Junior explorer Impact Minerals (ASX: IPT) says new assays from first pass reconnaissance drilling at the Little Broken Hill Gabbro (LBHG) target in New South Wales have confirmed the highly-prospective nature of the large and poorly-explored intrusion.
Drill holes were completed at the Rockwell and Western Contact anomalies to test the basal ultramafic unit, and at Central LBHG to look for halos or “leakage anomalies” within the upper gabbro units.
Standout intercepts from Rockwell were 51m at 0.3 grams per tonne gold-palladium-platinum (3PGE) from 140m, including 6m at 0.5% copper, 0.4% nickel and 0.3g/t 3PGE from 154m; and 5m at 0.5% copper, 0.4% nickel and 0.6g/t 3PGE from 161m; and 1m at 0.2% copper and 1.1g/t 3PGE from 186m.
Other results with robust widths and modest grades were 11m at 0.8g/t 3PGE from 101m, including 1m at 1.0g/t and 0.15% copper from 105m; and 11m at 0.3g/t 3PGE from 40m, including 2m at 0.7g/t from 47m, and 18m at 0.1g/t from 245m.
Impact said the results indicate PGE-copper-nickel mineralisation extends to a depth of at least 150m from surface and for at least 1,500m along trend at Rockwell.
“Virtually every drill hole that has penetrated the basal ultramafic unit has intersected anomalous PGE with variably anomalous nickel and copper,” the company noted.
“In all locations, the mineralisation is open along trend and down dip and this is all very encouraging for the potential discovery of a significant nickel-copper-PGE deposit at the base of the LBHG given the very small area tested thus far.”
Three shallow scout holes to test the basal unit at Western Contact were completed over a 1km strike extent, with two returning encouraging anomalous results of 6m at 500 parts per million copper and 0.2g/t 3PGE from 83m, including 2m at 0.3% copper, and 0.2g/t 3PGE from 89m; 3m at 0.1% copper and 0.4g/t 3PGE from 94m; and 7m at 0.3g/t 3PGE from 146m.
The ultramafic unit in the third hole was reported to contain weak 3PGE of up to about 20ppb over its entire 12m width.
Given the wide drill spacing and random location of the holes, Impact said the results confirm the prospectivity of the basal ultramafic unit over many kilometres of strike along the Western Contact target.
The Central LBHG anomaly is on a major west-northwest-trending fault cross-cutting the entire LBHG and interpreted to be a “feeder zone” through which magma migrated from depth into the main intrusion.
These zones are common locations for the deposition of nickel-copper sulphides, such as at the giant Voiseys Bay nickel deposit in Canada.
Central’s feeder zone is believed to be most prospective at depth where it intersected the basal ultramafic unit, and was drilled to test for near-surface halos or “leakage anomalies” originating from massive sulphide bodies buried deeper within the intrusion.
Of 30 holes completed, 12 returned strong results and an area of 1,000m by 500m with anomalous copper and 3PGE was identified over the interpreted feeder zone.
One stand out gold-copper intercept associated with quartz veins in the target feeder zone fault returned 4m at 0.13% copper and 1.5g/t gold from 150m, including 1m at 1.3g/t gold and 0.18% copper from 151m; and 1m at 4.5g/t gold and 0.17% copper from 152m.
Mineralisation at depth
Impact said the results were supportive of more significant mineralisation at depth, in and around the feeder zone.
Modelling of magnetic and gravity data at the LBHG, which is part of Impact’s wholly-owned Broken Hill project, is now underway to determine the likely depth to the base of the intrusion.
The results will guide further drilling and establish the efficacy of a ground electromagnetic survey in identifying conductive zones that may represent massive nickel-copper sulphide deposits.