Visible sulphide mineralisation has been intersected in diamond drill core for the first time at Impact Minerals’ (ASX: IPT) Little Broken Hill Gabbro and Red Hill prospects within its Broken Hill nickel-copper-platinum group element project in New South Wales.
A hole at Little Broken Hill Gabbro was drilled between two traverses of earlier reverse circulation drilling where the company discovered “very encouraging” mineralisation over at least 1,500m of strike within the “very poorly explored” basal ultramafic unit.
Standout results 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, including 1m at 2.3g/t 3PGE, 0.4% nickel and 0.2% copper from 73m and 1m at 2.6g/t 3PGE, 0.7% nickel and 0.2% copper from 79m.
The hole intersected the basal 95m of Little Broken Hill Gabbro comprising 71m of gabbro which overlies the target basal ultramafic unit believed to be 24m thick.
The entire ultramafic unit contains trace to 1% disseminated sulphide with a zone of more intense blebby and vein sulphide (comprising pyrite, pyrrhotite, chalcopyrite and pentlandite in decreasing order) from 95m to 98m down hole.
Impact managing director Dr Mike Jones said first impressions confirmed potential for the basal ultramafic unit to host a significant massive sulphide deposit or a PGE-dominant low sulphide deposit.
“It is great to get a first look at the high tenor PGE-dominant mineralisation at the base of Little Broken Hill Gabbro,” he said.
“The textures indicate the mineralisation is directly associated with magmatic processes at the base of host ultramafic unit and which have the potential to form a massive sulphide deposit in the right trap such as a basal channel structure as we have already discovered at Platinum Springs.”
Assays have been pushed back to August due to current delays in laboratories across the country.
Impact’s previous exploration work has shown the Little Broken Hill Gabbro prospect to be of similar size, age, chemical composition and in the same geodynamic setting as the giant Jinchuan nickel-copper-PGE deposit in China which hosts 550 million tonnes at 1.1% nickel, 0.7% copper and 0.5g/t PGE.
This latest round of exploration represents the end of the first scout phase of drilling at the prospect and the results are considered to be “very encouraging” for the discovery of a Jinchuan-style deposit.
“It is evident that there is potentially a very large inventory of metals contained within the target basal unit and extensive follow-up drilling is clearly required at many places,” Dr Jones said.
Red Hill drilling
At Red Hill, two diamond holes were completed to follow-up a standout drill intercept in January to test the southern contact of the Red Hill chonolith intrusion.
One of the holes returned a best result of 138m at 0.3g/t 3PGM (palladium-platinum-gold) from surface with higher-grade intercepts of 2m at 2.3g/t 3PGE from 75m, and 12m at 1.5g/t 3PGM and 0.2% copper from 103m, which includes 2m at 2.3g/t 3PGM, 0.3% copper and 0.3% nickel from 109m, and 2m at 1.1g/t 3PGM and 0.2% copper from 135m.
Impact said the holes intersected the basal contact of the intrusion at a depth of about 450m below surface, with evidence of trace to 1% disseminated sulphide (predominantly pyrite) in many places throughout.
The depth and shape of the Red Hill intrusion was estimated prior to drilling using magnetic inversion modelling which suggested the intrusion was very steeply dipping.
Drilling intersected the contact at a shallower level than anticipated from the model and indicates the intrusion likely has a shallower north-east plunge and is still open at depth.
A revision of the magnetic inversion model using the new information will now be conducted to help confirm this.