Western Mines Group’s (ASX: WMG) understanding of its Mulga Tank project in Western Australia’s Eastern Goldfields has taken a leap forward with new drilling data confirming its interpreted komatiite channels are likely to host high grade Kambalda-style nickel sulphides.
The company’s latest five reverse-circulation (RC) drillholes comprise Western Mines’ first regional foray outside its extensive Mulga Tank disseminated and massive sulphide nickel complex in the Minigwal Greenstone Belt, 190km northeast of Kalgoorlie.
Western Mines' says it now has compelling data including mapping of the geophysical shapes of the thin, channel-like structures radiating from the main nickel complex. It is also poring over data from microscopic rock studies and analytical results typical of high magnesium komatiite rocks that point to fertile nickel, sulphur and metallic sulphide signatures.
The long, thin channel-like structures – the longest of which is nicknamed “The Panhandle” - extend for up to 15km north and northwest from the main complex and have long been a source of intrigue and speculation by the company and scores of interested Mulga Tank watchers.
After a concentrated and highly successful drilling campaign at the main deposit over the past 18 months, Western Mines has put all the speculation and theorising to the blowtorch to determine what the curious elongate bodies are and what they might mean for the project.
The most impressive figures came from a drillhole designated EIS6 that intercepted 100m at 0.24 nickel, 132 parts per million (ppm) cobalt, 49ppm copper and 23ppb platinum-palladium from 163m. The best included intercept in that interval is 4m at 0.43 per cent from 195m.
A second deeper run in the EIS6 drill hole comprises 54m at 0.28 per cent nickel from 273m, with a best included intercept of 4m at 0.36 per cent nickel from 319m.
Drilling at the adjacent EIS7 hole intercepted 55m at 0.25 per cent nickel, 128ppm cobalt, 91ppm copper and 21ppb platinum-palladium from 156m, including 10m at 0.32 per cent nickel from 195m. It also had a separate intercept of 173m going 0.22 per cent nickel from 215m, including 4m at 0.33 per cent nickel from 329m.
Four of the five new RC drill holes were co-funded by a $98,000 WA Government Exploration Incentive Support grant that provided 50 per cent of the direct drilling costs to explore the channel structures and the interpreted rock types of the regional-scale greenstone belt.
The additional five-hole program comprised a 1411m regional component of the company’s Phase-3 RC program which targeted the possible komatiite channels - interpreted from aeromagnetic imagery – that are also associated with mobile magneto-telluric (MT) geophysical anomalies.
All five holes successfully confirm the interpreted geology, with olivine cumulate/dunite and komatiite and/or high magnesium oxide mafic rock types encountered in all of the holes and visible sulphide mineralisation seen in both of the EIS6 and EIS7 drillholes.
With the help of an Exploration Incentive Scheme grant we set out to test our hypothesis and the geological interpretation of the Minigwal Greenstone Belt - largely based on aeromagnetics, as we’re under sand cover. The holes were successful in that they confirm komatiite and olivine cumulate lithologies, geochemical assays demonstrate a high MgO fertile environment and abundant visible sulphide mineralisation was encountered which mineralogical investigation confirms as pentlandite. I’d say these are quite remarkable results.
Western Mines’ Managing Director Dr Caedmon Marriott
Komatiites are among the most ancient lavas, representing some of the oldest ultramafic magmatic rocks preserved in the Earth’s crust and may be around 3.5 billion-years-old in some examples.
Komatiite-hosted nickel sulphide deposits represent some of the world’s biggest nickel deposits and are often of higher grade than intrusion-related or lateritic nickel deposits. WA hosts several world-class examples of komatiite-hosted nickel sulphide deposits such as those at Kambalda, Mt Keith and Perseverance.
The two important classes of Archean iron-nickel-copper sulphide deposits in WA are those hosted by coarse-grained adcumulate dunites such as at Agnew and Mount Keith – or otherwise by komatiitic lavas such as at Kambalda.
Western Mines’ holes EIS6 and EIS7 were collared side-by-side, about 4.2km north-west of the western margin of the main complex, as a fence across a 1.5km-long highly-magnetic zone within the longest of the interpreted channels which forms The Panhandle.
The holes were drilled to 342m and 388m down-hole depths.
Western Mines’ previous drilling of three diamond holes within The Panhandle and one historical diamond hole encountered multiple zones and types of komatiite rocks and expectations were high for similar successes which proved forthcoming.
Hole EIS6 intersected about 250m of altered komatiite units that indicate a potentially fertile nickel sulphide environment, as demonstrated by logged intervals of disseminated sulphide mineralisation and remobilised sulphide veining.
Hole EIS7 was drilled to a depth of 388m and also intersected about 300m of altered olivine cumulate, with disseminated sulphide mineralisation logged over about half of the length of the hole.
Analyses from EIS6 averaged a relatively high magnesium oxide content of 43.1 per cent and 1.56 per cent alumina over the 276m ultramafic part of the hole, while EIS7 revealed a 46.4 per cent magnesium oxide content and 0.58 per cent alumina over 313m of ultramafic rocks.
Western Mines says the geochemical results show broad intervals of high temperature, high magnesium oxide adcumulate olivine cumulate for the majority of the holes, indicating a potentially fertile environment for nickel sulphide mineralisation.
Those broad zones are interspersed with narrow flows of lower temperature, higher alumina komatiite, running about 2 per cent alumina.
Importantly, several nickel sulphide mineralised intersections are noted within the broad, high magnesium oxide target zones and are generally defined by a combination of various geochemical indicators.
These include considerations such as nickel greater than 0.15 per cent and sulphur more than 0.1 per cent, with copper greater than 20ppm and platinum-palladium combined to yield more than 20ppb, along with a sulphur to nickel ratio of more than 0.5.
The single non-grant funded RC hole was drilled 2km north of the complex into a small magnetic high that appears disconnected from the main complex body.
It intercepted two intervals each of about 30m length exhibiting low temperature komatiite with magnesium oxide in the range of 20-25 per cent which seems to indicate a narrower, smaller volume of material that cooled more rapidly.
The other two EIS holes (EIS 4 and 5) were drilled into two separate smaller magnetic highs on two separate interpreted channel structures between about 1km and 2km long and about 6.2 and 4.9km northwest respectively of the western margin of the main complex.
Hole EIS4 appears to be similar to the above non-grant funded hole, encountering two 20-30m thick low temperature komatiite flows with magnesium oxide in the range of 20-25 per cent.
Hole EIS5 analyses appear more consistent with basaltic geology logged in the field as opposed to the more prospective ultramafics, which is interesting, given its channel-like morphology.
Geochemical assays have now been received for the five holes and petrological investigation has also been undertaken on several samples from the EIS6 and EIS7 holes which confirm the presences of the high grade nickel sulphide mineral pentlandite.
Western Mines' technical director Dr Ben Grguric has also completed mineralogical thin section work on samples from the same two EIS holes to characterise the rock types and the sulphide species observed in the holes and has confirmed pentlandite as the main species present.
Similar channel-like bodies up to 4km further northwest from those drilled recently appear to be continuations of the same potential host rocks drilled in the recent program, with packages of high magnesium komatiite rocks which could be up to 300m thick.
Confirmation of a potentially viable fertile nickel-bearing komatiite system in the regional zone around the major Mulga Tank nickel complex is a major boost to the company’s understanding of the layout of the entire complex and geological events leading to its overall development.
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