TIDMMML
RNS Number : 9681J
Medusa Mining Limited
14 August 2012
Medusa Mining Limited
("Medusa" or the "Company")
Co-O Mine Geology and Mineralisation Update
14 August 2012
Medusa Mining Limited ("Medusa" or the "Company"), through its
Philippines operating company Philsaga Mining Corporation, advises
that
1. The Conceptual Exploration Target** of 3,000,000 ounces in
9,800,000 tonnes to 7,000,000 ounces in 23,500,000 tonnes using a
grade range of 9 to 11 g/t gold with a preferred average grade of
10 g/t gold remains valid. The current deposit size is
approximately 2,520,000 comprising current resources and past
production. Within the resource model area there are currenly 979
drill hole intersections not yet included in the model.
2. Work is underway on zones of multiple epithermal and
stockwork veining which may have bulk mining potential.
Examples include:
Hole Number Width Grade (uncut)
(metres) (g/t gold)
EXP 070 40.05 2.91
EXP 073 22.50 4.46
EXP 101 15.05 19.64
EXP 121 18.45 9.35
EXP 124 14.70 4.05
EXP 134 10.75 12.45
EXP 140 17.30 4.17
3. Major advances have been made during the year in
understanding the Co-O Mine geology as summarised below:
(i) The andesitic volcanic sequence at Co-O has been intruded by
several andesitic to dioritic stocks;
(ii) The stocks and some of the volcanics were then over-printed
in parts by porphyry-related copper-gold mineralisation with grades
of 0.1 to 0.2% copper and 0.1 to 0.2 g/t gold, eg, EXP089: 198.65
metres at 0.13 % copper and 0.23 g/t gold, and EXP127: 789.60
metres at 0.12 % copper and 0.15 g/t gold. The source porphyry
intrusive for this mineralisation has not yet been located;
(iii) The volcanic - intrusive complex was then cut by a large,
funnel-shaped or flaring diatreme breccia pipe approximately 1,500
metres in diameter at surface that is well-preserved. The diatreme
exploded through to the original surface depositing maar material
peripheral to and on top of the diatreme;
(iv) The Co-O epithermal vein mineralisation post-dates the
diatreme and maar material, and, in places, is superimposed on the
earlier porphyry-related mineralisation. The veins generally die
out within a few metres of penetrating the diatreme breccia due to
its poor "cracking" charcteristics;
(v) The diatreme breccia flare and the associated maar deposits
obscure vein extensions to the east, and some veins immediately
adjacent to the Oriental Fault. The veins continue uninterrupted
under the northern flare and maar deposits and are open to the
east;
(vi) The implications of the diatreme recognition and
delineation are that there is no longer the need to invoke
substantial displacement along the Oriental Fault, and that the
strong vein mineralisation should continue to similar depths on the
west side of the Oriental Fault as that already delineated on the
east side.
Peter Hepburn-Brown, Managing Director commented:
"As we continue to extend the size of the area of
mineralisation, our confidence in the validity of the Conceptual
Exploration Target size is enhanced. This year has again justified
that level of confidence.
We have made major advances in the understanding of the Co-O
Mine geology and potential during the year. This has been
highlighted by the identification of extensive porphyry-related
copper-gold mineralisation with the potential that it is connected
to a major primary porphyry copper-gold source in the immediate
vicinity.
We are currently reviewing and re-interpreting significant zones
of multiple epithermal veining and stockworks which will be
investigated for bulk mining techniques.
It is still very apparent that the Co-O vein system is open in
all directions providing potential for resource inhancements for
many years."
** The potential target size and grade is conceptual in nature,
and there has been insufficient exploration to define a mineral
resource, and it is uncertain if further exploration will result in
the target being defined as a mineral resource.
Co-O MINE CONCEPTUAL TARGET **
Drilling since the estimate of the Conceptual Exploration Target
announced on 18 January 2010 has continued to expand the vein
system, as supported not only by the 2012 global resource estimate
of 2,019,000 ounces, but also by the 979 drill hole intersections
>2g/t gold over >0.2 metres which are not yet included in the
resource model.
