TIDMSO4
RNS Number : 0197V
Salt Lake Potash Limited
25 January 2017
25 January 2017 AIM/ASX Code: SO4
SALT LAKE POTASH LIMITED
Trenching and Pump Testing at Lake Wells Confirms Brine Production Potential of the Shallow
Aquifer
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Salt Lake Potash Limited (SO4 or the Company) is pleased to
advise that initial pump testing of trial trenches at the Lake
Wells Project (the Project) has returned excellent results,
substantially increasing the Company's confidence in the
hydrogeological model for extraction of brine from trenches for
production of Sulphate of Potash (SOP) by solar evaporation.
Surface Aquifer Exploration Program Highlights:
Ø An 8.5 tonne amphibious excavator has completed 207 shallow
test pits and 8 trial trenches at the Lake Wells Project.
Ø Sustained pump tests have been completed on two trenches in
the southern part of the Lake. Highlights include:
- Flow rates above 1 litre per second (L/s) from a 50m long
trial trench recorded during the duration of the test.
- Modelled annual flow rates of 1.1 - 1.3L/s based on a 1 year
simulated model of the results recorded during the 50m trial trench
pump test.
Ø The results from these initial trench pump tests have
confirmed the potential of trenching to produce sufficiently large
volumes of brine and will provide valuable data for the
pre-feasibility study.
Ø The Company gained valuable geotechnical information about the
material stability and the competency of the open trenches while
brine flowed into them from the surrounding aquifer.
Ø The trench excavating process also yielded valuable
geological, hydrogeological and geotechnical results for siting and
designing on-lake evaporation ponds.
Ø Work is ongoing on both the surface aquifer, and drilling and
test pumping of the deeper paleochannel aquifer, to refine the
brine production model for the Project.
CEO Matt Syme commented "We are very pleased with the results of
the initial trenching campaign at Lake Wells. The sustained pump
tests results provide a high level of confidence the potential for
substantial brine production from shallow trenches. The test pits
and trenches are also providing a wealth of very important
geological and geotechnical data which will be very important for
the ongoing feasibility studies for the Project."
Surface Aquifer Exploration Program
In November 2016, the Company mobilised an 8.5 tonne amphibious
excavator to gather further geological and hydrological data about
the shallow brine aquifer hosted by the Quaternary Alluvium
stratigraphic sequence in the top 20 meters of Lake Wells.
The aim of the program is to evaluate the geology of the shallow
Lake Bed Sediments, and to undertake pumping trials to provide
estimates of the potential brine yield from trenches in the shallow
sediment.
The excavator program is also providing important geological and
geotechnical information for potential siting and construction of
on-lake brine evaporation ponds.
The program to date included the excavation of 207 test pits in
three tranches over the lake playa. The test pits were generally
excavated to 1 meter x 1.5 meters and a depth of 4 meters and are
representative of the shallow stratigraphy of the Lake playa.
The test pits were logged for geology, hydrology and brine
chemistry during the excavation process. Particle Size Distribution
(PSD) samples and brine samples were taken from each pit.
The test pits were also subject to short duration pumping tests
in order to analyse the recovery of the brine levels in the test
pits.
Based on the geology and hydrological information from the test
pits, a number of sites for excavation of larger test trenches were
chosen, reflecting the variability of the geology and hydrogeology
encountered in the lake playa sediments.
A total of eight trenches were excavated on the chosen sites,
each approximately 4.5 meters deep and between 25 meters to 50
meters long. Benching was used to provide geotechnical stability
for the trench sidewalls and the resulting trenches are
approximately 5m wide at the surface and 1m wide at the base.
Five of the trenches were located in the southern end of the
Lake Wells, in close proximity to the Evaporation Trial Site. To
date two trenches have been test pumped.
Geology of the shallow sediments
Based on the widespread test pits the shallow aquifer geology is
reasonably uniform across the Lake. The shallow sediment is
generally composed of Cenozoic (Quaternary - Holocene) brown to
white to red, unconsolidated, gypsiferous sand, silt and clay with
a strong overprint of ferric oxides from 0.5 to around 3 - 8m
depth. Dominated by sub-angular, well sorted, very fine to medium
quartz sand, the sand commonly grades progressively to a more silt
and clay dominated sediment with depth, with occasional interbedded
sand lenses. Authigenic prismatic and tabular gypsum is common,
growing in discontinuous, vein-like structures throughout the unit,
with a large variety of crystal sizes. Minor, medium-grained lithic
fragments can be found throughout this gypsum.
