.2.1
Assays
Descriptive global statistics for all non-zero copper, gold,
silver, and molybdenum assays are presented in Figure 14.2.1. The distribution
of drill holes relative to the extent of the block model is shown in Figure
14.2.2.
Figure
14.2.1 Pebble
Deposit Assay Database Descriptive Global Statistics
Statistic (Non-zero) |
Length (ft) |
Ag (ppm) |
Au (g/t) |
Cu (%) |
Mo (ppm) |
Mean |
9.97 |
1.57 |
0.32 |
0.33 |
191.3 |
Median |
10.00 |
1.00 |
0.23 |
0.26 |
130 |
Standard Deviation |
1.86 |
5.02 |
1.50 |
0.31 |
298.26 |
Coefficient of Variation |
0.19 |
3.20 |
4.63 |
0.94 |
1.56 |
Kurtosis |
23.31 |
30529 |
41613 |
28.36 |
2,455 |
Skewness |
2.1 |
155.3 |
189.9 |
2.9 |
29.00 |
Minimum |
0.001 |
0.1 |
0.001 |
0.001 |
0.20 |
Maximum |
55 |
1030 |
334.8 |
9.29 |
32200 |
Count |
59105 |
58876 |
59114 |
58912 |
59114 |
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Figure
14.2.2 Pebble
Deposit Plan View of Drill Holes and Block Model Extent (red rectangle)
Metal distribution within the Pebble deposit is affected by
lithology, alteration, weathering and structure such that the distribution
cannot be constrained on the basis of a single attribute. Further, the
distribution of each of the metals differs in accordance with the differing
response of those metals to the thermal and chemical environments prevailing at
the time of deposition. Therefore, different domains were used for each of the
four metals. These domains are tabulated in Figure 14.2.3; the domains for
copper are shown in section view in Figure 14.2.8.
Descriptive statistics were generated for each of the metal
domains; these are summarized graphically as box-and-whisker plots in Figure
14.2.4 to Figure 14.2.7.
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Figure
14.2.3 Pebble
Deposit Metal Domains
Domain |
Code |
Explanation |
Ag low grade |
40 |
Hypogene at depth |
Ag moderate grade |
41 |
Hypogene West near surface |
Ag Hypogene Northeast |
42 |
North of ZE fault |
Ag Hypogene Southeast |
43 |
South of ZE fault |
Ag |
44 |
6348 Domain (not used in
estimate) |
Au low grade |
40 |
Hypogene at depth |
Au moderate grade |
41 |
Hypogene West near surface |
Au Hypogene Northeast |
42 |
North of ZE fault |
Au Hypogene Southeast |
43 |
South of ZE fault |
Au |
44 |
6348 Domain (not used in
estimate) |
Cu Leach |
1 |
Cu/Leach |
Cu Supergene |
2 |
Cu/Supergene |
Cu low grade |
40 |
Hypogene at depth |
Cu moderate grade |
41 |
Hypogene Westnear surface |
Cu Hypogene Northeast |
42 |
North of ZE fault |
Cu Hypogene Southeast |
43 |
South of ZE fault |
Mo low grade |
40 |
Below 70ppm cap |
Mo high grade |
41 |
Above 70ppm cap west |
Mo high grade Northeast |
42 |
Above 70ppm cap, north of ZE
fault |
Mo high grade Southeast |
43 |
Above 70ppm cap, south of ZE
fault |
Mo low grade |
45 |
Below base cap |
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Figure
14.2.4 Pebble
Deposit Copper Assay Domain Box-and-Whisker Plots
Note: M
= arithmetic mean
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Figure
14.2.5 Pebble
Deposit Gold Assay Domain Box-and-Whisker Plots
Note: M
= arithmetic mean
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Figure
14.2.6 Pebble
Deposit Molybdenum Assay Box-and-Whisker Plots
Note:
M = arithmetic mean
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Figure
14.2.7 Pebble
Deposit Silver Assay Box-and-Whisker Plots
Note:
M = arithmetic mean
There are four basic domains for copper, gold, molybdenum and
silver, plus additional leach and supergene domains for copper. A north-south
boundary separates the flat-lying western portion of the deposit from the
east-dipping eastern portion of the deposit. These two portions are different in
a number of respects. An east-west fault divides the eastern portion of the
deposit into northeast and southeast quadrants. The west half of the deposit has
high-grade and low-grade domains that are separated by a planar, gently
east-dipping interface that extends into the eastern portion of the deposit
beneath the northeast and southeast hypogene domains.
As can be seen from the box-and-whisker plots, the
fault-bounded domains have similar average grades for all metals so their
separation into separate domains is principally useful for variographic
analysis. The low-grade domain is, for all metals, clearly dissimilar from the
others despite physical continuity and therefore requires domain status. The
copper leach zone is also clearly distinguishable although the supergene zone is
not markedly different from the other high-grade domains. Five of the six
domains are shown in Figure 14.2.8. This east-west section is located north of
the east west trending ZE fault so zone 43 is not visible. The east-west divide
is clearly visible between zones 41 in the west and 42 in the east.
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Figure
14.2.8 Pebble
Deposit Copper Grade Domains
14.2.2
Capping
Capping is the process of reducing statistically anomalous high
values (outliers) within a sample population in order to avoid the
disproportionate influence these values could have on block estimation. The
determination of appropriate capping levels is subjective but is commonly
established by reference to cumulative frequency plots of the metal assays.
Prominent breaks in the plot line, particularly at the upper end, infer a
sub-population of values separate from the main population. The break in the
trend defines the capping value and all assays above that point are reduced to
the capping value.
Capping values applied to the Pebble assays were determined for
each domain and are shown in Figure 14.2.9.
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Figure
14.2.9 Pebble
Deposit Capping Values
Code |
Explanation |
Units |
Cap |
40 |
Ag - Hypogene at depth |
g/t |
35 |
41 |
Ag - Hypogene West near surface |
g/t |
19 |
42 |
Ag - North of ZE fault |
g/t |
13 |
43 |
Ag - South of ZE fault |
g/t |
70 |
40 |
Au - Hypogene at depth |
g/t |
2.8 |
41 |
Au - Hypogene West near surface |
g/t |
7.0 |
42 |
Au - North of ZE fault |
g/t |
7.7 |
43 |
Au - South of ZE fault |
g/t |
4.3 |
1 |
Cu - Leach |
% |
0.25 |
2 |
Cu - Supergene |
% |
2.2 |
40 |
Cu - Hypogene at depth |
% |
0.8 |
41 |
Cu - Hypogene West near surface |
% |
2.0 |
42 |
Cu - North of ZE fault |
% |
2.4 |
43 |
Cu - South of ZE fault |
% |
2.4 |
40 |
Mo - Below 70ppm cap |
ppm |
300 |
41 |
Mo - Above 70ppm cap west |
ppm |
2100 |
42 |
Mo - Above 70ppm cap, north of
ZE fault |
ppm |
2800 |
43 |
Mo - Above 70ppm cap, south of
ZE fault |
ppm |
2800 |
14.2.3
Composites
Compositing to a common length overcomes the influence of
sample length on grades within the resource estimate. Samples were composited to
50 ft lengths to match the anticipated bench height. Although the compositing is
not intended to ensure the composite intervals will coincide with the benches,
the composite length results in grades that match the resolution of those that
can be expected from bench-scale sampling. The number of composites and their
mean values, are given in Figure 14.2.10.
Figure
14.2.10 Pebble Deposit
Composite Mean Values
Metal |
Composites |
Mean |
Ag (g/t) |
16,210 |
1.17 |
Au (g/t) |
12,254 |
0.31 |
Cu (%) |
16,184 |
0.24 |
Mo (ppm) |
16,170 |
140 |
Bulk Density |
9,830 |
2.62 |
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The database contains values for 9,830 bulk density
measurements. These measurements were made on 0.1 -m samples of drill core
selected from locations throughout the Pebble deposit so as to reasonably
reflect deposit-wide variations in rock mass. These values were not composited
because they are spatially isolated and not appropriate for compositing, but
were imported directly into the composite table. Five separate bulk density
domains were identified:
|
1. |
Pyrite cap within the western portion of the deposit
(SGZ1); |
|
|
|
|
2. |
Pyrite cap within the eastern portion of the deposit
(SGZ2); |
|
|
|
|
3. |
Cretaceous hanging wall (SGZ3); |
|
|
|
|
4. |
Tertiary unmineralized rock east of the ZG1 Fault
(SGZ10); and, |
|
|
|
|
5. |
Tertiary unmineralized rock west of the ZG1 Fault
(SGZ11). |
The kriged bulk density measurements within these domains were
used to estimate tonnages.
14.4 |
GEOLOGICAL INTERPRETATION |
The Pebble deposit extends for a strike length of approximately
13,000 ft, a width of 7,700 ft, and to a depth of at least 5,810 ft. As
mentioned in Sections 14.1 and 14.2, for the purpose of resource estimation, the
Pebble deposit has been partitioned into metal domains. These domains are
defined by deposit orientation, structure and grade. Two boundaries are common
to all metals: 1) the north-south divide that separates the deposit into east
and west portions and marks a change in the dip of the stratigraphy from flat
lying to gently east dipping, and 2) the east-trending fault (ZE Fault) that
divides the eastern portion of the deposit into two zones. The shape and
location of the domain boundary differs among the metals but in general is
gently east-dipping and separates an upper higher-grade zone (copper, gold and
silver) from a lower grade zone. East of the east-west divide the higher-grade
zone is divided into a north and a south domain by the ZE Fault; the lower-grade
zone underlies both western and eastern parts of the deposit. In the case of
molybdenum, in contrast to the other metals, the upper, western zone is
lower-grade and the underlying zone is higher grade. There are two additional
domains for copper: leached and supergene; both are located in the near-surface
western portion of the deposit. Copper grade distribution is further constrained
by two lower-grade domains that overlie portions of the east and west halves of
the deposit. The gold domains also contain a very small low-grade domain
immediately above the western higher-grade domain.
The bulk density domains are described in Section 14.3.
Separate variables were set up in the block model for each of
the metals, each metal domain and for bulk density (noted as SG0-3 and SG10 in
Figures 14.5.1 and Figure 14.5.2) . This approach allowed for the application of
a unique suite of search strategies and kriging parameters to each metal domain
based on its geostatistical characteristics.
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The Pebble variography and search ellipse parameters are
presented in Figure 14.5.1 and Figure 14.5.2, respectively.
