Visible nickel sulphides found in four holes during Western Mines Group’s (ASX: WMG) latest drilling campaign at its Mulga Tank complex in Western Australia’s Eastern Goldfields region has added an intriguing new edge to the burgeoning project.
The fresh evidence of potentially wide-spread sulphides at Mulga Tank comes after the company completed a five-hole program to test what it had interpreted as nickel-bearing channel flows. The campaign represented the first regional drilling to test the extensive north-west-trending channel system – the main part of which forms a distinctive “panhandle” to the main Mulga Tank nickel-rich ultramafic complex near Lake Minigwal, north-east of Kalgoorlie.
Four of the five reverse-circulation (RC) holes were drilled with the aid of one of the company’s two exploration incentive scheme EIS grants.
The panhandle feature stands out in geophysical data as a 15km-long arcuate, linear, “channel-like” feature between 500m and 1km wide, emanating from the principal centre of the Mulga Tank complex for more than 15km. The linear dimension is about three-times the diameter of the entire main centre of the complex, which the company has been exploring with intensive drilling and geophysics in the past two years.
That work has already defined extensive nickel mineralisation and management believes it has the strong potential to become an economic “hybrid” deposit that combines an extensive, shallow disseminated nickel-rich zone and a deeper massive sulphide nickel-rich zone.
The main panhandle initially extends north-westward from the main body of the complex for about 4km before swinging in a 4km-long gradual arc to a new north/north-west direction for the remaining 7km to 8km. It appears in geophysical magnetic data to make and break along its trend and is also is accompanied and partly mirrored by a parallel 10km-long sinusoidal trend that sits about 500m to 1.2km to the east of the main channel.
Another separate 5km-long channel branches off to the north/northwest from the main complex and gently curves to the north-east. Additionally, at least four distinctive short channel-like bodies – each about 1.5km long – are arrayed between about 1.5km to 2km to the east of the previously described north-trending channel, north of the main complex.
Management believes the suite of short bodies could indicate a set of sub-parallel repetitions of mafic or ultramafic intrusives emplaced into a set of parallel structures.
The main goal of this regional drilling was to confirm the interpreted geology of the belt, largely based on aeromagnetics. The holes were successful in that all showed intersections of komatiite, dunite and/or high MgO ultramafic lithologies.
Western Mines Group Managing Director Dr Caedmon Marriott
The company’s four EIS holes have been drilled at various points into the inferred channel system.
The first was drilled to a depth of 246m near the northern extremity of the separate 5km-long north-east trending channel and it intercepted mixed granodiorite, basalts and ultramafic rocks. The ultramafics contain minor disseminated sulphides, while more significant disseminated pyrite was noted in quartz veining on basalt-granodiorite contacts and in altered granodiorites and was sampled for gold.
The second was drilled to 231m at the south-eastern extremity of the sinusoidal parallel channel, about 5km north-west of the main complex, to test a pronounced high-intensity magnetic response thought to represent prospective channel-filling ultramafic rocks. It intersected an alternating sequence of granodiorite and basalt and sulphidic quartz carbonate veining with disseminated pyrite and was sampled for possible gold mineralisation.
The remaining two holes sit side-by-side on the main panhandle, about 4km north-west of the main body of the complex, and were designed to test a distinct magnetic high.
The first hole in the pair was drilled to 342m depth and intersected about 250m of variably-altered ultramafic rocks, some similar to those observed in the main complex. Several intervals of disseminated semi-massive sulphide mineralisation and remobilised sulphide veining were logged.
The second hole was drilled to 388m and intersected about 300m of variably-altered ultramafic rocks similar to those noted in its companion hole, with disseminated sulphide being logged throughout about half of the hole.
A fifth RC hole was put in about 2km north of the main body of the complex on the southernmost of the suite of four intriguing small magnetic signatures, which are interpreted to reflect ultramafic units or channel flows. It intercepted a sequence of granodiorite, basalts and ultramafic rocks, with minor disseminated sulphides being observed in some of the prospective ultramafic intervals.
Western Mines says the findings greatly extend its understanding of the peripheral linear magnetic bodies extending from and surrounding the north-west and northern areas around the main Mulga Tank complex.
The indications of potential gold occurrences on granite-greenstone contacts with associated sulphidic quartz add an interesting fillip to the story as the Mingwal greenstone complex has never been explored for gold with any intensity.
The key finding of the program has been that visible sulphides have been logged in several of the ultramafic units intercepted, which includes about 150m of disseminated sulphide mineralisation in one of the pair of the EIS holes in the main panhandle and also in intersections of semi-massive or remobilised sulphide in its companion hole.
Western Mines views the results, from what are essentially scout lithological test holes, as outstanding and says they highlight the regional belt-scale potential of the Mulga Tank nickel sulphide mineral system.
Analytical results are awaited for all of the holes.
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