The range for the Conceptual Exploration Target remains well
supported at 3,000,000 ounces in 9,800,000 tonnes to 7,000,000
ounces in 23,500,000 tonnes using a grade range of 9 to 11 g/t gold
with a preferred average grade of 10 g/t gold as shown in Table
III.
The combination of past production of approximately 510,000
ounces and the current global resource of 2,019,000 ounces
indicates the deposit size is approaching the lower end of the
Conceptual Exploration Target size range.
The additional support for this target is listed below:
- The total ounces already accounted for by the current global
resource and past production is approximately 2,529,000 ounces.
- An increase in strike length by 400 metres to 2,000 metres as
supported by drilling results available in various recent drilling
announcements.
- As shown on the composite longitudinal projection in Figure 1
(please see link at the end of this announcement), all new drill
holes since 30 June 2011 in the deposit with assays of >=0.2
metres at >=2 g/t gold up to 30 June 2012 have been added and
support the mineralisation continuing to depth. The assay support
levels at depth is increasing as drilling progresses with the
deepest intersection to date recorded at 1,073 metres below surface
of 1.0 metre at 10.39 g/t gold.
- Figure 2 (please see link at the end of this announcement)
shows a longitudinal projection of the resource model and the 979
intersections within the projection which have not yet been
included in the 2012 model. This will add significant resources as
more data and interpretations improve the continuity of the
intersections.
Figure1. (please see link at the end of this announcement)
Composite longitudinal projection of the Co-O Mine showing the
diatreme and all drill hole intersections below Level 6
Figure 2. (please see link at the end of this announcement)
Composite longitudinal projection of the Co-O Mine showing the
diatreme and the 979 drill holes not yet included in the resource
model.
Table I. Co-O Mine Conceptual Exploration Target matrix **
Strike Depth Aggregate Conceptual Gold Conceptual
length below vein width tonnes grade contained
(metres) Level (metres) (g/t) ounces
I (metres)
1,500 500 5 9,825,000 10 3,159,000
8 15,720,000 10 5,054,000
10 19,650,000 10 6,318,000
750 5 14,737,000 10 4,738,000
8 23,580,000 10 7,581,000
10 29,475,000 10 9,477,000
1000 5 19,650,000 10 6,318,000
8 31,440,000 10 10,109,000
10 39,300,000 10 12,636,000
2,000 500 5 13,100,000 10 4,212,000
8 20,960,000 10 6,739,000
10 26,200,000 10 8,424,000
750 5 19,650,000 10 6,318,000
8 31,440,000 10 10,109,000
10 39,300,000 10 12,636,000
1,000 5 26,200,000 10 8,424,000
8 41,920,000 10 13,479,000
10 52,400,000 10 16,848,000
Notes:
(i) Approximately 510,000 ounces already mined from the
deposit;
(ii) SG of 2.62 used for all estimates
(iii) Tonnes and ounces estimates rounded down to nearest 1,000;
and
(iv) Highlighted cases indicate most geologically reasonable
based on current knowledge
** The potential target size and grade is conceptual in nature,
and there has been insufficient exploration to define a mineral
resource, and it is uncertain if further exploration will result in
the target being defined as a mineral resource.
Co-O MINE LOCAL GEOLOGY
The Co-O Mine area is underlain by a probable Eocene (56 to 34
million years) to Oligocene (34 to 23 million years) age, gently
north-dipping sequence of basaltic andesitic to andesitic volcanic
flows and minor volcaniclastics (Fig. 3).
Figure 3. (please see link at the end of this announcement) Co-O
Mine area interpreted geological map showing section lines A-A' and
B-B'.
This sequence is intruded by Oligocene andesitic to dioritic
stocks and dikes dated at 32 million years old and cut by
north-trending steep faults with the Oriental Fault identified as
the most significant fault to date (Sonntag & Hagemann,
2010).