Figure
14.5.1 Pebble
Deposit Variogram Parameters
Domain |
Variogram Weights |
S1 Axis Range (ft) |
S2 Axis Range (ft) |
S0 |
S1 |
S2 |
Major |
Semi-major |
Minor |
Major |
Semi-major |
Minor |
Ag40 |
0.52 |
0.41 |
0.00 |
750 |
475 |
1,500 |
0 |
0 |
0 |
Ag41 |
0.30 |
0.33 |
0.00 |
450 |
360 |
475 |
0 |
0 |
0 |
Ag42 |
0.08 |
0.34 |
0.26 |
600 |
600 |
600 |
700 |
2,250 |
1,500 |
Ag43 |
0.13 |
0.49 |
0.00 |
1,300 |
800 |
1,200 |
0 |
0 |
0 |
Au40 |
0.46 |
0.54 |
0.00 |
700 |
700 |
350 |
0 |
0 |
0 |
Au41 |
0.16 |
0.26 |
0.29 |
250 |
250 |
200 |
1,200 |
850 |
800 |
Au42 |
0.43 |
0.57 |
0.00 |
1,100 |
1,500 |
800 |
0 |
0 |
0 |
Au43 |
0.20 |
0.70 |
0.00 |
900 |
600 |
450 |
0 |
0 |
0 |
Cu1 |
0.31 |
0.48 |
0.21 |
700 |
700 |
350 |
700 |
700 |
350 |
Cu2 |
0.40 |
0.60 |
0.00 |
900 |
520 |
520 |
0 |
0 |
0 |
Cu40 |
0.15 |
0.60 |
0.00 |
1,400 |
1,300 |
550 |
0 |
0 |
0 |
Cu41 |
0.11 |
0.25 |
0.30 |
450 |
700 |
450 |
4,000 |
1,300 |
1,300 |
Cu42 |
0.13 |
0.12 |
0.30 |
370 |
500 |
700 |
1,400 |
1,100 |
700 |
Cu43 |
0.12 |
0.49 |
0.00 |
1,500 |
1,300 |
500 |
0 |
0 |
0 |
Mo40 |
0.28 |
0.72 |
0.00 |
900 |
200 |
450 |
0 |
0 |
0 |
Mo41 |
0.19 |
0.16 |
0.30 |
600 |
1,000 |
500 |
1,700 |
1,000 |
1,600 |
Mo42 |
0.38 |
0.19 |
0.35 |
1,200 |
1,200 |
1,200 |
1,200 |
1,200 |
1,200 |
Mo43 |
0.47 |
0.23 |
0.30 |
1,300 |
1,900 |
900 |
1,900 |
2,000 |
1,000 |
SG0 |
0.44 |
0.56 |
0.00 |
1,350 |
1,350 |
800 |
0 |
0 |
0 |
SG10 |
0.34 |
0.41 |
0.00 |
1,350 |
850 |
950 |
0 |
0 |
0 |
SG1 |
0.46 |
0.54 |
0.00 |
640 |
485 |
450 |
0 |
0 |
0 |
SG2 |
0.37 |
0.63 |
0.00 |
1,700 |
1,280 |
500 |
0 |
0 |
0 |
SG3 |
0.42 |
0.40 |
0.00 |
1,825 |
1,610 |
900 |
0 |
0 |
0 |
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Figure
14.5.2 Pebble
Deposit Search Ellipse Parameters
Domain |
Ellipse Orientation (°) |
Ellipse Dimensions (ft) |
Bearing |
Plunge |
Dip |
Major |
Semi-major |
Minor |
Ag40 |
120.0 |
0.0 |
60.0 |
565 |
355 |
1,125 |
Ag41 |
180.0 |
0.0 |
0.0 |
340 |
270 |
355 |
Ag42 |
130.0 |
0.0 |
-60.0 |
525 |
1,690 |
1,125 |
Ag43 |
20.0 |
40.0 |
0.0 |
975 |
600 |
900 |
Au40 |
0.0 |
-0.5 |
0.0 |
510 |
510 |
260 |
Au41 |
70.0 |
0.0 |
-0.5 |
800 |
600 |
560 |
Au42 |
290.0 |
20.0 |
0.0 |
825 |
1,110 |
600 |
Au43 |
79.0 |
-17.0 |
-10.0 |
715 |
460 |
350 |
Cu1 |
40.0 |
0.0 |
0.0 |
550 |
530 |
270 |
Cu2 |
30.0 |
0.0 |
-0.5 |
675 |
390 |
400 |
Cu40 |
72.0 |
-30.0 |
-28.0 |
1,100 |
1,020 |
425 |
Cu41 |
53.0 |
-20.0 |
-79.0 |
2,900 |
950 |
950 |
Cu42 |
290.0 |
40.0 |
-0.5 |
1,023 |
830 |
540 |
Cu43 |
310.0 |
58.0 |
-17.0 |
1,180 |
1,030 |
400 |
Mo40 |
160.0 |
0.0 |
90.0 |
720 |
155 |
350 |
Mo41 |
180.0 |
0.0 |
-90.0 |
1,200 |
800 |
1,200 |
Mo42 |
130.0 |
0.5 |
-90.0 |
900 |
890 |
900 |
Mo43 |
143.0 |
-68.0 |
-26.0 |
1,230 |
1,430 |
710 |
SG0 |
30.0 |
0.0 |
0.0 |
1,000 |
1,000 |
600 |
SG10 |
40.0 |
0.0 |
-90.0 |
1,050 |
450 |
550 |
SG1 |
88.0 |
6.0 |
40.0 |
450 |
350 |
325 |
SG2 |
117.0 |
-34.0 |
22.0 |
1,300 |
1,000 |
370 |
SG3 |
80.0 |
0.0 |
0.0 |
1,300 |
1,200 |
660 |
14.6 |
RESOURCE BLOCK MODEL |
The block model parameters are set out in Figure 14.6.1.
Figure
14.6.1 Pebble
Deposit 2014 Block Model Parameters
Origin* |
Coordinates |
Dimensions |
Number |
Size (ft) |
Rotation (°) |
X |
1396025 |
Columns |
279 |
75 |
0 |
Y |
2147800 |
Rows |
246 |
75 |
- |
Z |
-5500 |
Levels |
150 |
50 |
- |
Note: *Denotes lowermost left-hand corner of the block model.
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Grade interpolation was carried out in three passes: the search
ellipse used for the first pass had axes that measured 95% of the variographic
range (those shown in Figure 14.5.2), the second pass used search ellipse axes
equal to 150% of the range and the third pass used search ellipse dimensions
equal to 300% of the range.
The first and second passes were limited to a minimum of eight
and a maximum of 24 composites, with a maximum of three composites from any one
drill hole. For the third pass the minimum number of composites was set to five.
Domain boundaries were soft (interpolation using values from
adjacent domains) with the exception of the low-grade domain for all metals for
which the boundaries were hard. Interpolation within the low-grade domain was
restricted to composite values within that domain. The leach and supergene
copper domains also had hard boundaries. The boundary restrictions are set out
in Figure 14.7.1.
Figure
14.7.1 Pebble
Deposit Interpolation Domain Boundaries
Domain Estimated |
Domains Sourced |
Ag40 |
Ag zone 40 |
Ag41 |
Ag zone 41, 42, 43 |
Ag42 |
Ag zone 42, 41 |
Ag43 |
Ag zone 43, 41 |
Au40 |
Ag zone 40 |
Au41 |
Au zone 41, 42, 43 |
Au42 |
Au zone4 2, 41 |
Au43 |
Au zone 43, 41 |
Cu1 |
Cu zone 1 |
Cu2 |
Cu zone 2 |
Cu40 |
Cu zone 40 |
Cu41 |
Cu zone 41, 42, 43 |
Cu42 |
Cu zone4 2, 41 |
Cu43 |
Cu zone 43, 41 |
Mo40 |
Mo zone 40 |
Mo41 |
Mo zone 41, 42, 43 |
Mo42 |
Mo zone 42, 41 |
Mo43 |
Mo zone 43, 41 |
14.8 |
REASONABLE PROSPECTS OF ECONOMIC EXTRACTION |
The resource estimate is constrained by a conceptual pit that
was developed using a Lerchs-Grossman algorithm and is based on the parameters
set out in Figure 14.8.1.
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Figure
14.8.1 Pebble
Deposit Conceptual Pit Parameters
|
Parameter |
Units |
Cost
($) |
Value |
Metal Price |
Gold |
$/oz |
- |
1540.00 |
|
Copper |
$/lb |
- |
3.63 |
|
Molybdenum |
$/lb |
- |
12.36 |
Metal Recovery |
Copper |
% |
- |
89 |
|
Gold |
% |
- |
72 |
|
Molybdenum |
% |
- |
82 |
Operating Cost |
Mining (mineralized material or waste) |
$/ton mined |
1.01 |
- |
|
Added haul lift from depth |
$/ton/bench |
0.03 |
- |
|
Process |
|
|
|
|
-Process cost adjusted by total crushing energy |
$/ton milled |
4.40 |
- |
|
-Transportation |
$/ton milled |
0.46 |
- |
|
-Environmental |
$/ton milled |
0.70 |
- |
|
-G&A |
$/ton milled |
1.18 |
- |
Block Model |
Current block model |
ft |
- |
75 x 75 x 50 |
Density |
Mineralized material and waste rock |
- |
- |
Block model |
Pit Slope Angles |
- |
degrees |
- |
42 |
14.9 |
MINERAL RESOURCE CLASSIFICATION |
Resources are classified as Measured, Indicated and Inferred.
For a block to qualify as Measured, the average distance to the nearest three
drill holes must be 250 ft or less of the block centroid. For a block to qualify
as Indicated, the average distance from the block centroid to the nearest three
holes must be 500 ft or less. For a block to qualify as Inferred, a single drill
hole must be within 600 ft laterally and 300 ft vertically.
The resource has been tabulated on the basis of copper
equivalency (CuEq); gold and molybdenum are converted to equivalent copper grade
and those equivalencies are added to the copper grade. Silver grades were not
estimated in 2011; therefore, to permit a direct comparison between the 2011 and
2014 resource estimates, silver was not included in the 2014 CuEq calculation.
To further maintain the comparison between the previous and current estimates,
the CuEq formula is predicated upon the metal prices and metal recoveries used
in the 2011 estimate. This does not affect the actual metal grades reported,
only their equivalent copper grades when calculating the copper equivalent
value.
Metallurgical testing has determined that metal recoveries in
the western portion of the deposit (west of State plane easting 1405600) can be
expected to be higher than those for the eastern portion of the deposit.
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Therefore, separate equivalency estimates were made for the
western and eastern portions of the deposit. The formulae used for the
conversion are given as follows:
CuEq General Equation = |
Cu% + ((Au g/t * (Au recovery / Cu recovery) * (Au $
per gram / Cu $ per %)) + ((Mo ppm *(Mo recovery / Cu recovery) *
((Mo $ per %) / Cu $ per %)) |
|
|
CuEq (Pebble West) = |
Cu% + ((Au g/t * (0.696/0.85) * (29.00/40.75)) + ((Mo
ppm * (0.778/0.85) * (275.58/40.79)) |
|
|
CuEq (Pebble East) = |
Cu% + ((Au g/t * (0.768/0.893) * (29.00/40.79)) + ((Mo
ppm * (0.837/0.893) * (275.58/40.79)) |
Where:
-
Pebble West Au recovery = 69.6%;
-
Pebble East Au recovery = 76.8%;
-
Pebble West Cu recovery = 85%;
-
Pebble East Cu recovery = 89.3%;
-
Pebble West Mo recovery = 77.8%;
-
Pebble East Mo recovery = 83.7%;
-
Cu price = $1.85/lb;
-
Au price = $902/oz;
-
Mo price = $12.50/lb;
-
all metal prices are based on the estimate in the 2011 technical report;
-
g/oz = 31.10348; and,
-
lb/% = 22.046.
