Impact Minerals identifies ‘very large’ copper halo at Apsley prospect within Commonwealth project
Impact says the halo may be part of a system that is similar to Newcrest’s Ridgeway deposit.
A “very large” halo of copper has been identified in first-pass, widely-spaced reconnaissance drilling at Impact Minerals’ (ASX: IPT) Apsley prospect within the wholly-owned Commonwealth project in New South Wales’ Lachlan copper-gold province.
The company has suggested the halo may be part of the outer zone of a large alteration system around an alkaline porphyry copper-gold deposit similar to Newcrest Mining’s (ASX: NCM) Ridgeway deposit 100km south of Apsley, and Alkane Resources’ (ASX: ALK) Boda discovery to the north.
Both projects are hosted by rocks of the same age and geochemistry as at Apsley.
Halo composition
The halo has been defined at copper values of more than 100 parts per million in continuous zones up to nearly 250m thick and potentially extending over an area of at least 1000 square metres.
It comprises numerous thinner zones up to about 80m thick containing between 200ppm and 250ppm copper and these include thick zones of up to 4,700ppm copper related to narrow quartz-sulphide veins.
The halo is believed to contain widespread low-level molybdenum and constitutes a “significant inventory” of copper.
The different rock types within the halo are variably altered to chlorite, epidote and hematite with lesser biotite and disseminated very fine grained pyrite and weak disseminated copper sulphides.
Impact said there is strong K-feldspar alteration in places and specifically within the first hole which intersected a 60m-thick zone of more intense alteration associated with the porphyry unit.
Drilling program
Drilling at Apsley comprised 17 reverse circulation scout holes for 4,954m to depths of up to 402m and tested previously-defined specific coincident geophysical induced polarisation (IP) and soil geochemistry anomalies prospective for porphyry copper-gold deposits.
The most encouraging results defining the copper halo were returned from 14 holes completed across 1sq km in the central part of the prospect.
The holes intersected a variety of porphyry, volcanic and variably carbonaceous and pyrite- rich sedimentary rocks dipping west at shallow to moderate angles.
The pyrite-bearing sedimentary units were found to be the source of the strongest IP anomalies.
Size of the halo
The size of the halo has been deemed significant given the reconnaissance nature of the drill program which was done at very broad spacings with many hundreds of metres between most drill holes.
“The Ridgeway deposit, which lies 400m below surface, was not discovered until the drill density was at a spacing of 200 square metres between drill holes,” the company said.
“Accordingly [we believe] there is plenty of scope to find a Ridgeway-sized deposit within the copper halo at Apsley.”
Further work
Impact said the Apsley target was drilled because of its strong combined geophysical and geochemical anomalies however the results are not as definitive as that required for immediate follow-up drilling.
Further drilling is required, possibly to some depth, in several areas, but further studies on the nature and composition of the alteration minerals are needed first in order to determine if more accurate vectors to the system’s core can be found.
Impact confirmed the current COVID-19 lockdown in NSW has put a hold on any further exploration work at Commonwealth for the remainder of the year.