There are three large outcropping intrusives, namely the Nangka,
Road 17 and Pinayungan Intrusives, located east and southwest of
the Co-O vein system, and several smaller ones in the vicinity. The
Nangka and Pinayungan Stocks are in place while the rest are
"floating" in the Co-O Diatreme including the large Road 17 Mega
Block as explained below. At depth, Nangka Stock enlarges beneath
the Co-O Diatreme to become a 400 metres east-west by >800
metres north-south body.
Porphyry-related copper-gold mineralization is hosted only in
the Nangka Stock and the surrounding volcanics (Figs 4 to 6).
After a period of substantial uplift and erosion, a
diatreme/maar complex explosively intruded all the above rock types
(Figs. 3 to 6). Its presence explains the general absence of near
surface epithermal veins east of the Oriental Fault instead of
invoking a large down thrown movement of the zone as the veins are
masked by the flare of the diatreme.
Note: diatremes are generally caused by the explosive release of
gases and fluids from the catastrophic mixture of ground water from
the surface and magma at depth.These gases and fluids force their
way to the surface, causing pipe-like columns of broken or
brecciated rock that flare outwards near surface producing funnel
shaped features that are often concave on the surface after the
explosive activity has ceased. The clouds of rock fragments and
dust that are released settle around the annulus of the diatreme
and also on top of the diatreme. If the diatreme surface remains
concave or a natural depression, younger sediments will commonly
accumulate in the depression, frequently under a lake that forms in
the depression.
Figure 4. (please see link at the end of this announcement)
North-south cross section of the interpreted geology along section
line A-A looking west.
Figure 5. (please see link at the end of this
announcement)East-west longitudinal projection of the interpreted
geology along section line B-B' looking north.
The Co-O Diatreme is upward flaring in all directions towards
the surface, measuring about 1.5 kilometres in diameter, and
narrows down at depth like a funnel of unknown dimensions. Its root
is probably located at the southern part of the Road 17 Intrusive.
It is inferred that the diatreme may easily reach 1 kilometre or
more in depth as indicated by its surface dimension wherein the
vertical extent is more than its lateral extent. The maar
volcanics, which are the extrusive equivalent of the diatreme and
deposited by the explosive activity of the diatreme, are still
largely intact in the eastern and partly in the northern fringe of
the diatreme and some isolated preserved outcrops to the west side
of the Oriental Fault. The maar rocks consist of andesitic crystal
lithic tuffs, with some dacitic facies, sometimes exhibiting crude
to laminated subhorizontal bedding, minor intercalations of tuff
breccias, accretionary lapilli tuffs and thinly bedded carbonaceous
tuffaceous mudstones (Photos 1 and 2 (please see link at the end of
this announcement)). The presence of accretionary lapilli tuff
would indicate base surge deposits which were emplaced by violent
subhorizontal blasts emanating from the diatreme's throat.
Photo1. (please see link at the end of this announcement)
Contact of the upper andesite porphyry to diorite megablock with
the underlying diatreme (Hole EXP093: 101 to110.55 metres).
Mega Blocks of the maar tuff and intrusive are floating in the
diatreme representing fallen blocks and roof pendants in the upper
part of the diatreme. The largest mega-block is the Road 17 Mega
Block, about 400 metres wide by 800 metres long, located at the
eastern portion of the diatreme and which is exposed on the surface
(Figs 3 to 5 and Photo 1(please see link at the end of this
announcement)).
After the emplacement of the diatreme/maar complex, mineralised
hydrothermal breccias followed by epithermal gold veins were
formed, overprinting the older porphyry-related copper-gold
mineralisation. The veins generally strike west-northwest to due
west and dip 55 to 75[deg] to the north for all veins except the
Central Vein which is vertically dipping.
Post-mineral re-activation of pre-existing north-trending
faults, represented by the Oriental Fault and other sub-parallel
faults, cut the epithermal veins, showing dextral (right lateral
strike-slip) movement with a diagonal component (Standing &
Noble, 2011). This faulting displaces the veins laterally to the
south and downward by a few metres to several tens of metres.