14.11 |
BLOCK MODEL VALIDATION |
The resource estimate was validated in two ways.
The block model was inspected visually for correspondence
between composite grades and block grades. This inspection was carried out on
vertical sections at 100-foot intervals both east-west and north-south. There is
close agreement between composite and block grades. By way of example, Figure
14.11.1 shows the correlation between block and composite copper grades for
vertical section 2158700 N.
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Figure 14.11.1 |
Pebble Deposit Vertical Section 2158700N Block and
Composite Copper Grades; Section Line Location Shown in Figure
7.3.1 |
The second type of validation consisted of the numerical
comparison of block grades and the mean value of composite grades used for
estimating the block grade estimate. The comparison for copper, presented in
Figure 14.11.2 shows that there is reasonable agreement between the two,
particularly at lower grade thresholds.
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Figure 14.11.2
Pebble Deposit Block Versus Composite Copper Grades
Threshold
CuEq
% |
Block Grade |
Comp Grade |
|
Block Grade |
Comp Grade |
|
Block Grade |
Comp Grade |
Cu % |
Cu % |
|
Cu % |
Cu % |
|
Cu % |
Cu % |
Measured |
|
Indicated |
|
Inferred |
0.3 |
0.40 |
0.40 |
|
0.58 |
0.58 |
|
0.52 |
0.52 |
0.4 |
0.50 |
0.49 |
|
0.67 |
0.67 |
|
0.60 |
0.60 |
0.5 |
0.60 |
0.56 |
|
0.74 |
0.73 |
|
0.68 |
0.66 |
0.6 |
0.69 |
0.63 |
|
0.82 |
0.80 |
|
0.76 |
0.73 |
0.7 |
0.76 |
0.66 |
|
0.91 |
0.87 |
|
0.86 |
0.81 |
0.8 |
0.84 |
0.68 |
|
0.99 |
0.94 |
|
0.96 |
0.89 |
0.9 |
0.93 |
0.63 |
|
1.09 |
1.02 |
|
1.05 |
0.96 |
14.12 |
COMPARISON WITH PREVIOUS ESTIMATE |
Figure 14.12.1 shows the percent difference between tonnages
and metal grades for the 2011 and 2014 Pebble resource estimates. Although the
2014 estimate incorporated modifications to the grade domain boundaries as well
as a new conceptual pit based on updated metal prices, the differences between
the two estimates are negligible except as concerns resource classification. The
additional holes drilled since the 2011 estimate have served to elevate
approximately 500 Mt to the Indicated category.
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Figure 14.12.1
Pebble Deposit Comparison between 2011
and 2014 Resource Estimates
Pebble Deposit Resource
Estimate 2014 |
Pebble Resource Estimate
2011 |
Percent Change
(2014-2011) |
Threshold
CuEq% |
CuEq% |
Tonnes |
Cu
(%) |
Au
(g/t) |
Mo
(ppm) |
CuEq% |
Tonnes |
Cu
(%) |
Au
(g/t) |
Mo
(ppm) |
CuEq% |
Tonnes |
Cu
(%) |
Au
(g/t) |
Mo
(ppm) |
Measured |
0.3 |
0.65 |
527,000,000 |
0.33 |
0.35 |
178 |
0.65 |
527,000,000 |
0.33 |
0.35 |
178 |
0.00% |
0.00% |
0.00% |
0.00% |
0.00% |
0.4 |
0.66 |
508,000,000 |
0.34 |
0.36 |
180 |
0.66 |
508,000,000 |
0.34 |
0.36 |
180 |
0.00% |
0.00% |
0.00% |
0.00% |
0.00% |
0.6 |
0.77 |
279,000,000 |
0.40 |
0.42 |
203 |
0.77 |
277,000,000 |
0.40 |
0.42 |
203 |
0.00% |
0.72% |
0.00% |
0.00% |
0.00% |
1.0 |
1.16 |
28,000,000 |
0.62 |
0.62 |
302 |
1.16 |
27,000,000 |
0.62 |
0.62 |
301 |
0.00% |
3.57% |
0.00% |
0.00% |
0.33% |
Indicated |
0.3 |
0.77 |
5,912,000,000 |
0.41 |
0.34 |
245 |
0.80 |
5,414,000,000 |
0.43 |
0.35 |
257 |
-3.90% |
8.42% |
-4.88% |
-2.94% |
-4.90% |
0.4 |
0.82 |
5,173,000,000 |
0.45 |
0.35 |
260 |
0.85 |
4,891,000,000 |
0.46 |
0.36 |
268 |
-3.66% |
5.45% |
-2.22% |
-2.86% |
-3.08% |
0.6 |
0.99 |
3,450,000,000 |
0.55 |
0.41 |
299 |
1.00 |
3,391,000,000 |
0.56 |
0.41 |
301 |
-1.01% |
1.71% |
-1.82% |
0.00% |
-0.67% |
1.0 |
1.29 |
1,411,000,000 |
0.77 |
0.51 |
343 |
1.30 |
1,422,000,000 |
0.77 |
0.51 |
342 |
-0.78% |
-0.78% |
0.00% |
0.00% |
0.29% |
Inferred |
0.3 |
0.54 |
4,460,000,000 |
0.25 |
0.26 |
222 |
0.53 |
4,835,000,000 |
0.24 |
0.26 |
215 |
1.85% |
-8.41% |
4.00% |
0.00% |
3.15% |
0.4 |
0.68 |
2,630,000,000 |
0.33 |
0.30 |
266 |
0.66 |
2,845,000,000 |
0.32 |
0.30 |
259 |
2.94% |
-8.17% |
3.03% |
0.00% |
2.63% |
0.6 |
0.89 |
1,290,000,000 |
0.48 |
0.37 |
291 |
0.89 |
1,322,000,000 |
0.48 |
0.37 |
289 |
0.00% |
-2.48% |
0.00% |
0.00% |
0.69% |
1.0 |
1.20 |
360,000,000 |
0.68 |
0.45 |
377 |
1.20 |
353,000,000 |
0.69 |
0.45 |
379 |
0.00% |
1.94% |
-1.47% |
0.00% |
-0.53% |
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14.13 |
FACTORS THAT MAY AFFECT THE RESOURCE ESTIMATES |
These mineral resource estimates may ultimately be affected by
a broad range of environmental, permitting, legal, title, socio-economic,
marketing and political factors commensurate with the specific characteristics
of the Pebble deposit (including its scale, location, orientation and
poly-metallic nature) as well as its setting (from a natural, social,
jurisdictional and political perspective).
The Pebble Project has been the subject of considerable
environmental activism and political and legal opposition, which is detailed in
the public record and may affect the resource estimate. The QP is unable to
offer any assessment of the likelihood of permitting a future mine at Pebble as
it is beyond the scope of this report.
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There are no properties adjacent to the Pebble Project relevant
to this report.
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16.0 |
OTHER RELEVANT DATA AND INFORMATION |
16.1.1 Jurisdictional
Setting
The Pebble Project is located in Alaska; a state with a
constitution that encourages resource development and a citizenry that broadly
supports such development. Alaska has a strong tradition of mineral development
and hard-rock mining.
Environmental standards and permitting requirements in Alaska
are stable, objective, rigorous and science-driven. These features are an asset
to projects like Pebble that are being designed to meet U.S. and international
best practice standards of design and performance. Alaska has an experienced
Large Mine Permitting Team (LMPT) to facilitate the permitting process and
ensure an integrated strategy for federal and state permitting.
The Pebble deposit is located on state land that has been
specifically designated for mineral exploration and development. The Pebble
Project area has been the subject of two comprehensive land-use planning
exercises conducted by the Alaska Department of Natural Resources (ADNR); the
first in the 1980s and the second completed in 2005. ADNR identified five land
parcels (including Pebble) within the Bristol Bay planning area as having
significant mineral potential, and where the planning intent is to accommodate
mineral exploration and development. These parcels total 2.7% of the total
planning area (ADNR, 2005).
16.1.2 Environmental
and Social Setting
The Pebble deposit is located under rolling, permafrost-free
terrain in the Iliamna region of southwest Alaska, approximately 200 miles
southwest of Anchorage and 60 miles west of Cook Inlet. The surface elevation
over the deposit ranges from approximately 800 to 1,200 ft amsl, although
mountains in the region reach 3,000 to 4,000 ft amsl. Vegetation generally
consists of wetland and scrub communities with some coniferous and deciduous
forested areas that become more common eastward toward the Aleutian Range.
The deposit area lies within the upper reaches of the Koktuli
River and Upper Talarik Creek (UTC) drainages. Approximately 17 miles from the
deposit area, the North Fork (NFK) and South Fork (SFK) streams merge to form
the main Koktuli River. The Koktuli River is tributary to the lower Mulchatna
River, which drains via the lower Nushagak River to Bristol Bay at Dillingham,
some 220 river miles southwest of the deposit area. The UTC flows into Iliamna
Lake, which in turn drains into Bristol Bay via the Kvichak River some 140
river/lake miles to the southwest (Figure 16.1.1) .
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Figure
16.1.1
Bristol Bay Watersheds
The Kvichak and Nushagak river systems are two of nine major
systems that drain to Bristol Bay and support important Pacific salmon runs,
most notably sockeye salmon (Jones et al., 2013). The Kvichak and Nushagak
watersheds total some 23,000 square miles, of which the NFK, SFK and UTC Project
watersheds comprise only 400 square miles, or approximately 1% of the total
Bristol Bay watershed. Government data indicate that, over the past decades, the
combined Kvichak and Nushagak river systems have contributed about 20 to 30% of
total Bristol Bay sockeye salmon production.
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Thus, some 70 to 80% of Bristol Bay sockeye production is
hydrologically isolated from any potential effects of the Pebble Project. Based
on field studies conducted by the Pebble Partnership over ten years, along with
other government studies, e.g. Alaska Department of Fish and Game (ADFG) 2009,
independent consultants estimated that, at 400 square miles, the three
watersheds surrounding Pebble (NFK, SFK and UTC) generally produce less than
0.5% of the total Bristol Bay sockeye run (harvest plus escapement).
