Important Preliminary Exploration Target Highlights Large Scale Potential and High Grade of Lake Throssell Sulphate of Potash Project

Lake Throssell Sulphate of Potash Project

Sulphate of Potash Project at Lake Throssell – a Recent High-Grade Find

  • For the emerging Lake Throssell SOP discovery, an initial JORC compliant Exploration Target has been identified.
  • The Exploration Goal encompasses a strike length of 70 kilometres of the interpreted palaeovalley, which is part of a total strike length of 112 kilometres under tenure, which includes neighbouring tenements under application.
  • In the profile, high grades and numerous potential aquifers are encountered, indicating that trenching and deep development bores are feasible.
  •     Additional tenements under application to the north and south of the Exploration Goal    provide excellent potential to increase it.

The Exploration Target shows that Lake Throssell has the potential to become a major, multi-decade SOP production centre, with significant competitive advantages such as proximity to infrastructure and services.
Trigg Mining Limited (ASX: TMG) (Trigg or the Company) is pleased to announce that for its 100 percent-owned Lake Throssell Sulphate of Potash (SOP) Project, located 170 kilometers east of Laverton in Western Australia, it has established an initial Exploration Target of approximately 7.5 to 27 million tons at a grade ranging between 9,000 and 10,000 mg/L SOP equivalent.
The Exploration Target’s future quantity and grade are purely hypothetical. There hasn’t been enough research to come up with a Mineral Resource estimate. Further exploration may or may not result in the estimation of a Mineral Resource.
The Exploration Goal is focused on the results of exploration activities completed to date on granted tenement E38/3065, which covers a 36-kilometer strike length of the interpreted palaeovalley. Extrapolating an additional 34 kilometers of strike length into tenement applications E38/3544, E38/3483, E38/3458, and E38/3537, which are thought to have similar geology and brine characteristics.
“Defining the Exploration Target is a very significant first step towards assessing the value of the enormous opportunity we have in front of us at the Lake Throssell SOP Project,” said Keren Paterson, Trigg Mining’s Managing Director. These preliminary findings are promising and reinforce our belief that Lake Throssell has the potential to host a long-term, low-cost source of primary sulphate of potash for global food security.
There is still room to build on this Exploration Goal, which covers the first 70 kilometers of the 112-kilometer-long interpreted palaeovalley. We will continue to extend our awareness of the potential of this vast high-grade SOP system with the latest air-core drilling program and planned field work.
Lake Throssell is well placed for potential growth, with rail access at Leonora, an airport and commercial mining support at Laverton, and a gas pipeline at Yamarna, which is 20 kilometers to the south of our tenure. The Great Central Road is being upgraded to become the Outback Highway, and we hope that it will hit the mine gate before development begins. The new air-core drilling program has been extended to approximately 50 holes and is progressing well as a result of these very encouraging results. Weather permitting, the program is on schedule to be completed by the end of February, and we expect to receive the assay results four weeks later. These findings would pave the way for our first Inferred Mineral Resource estimate for Lake Throssell, which will be the Company’s second since listing.”
Exploration Goal Overview
The following pages of this announcement contain the initial Exploration Target for the Lake Throssell SOP Project, as well as supporting details and data for the Exploration Target:
The Exploration Target’s future quantity and grade are purely hypothetical. There hasn’t been enough research to come up with a Mineral Resource estimate. Further exploration may or may not result in the estimation of a Mineral Resource.
Summary of Exploration Programs at Lake Throssell So far, the following programs have been implemented:
Drilling with a Lake Surface Hand Auger – 16 holes (December 2019); Gravity Survey – 200 km of survey (May & August 2020); Heli-Rotary Auger Drilling – 26 holes (August 2020); and 50-hole air-core drilling – on-going (due to be completed in late February 2021).
Drilling and sampling with a hand auger
In December 2019, a preliminary lake surface auger program was completed to determine the brine grade in shallow lake sediments. A total of 16 auger holes with a depth of up to 1.2m is completed.
The holes found a typical lake surface sequence of gypsum, silt, and clay, with brine at around 0.3 meters below ground level (bgl). About 0.3m and the end-of-hole, brine samples were taken from each hole.
The highest result was 6,660mg/L potassium (14,800mg/L SOP equivalent) in the brine study, suggesting the presence of high-grade SOP in the lake surface.
Figure 1 depicts the collar sites, while Appendix 1 contains the brine assays and related geological details.
Geophysical Gravity Survey
In May 2020, a preliminary ground gravity survey was completed, followed by an infill survey in August 2020, with the aim of identifying drilling targets within the palaeovalley system as a first step toward identifying a palaeochannel basal aquifer to target with potential output bores.
The surveys included 1040 stations spaced approximately 200 meters apart on traverses perpendicular to the palaeovalley’s assumed alignment. Gridding the Bouguer anomaly and regional separation from the Bouguer anomaly were used to create a residual gravity anomaly that is thought to reflect the large palaeovalley geometry.