After another episode of uplift and erosion, a thin veneer of
polymictic conglomerate to a maximum thickness of about 30 metres,
was deposited on top of the diatreme/maar complex (Fig. 3). The
conglomerate consists of rounded to subangular clasts of all the
pre-existing rocks including rare feldspar porphyry intrusive
(which is common in the Tambis area), epithermal vein material, and
petrified and young carbonised wood (Photo 2 (please see link at
the end of this announcement)). This conglomerate contains alluvial
gold.
Photo 2. (please see link at the end of this announcement)
Polymictic conglomerate with carbonised wood and quartz vein
clasts.
MINERALISATION
There are two mineralisation styles in the Co-O Mine area,
namely the:
1. earlier or older porphyry-related copper-gold style, and
2. later or younger intermediate sulphidation epithermal
gold-rich quartz vein style in the Co-O Mine
Since the epithermal gold veins are usually emplaced within
about 1 kilometre from the paleo-surface while a porphyry copper
system is emplaced at least 2 kilometres from the paleo-surface,
there has been substantial uplift and passage of time between the
two mineralisation events since the former overprinted the latter.
Also, very little erosion of the epithermal veins has taken place
since the older near-surface maar facies is still essentially
intact. This is corroborated by the recent fluid inclusion study of
Hagemann & Grignola (2012) which concluded that the paleo-depth
of epithermal vein formation is about 61 to 295 metres.
Porphyry-related Copper-Gold Mineralisation
The porphyry-related copper-gold mineralisation is generally
weak and is hosted in the Nangka Intrusive and the surrounding
volcanics (Fig. 4). The mineralisation is not classical porphyry
copper-gold since the alteration is chloritic to propylitic instead
of the conventional potassic, sericitic and/or sericite-chlorite,
and due to the local presence of lead-zinc sulphides together with
chalcopyrite. Also the Nangka Intrusive is still considered a
pre-mineral host rock and not the causative intrusive, i.e. the
intrusive that brought about the mineralisation. This is evidenced
by the fact that mineralisation is irregular in distribution within
the stock, and consequently is currently termed "porphyry-related"
copper-gold mineralisation.
The mineralisation occurs in four irregularly shaped
discontinuous zones along a northerly trending corridor about 650
metres east-west by 850 metres north-south. The northern and
southern mineralised zones are more developed than the centrally
located ones. Also, the mineralised zones are positioned deeper
towards the south. Figure 4 (please see link at the end of this
announcement) shows that the northern mineralised zone lies between
the surface and mine Level 7, while the southern zone is generally
at mine Level 4 to below Level 16, and that the mineralisation is
confined mainly at the northern and southern margins of the stock
(Fig. 4). The northern mineralised zone is 250 to 400 metres wide
by 400 metres vertically while the southern zone is 150 to 300
metres wide by >600 metres vertically. Vertical hole EXP127 on
Figure 4 (please see link at the end of this announcement) shows
that the mineralisation is likely still open at >1 kilometre
below the surface as indicated in Table II.
Table II. Examples of porphyry-related copper-gold
mineralisation intersections using 1g/t gold upper cut
Hole East North Dip Azimuth From Interval % Cu g/t
ID ([deg]) ([deg]) (m) (m) Au
(cut)
EXP089 614542 912901 -55 180 328.10 198.65 0.13 0.23
EXP127 614551 912592 -0 -90 326.10 789.60 0.12 0.15
The copper-gold mineralisation is characterised by sheeted to
multi-directional <1 to 2 mm grey quartz-sulphide veinlets and
rare sulphide fracture fills and disseminations. Veinlet density is
about 2 to >10 per metre. The sulphides consist of <1 to 3 %
pyrite, <0.1 to 0.5 % chalcopyrite, and sporadic occurrence of
sphalerite and galena. These veinlets are overprinted by epithermal
veins in some areas as shown in Photo 3 (please see link at the end
of this announcement).
Photo 3. (please see link at the end of this announcement)
Chloritic altered andesite porphyry intrusive with porphyry-related
2-3mm wide greyish quartz-sulphide veinlets (0.14 to 0.18% Cu &
0.14 to 0.23 g/t Au) overprinted by a 200 mm wide milky epithermal
quartz vein (98.76 g/t Au) and other narrower ones. (Hole EXP089:
377.75 to 382.35 metres).