Wildlife using the deposit area includes various species of
raptors and upland birds, brown bear, caribou and moose. Although no listed
species are known to use the deposit area, several species listed under the
Endangered Species ActStellers Eider, Sea Otter, Stellers Sea Lion, and the
Cook Inlet Beluga Whaleas well as harbour seals protected under the Marine
Mammal Protection Act, are known to be present in Cook Inlet and some western
Cook Inlet shoreline communities. As the Pebble Project moves forward, the
Pebble Partnership will conduct detailed wildlife surveys of potential port
sites at Cook Inlet to more fully characterize wildlife conditions.
The deposit area and areas of potential transportation
corridors are isolated and sparsely populated. The Pebble deposit is located
primarily within the Lake and Peninsula Borough, which has a population of about
1,500 persons in 18 communities. In the deposit area, the closest communities
comprise three villagesIliamna, Newhalen and Nondaltonabout 17-19 miles from
the deposit site. The largest village population size is about 250 full-time
residents. There are local roads in the village areas and summer barges up the
Kvichak River and on Iliamna Lake. The airport at Iliamna provides the only
year-round access to and from the area.
The total population within the Bristol Bay region is
approximately 7,600. The main population center of the region is Dillingham,
located on Bristol Bay approximately 130 miles southwest of the deposit. It has
a population size of about 2,300, or 30% of the region.
16.2 |
BASELINE STUDIES
EXISTING ENVIRONMENT |
Northern Dynasty began an extensive field study program in 2004
to characterize the existing physical, chemical, biological and social
environments in the Bristol Bay and Cook Inlet areas where the Pebble Project
might occur. The Pebble Partnership compiled the data for the 2004 to 2008 study
period into a multi-volume Environmental Baseline Document (PLP, 2012). As well,
supplemental environmental reports that incorporate data from the period 2009 to
2012 are in preparation. The EBD is publicly available at http://pebbleresearch.com/. These studies have been
designed to:
-
Fully characterize the existing biophysical and socioeconomic environment;
-
Support environmental analyses required for effective input into the Pebble
Project design;
-
Provide a strong foundation for internal environmental and social impact
assessment to support corporate decision-making;
-
Provide the information required for stakeholder consultation and eventual
mine permitting in Alaska; and,
-
Establish a baseline for long term monitoring to assess potential changes
associated with future mine development.
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The baseline study program includes:
|
surface water |
|
wildlife |
|
groundwater |
|
air quality |
|
surface and groundwater quality |
|
cultural resources |
|
geochemistry |
|
subsistence |
|
snow
surveys |
|
land use |
|
fish
and aquatic resources |
|
recreation |
|
noise |
|
socioeconomics |
|
wetlands |
|
visual aesthetics |
|
trace
elements |
|
climate and meteorology |
|
fish
habitat stream flow modeling |
|
Iliamna Lake |
|
marine |
|
|
The following sections highlight key environmental topics; more
detail is provided in the EBD (2012).
16.2.1 Climate
and Meteorology
Meteorological monitoring consists of six meteorological
stations located in the mine (Bristol Bay drainage) study area and three
stations located in the Cook Inlet study area (PLP, 2012). Meteorological
monitoring in the area near the deposit occurs at an elevation between 800 to
2,300 ft amsl. Monitoring in the Cook Inlet study area occurs near sea level.
Data collected at all stations has included wind speed and
direction, wind direction standard deviation and air temperature. Collected data
at stations where instrumentation has been installed include differential
temperature, solar radiation, barometric pressure, relative humidity,
precipitation and, in summer, evaporation. As of 2014, meteorological monitoring
is ongoing at the main station (Pebble 1) near the deposit. Monitoring at the
remaining stations was suspended in 2013 after sufficient baseline data was
collected.
Mean monthly temperatures in the deposit area range from about
55°F in summer to 2°F in winter. Precipitation averages approximately 54 inches
per year, about one-third of which falls as snow. The wettest months are August
through October.
As the Pebble Project design moves forward, additional
meteorological data will be collected.
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16.2.2
Surface Water Hydrology and Quality
16.2.2.1 SURFACE
WATER HYDROLOGY
The Bristol Bay drainage basin encompasses 41,900 square miles
in southwest Alaska (Figure 16.2.1) . The Nushagak and Kvichak watersheds
constitute 49% of the Bristol Bay basin area. The general deposit location
straddles the watershed boundary between the SFK and UTC and lies close to the
headwaters of the NFK. The study area encompasses the drainages of these three
watercourses as well as the headwaters of Kaskanak Creek (KC). While the deposit
area and potential mine footprint does not affect the Kaskanak Creek headwaters,
it was included in the study design to allow for comprehensive long term
monitoring of mine operations.
Figure
16.2.1 Local
Watershed Boundaries
The map shows the study area, which is principally defined as
the 400 square miles within the SFK, NFK and UTC drainages.
Annual stream flow patterns in the mine study area are
generally characterized by a bi-modal hydrograph with high flows in spring
resulting from snowmelt and low flows in early to mid-summer resulting from dry conditions and depleting snow packs. Frequent rainstorms in
late summer and early autumn contribute to another high-flow period. The lowest
flows occur in winter when most precipitation falls as snow and remains frozen
until spring. Loss and gain of surface flow to groundwater plays a prominent
role in the flow patterns of all study area creeks and rivers, causing some
upstream sites to run dry seasonally while causing others to be dominated by
baseflow due to gains.
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During winter and summer low-flow periods, stream flows are
primarily fed by groundwater discharge. Observed baseflows were higher during
summers than winters due to snowmelt recharge of aquifers and intermittent
rainstorms. Baseflows were lowest in late winter after several months without
surface runoff. Low-flow conditions are also influenced by fluctuations in
surface storage features such as lakes, ponds and wetlands; however, changes in
surface storage are minimized during the late winter freeze.
16.2.2.2
SURFACE WATER QUALITY
Surface water quality sampling within the study area occurred
between 2004 and 2008 at numerous locations in the NFK, SFK, UTC and KC
drainages. Stream samples were collected from 44 locations during 50 sampling
events from April 2004 through December 2008. Lake and pond samples were
collected from 19 lakes once or twice per year during 2006 and 2007. Seep
samples were collected from 11 to 127 sample locations, depending on the year,
two to five times per year. Altogether, over 1,000 samples were collected from
streams, more than 600 samples from seeps, and approximately 50 samples from
lakes.
Surface water in the study area is characterized by cool, clear
waters with near-neutral pH that are well-oxygenated, low in alkalinity, and
generally low in nutrients and other trace elements. Water types ranged from
calcium-magnesium-sodium-bicarbonate to calcium-magnesium-sodium-sulphate. Water
quality occasionally exceeded the maximum criteria for concentrations for
various trace elements. Additionally, cyanide was present in detectable
concentrations; there were consistently detectable concentrations of dissolved
organic carbon; and no detectable concentrations of petroleum hydrocarbons,
polychlorinated biphenyls (PCBs), or pesticides found.
16.2.3 Groundwater
Hydrology and Quality
16.2.3.1.
GROUNDWATER HYDROLOGY
Beginning in 2004, Northern Dynasty established an extensive
groundwater monitoring network across the study area. Initially the groundwater
quality monitoring network consisted of 21 wells at 10 locations. The Pebble
Partnership expanded the monitoring network throughout the study period as the
understanding of the groundwater flow regime and chemistry was refined. By 2008,
the monitoring network consisted of 39 wells at 20 locations. More than 200
response tests have been conducted in shallow wells that have been installed
throughout the study area for the baseline assessment. In general, a greater
proportion of response tests in the overburden materials indicated higher
hydraulic conductivity estimates for the overburden than for the shallow bedrock
(PLP, 2012).
Generally, there is a strong correlation between groundwater
levels and stream flows in the study area; the highest groundwater levels were
recorded during spring runoff and/or during fall rains and the lowest
groundwater levels were recorded just before spring runoff. The potential for
baseflow to sustain stream flows at the upper reaches of tributaries is limited,
given the limited groundwater storage capacity of the overburden and upper bedrock aquifers. Where substantial thicknesses of
permeable alluvium are present downstream, the sustained baseflow in the main
streams during winter indicates considerable storage in the overburden aquifer.
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EBD 2012 identified three groundwater divides within the study
area, generally reflecting the three surface water drainage basins (NFK, SFK and
UTC). Based on the water balance model prepared by Schlumberger (PLP, 2012), it
has been estimated that more than 95% of the water that recharges groundwater
within the three surface water drainages also discharges within the same
drainage basin. Although some cross-basin transfer occurs, it is well
understood.
16.2.3.2. GROUNDWATER
QUALITY
Groundwater wells were located within the Pebble deposit
resource area (10 wells at seven locations), and along the three surface water
drainage basins identified as reflective of groundwater flow from the Pebble
deposit resource area. The EBD 2012 compared the results of groundwater quality
sampling with the most stringent benchmark water quality criteria derived from
Title 18 of the Alaska Administrative Code, Chapter 75 (18AAC75), and Alaska
Water Quality Criteria (ADEC, 2008).
16.2.4 Geochemical
Characterization
Northern Dynasty and the Pebble Partnership conducted a
comprehensive geochemical characterization program to understand the metal
leaching (ML) and acid rock drainage (ARD) potential associated with the rock
types present in the general deposit area within the Pebble Project study area.
The ML/ARD study was designed to characterize the materials that could be
produced from the mining and milling process at the Pebble deposit, including
both waste rock and tailings material (PLP, 2012). Classification of acid
generating potential is based on Mine Environment Neutral Drainage (MEND, 1991)
guidelines that classify rock as potentially acid generating (PAG), uncertain or
non-PAG based on the neutralization potential ratio (NPR), defined as the
neutralization potential (NP) divided by maximum potential acidity (MPA).
Detailed characterization and classification of PAG and non-PAG materials enable
engineers to design appropriate materials handling, sorting and storage
strategies to ensure the long-term protection of water quality.
Acid-base accounting results indicate that the Tertiary units
are dominantly non-PAG. No samples of Tertiary rock generated acidic conditions
under field or laboratory conditions. Minor components of the Tertiary volcanic
rocks (less than 1% based on testing) contain pyrite mineralization and have
been found to be PAG. The pre-Tertiary samples from the porphyry-mineralized
rock from the deposit area have variable acid generation potential. Pre-Tertiary
rock was found to be dominantly PAG due to elevated acid potential (AP) values
resulting from increased sulphur concentrations and limited NP resulting from
lack of carbonate minerals. In the pre-Tertiary samples, acidic conditions occur
quickly in core with low NP. Field data suggest that the onset to acidic
conditions is about 20 years, while laboratory kinetic tests show that the delay
to the onset of acidic conditions is expected to be between a decade and several
decades for PAG rock.
The majority of the overburden samples analyzed have been
classified as non-PAG, with very low total sulphur content dominated by
sulphide. For pre-Tertiary material, metal mobility tests identified copper as
the main contaminant in the leachate. Subaqueous conditions also produced the
dissolution of gypsum and iron carbonate, as well as arsenic leaching.
Weathering of the mineralized pre-Tertiary material under oxidizing conditions
produced an acidic leachate dominated by sulphate and calcium. Non-PAG tests
indicated that the oxidation of pyrite resulted in low pH conditions, which
increased metal mobility.