The gravity highs are well associated with mapped outcropping Paterson as compared to established geology. Within the Throssell palaeovalley system, formation and gravity lows are found within areas of low-lying regolith cover, providing trust in the regional model and a general understanding of comparative palaeovalley in the region.
Drilling and sampling with a rotary auger
The program was completed in July 2020 with the use of a heli-rotary auger rig that targeted the top sequence of potentially trench-able lake surface sediments to a maximum depth of 10 meters. The software used 26 drill holes to collect deeper brine samples and core samples for porosity testing around the entire playa-lake floor. Figure 1 shows the positions of the drill holes.
In the top 5 meters, the program encountered gypsum-dominated sandy silt and clay. The gypsum layers were up to 0.2m thick, and they were often correlated with strong to excellent brine in-flow rates, implying that these zones were more permeable.
Three holes had minor sand and gravel layers, with one (LTAG19) containing a clay/silt backed sand interval of at least 1.3m with rounded pebbles. Below 5m, a clay-dominated series with less gypsum and rising density is present.
Two holes were planned as part of the program to measure the characteristics of the surficial series within the islands (LTAG04 and LTAG05). Drilling and brine analysis have confirmed a lack of brine flow, implying that these areas have lower permeability and lower grade brine.
Throughout the drilling process, core samples were collected in Lexan tubes for laboratory sampling and analysis of porosity and permeability.
During the program, brine samples were collected by bailing the hollow stem of the auger at a known interval to provide a representative sample.
From the end-of-hole to around 0.3m below ground level, brine was commonly found. The rotary auger program’s brine analysis yielded grades of up to 6,520 mg/L potassium (14,500 mg/L SOP equivalent), with an average of 5,070 mg/L potassium (11,300 mg/L SOP equivalent), which are comparable to the hand auger brine analysis. Appendix 1 contains a summary of collar positions, hole depths, encountered geology, and brine analysis.
Drilling with an air core
The air-core drilling program began in late November to test aquifer targets identified by the gravity survey at the base of the palaeovalley series. The palaeovalley’s deepest sections are thought to be the most promising for sand and gravel aquifer sequences deposited in a palaeochannel climate.
The drill program was delayed due to rainy weather, with 16 holes drilled prior to a weather break on December 21st for a total of 1,806m to a maximum depth of 130m (Figure 1 and Appendix 1), according to an ASX announcement dated December 21st, 2021.
The completed holes are in the northern portion of the central tenement E38/3065, and they have confirmed the existence of a large palaeovalley system about 100 meters deep with a range of deep aquifer targets of varying thickness.
The program’s brine analysis revealed that the basal sediments contain brine with a similar composition and grade to the surficial sediments, with an average brine grade of 4,386 mg/L potassium (9,780 mg/L SOP equivalent) to date, according to an ASX announcement dated January 22, 2021.
The latest and extended drill program, consisting of 50 holes, is scheduled to be completed by the end of February, providing further evidence of the geology and brine grade distribution on the E38/3065 tenement’s western and central ends.
Summary of Geological Information
Table 1 below gives a rundown of the geology encountered so far on the project.
Other lakes and palaeovalley sequences in the area have similar geology. A gypsum-dominated evaporite surface is overlain by clayey-dominated sequences with occasional thin granular and concrete zones.
These are on top of a thick sequence of stiff lacustrine clay, which serves as a regionally confining aquitard with very low vertical hydraulic conductivity, separating the palaeovalley’s upper and lower sediments hydraulically.
A low-energy fluvial system of silty fine sand with clay bands, with occasional layers of less silty sand, lies underneath the lacustrine clay series. The Paterson Formation, of Permian age, is present in the base of the palaeovalley as unconsolidated glacial fluvial sediments of mixed gravel, sometimes with a silty matrix, at the base of this low energy fluvial system of Eocene age.
A saprolite zone of weathered bedrock, including Permian and Proterozoic sandstone, quartzite, and mudstone, lies underneath the unconsolidated fluvial glacial deposits. Figure 3 depicts a schematic cross-section of Lake Throssell.
Table 1 shows the aquifer potential of each stratigraphic layer to provide an indication of brine abstraction potential; however, test pumping of each of the aquifer zones is needed to validate their potential. Trenching can be used to target the lake’s surface in the future, while development bore goals include Eocene fluvial sediments, Permian glacial fluvial sediments, and saprolite.
Table 1: Current Interpreted Geological Stratigraphy at Lake Throssell
Characteristics of Brine
The popular hand auger and heli-rotary auger drill programs yielded enough samples to map brine potassium concentration across the lake surface.
