First Au Limited (ASX:FAU) has been undertaking additional test work on its Gimlet project near Kalgoorlie in Western Australia, to advance the project through demonstrating its economic potential.
The test work has demonstrated high recovery rates from the treatment and processing of gold bearing materials from Gimlet.
The testing that has been completed to date has demonstrated gold recovery rates of 87.99%.
The current phase of the Gimlet testwork program was initiated to determine various metallurgical parameters relevant to gold extraction, and was a follow-up to previous test work carried out by IMO Metallurgy in July 2019.
FAU engaged Upside Metallurgy to oversee the current phase of metallurgical test work conducted by ALS Metallurgy, to further explore suitable processing options for the Gimlet project.
A master composite sample was prepared utilising diamond drill core.
The master composite was split into two composites, where the first was subject to comminution (reducing the sample material to smaller fragments) test work, and the second to recovery test work.
Both Abrasion Index and Bond Ball Work Index tests made up the comminution phase of test work.
The recovery testwork program was designed to explore the potential recovery that could be achieved using a flotation and oxidative leach process route.
The testing involved initially using flotation to produce a flotation concentrate, which was then subject to oxidative leach and subsequent cyanide leaching.
The flotation tail was subject to gravity concentration and subsequent cyanide leaching to determine if leaching the flotation tail would increase recovery rates.
The principal findings were:
- Comminution test work showed that Gimlet is a relatively soft ore (13.3kWh/t) and has a very low Bond abrasion index (0.0129)
- The gold feed grade of the composite sample subjected to recovery testwork was 4.85g/t
- Flotation of the ore produced a concentrate gold grade of 33.16g/t, with a stage recovery of 91.93%. Mass pull to the concentrate stream was 13.44%
- The flotation tail stream, which was subject to gravity concentration and subsequent gravity tails leaching, contributed to 2.4% of overall recovery
- The oxidative and subsequent cyanide leach stage recovery was 93.0%
- The combined flotation, oxidative and cyanide leach recovery was 85.50%
- The combined overall recovery (Flotation + Oxidative Leach + Flotation tailings cyanide leach) was 87.99%
- The final tail grade achieved was 0.58g/t
FAU will consider further metallurgical testing to determine the optimal gold recovery processing route in the oxidative leach and cyanide leach stages which has the potential to increase recovery rates.
In addition to the metallurgical works undertaken, FAU has also assessed other areas of the project.
The company has engaged consultants to undertake preliminary modelling of open-pit design and underground mining options.
These works are early stage and based on a limited amount of geotechnical and hydrogeological information, however, it has proven useful in identifying future options to move the project forward.
As part of the preliminary optimization works, FAU has also undertaken a review of the existing resource model.
The review has highlighted areas of potential upside to the existing resource, particularly to the north end of the resource where FAU believes it is open at depth below 90m.
The company sees further opportunity for exploration success at Gimlet and is also encouraged by the recent exploration success of Horizon Minerals along strike within the Binduli-Teal area.
FAU has undertaken a review of the exploration potential within the tenement outside the resource area, with several target areas identified for a future aircore drilling program.