Trench P1a (25m)
The geological sequence in P1a consisted of a 0.7m layer of
surficial coarse grained evaporate sand overlying silt and clay
with evaporate clasts to 3m depth. Plasticine clays were
encountered from 3m to the base of the trench. The trench appears
to have average brine flows in visual comparison to other trenches
and test pits.
Trench P1c (50m)
For P1c the geological sequence includes a 0.4m thick layer of
surficial coarse-grained evaporite sand overlying silt with
evaporite clasts to 2m depth. The interval from 2m to 2.8m
comprised a stiff fractured/fissured clay that yielded significant
brine. Sediment from 2.8 to 3.6m was soft clay and the underlying
interval to total depth of 4.4m was silt and fine grained evaporate
sands that also yielded brine.
Sustained Test Pumping Results
Trenches were test pumped for several days using a pair of
centrifugal suction pumps yielding up to 4L/s each. The test
pumping process involved pumping out the trench volume with both
pumps until the brine level was drawn down to a predetermined level
above the trench floor. The pump yields were then restricted to
keep the brine in the trench at this predetermined level. The brine
from the trench was disposed away from the test trenches to prevent
recycling of brine and creating an artificial recharge
boundary.
Observation wells were constructed at distances varying from 10,
20, 50, and 76 meters away from the trenches to measure the water
table drawdown in the surrounding aquifer during trench pumping.
These wells were logged for geological information and constructed
with slotted 50mm casing to the bottom of the well at 6 meters
below surface.
The brine level elevations were measured with water data loggers
in both the trench and the observation wells and verified during
the test pumping with manual readings. The cumulative brine yield
from the pumps were measured with a calibrated flow meter.
Standing water level of the brine was approximately 0.5m below
ground surface at each trench and in the observation wells before
test pumping started.
Data Analysis
The data from the trench test pumping were analysed and
processed based on the measured brine flows, water level readings
in the trenches and the observation wells.
Note that the amount of brine pumped daily from the trenches
decreased after one day in P1a and two days in P1c. This is due to
the removal of the trench storage. After this initial period the
inflows were from the surrounding aquifer material.
As expected, the aquifer material surrounding the P1c trench
displayed more permeability than the material surrounding the P1a
trench.
P1a Detail Analysis
The brine level in the trench was drawn down by 1.4m to
stabilise at approximately 1.7m below ground surface. Pumping was
then continued at a lower rate to maintain a constant brine level
in the trench and balance brine inflow to the trench with pumping.
By the end of the 8.3 day trial the flow rate from the trench had
reduced to 38m(3) /day (0.6L/s) as the surrounding material close
to the 25 meter long trench was dewatered.
P1c Detail Analysis
The brine level in the trench was drawn down by 2m to stabilise
at approximately 2.5m below ground surface, pumping was then
continued to maintain a stable water table in the trench, while
brine inflow from the surrounding sediment balanced pumping from
the trench. By the end of the trial the pumping rate required to
maintain a stable brine level had decreased to approximately
130m(3) /day (1.6L/s) as the surrounding material close to the
trench was dewatered.
Two rain events occurred during the P1c pumping trial, the first
on 3 December 2016 (day 2 of the trial) and the second on 5
December 2016 (day 4 of the trial). The magnitude of each rain
event was approximately 20mm, and the effect of rainfall recharge
is observed in rising brine levels measured at monitoring bores
around the trench.
These observations indicate the importance of recharge on the
long-term water balance of the shallow lake bed aquifer.
Observation bores to the northeast of the trench exhibited
significantly greater water table drawdown than the observation
bores to the southwest indicating that the sediment is more
permeable toward the northeast of the trench. Two permeability
zones were applied in the model, a high permeability zone to the
northeast of the trench and a lower permeability zone to the
southwest.
Numerical Flow modelling
A MODFLOW numerical flow model was constructed for each trench
site using Visual Modflow software system (McDonald and Harbaugh
(1988)(1) , SWS, 2011(2) ) based on the geological and
hydrogeological data for each site.
The models were calibrated to the pumping flow rate and water
table drawdown measured during each test. These calibrated models
provide estimates of the hydraulic properties of the Lake Bed
Sediments which will be used to inform the Pre-Feasibility Study
for the project.