The porphyry-related copper-gold mineralization is generally
weak. Values range from 0.11 to a maximum of 0.31 % Cu and 0.11 to
0.24 g/t Au with a Cu:Au ratio of about 1:1 to 1:2.
It is the presence of epithermal gold veins/stockworks that
increases the gold grade of the overprinted porphyry-related
copper-gold mineralisation. Thirty eight EXP holes containing wide
zones of both porphyry-related copper-gold and epithermal gold
veins have been identified to date, some of which are shown in
Table III. Other potential wide multiple vein zones outside the
copper zone have also been identified, These zones will be
considered for underground bulk mining as additional data becomes
available and interpretation work progresses.
Table III. Examples of EXP holes with wide mineralisation zones
using a 2 g/t Au intersection boundary cut-off
Hole East North Dip Azimuth From Interval g/t
([deg]) ([deg]) (m) (m) Au (uncut)
EXP067 614484 913297 -50 160 561.15 11.65 3.27
EXP070 614398 913159 -50 160 444.45 40.05 2.91
542.40 7.75 4.06
EXP072 614503 912978 -50 180 316.60 12.80 3.39
390.00 9.80 2.11
EXP073 614271 913339 -50 160 780.30 22.50 4.46
EXP074 614212 913281 -50 160 571.20 15.20 2.70
EXP081 614349 912938 -50 180 231.50 12.10 2.66
EXP089 614542 912901 -55 180 340.85 11.70 3.99
EXP095 614066 913152 -47 160 490.70 12.05 2.30
529.00 14.15 2.29
598.20 21.80 2.64
EXP101 613838 912888 -47 190 387.70 15.05 19.64
EXP120 614586 913271 -50 160 474.40 15.15 2.49
EXP121 614551 912992 -55 180 568.65 18.45 9.35
EXP124 614549 913123 -52 160 452.05 14.70 4.05
EXP134 614604 913032 -65 180 815.70 10.75 12.45
EXP140 614659 913216 -54 180 484.05 17.30 4.17
Notes:
(i) Intersection widths are downhole drill widths not true
widths;
(ii) Assays denoted by are by Philsaga Mining Corporation's
laboratory;
(iii) Grid coordinates based on the Philippine Reference System
92.
Epithermal Gold Mineralisation
The intermediate sulphidation epithermal gold mineralisation has
overprinted the porphyry-related copper-gold mineralisation.
Initiation of the epithermal system is represented by
structurally controlled, discontinuous, and commonly narrow <1
to 5 metre wide hydrothermal breccias which are sometimes
mineralised but generally <1 g/t gold. A large barren
hydrothermal breccia body, 75 metres by 270 metres, has been
recognised at the south-western portion of the area (Fig. 3).
The hydrothermal breccias were followed by the formation of the
main stage well-mineralised epithermal quartz veins which
occasionally penetrated the edges of the diatreme/maar complex and
sometimes cut the hydrothermal breccias. It is clear that the
epithermal gold veins prefer the competent pre-breccia rocks which
crack easily and cleanly compared with the diatreme which is
incompetent and has poor cracking characteristics. The exceptions
are the Ka Opong and Road 17 veins which clearly cut the upper part
of the maar volcanics and where test drilling of these veins within
the maar rocks has so far located only low grade gold values.
The relationship of the epithermal gold veins and the diatreme
in the mine on Level 6 is shown in Figure 6. (please see link at
the end of this announcement)
Figure 6. (please see link at the end of this announcement) Co-O
mine Level 6 geology showing the outline of the diatreme breccia,
the porphyry-related copper zones and epithermal gold veins from
the resource model. Section lines A-A' and B-B' marked.
The epithermal quartz veins are dominantly westerly trending and
sub-vertical, with lesser 40 to 50 dipping veins. In summary, some
of the vein characteristics are:
- the veins are polyphasal exhibiting massive, banded and vein
breccia textures;
- the high gold grades are associated with crustiform-colloform
banding; and
- the sulphides comprise mainly pyrite, <1 to 5 %, and minor
sphalerite, chalcopyrite, galena.