The average potassium concentration in the surficial sediments is approximately 5,118 mg/L (11,410 mg/L equivalent SOP), with the lowest concentration at LGA26 of 2,810 mg/L (6,270 mg/L equivalent SOP) and the maximum concentration at LT016 of 6,660 mg/L (14,850 mg/L equivalent SOP).
The deep air-core brine analysis software is currently restricted to Lake Throssell’s northern reaches. Importantly, the potassium concentration and brine characteristics found so far are similar to those found at the lake’s surface, suggesting a continuous brine pool with slight dilution at depth.
With a low Na:Mg ratio and a high SO4 concentration, the brine chemistry is favorable for solar evaporative concentration and lower waste salts. The findings also indicate that the down-hole potassium grade profile inside individual drill holes is fairly stable, with some slight potassium reduction and magnesium increase.
Table 2 shows the main average characteristics of the brine based on the sampling done so far at Lake Throssell.
Table 2: Key Average Brine Characteristics of Lake Throssell
Note – all concentrations based on average of all samples obtained to date and not spatially weighted. SOP is calculated from k x 2.23.
Specific Yield and Porosity
Total porosity determines the total amount of brine in a deposit, while porosity is made up of particular retention (also known as retained porosity) and specific yield (also known as effective porosity). The percentage amount of water that can be drained by gravity from a saturated volume of sediment is known as specific yield. The percentage volume retained under gravity drainage is known as precise retention. The basic yield is a ratio that is used to determine how much of a brine deposit can be drained. In addition to the specific yield, portions of specific retention in the lake surface are available, but additional modifying factors around lake recharge effects must be calculated before quantification.
Core plugs collected from the Lexan tubes during the heli-rotary auger program were used to calculate total porosity and precise yield in the laboratory.
The saturated centrifuge method was used to analyze core plugs of lake surface sediments taken at Corelabs in Perth. With an average total porosity of 38.1 percent and an average individual yield of 17.2 percent, the findings show that the sequence is relatively consistent in the profile. Table 3 summarizes the findings.
Table 3: Total Porosity and Specific Yield Estimates
The Exploration Target’s Foundation
The Exploration Goal is a prediction of a mineral deposit’s exploration potential. The Exploration Target calculates a lower and upper estimate for a brine-hosted deposit by varying the geological extent, drainable porosity, and brine grade within acceptable bounds using the information provided in this study.
A combination of the geological description in Table 1, the gravity model, the mapped outcropping geology, and the conceptual model of regionally defined palaeovalley systems is used to assess the geological extent (area and thickness).
The lake surface has been cleared of islands, and the amount of alluvial clay sediment has been calculated. The brine grade range has been factored for the pending tenements where no data is currently available and is based on the average brine grades as shown in Table 2 for the upper and lower estimates.
Drainable porosity was derived from the core analysis in Table 4 from unique yield for the surface sediments, while appropriate estimates based on the lithological descriptions encountered during deep air-core drilling were given for all other stratigraphic units (as recommended by the AMEC Brine Guideline).
The Exploration Goal includes the granted tenement E38/3065 as well as the nearby pending tenements that are currently being applied for. Since no work on the pending tenements has been done, all figures are focused on extrapolation from the work completed on E38/3065. Trigg sees no reason why these tenements will not be issued in the future at the time of publishing.
Due to the relatively unknown existence of the geology, brine grade, and precise yield in the pending tenements, the Exploration Goal has a wide range. In contrast, the granted tenement, especially the lake surface on the granted tenement, is relatively well constrained.
The Exploration Target’s future quantity and grade are purely hypothetical. There hasn’t been enough research to come up with a Mineral Resource estimate. Further exploration may or may not result in the estimation of a Mineral Resource.
Table 4: Lake Throssell Exploration Target
Note: Errors may be present due to rounding, approximately 1.8 Mt in the lower estimate and 8.2 Mt in the upper estimate of equivalent SOP is present in Exploration License Applications E38/3544, E38/3483, E38/3458 and E38/3537. SOP is calculated by multiplying potassium by 2.23.
Work in the Future
The air-core drilling program is expected to be completed in February 2021, with additional brine analysis and soil laboratory sample analysis to follow, with the aim of estimating a maiden Inferred Mineral Resource for the deposit.
Subject to permitting, a lake surface test pitting and trenching program is planned for Q2 2021, followed by a water well drilling and testing program for H2 2021 to validate aquifer properties of each of the stratigraphic units. These are the next steps in advancing the mineral resource estimate’s confidence level toward an Indicated Mineral Resource, and they will guide future economic studies.
Exploration activities will be extended into these areas until the tenements under application have been granted, in order to measure the extents of the Exploration Goal.

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