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16.2.5 Wetlands
Section 404 of the Clean Water Act (CWA) governs the
discharge of dredged or fill materials into waters of the U.S., including
wetlands. The U.S. Army Corps of Engineers (USACE) issues Section 404 permits
with oversight by the U.S. Environmental Protection Agency (EPA). Given the
Pebble Projects location and scope, the information required to support the
Pebble Partnerships eventual Section 404 permit application is significant.
Accordingly, Northern Dynasty and the Pebble Partnership conducted an extensive,
multi-year wetlands study program at Pebble in both the Bristol Bay and Cook
Inlet drainages.
The study area is much larger than the deposit area. This
entire study area has been mapped to determine the occurrence of wetlands and to
characterize baseline conditions. Overall, water bodies, wetlands and
transitional wetlands represent 9,826 acres, or 33.4%, of the study area. Of the
375 water features evaluated in the overall study area, 308 (82.1%) were
classified as lakes or perennial ponds, the vast majority of which were open
water. The remaining 67 water features (17.9%) were classified as seasonal ponds
or the drawdown areas of perennial ponds, which were roughly evenly encountered
as open water or partially vegetated/barren ground.
A preliminary wetlands delineation in the field has been
conducted, along potential transportation corridors from the deposit area to
potential port sites on Cook Inlet. The Pebble Partnership will continue mapping
wetlands and vegetation along potential transportation corridors.
16.2.6
Fish, Fish Habitat and Aquatic Invertebrates
Extensive aquatic habitat studies, initiated in 2004, have
continued annually. They have varied in scope, study area and level of effort,
as the information base has grown and specific data needs have become more
defined. The aquatic habitat study program encompassed the three main deposit
area drainages (NFK, SFK and UTC) and the Koktuli River, and in and around
Iliamna Lake. Completed studies include:
-
Fish population and density estimates using various field methods (dip
netting, electro-fishing, snorkeling and aerial surveys);
-
Fish habitat studies (main-channel and off-channel transects and habitat
preferences);
-
Fish habitats/assemblages above Frying Pan Lake;
-
Salmon escapement estimates;
-
Spring spawning counts and radio telemetry for rainbow trout;
-
Radio telemetry of arctic grayling to assess stream fidelity;
-
Overwintering studies for salmon, trout and grayling;
-
Frying Pan Lake northern pike population estimate;
-
Geo-referenced video aquatic habitat mapping;
-
Intermittent flow reach, habitat and fish use; and,
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- Fish tissue measurements for trace metals.
16.2.6.1.
FISH AND FISH HABITAT
Project Site
The Kvichak and Nushagak river systems are two of the nine
major systems that drain into Bristol Bay and support important runs of sockeye
salmon, as well as other salmon species. This sockeye population supports valued
commercial, subsistence and sport fisheries. Government studies, e.g. ADFG,
2009, indicate that, over the past decades, the combined Kvichak and
Nushagak-Mulchatna river systems have contributed about 20 to 30% of total
Bristol Bay sockeye salmon production.
Thus, some 70 to 80% of Bristol Bay sockeye production is
hydrologically isolated from any potential effects of the Pebble Project. The
total area of the Kvichak and Nushagak-Mulchatna river systems is some 23,000
square miles, of which the NFK, SFK and UTC watersheds near the deposit site
account for only about 400 square miles, or about 1.8% . Based on the Pebble
Partnerships extensive field studies and other government studies, independent
consultants estimated that these three watersheds generally produce less than
0.5% of the total Bristol Bay sockeye run (i.e. harvest plus escapement).
The deposit area is characterized by small headwater streams of
poor habitat quality and low fish density. Fish production is naturally limited
by physical and chemical factors in these reaches, most notably intermittent
flow with extreme low flow hydrology and oligotrophic conditions that constrain
aquatic productivity. The lowest reaches of the three study area streams outside
the deposit area have more stable hydrologic conditions and support numerous
salmon and resident species.
The macro-invertebrate and periphyton studies near the Pebble
deposit are part of the overall program of baseline investigations to describe
the current aquatic conditions in the study area. Baseline information on
macro-invertebrate and periphyton community assemblages is valued because the
biota are essential components of the aquatic food web, and their community
structure, particularly with respect to the more sensitive taxa, are an
indicator of habitat and water quality.
The main objective of the macro-invertebrate and periphyton
field and laboratory program was to characterize the diversity, abundance and
density of macro-invertebrates and periphyton within freshwater habitats in the
study area. Macro-invertebrates and periphyton were sampled in the study area in
2004, 2005 and 2007 as part of the environmental baseline studies for the Pebble
Project. In 2004, 20 sites in the study area were sampled and of these, eight
sites (five in the immediate vicinity of the deposit) were selected for
continued sampling in 2005, and 10 were sampled in 2007.
Potential Transportation Corridor Options
Transportation corridor options consist of the main access
route between the deposit area and potential port sites on Cook Inlet, as well
as any shorter spurs that would be used to link a mine site with Iliamna
Village.
Data from the AWC and field observations by independent experts
indicate that many, but not all, waters in the area support anadromous fish
populations, including all five Pacific salmon species (Chinook, sockeye, coho,
pink, and chum) plus steelhead and rainbow trout, Dolly Varden, and arctic char.
Population densities vary based on stream size and morphology, which can restrict
population sizes or limit access to upstream habitats. The Pebble Partnership
will conduct additional fish habitat surveys along corridor routes, including
Cook Inlet locations, during a later phase of the Pebble Projects
development.
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16.2.7 Marine
Habitats
16.2.7.1.
MARINE NEARSHORE HABITATS
The nearshore marine habitat study area focused on areas in the
lower Cook Inlet region. The western shorelines from Kameshak Bay north to Knoll
Head are composed of a diversity of habitats, including steep rocky cliffs,
cobble or pebble beaches and extensive sand/mud flats. Eelgrass is found at a
number of locations and habitats; eelgrass, along with macro-algae, is an
important substrate for spawning Pacific herring. Overall, the habitats in the
study area provide a wide range of habitat types, resulting in a wide range of
biological assemblages.
Preliminary data gathered at Amakdedori beach in 2013 indicate
that Pacific herring are the predominant species present in the nearshore
environment, with smaller populations of Dolly Varden and pink salmon.
16.2.7.2.
MARINE BENTHOS
The littoral and subtidal habitats in lower Cook Inlet support
diverse communities of marine and anadromous species of ecological and economic
importance. The marine benthos studys intent was to characterize benthic
assemblages in marine habitats in the lower Cook Inlet region.
The marine investigations were undertaken over a five-year
period from 2004 to 2008, and included several habitat sampling events, mostly
in mid to late summer. Each intertidal habitat type provides feeding areas for
different pelagic and demersal fish and invertebrates that forage over the
intertidal zone during high tides. The estuarine and nearshore rearing habitats
of juvenile salmonids are an important component of the intertidal zone,
especially for pink and chum salmon that out-migrate from streams along the
shoreline and elsewhere in Cook Inlet. Another important component of the
intertidal zone is the substrate used for spawning by Pacific herring.
16.2.7.3.
NEARSHORE FISH AND INVERTEBRATES
The study of nearshore fish and macroinvertebrates has been
undertaken to collect baseline data on the abundance, distribution and
seasonality of major aquatic species on the western side of Cook Inlet (PLP,
2012). These marine investigations were undertaken between 2004 and 2008. The
study area is a complex marine ecosystem with numerous fish and
macro-invertebrate species that use the area for juvenile rearing, refuge, adult
residence, migration, foraging, staging and reproduction.
The study area also functions as a rearing area for juvenile
Pacific herring. Herring was the dominant fish species, and young-of-the-year
and one-year-olds were the dominant life stages found from March through
November in the several sampling years, with peak occurrences noted during the
summer (PLP, 2012).
The nearshore area is also a rearing area for juvenile salmon,
which, as a group, were second to herring in abundance. Juvenile pink and chum
salmon were the most abundant salmonid species, and showed a typical spring and
summer outmigration as young-of-the-year fish. Juvenile chum displayed a short
outmigration period during May and June, while juvenile pink salmon remained
in the area into August. Both species were largely gone by September.
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The Pebble Partnership will be conducting more detailed surveys
as the Pebble Project moves forward.
16.3 |
POTENTIAL ENVIRONMENTAL EFFECTS AND PROPOSED MITIGATION MEASURES |
The application of sound engineering, environmental planning
and best management practices, including compliance with existing U.S. federal
and state environmental laws, regulations and guidelines, will ensure that all
of the environmental issues associated with the development and operation of the
Pebble Project can be effectively addressed and managed.
The major environmental pathways include air, water and
terrestrial resources. During the preliminary stages of the Pebble Project,
Northern Dynasty identified key environmental issues and design drivers that
have formed the basis of baseline data collection, environmental and social
analysis and continuing stakeholder consultations influencing the Pebble Project
design. The effects assessment has confirmed these as important issues and
design drivers, and has identified mitigation measures for each. The key
mitigation strategies for these drivers include:
-
Water: development of a water management plan that maximizes the collection
and diversion of groundwater, snowmelt and direct precipitation away from the
mine site;
-
Wetlands: implementation of a water management plan (in accordance with
USACE guidelines and regulations) to reduce wetland impacts;
-
Aquatic habitats: development of a water management plan and habitat
mitigation measures that includes strategies to effectively manage the release
of treated water in compliance with anticipated regulatory requirements to
maintain downstream flows and to protect downstream fish habitat and aquatic
environments;
-
Air quality: implementation of air emissions and dust suppression
strategies; and,
-
Marine environment: minimize the port facilitys footprint in the
intertidal zone, particularly in soft sediment intertidal areas.
Direct integration of these and other appropriate measures into
the Pebble Project design and operational strategies are expected to effectively
mitigate possible environmental effects and minimize residual environmental
effects associated with the construction, operation and eventual closure of any
proposed mine at the Pebble Project.
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16.4 |
ECONOMY AND SOCIAL CONDITIONS |
The Alaska economy is dependent on natural resources for both
employment and government revenue. Oil and gas, mining, transportation,
forestry, fishing and seafood processing, as well as tourism, represent a
significant proportion of the overall private sector economy, with oil and gas
contributing some 90% of state government revenues on an annual basis. At
$49,436 in 2012, per capita personal income in Alaska is above the national
average of $43,735, while unemployment is generally below the national average
(State of Alaska, 2013).
Of the nearly 740,000 people living in Alaska on a full-time
basis, approximately 400,000 live in the greater Anchorage area. Approximately
15% of Alaskas population is of Native ancestry.
At some 42,000 square miles, the Bristol Bay region of
southwest Alaska is vast and sparsely populated, with less than 1 person for
each 5 square miles of land area. Population density in the Lake and Peninsula
Borough is even lower, with one person per 14 square miles, making it the most
sparsely settled county, parish or borough in the United States.