Fluid inclusion studies on mine vein samples during the year
concluded:
- the temperature of formation was 210 to 280[deg] C and within
approximately 60 to 300 metres below the paleo-surface;
- the fluid salinities were generally low, i.e. 0 to 6.7 wt %
NaCl equivalent; and
- that the above ranges fall well within the epithermal range of
deposition.
Alteration types identified are:
- silicic (quartz +/- illite-calcite) - confined to vein zones
and hydrothermal breccias;
- argillic (illite +/- quartz-calcite) - surrounds the veins -
millimetres to hundreds of metres; and
- chloritic to propylitic (chlorite +/- epidote +/-
smectite-calcite) - increases and finally dominates at depth.
At surface, the mapped alteration shows that the:
- veins are within a laterally extensive mushroom-shaped
argillic envelope which is,
- in excess of 1.5 km x 1.5 km in area, and
- clearly associated with gold vein mineralisation;
- outlying chloritic to propylitic zone is overprinted by
argillic alteration; and
- propylitic zone is considered to be regional in extent, i.e.
pre-mineral.
The alteration patterns at depth are:
- the argillic envelope abruptly tapers down along the veins
until only a few metres to millimetres wide;
- the chloritic to propylitic alteration zone increases and
finally dominates at depth; and
- there appears to be no identifiable pattern between the
chloritic and propylitic zones.
References
Angeles, C.A., 2012. May-June 2012 Progress Report for Philsaga
Mining Corporation. Internal Report.
Hagemann, S. & Grignola, S., 2012. Quartz vein textures,
fluid inclusion petrography, microthermometry and interpretation of
fluid inclusion data from the Co-O Deposit, Mindanao, Philippines.
Internal Report.
Sonntag, I. & Hagemann, S., 2010. Geological and Geochemical
Evolution of the Central Eastern Mindanao Ridge, Philippines: The
Co-O Mine and District, the Borobo Fault Corridor and the Lingig
Area. The University of Western Australia Centre for Exploration
Targeting. Internal Report.
Standing, J. & Noble, M., 2011. Structural Analysis of the
Vein and Fault Achitecture at the Co-O Gold Mine, Mindanao Island,
Republic of the Philippines, Medusa Mining Ltd. Internal
Report.
For further information please contact:
Australia
Medusa Mining Limited +61 8 9367 0601
Peter Hepburn-Brown, Managing
Director
United Kingdom
Fairfax I.S. PLC (Financial
Adviser & Broker) +44 (0)20 7598 5368
Ewan Leggat/Laura Littley
Information in this report relating to Exploration Results has
been reviewed and is based on information compiled by Mr. Geoff
Davis, who is a member of The Australian Institute of
Geoscientists. Mr. Davis is the Non-Executive Chairman of Medusa
Mining Limited and has sufficient experience which is relevant to
the style of mineralisation and type of deposits under
consideration and to the activity which he is undertaking to
qualify as a "Competent Person" as defined in the 2004 Edition of
the "Australasian Code for Reporting of Exploration Results,
Mineral Resources and Ore Reserves". Mr. Davis consents to the
inclusion in the report of the matters based on his information in
the form and context in which it appears.
DISCLAIMER
This announcement may contain certain forward-looking
statements. The words 'anticipate', 'believe', 'expect', 'project',
'forecast', 'estimate', 'likely', 'intend', 'should', 'could',
'may', 'target', 'plan' and other similar expressions are intended
to identify forward-looking statements. Indications of, and
guidance on, future earnings and financial position and performance
are also forward-looking statements.
Such forward-looking statements are not guarantees of future
performance and involve known and unknown risks, uncertainties and
other factors, many of which are beyond the control of Medusa, and
its officers, employees, agents and associates, that may cause
actual results to differ materially from those expressed or implied
in such statements.
Actual results, performance or outcomes may differ materially
from any projections and forward-looking statements and the
assumptions on which those assumptions are based.
You should not place undue reliance on forward-looking
statements and neither Medusa nor any of its directors, employees,
servants or agents assume any obligation to update such
information.
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