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Mulga Tank potential firms further for Western Mines

Updated: Apr 30

Western Mines Group core nickel sulphides from Mulga Tank. Credit: File

Western Mines Group has revealed that analytical testwork comparing aqua regia and four-acid digests on samples from a shallow 130m nickel sulphide intercept at its promising Mulga Tank Complex show better than a 98 per cent similarity in nickel dissolution.

The company says good recovery and remarkable grade homogeneity of the disseminated nickel sulphides were shown in both methods. It believes it can now consider a future review on the feasibility of open-pit mining, potentially to as deep as 250m, preceded by straight-forward, low-cost pre-strip of overlying sands.

Management selected 94 diamond-core samples from hole “MTD026”, covering the full extent of the intercept from between 116m to 246m downhole. Sample lengths were mostly 1m or 2m long.

The company’s original analysis of the intercept showed an average of 0.31 per cent nickel, 136 parts per million cobalt and 122ppm copper and included a higher-grade zone of 13m at 0.35 per cent nickel, 142ppm cobalt and 301ppm copper, from 157m.

In the dissolution testwork, the aqua regia digest yielded an overall average grade across the 130m intercept of 0.3 per cent nickel, 132ppm cobalt and 121ppm copper, while the four-acid digest showed an overall average grade of 0.305 per cent nickel, 136ppm cobalt and 122ppm copper.

Management says the nickel in the samples is predominantly associated with sulphide mineralisation, as opposed to being tied up in silicate minerals, and that the material appears to be amenable to conventional processing, with the potential for high levels of recovery.

This basic comparison testwork has now been completed on five holes showing significant intersections of disseminated sulphide mineralisation and attempts to further prove the disseminated nickel mineralisation at Mulga Tank is hosted in potentially recoverable sulphide form - these very positive results clearly demonstrate it likely is. We’re conscious of exploring by economics and deliberately selected shallow intervals found in the top few hundred vertical metres that could be amenable to a large-scale open pit scenario. The drilling results to date show the potential for the Mulga Tank Complex to host large volumes of nickel in sulphide form. Western Mines Group managing director Dr Caedmon Marriott

The company also notes that the four-acid attack is marginally more effective at achieving total dissolution of the sample material and freeing up the metals. It says the remarkable similarity of the original analytical data to the dissolution results goes some way to demonstrating the homogeneity of nickel and other metal grades in the sample material.

The revelations come just a day after Western Mines released highly-encouraging results from the same hole at Mulga Tank, which sits within the Minigwal Greenstone Belt in Western Australia’s Eastern Goldfields region. Results show an almost continuous 840m run of mineralisation containing eight broad intercepts of disseminated nickel sulphide mineralisation that range in individual downhole widths from 32m to 258m, with grades ranging from 0.24 per cent to 0.40 per cent nickel and an overall average grade of 0.31 per cent.

The hole was drilled to a total depth of 1548.3m at a dip of about 75 degrees. It means that in the undeformed, right-way-up structure of the Mulga Tank ultramafic lopolith, reported intercepts are likely to be close to true thickness.

The company says the intercept corresponds well with similar mineralisation at the same depth found in previous drillholes. It now believes it forms a section line across the complex over a horizontal distance of about 2.3km, where potentially economic near-surface disseminated nickel mineralisation exists to a vertical depth of about 250m beneath an average of about 60m of sand cover.

Management had already considered the zone to be amenable to large-scale open-pit mining.

The company elected to compare digest methods to determine the proportion of nickel mineralisation associated with sulphide and potentially iron, relative to the proportion of nickel in silicate, which is usually unrecoverable during processing.

Aqua regia is a partial digestion technique using nitric and hydrochloric acid. It is a less aggressive method than four-acid attack and does not dissolve silicate minerals, meaning that silicate-associated nickel minerals, such as those that occur in olivine, are not dissolved to any significant degree and total nickel results will most likely be erroneous.

Four acid digestion uses a combination of nitric, perchloric and hydrofluoric acid with a final dissolution stage using hydrochloric acid. It breaks down most silicate and oxide minerals, allowing for a near-total analysis of most minerals and provides a better total result.

Early drilling results from the project show multiple long sulphide intercepts that not only point to the potential for Mulga Tank to host massive volumes of conventionally-treatable disseminated nickel sulphides, but also open a new possibility for the project, where the economics of any envisaged mining might be significantly enhanced.

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