Drilling at the Little Broken Hill Gabbro target within Impact Minerals’ (ASX: IPT) wholly-owned Broken Hill copper-nickel-platinum group elements project in NSW has intercepted a 100m zone of sulphide mineralisation, with a 50m interval containing copper.
The zone of disseminated to blebby magmatic iron sulphides (up to 5% pyrite) sits within a strongly-magnetic gabbro unit close to an interpreted feeder zone and contains a 50m-thick intercept with up to 500 parts per million copper.
Feeder zones are believed to be reliable indicators of copper-nickel-PGE mineralisation in major deposits globally.
The presence of magmatic sulphides with copper is considered to be an important indicator of “sulphide saturation”, which is a key requisite for the formation of large copper-nickel-PGE deposits within mafic and ultramafic intrusions.
The discovery is believed to be part of an outer halo of sulphide surrounding a copper-nickel-PGE massive sulphide deposit along trend or at depth.
A similar halo is present around feeder zones at the Eastern Deeps deposit within the world-class Voisey’s Bay system in Canada.
It is possible that the new sulphide zone at LBHG has intersected an outer halo of disseminated sulphide and further drilling could provide vectors to the ultimate target of massive sulphide.
‘Exciting step forward’
Impact managing director Dr Mike Jones said the discovery of a thick zone of copper-bearing magmatic sulphides near to feeder zones has been “an exciting step forward” in the company’s exploration at LBHG.
“We have fairly strong evidence that sulphide saturation was reached within the intrusion, potentially leading to the deposition of massive sulphides in or around the entry point to the magma chamber,” he said.
“Such an entry point is likely to lie at depth around one of the feeder zones, similar to Voisey’s Bay, and this has helped us identify areas for more focused work and follow-up drilling.”
Basal unit extension
Impact’s exploration also extended the 25m-thick basal ultramafic unit of LBHG to 1,650m along trend.
The company successfully intersected the poorly-explored unit at 180m downhole, extending it by 150m to the south.
The prospective ultramafic contains up to 0.1% copper as measured with a hand-held XRF (x-ray fluorescence) instrument and the company said there is a likelihood the unit will also carry PGMs.
Impact has previously discovered laterally-extensive copper-nickel-PGE mineralisation in the same location, including visible disseminated nickel-copper sulphides over at least 1,500m of trend.
Best results reported in December and April were 61m at 0.4 grams per tonne 3PGE from 31m, which includes 12m at 1.4g/t 3PGE and 0.2% copper from 73m, and including 1m at 2.3g/t 3PGE, 0.4% nickel and 0.2% copper from 73m and 1m at 2.6 g/t 3PGE, 0.7% nickel and 0.2% copper from 79m.
“There is significant potential for massive sulphides along the entire 7km-long intrusion and we are looking forward to the downhole [electromagnetic] surveys and follow up drilling in the coming months,” Dr Jones said.