Impact Minerals looks to be zeroing in on the source of the nickel-PGE mineralisation at its Little Broken Hill Gabbro discovery in western New South Wales, with diamond drilling returning a 100-metre-thick intercept containing up to 5 per cent iron sulphide. Intriguingly, the intercept contains a 50m-wide zone of anomalous copper mineralisation the company says bears the hallmarks of the mineralised halo surrounding the massive Voisey’s Bay nickel-copper-cobalt deposit in Canada.
Impact’s initial evaluation of the drill core, utilising geological logging and a portable XRF analyser, has revealed the presence of sulphides with magmatic textures that kick at up to 500 parts per million copper, indicating the presence of both pyrite and chalcopyrite in the system. These magmatic sulphides are regarded as gauges of “sulphide saturation”, an important precursor for the formation of large-scale nickel-PGE mineralisation in mafic-ultramafic intrusions around the world.
Impact Minerals Managing Director, Mike Jones said:
“To find such a thick zone of copper-bearing magmatic sulphides where anticipated close to our interpreted feeder zones is a tremendously exciting step forward in our exploration at the Little Broken Hill Gabbro. We now have pretty strong evidence that sulphide saturation was reached within the intrusion thus potentially leading to the deposition of massive sulphides in or around the entry point to the magma chamber.”
“Such an entry point is likely to lie at depth around one of the feeder zones, similar to Voisey’s Bay, and this has now helped identify areas for more focused work and follow-up drilling.”
Impact’s exploration has now delineated the mineralised ultramafic unit within the Little Broken Hill Gabbro over more than 1,600m of strike that remains sparsely tested by drilling. Both geophysics and stratigraphic drilling indicate the target lithology is about 180m below surface, with shallow drilling having already returned a string of promising intercepts including 61m at 0.4 grams per tonne 3PGE from only 31m down-hole. The tenor of this mineralisation could be a sign of what lies at depth.
Impact’s previous drilling deep drilling indicates the host sulphidic unit is about 25m thick, leaving significant area in which to develop a significant nickel-copper-PGE deposit.
The company says its discovery, east of the famed Broken Hill mining centre, shares key characteristics with a number of world-class disseminated sulphide nickel-PGE deposits, including a similar-sized footprint, age of formation, chemical composition and structural setting.
Examples of this style of deposit include the massive Jinchuan nickel-copper-PGE deposit in central China that boasts an endowment of more than 550 million tonnes of ore grading 1.1 per cent nickel, 0.7 per cent copper and 0.5 g/t PGE.
The other ‘type’ example of this mineralisation is the revered Voisey’s Bay on the east coast of Canada, discovered in the early 1990s and later purchased by base metals miner Inco in 1996 for C$4.3 billion.
Voisey’s Bay carries resource grades of more than 1.6 per cent nickel and 0.9 per cent copper and now pushes out about 6,000t of nickel-copper concentrate per day.
Curiously, whilst only a handful of Impact’s drill holes have penetrated the basal target unit in the Little Broken Hill gabbro, all the holes have returned anomalous nickel, copper and PGE mineralisation. These results hint at a very large endowment of base and precious metals within the host stratigraphy and provide impetus to accelerate the company’s discovery program in the region.
With samples already in the lab from diamond drilling and Impact offering up the potential for a large-scale nickel-PGE discovery in the sulphide-rich Broken Hill terrane, the company is now preparing to step up its activity in an emerging nickel province with EM crews set to hit the ground in the weeks ahead.
That is likely to pave the way for a return to drilling later this year.
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By Matt Birney
