Blackstone said the discovery included near-surface downhole intervals of up to 60m and visual estimates of up to 20% sulphide mineralisation.
King Cobra features the first-ever intersection of massive sulphide vein and breccia styles of sulphide mineralisation within the Ban Phuc, with Blackstone hopeful the intrusion may provide vectors towards the high grade "feeder zone" mineralisation.
"We feel that the discovery of the King Cobra zone is a step change for exploration of the deposit," Blackstone said.
"A substantial thickness of disseminated and potentially higher-grade nickel-PGE mineralisation within a few metres of surface may prove to be a bulk mineable opportunity."
Blackstone aims to deliver a maiden resource on the disseminated nickel sulphides at Ban Phuc "over the coming months", with the junior saying it would investigate the potential to restart the existing Ban Phuc concentrator through focused exploration on both the massive sulphide and disseminated sulphide mineralisation.
Mining by the previous project owner earlier this decade focused only on the massive sulphide mineralisation.
Blackstone started the December quarter with A$5 million cash, having raised about $4.5 million late in September by issuing new shares priced at 15c each.
Shares in Blackstone gained 9% to 12.5c in early trade, capitalising the company at $24 million.