Western Mines Group has notched up another milestone in its intriguing Mulga Tank nickel play with the completion of a grid-based reverse-circulation (RC) program for 7035.5m drilled at an average hole depth of 320m.
The campaign’s 22 holes produced 5721 samples of 1m each in the testing of an extensive, shallow disseminated nickel sulphide zone beneath ubiquitous deep sand cover in the Minigwal greenstone belt north-east of Kalgoorlie in Western Australia’s Eastern Goldfields region.
The samples have been delivered to a Perth laboratory for analysis and the company expects the first results in about a week, with more to come in the next two months.
The RC drilling at the nickel-copper-platinum group elements (PGE) project began in September after Western Mines was prompted by logging and analysis of six diamond drillhole cores that revealed a distinct continuous shallow zone of disseminated nickel sulphide mineralisation across the centre of the Mulga Tank ultramafic complex.
The zone lies beneath the sand cover, which averages about 60m to 70m depth. The deep sand frustrates conventional geochemistry and all but the most determined drilling, which requires techniques that have not always been available to previous explorers.
That goes some way to explaining the limited useful exploration history of the area.
The team have done a great job in completing this 22-hole, 7000m program in just over 6 weeks - successfully dealing with the sand cover that has hampered a number of historical RC programs. The holes targeted a significant portion of the main body of the Complex and will yield extremely valuable data in testing the lateral continuity of shallow disseminated mineralisation, as well as beginning to systematically characterise the geology of the Complex. Western Mines Group managing director Caedmon Marriott.
The RC drilling program was designed to systematically test the depth and lateral continuity of the shallow, weathered or partly-weathered uppermost zone of disseminated nickel sulphide mineralisation observed in the six diamond holes, with two potentially complementary ideas in the company’s mind.
Firstly, reconnaissance mineralogical sampling and powder x-ray diffraction analysis on 13 core samples, taken from above 310m depth in five of the shallower diamond holes, revealed up to 8 per cent brucite and up to 12 per cent hydrotalcite group minerals.
Brucite is a key mineral in the passive carbonation of ultramafic mine tailings at the Mt Keith nickel mine, which sequesters 40,000 tonnes of carbon dioxide from the atmosphere each year.
Secondly, the same zone presents the possibility for open-pit mining of a considerable tonnage of potential disseminated nickel ore. That would require pre-stripping of up to 70m or more of sand cover, including a considerable allowance for pit-wall lay-back, which could be set aside for later rehabilitation, followed by open-pit mining.
The mining could extend to a depth ranging from 250m up to more than 300m, yielding a handy lower-cost initial resource and useful in-pit portal access to any future underground mining.
Clearly, there is much work to do on both possibilities. But to add to the potential upsides, deep diamond drilling is showing that nickel sulphide mineralisation gets better with increasing depth.
The company says the RC holes, which will almost certainly shed more light on the possibilities, were spaced at about 500m-by-300m through an area measuring 2500m-by-1000m area across the centre of the complex.
Each hole was designed to a minimum target depth of about 300m, which was achieved in all but three holes. The top 60m or so of each hole, or 1321m in total, comprised mud-rotary drilling through the sand cover and all samples were taken from the bottom section of the drilling.
Notably, one RC drill hole was pushed on to 522m, with significant disseminated sulphide mineralisation being observed.
Management says the program is the first systematic drilling of the complex and assuming an average drillhole depth of about 320m and 60m of sand cover, it tests an estimated volume of 650 million cubic metres of the central area, or more than 1.5 billion tonnes of rock.
Western Mines says results from the drilling should offer a marked leap in its understanding of the geology of the complex and its potential to host a significant disseminated nickel sulphide deposit amenable to large-scale open-pit mining.
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