Perth-based explorer Trigg Mining (ASX: TMG) has moved closer to progressing its wholly-owned Lake Throssell sulphate of potash (SOP) project in Western Australia with the completion of a critical lake trenching and test pumping program.
Brine pumping trials from test trenches at the project have demonstrated the abstraction potential of the lake surface aquifer, which would be the target for initial production from a trench network.
The trials aimed to determine the drainable porosity (specific yield) and hydraulic conductivity properties for the upper section of the aquifer.
Two test trenches (each 100m long) and seven test pits were distributed across the current resource, each comprising a small pumping trench up to 9m long and an adjacent monitoring pit.
The trenches were dug using a 15-tonne amphibious excavator and pumped until water levels in the majority of the pits had stabilised over a period of approximately 10-11 days.
Brine quality and levels, as well as flow rates were frequently monitored, and results ranged from 4,610 milligrams per litre potassium (or 10.28kg per cubic metre equivalent SOP) to 6,070mg/L potassium (or 13.54kg/m3 equivalent SOP).
The numbers are believed to align well with the lake surface inferred resource grade of 4,867 mg/L potassium (10.85kg/m3 of equivalent SOP).
Upgrading the resource
Trigg confirmed brine extraction from the trial trenches and pits showed drainable porosity and hydraulic conductivity properties support the modelling required to upgrade Lake Throssell’s maiden mineral resource announced in May of 14.2 million tonnes drainable SOP at 4,638mg/L potassium (10.34kg/m3 equivalent SOP).
Test pumping results identified a “highly heterogenous” lake system with specific yields ranging from 0.1 to 0.4 and hydraulic conductivity from 0.1m/d to 340m/d.
The high numbers are believed to correlate with gypsum-dominated zones, while the low numbers relate to clay-dominated areas.
Trigg managing director Keren Paterson said testing will pave the way for the completion of resource estimation work this quarter and will underpin the project’s scoping study.
“This is a significant and encouraging milestone that provides further evidence that we have a very large and potentially company-making asset at Lake Throssell,” she said.
“The program has delivered highly encouraging results and provided valuable data on the key characteristics of the surficial aquifer.”
Lake Throssell is located 170km east of Laverton on the Great Central Road connecting Laverton, WA to Alice Springs in the Northern Territory.
The high-grade project covers 694sq km of granted and pending tenements comprising 190sq km of salt-lake playa and 70km of underlying interpreted palaeochannels.