The Bristol Bay regions roughly 7,600 inhabitants reside in 31
villages, with just one (Dillingham) exceeding 1,000 residents. The average
Bristol Bay community is home to about 150 people. Some 70% of the regions
full-time residents are Alaska Native, descending from three major language
groups: Yupik Eskimos, Aleuts and Athabaskans.
The private sector economy of the Bristol Bay region is
dominated by commercial salmon fishing. Although the resource upon which the
industry is based remains healthy, the economics of the fishery have declined
significantly over the past several decades due to the rise of global salmon
aquaculture and various domestic policy and market factors. Ex-vessel prices for
sockeye salmon, the dominant species in the Bristol Bay fishery, have fallen
from an inflation-adjusted peak of $3.75/lb in 1988 to a 10-year average of just
under $1.00/lb in the 1990s and $0.60/lb in the 2000s. In recent years,
ex-vessel prices have exceeded $1.00/lb.
As a result of these declines, the percentage of Bristol Bay
fishing licenses and related employment held by residents of the region has
fallen precipitously over the past 20 years, as has the regions overall
economic health. Bristol Bays economy today is characterized by a high
proportion of non-resident labour and business ownership. Key private-sector
industries are highly seasonal, such that unemployment among year-round
residents is particularly high.
Bristol Bay communities also face among the highest costs of
living in the U.S., due to the requirement to fly in many of the goods and
commodities required for daily life, including fuel for heating homes and
operating vehicles. Energy costs, in particular, are a significant deterrent to
economic development.
As a result of a lack of jobs and economic opportunity in the
region, Bristol Bay communities are slowly losing population as residents seek
opportunities in other parts of the state. For example, the population of the
Lake and Peninsula Borough declined 17% between 2000 and 2010, while the Bristol
Bay Borough lost more than 23% of its population. In several communities,
schools have closed or are threatened with closure as a result of diminishing
enrolment.
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A subsistence lifestyle is practiced by the vast majority of
residents of Bristol Bay communities, including fishing for salmon and other
species, hunting of terrestrial mammals and birds, and gathering berries.
Salmon, in particular, are considered a critically important resource for the
region, from a cultural, economic and environmental perspective.
16.4.1
Community Consultation and Stakeholder Relations
Since 2004, the Pebble Partnership and its predecessor Northern
Dynasty have undertaken a comprehensive stakeholder relations and community
outreach program. In addition to ensuring that relevant stakeholder groups and
individuals receive early notification of all work programs, the objectives of
the Pebble Partnerships stakeholder and community relations program are:
-
To provide regular progress updates on project-related activities,
opportunities and planning;
-
To seek input on stakeholder priorities, issues and concerns, and provide
feedback on how they are being addressed;
-
To educate stakeholders on responsible resource development and modern
mining principles and practices;
-
To maximize economic and community benefits associated with the Pebble
Project, both in the exploration and development phase and during mine
operations; and,
-
To provide opportunities for two-way dialogue and the development of
long-term, respectful and mutually beneficial relationships.
The Pebble Partnership has developed a dedicated and
knowledgeable stakeholder relations team to implement this program. In addition
to stakeholder relations staff in Anchorage, the team includes two
representatives living in Bristol Bay communities. The Pebble Partnership has
provided ongoing training for all of its community relations personnel.
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17.0 |
INTERPRETATION AND CONCLUSIONS |
The 2014 Technical Report for the Pebble Project has been
completed in accordance with NI 43-101. The report describes the results of a
2014 resource estimate for the Pebble Project as well as the result of
metallurgical, environmental and exploration programs to the effective date of
the report. These programs suggest that the project merits follow up with
further technical and economic studies leading to an advancement of the project
to the next level of development.
17.2 |
GEOLOGY AND MINERAL
RESOURCE ESTIMATE |
The Pebble property hosts a globally significant
copper-gold-molybdenum-silver deposit. The exploration and drilling programs
completed thus far are appropriate to the type of the deposit. The exploration,
drilling, geological modelling and research work support the interpreted genesis
of the mineralization.
It is the opinion of the relevant QPs of this report that the
drill database for the Pebble deposit is reliable and sufficient to support the
purpose of this technical report and a current mineral resource estimate.
Estimations of mineral resources for the Pebble Project conform
to industry best practices and meet requirements of the Canadian Institute of
Mining and Metallurgy.
Factors which may affect the Mineral Resource estimate include
changes to the geological, geotechnical and geometallurgical models, infill
drilling to convert mineral resources to a higher classification, drilling to
test for extensions to known resources and collection of additional bulk density
data. Additional factors which may affect the open pit shell used to constrain
the estimates are commodity prices, assumptions used to estimate metallurgical
recoveries and pit slope angles. It should be noted that all factors pose
potential risks and opportunities, of greater or lesser degree, to the current
mineral resource.
The resources at Pebble continue to provide a number of
opportunities for expansion of mineralization.
17.2.1
Updating of Inferred Resource
Approximately 40% of the currently estimated resource is
classified as Inferred. The resource used as the basis for a prefeasibility or
feasibility study, as defined by NI 43-101, must be classified as Measured or
Indicated: therefore, some portion of the resource must be upgraded by infill
drilling. It is likely not necessary or desirable to upgrade all of the Inferred
Resource in the immediate future, but the prioritization of areas to be upgraded
should involve an integrated study of future mining and metallurgical
objectives.
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17.2.2 Eastern
Extension
Drill hole 6348 is perhaps the most significant drill
intersection in the Pebble deposit. It intersected 949 ft of mineralization with
an average grade of 1.24% copper, 0.74 g/t gold and 0.042% molybdenum, or 1.92%
CuEq (using 2011 metal prices and recovery assumptions), before the hole was
lost at a depth of 5,663 ft in the ZG1 Fault (Figure 17.2.1) . This drill hole
lies east of the ZG1 Fault and follow up drilling of the Cretaceous host rocks
to this mineralization has not yet been completed, thereby leaving the extent of
this high-grade mineralization unknown. This area represents a significant
exploration target. Given the depth of this target and the expense of drilling
at the Pebble Project, it is recommended that a study be undertaken to determine
the best approach. Such a study would determine the best drill pattern to be
employed, outline any potential issues and determine the type of equipment which
will optimize the chances of successful completion of follow-up holes.
Figure
17.2.1
Untested Exploration Potential East of Drillhole 6348
17.2.3
Block Model Update
The extensive metallurgical testwork conducted on the Pebble
deposit demonstrates the deposit contains significant amounts of rhenium.
Initial analysis suggests recovery of rhenium from molybdenum concentrate could
have a positive impact on project economics. Additional studies of this
opportunity should be conducted, including metallurgical testwork, market
assessment and update of the project geological block model. Since assay for
rhenium only dates from circa 2007, a number of pulps from earlier drilling
would require re-assaying.
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17.3 |
METALLURGICAL TESTWORK AND PROCESS DESIGN |
Metallurgical testwork and associated analytical procedures
were performed by recognized testing facilities with extensive experience with
this analysis, with this type of deposit, and with the Pebble Project. The
samples selected for the comminution, copper/gold/molybdenum bulk flotation, and
copper molybdenum separation testing were representative of the various types
and styles of mineralization present at the Pebble deposit. The test results on
variability samples derived from the 103 lock cycle flotation tests indicate
that marketable copper and molybdenum concentrates can be produced with gold and
silver contents that meet or exceed payable levels in representative smelter
contracts.
As the project advances, the following testwork should be
considered:
-
Additional copper molybdenum separation testwork in order to optimize
molybdenum and rhenium grade and recovery to the molybdenum concentrate, and
reduce levels of copper reporting to the molybdenum concentrate.
-
Include silver assays in all product streams for future locked cycle tests
in order to improve the confidence level of the silver mass balance, and
potentially optimize silver recovery. At present, only 10 locked cycle tests
were assayed for silver in all product streams, while the remainder of tests
contained silver assays for the bulk concentrate only.
-
Ensure that the number of comminution and flotation variability samples
tested for each respective geometallurgical domain unit reflects the timing
and expected proportions of each contained within future engineering mine
plans.
The Pebble Project would be subject to a mine permitting
process in Alaska. Exploration activities completed to date have been conducted
under the relevant permits.
The following mitigation strategies have been identified for
key environmental drivers:
-
Water: development of a water management plan that maximizes the collection
and diversion of groundwater, snowmelt, and direct precipitation away from the
mine site;
-
Wetlands: implementation of a water management plan (in accordance with
USACE guidelines and regulations) to reduce wetland impacts;
-
Aquatic Habitats: development of a water management plan that includes
strategies to effectively manage the release of treated water in compliance
with anticipated regulatory requirements to maintain downstream flows and to
protect downstream fish habitat and aquatic environments;
-
Air Quality: implementation of air emissions and dust suppression
strategies; and,
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-
Marine Environment: minimize the port facility’s footprint in the intertidal zone, particularly in soft sediment intertidal areas.
Direct integration of these measures into project design and operational strategies are expected to effectively mitigate possible environmental effects and minimize residual environmental effects associated with the construction, operation, and
eventual closure of any proposed mine at the Pebble Project.
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The immediate priority is to maintain the project in good
standing and continue environmental monitoring.
Site operations, property maintenance and sample storage |
$1,811,000 |
-
Annual state rentals are required to maintain the Pebble claims in good standing.
-
Activities to maintain Pebble Partnership’s site facilities and core storage. These include care and maintenance staff, facilities leases, utilities for these facilities, and other associated costs.
Environmental baseline data collection |
$302,000 |
-
A minor environmental base line data collection program is necessary during
2015, as 10 years of data have been acquired.
-
These activities include meteorology and stream flow monitoring, support at
site, and staff to manage the work.
18.2 |
ADDITIONAL RECOMMENDATIONS |
The QPs have recommended two other components of work to
support prefeasibility work at a later date, to be undertaken as funds become
available.
Additional resource evaluation
-
The deposit remains open in a number of locations, including adjacent to
Hole 6348, which identified high grade mineralization down-dropped on the east
side of the ZG1 graben-bounding fault. The first step would be to complete an
analysis to determine optimal methods for follow up drill testing of this
area.
-
The resource classification must be improved for a NI 43-101 compliant
prefeasibility study. The first step would be to complete a conditional
resource simulation to determine the optimal drill spacing to move inferred
resources to higher classifications.
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- Supplemental geochemical analyses should be undertaken to incorporate
silver and rhenium in the block model estimation.
Additional metallurgical testwork
-
Additional copper-molybdenum separation testwork is recommended to optimize
metal grade and recovery to the molybdenum concentrate in support of a
prefeasibility study.
-
Ensuring sample numbers for comminution and flotation variability tests for
each respective geometallurgical domain unit reflects the timing and expected
proportions of each contained.
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Phillips, C.H., Gambell, N.A., and Fountain, D.S., 1974,
Hydrothermal alteration, mineralization and zoning in the Ray deposit: Economic
Geology, v. 69, p. 1237-1250.