The models assume consistent hydraulic properties of the Lake
Bed Sediment within the zone of influence of pumping. To date
insufficient data is available to characterise any extended spatial
variability in the geology.
(1) McDonald and Harbaugh (1988), A modular three-dimensional
finite-difference groundwater flow model. USGS. Techniques of Water
Resources Investigations book 6, chapter A1
(2) SWS, 2010, Visual Modflow users Guide, Schlumberger Water
Services
Modelling results
P1a P1c
------------------------------------- ------------- -----------------
Trench Depth 4.5 m 4.5 m
------------------------------------- ------------- -----------------
Trench Length 25 m 50 m
------------------------------------- ------------- -----------------
Total Volume Pumped 557 m(3) 1,240 m(3)
------------------------------------- ------------- -----------------
Duration of Pumping 8.3 days 7.3 days
------------------------------------- ------------- -----------------
Average Flow Rate 67 m(3) /day 170 m(3) /day
------------------------------------- ------------- -----------------
Calibrated Model Aquifer Properties
Permeability 3 m/day 0.3 - 40 m/day
Drainable Porosity 10% 7%
------------------------------------- ------------- -----------------
Table 1: Trench Pumping Trial Overview
The results shown above indicate that the drainable porosity of
the aquifers are very similar while the permeability vary much more
due to the different geological settings of the trenches.
Longer term brine yield
The calibrated models developed for each trench were run for an
extended duration of 1 year to assess the expected longer term
brine yield from a test trench.
For each trench the calibrated model was run for a range of
rainfall recharge scenarios:
a) no recharge,
b) 10% of annual rainfall (22mm)
c) 15% of annual rainfall (34 mm).
Trench P1a yielded a total of 8,000 to 9,000m(3) (equivalent to
0.23 - 0.28L/s) over the 1 year simulation for the different
recharge scenarios while P1c yielded 36,000 to 40,000m(3)
(equivalent to 1.1 - 1.3L/s) over the 1 year simulation with the
same recharge scenarios. The difference in lengths (P1a = 25m, P1c
= 50m) did not account for large difference in pumped volume and it
is attributed to the fact that trench 1C is excavated into highly
permeable material.
P1a Long-term Yield
The long term yield of brine into trench P1a stabilised at
20m(3) /day (0.25L/s) for the 25 meter trench.
P1c Long-term Yield
The long term yield of brine into trench P1c stabilised at
105m(3) /day (1.2L/s) for the 50 meter trench.
Planned work
A further long-term pump test at Trench P1e is currently being
installed to provide additional brine extraction data, particularly
throughout the high rainfall and recharge seasons. Further test
pits and possibly trenches will also be excavated and logged in the
middle and northern parts of the Lake.
Meanwhile, off-lake aircore and mud rotary drilling of deeper
paleochannel aquifer targets continues. A further on-lake drilling
and test pumping program aimed at deeper paleochannel aquifer
targets is also planned.
Competent Persons Statement
The information in this report that relates to Exploration
Results for Lake Well's trench program is based on information
compiled by Mr Ben Jeuken, who is a member Australian Institute of
Mining and Metallurgy and the International Association of
Hydrogeologists. Mr Jeuken is employed by Groundwater Science Pty
Ltd, an independent consulting company. Mr Jeuken has sufficient
experience, which is relevant to the style of mineralisation and
type of deposit under consideration and to the activity, which he
is undertaking to qualify as a Competent Person as defined in the
2012 Edition of the 'Australasian Code for Reporting of Exploration
Results, Mineral Resources and Ore Reserves'. Mr Jeuken consents to
the inclusion in the report of the matters based on his information
in the form and context in which it appears
For further information please visit www.saltlakepotash.com.au
or contact:
Matt Syme/Sam Cordin Salt Lake Potash Limited Tel: +61 8 9322 6322
Colin Aaronson/Richard Tonthat/Daniel Bush Grant Thornton UK LLP (Nominated Adviser) Tel: +44 (0)207 383 5100
Nick Tulloch/Beth McKiernan Cenkos Securities plc (Broker) Tel: +44 (0) 131 220 6939
The information contained within this announcement is deemed to
constitute inside information as stipulated under the Market Abuse
Regulations (EU) No. 596/2014. Upon the publication of this
announcement, this inside information is now considered to be in
the public domain.
This information is provided by RNS
The company news service from the London Stock Exchange
END
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