Plafker, G., and Berg, H.C., 1994, Overview of the geology and
tectonic evolution of Alaska: in Plafker, G., and Berg, H.C., eds., The Geology
of Alaska: Geological Society of America, The Geology of North America, v. G-1,
p. 989-1021.
Rebagliati, C.M., and Haslinger, R.J., 2003, Summary report on
the Pebble copper-gold porphyry project, Iliamna Lake area, southwestern Alaska,
USA. Available on www.sedar.com.94 p.
Rebagliati, C.M., and Payne, J.G., 2006, 2005 summary report on
the Pebble porphyry copper-gold project, Iliamna Lake area, southwestern Alaska,
USA. Available on www.sedar.com.111 p.
Rebagliati, C.M., and Payne, J.G., 2007, 2006 summary report on
the Pebble porphyry copper-gold-molybdenum project, Iliamna Lake area,
southwestern Alaska, USA. Available on www.sedar.com.119 p.
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Rebagliati, C.M., Lang, J.R., Titley, E., Gaunt, J.D., Melis,
L., Barratt, D., and Hodgson, S., 2010, Technical report on the 2009 program and
update on mineral resources and metallurgy, Pebble copper-gold-molybdenum
project, Iliamna Lake area, southwestern Alaska, USA. Available on www.sedar.com, 194 p.
Rebagliati, C.M., Lang, J.R., Titley, E., Gaunt, J.D., Rennie,
D., Melis, L., Barratt, D., and Hodgson, S., 2008, Technical report on the 2007
program and updates on metallurgy and resources. Available on www.sedar.com.
Rebagliati, C.M., Lang, J.R., Titley, E., Gaunt, J.D., Rennie,
D., Melis, L., Barratt, D., and Hodgson, S., 2009, Technical report on the 2008
program and updates on mineral resources and metallurgy. Available on www.sedar.com.
Rebagliati, C.M., Payne, J.G., and Lang, J.R., 2005, 2004
summary report on the Pebble porphyry gold-copper project, Iliamna Lake area,
southwestern Alaska, USA. Available on www.sedar.com.79 p.
Rebagliati, M., and Lang, J., 2009, The Pebble porphyry
copper-gold-molybdenum discovery, Alaska, USA. Conference Proceedings, New
GenGold 2009, Case Histories of Discoveries, Perth, p. 121-132.
Rebagliati. C.M. and Haslinger, R.J., 2003. Technical Report on
the Pebble Project January 2003.
Rebagliati. C.M. and Haslinger, R.J., 2004. Technical Report on
the Pebble. January 2004.
Rebagliati. C.M. and Haslinger, R.J., Payne, J.G., and Price,
C.M., 2004. Technical Report on the Pebble Project. May 2004.
Rebagliati. C.M. and Payne, J.G., 2005. Technical Report on the
Pebble Project March 2005.
Rebagliati. C.M. and Payne, J.G., 2006. Technical Report on the
Pebble Project March 2006.
Rebagliati. C.M. and Payne, J.G., 2007. 2006 Summary Report on
the Pebble Porphyry Copper-Gold-Molybdenum Project. Iliamna Lake Area,
Southwestern Alaska, USA. March 2007. 119 pages.
Rebagliati. C.M., Lang, J.R., Titley, E., Gaunt, J.D., Melis,
L., Barratt, D., Hodgson, S., 2010. Technical Report on the 2009 Program and
Update on Mineral Resources and Metallurgy. Pebble Copper-Gold-Molybdenum
Project, Iliamna Lake Area, Southwestern Alaska, USA for Northern Dynasty
Minerals Ltd.
March 2010. 194 pages.
Rebagliati. C.M., Lang, J.R., Titley, E., Gaunt, J.D., Rennie,
D., Melis, L., Barratt, D., Hodgson, S., 2008. Technical Report on the 2007
Program and Updates on Metallurgy and Resources. March 2008.
Rebagliati. C.M., Lang, J.R., Titley, E., Gaunt, J.D., Rennie,
D., Melis, L., Barratt, D., Hodgson, S., 2009. Technical Report on the 2008
Program and Updates on Mineral Resources and Metallurgy. February, 2009.
Reed, B.L., and Lanphere, M.A., 1973, Alaska-Aleutian Range
batholith: Geochronology, chemistry, and relation to circum-Pacific plutonism:
Geological Society of America Bulletin, v. 84, p. 2583-2610.
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Rombach, C., and Newberry, R., 2001, Shotgun deposit: Granite
porphyry-hosted gold-arsenic mineralization in southwestern Alaska, USA:
Mineralium Deposita, v. 36, p. 607-621.
Schrader, C.M., 2001, Geochronology and geology of the Pebble
Cu-Au-Mo porphyry and the Sill Au-Ag epithermal deposits, southwest Alaska.
Unpublished M.Sc thesis, University of Georgia, Athens, 109 p.
Seedorff, E., Dilles, J.H., Proffett, J.M., Einaudi, M.T.,
Zurcher, L., Stavast, W.J.A., Johnson, D.A., and Barton, M.D., 2005, Porphyry
deposits: Characteristics and origin of hypogene features: in Hedenquist, J.W.,
Thompson, J.F., Goldfarb, R.J., and Richards, J.P., eds., Economic Geology
100thAnniversary Volume, 1905-2005. Society of Economic Geologists, p. 251-298.
Shah, A., Bedrosian, P., Anderson, E., Kelley, K., and Lang,
J., 2009, Geophysical data used to characterize the regional setting of the
Pebble porphyry deposit in southwest Alaska: Geological Society of America
Annual Meeting, Program with Abstracts, v. 41, p. 493.
Sillitoe, R.H., 2010, Porphyry copper systems: Economic
Geology, v. 105, p. 3-41.
Wallace WK, Hanks CL and JF Rogers, 1989, The southern Kahiltna
terrane: Implications for the tectonic evolution of southwestern Alaska. GSA
Bulletin 101, 1389-1407.
Wallace, W.E., Hanks, C.L., and Rogers, J.F., 1989, The
southern Kahiltna terrane: Implications for the tectonic evolution of
southwestern Alaska: Geological Society of America Bulletin, v. 101, p.
1389-1407.
Young, L.E., St. George, P., and Bouley, B.A., 1997, Porphyry
copper deposits in relation to the magmatic history and palinspastic restoration
of Alaska: in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of
Alaska: Society of Economic Geologists Monograph 9, p. 306-333.
Website
SEDAR (System for Electronic Document Analysis and Retrieval):
www.sedar.com
G & T Metallurgical Services Ltd., 2011. Copper Molybdenum
Separation Testing on a Pebble Bulk Concentrate. September 22, 2011.
Outotec (Canada) Ltd., 2010. Outotec Thickener Interpretations
and Recommendations for Test Data. Report TH-0493, Pebble Project, April 9,
2010.
Outotec (Canada) Ltd., 2010. Outotec Thickener Interpretations
and Recommendations for Test Data. Report TH-0497, Pebble Project. June 17,
2010.
SGS-Lakefield Research Ltd., 2010. An Investigation into the
Pebble East and Pebble West Metallurgical Programs. Project #12072-002 Final
Report, May 3, 2010.
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SGS-Lakefield Research Ltd., 2010. An Investigation into the
Recovery of Copper, Gold, and Molybdenum from Samples from Pebble East and West
Deposits. Project #12072-002-Report #2, May 10, 2010.
SGS-Lakefield Research Ltd., 2014. A Summary of Pebble East and
West Metallurgical Programs. September 5, 2014.
Alaska Department of Fish and Game (ADFG), 2010. 2009 Bristol
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Alaska Department Fish and Game (ADFG), 2013. Anadromous Waters
Catalog. https://www.adfg.alaska.gov/sf/SARR/AWC/index.cfm
Alaska Department of Natural Resources, 2005. Bristol Bay Area
Plan for State Lands. http://dnr.alaska.gov/mlw/planning/areaplans/bristol/pdf/bbap_complete.pdf
Jones, M. et al, 2012. 2012 Bristol Bay Area Management Report
No. 13-20.
Mine Environmental Neutral Drainage Program, 1991. Acid Road
Drainage Prediction Manual, MEND Project 1.16.1b, CANMET MSL Division,
Department of Energy, Mines and Resources, Canada.
PLP (Pebble Limited Partnership), 2012. Pebble Project
Environmental Baseline Document 2004 through 2008. Pebble Partnership,
Anchorage, AK (available online at http://pebbleresearch.com
State of Alaska, Department of Labor and Workforce Development,
January 18, 2013 Press Release No. 13-03.
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J. David Gaunt,
P.Geo.
15TH
FLOOR, 1040 WEST
GEORGIA ST.
VANCOUVER, BRITISH
COLUMBIA
Telephone: 604-684-6365 Fax:
604-662-8956
davidg@hdgold.com
I, J. David Gaunt, P.Geo., am a
Professional Geologist in the City of Vancouver, in the Province of British
Columbia.
|
1. |
I am co-author of this report entitled 2014 Technical
Report on the Pebble Project, Southwest Alaska, USA, effective date
December 31, 2014. I am responsible for sections 2 through 5, 6.3, 6.4,
14, 16 and 19.3, and jointly responsible for sections 1, 17 and 18 of this
report. |
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2. |
I have been involved with the project since 2001, and
co-authored technical reports in 2008 and 2009. |
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3. |
I am a member in good standing of: The Association of
Professional Engineers and Geoscientists of British Columbia, registration
No.20050, and The Prospectors and Developers Association of
Canada. |
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4. |
I am a graduate of Acadia University, Nova Scotia (B.Sc.,
Geology, 1985). |
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5. |
I have practiced my profession continuously since
graduation and have been involved in mineral exploration and resource
estimation for precious and base metals in Canada, USA, Mexico, Argentina,
Chile, Peru, Australia, Spain, Hungary, Afghanistan, China, and South
Africa. I have previous experience with intrusion related copper gold
deposits, notably Veladero, and Pebble. |
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6. |
As a result of my qualifications and experience I am a
Qualified Person as defined in National Instrument 43101. |
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7. |
I am not independent of the issuer, Northern Dynasty
Minerals Ltd. |
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8. |
I have visited the Pebble Project several times, most
recently on September 1st and 2nd, 2010, and have been involved
in the resource estimates relating to Pebble since 2001. |
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9. |
I have read National Instrument 43-101, Form 43-101FI and
this report has been prepared in compliance with NI 43-101 and Form
43-101FI. |
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10. |
I am not aware or any material fact or material change
with respect to the subject matter of this technical report, which is not
reflected in the report, the omission of which to disclose would make this
report misleading. |
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11. |
I consent to the filing of the subject Technical Report
with any stock exchange and any other regulatory authority and any
publication by them, including electronic publication in the public
company files on their websites accessible by the public, of the subject
Technical Report. |
Dated in Vancouver on this 4th day of February,
2015.
J. David Gaunt, P.Geo.
J. David Gaunt, P.Geo.
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James R. Lang Ph.D, P.Geo
15TH Floor, 1040 W. Georgia St.
Vancouver, British Columbia V6E 4H1
Ph: 604-684-6365;
e-mail: jimlang@hdimining.com
I, James R. Lang Ph.D, P.Geo., of Surrey, British Columbia,
Canada, do hereby certify that:
1) |
I am Senior Vice President Geology at Hunter Dickinson
Inc., with offices located at the address shown above. |
|
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2) |
I graduated with a B.Sc. in geology from Michigan State
University, East Lansing, Michigan, USA in 1983, and received M.Sc. and
PhD degrees in economic geology from the University of Arizona, Tucson,
Arizona, USA in 1986 and 1991, respectively. |
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3) |
I am a registered member of the Association of
Professional Engineers and Geoscientists of British Columbia, Registration
Number 25376. |
|
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4) |
I have worked as an economic geologist for 28 consecutive
years. |
|
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5) |
I have read the definition of qualified person set out
in National Instrument 43-101 (NI 43-101) and certify that by reason of
my education, affiliation with a professional association (as defined by
NI 43- 101) and past relevant work experience, I fulfill the requirements
to be a qualified person for the purposes of NI 43-101. |
|
|
6) |
I am co-author of this Technical Report titled 2014
Technical Report on the Pebble Project, Southwest Alaska, USA, effective
date December 31, 2014. I am solely responsible for sections 1.4, 6.1,
7.0, 8.0, 9.0, 15.0 and 19.1 and am jointly responsible for sections
10.0 and 17.2 of this report. |
|
|
7) |
I have been physically present at the project area every
year since 2003 for a total of over 625 days. From 2007 through 2010 I
acted as Chief Geologist for the project. My most recent visit was on
August 18-19, 2014. I am familiar with the geology, topography, physical
features, access, location and infrastructure. |
|
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8) |
I am not aware of any material fact or material change
with respect to the subject matter of the Technical Report that is not
reflected in the Technical Report, the omission to disclose which might
make the Technical Report misleading. |
|
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9) |
I am NOT independent of the issuer, Northern Dynasty
Minerals Ltd., applying all tests in Section 1.5 of National Instrument
43-101. In the last 12 months 100% of the writers income has been derived
from Hunter Dickinson Inc, and the writer holds securities and/or options
on securities of Northern Dynasty Minerals Ltd. |
|
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10) |
I have read National Instrument 43-101 and Form 43-101F1,
and the Technical Report has been prepared in compliance with that
instrument and form. |
|
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11) |
As of the date of the certificate, to the best of my
knowledge, information and belief, the technical report contains all
scientific and technical information that is required to be disclosed to
make the technical report not misleading. |
|
|
12) |
I consent to the filing of the Technical Report with any
stock exchange and any other regulatory authority and any publication by
them, including electronic publication in the public company files on
their websites accessible by the public, of the Technical
Report. |
Dated this 26th day of January, 2015
James R. Lang, Ph.D., P.Geo.
James R. Lang, Ph.D., P.Geo.
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Pebble Project, Southwest Alaska |
Eric D. Titley
15th Floor
1040 West Georgia Street,
Vancouver, British Columbia, Canada, V6E
4H1
Tel. 604-684-6365, Email: EricTitley@hdimining.com
I, Eric D. Titley, P.Geo. do hereby certify that:
I am Senior Manager | Resource Geology, at the above
address.
|
1. |
I am a graduate of the University of Waterloo, Waterloo,
Ontario with a Bachelor of Science degree in Earth Sciences (geography
minor) in 1980. |
|
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|
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2. |
I have practiced my profession continuously since
1980. |
|
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|
|
3. |
I am a Professional Geoscientist registered with the
Association of Professional Engineers and Geoscientists in the province of
British Columbia, Canada. |
|
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|
|
4. |
I have read the definition of qualified person set out
in National Instrument 43-101 (NI 43101) and certify that by reason of
my education, affiliation with a professional association (as defined in
NI 43-101) and past relevant work experience, I fulfill the requirements
to be a qualified person for the purposes of NI 43-101. |
|
|
|
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5. |
I am the author of sections 6.2, 11, and 12 and jointly
responsible for section 10 of the report entitled 2014 Technical Report
on the Pebble Project, Southwest Alaska, USA (the Technical Report).
The Technical Report has an effective date of December 31, 2014. The
Technical Report is based on my knowledge of the project area and drilling
database included in the Technical Report, and on review of published and
unpublished information on the property and surrounding areas. I conducted
a site visit of the Pebble Project on the 20th of September,
2011. |
|
|
|
|
6. |
At the effective date of the Technical Report, to the
best of my knowledge, information and belief, the part of the Technical
Report for which I am responsible, contains all the scientific and
technical information that is required to be disclosed to make the
technical report not misleading. |
|
|
|
|
7. |
I am not independent of Northern Dynasty and affiliated
companies applying the tests in section 1.5 of National Instrument
43-101. |
|
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|
|
8. |
I have had prior involvement with the property as an
author of technical reports in 2010, 2009 and 2008 and ongoing review of
the drilling database. |
|
|
|
|
9. |
I have read National Instrument 43-101 and Form 43-101F1,
and the Technical Report has been prepared in compliance with that
Instrument and Form. |
|
|
|
|
10. |
I consent to the filing of the Technical Report with any
Canadian stock exchange and other regulatory authority and any publication
by them, including electronic publication in the public company files on
their website accessible by the public, of the Technical
Report. |
Dated this 26th day of January 2015,
Eric D. Titley, P.Geo.
___________________
Eric
D. Titley, P.Geo.
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Pebble Project, Southwest Alaska |
Ting Lu, P.Eng., M.Sc.
I, Ting Lu, P.Eng., M.Sc., of Vancouver, British Columbia, do
hereby certify:
I am a Senior Metallurgical Engineer
with Tetra Tech WEI Inc. with a business address at 1000 - 885 Dunsmuir Street,
Vancouver, British Columbia, V6C 1N5.
This certificate applies to the
technical report entitled 2014 Technical Report on the Pebble Project,
Southwest Alaska, USA, effective date December 31, 2014 (the Technical
Report).
I am a graduate of Queens University,
Kingston, Ontario, Canada (M.Sc., 2006) and Taiyuan University of Technology,
Taiyuan, Shanxi, P.R. China (H.B. Sc., 1996). I am a member in good standing of
the Association of Professional Engineers and Geoscientists of British Columbia
(#32897). My relevant experience includes 15 years of experience in the mineral
processing industry. I worked on the Mt.
Milligan Copper-Gold Feasibility Study
Project with Terrane Metals Corp., the Kerr-Sulphurets-Mitchell (KSM)
Copper-Gold-Molybdenum Prefeasibility Study Project with Seabridge Gold Inc. and
the La Joya Silver-Copper-Gold-Lead-Zinc Preliminary Economic Assessment Project
with Silvercrest Mines Inc., Chile. I am a Qualified Person for the purposes
of National Instrument 43-101 (the Instrument).
I did not complete a personal
inspection of the Property.
I am responsible for Sections 1.6, 13.0, 17.3 and 19.2, and jointly responsible for Sections 1.9.2 and 18.2 of the Technical Report.
I am independent of North Dynasty
Minerals Ltd. as defined by Section 1.5 of the Instrument.
I have no prior
involvement with the Property that is the subject of the Technical Report.
I have read the Instrument and the
sections of the Technical Report that I am responsible for have been prepared in
compliance with the Instrument.
As of the date of this certificate, to
the best of my knowledge, information and belief, the sections of the Technical
Report that I am responsible for contain all scientific and technical
information that is required to be disclosed to make the Technical Report not
misleading.
Signed and dated this day of 26th January, 2015 at
Vancouver, British Columbia.
Ting Lu, P.Eng., M.Sc.
___________________________________________________
Ting Lu, P.Eng.,
M.Sc.
Senior Metallurgical Engineer
Tetra Tech WEI Inc.
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February 6, 2015
British Columbia Securities Commission
Ontario Securities Commission
Re: Northern Dynasty Minerals Ltd. (the “Corporation”) - Consent under NI 43-101
I, J. David Gaunt, P.Geo., do hereby consent to the public filing by Northern Dynasty Minerals Ltd. of the Technical Report titled “2014 Technical Report on the Pebble Project, Southwest Alaska, USA”, effective December 31, 2014. Additionally, I consent to the use of extracts or summaries from the Technical Report.
I confirm that I have read the Corporation’s Preliminary Short Form Prospectus and believe that it fairly and accurately represents the information contained in that part of the Technical Report that I am responsible for.
Sincerely,
J. David Gaunt, PGeo
_____________________________
J. David Gaunt, P.Geo.
February 6, 2015
British Columbia Securities Commission
Ontario Securities Commission
Re: Northern Dynasty Minerals Ltd. (the “Corporation”) - Consent under NI 43-101
I, James Lang, P.Geo., do hereby consent to the public filing by Northern Dynasty Minerals Ltd. of the Technical Report titled “2014 Technical Report on the Pebble Project, Southwest Alaska, USA”, effective December 31, 2014. Additionally, I consent to the use of extracts or summaries from the Technical Report.
I confirm that I have read the Corporation’s Preliminary Short Form Prospectus and believe that it fairly and accurately represents the information contained in that part of the Technical Report that I am responsible for.
Sincerely,
James Lang, PGeo
________________________
James Lang, P.Geo.
February 6, 2015
British Columbia Securities Commission
Ontario Securities Commission
Re: Northern Dynasty Minerals Ltd. (the “Corporation”) - Consent under NI 43-101
I, Eric Titley, P.Geo., do hereby consent to the public filing by Northern Dynasty Minerals Ltd. of the Technical Report titled “2014 Technical Report on the Pebble Project, Southwest Alaska, USA”, effective December 31, 2014. Additionally, I consent to the use of extracts or summaries from the Technical Report.
I confirm that I have read the Corporation’s Preliminary Short Form Prospectus and believe that it fairly and accurately represents the information contained in that part of the Technical Report that I am responsible for.
Sincerely,
Eric Titley, PGeo
_____________________________
Eric Titley, P.Geo.
February 6, 2015
British Columbia Securities Commission
Ontario Securities Commission
Re: Northern Dynasty Minerals Ltd. (the “Corporation”) - Consent under NI 43-101
I, Ting Lu, P.Eng., do hereby consent to the public filing by Northern Dynasty Minerals Ltd. of the Technical Report titled “2014 Technical Report on the Pebble Project, Southwest Alaska, USA”, effective December 31, 2014. Additionally, I consent to the use of extracts or summaries from the Technical Report.
I confirm that I have read the Corporation’s Preliminary Short Form Prospectus and believe that it fairly and accurately represents the information contained in that part of the Technical Report that I am responsible for.
Sincerely,
Ting Lu, PEng.
____________________________
Ting Lu, P.Eng.
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