New assays increase potential of large porphyry copper-gold discovery at Impact Minerals’ Commonwealth project
Impact says the halo may be part of a system that is similar to Newcrest’s Ridgeway deposit.
The potential for large intrusion-related gold and copper-gold deposits at Impact Minerals’ (ASX: IPT) wholly-owned Commonwealth project in New South Wales has been enhanced by new assay results from 27 rock chip samples at two new prospects.
The Greenobbys and Boda South targets, situated in the state’s Lachlan copper-gold province, were identified as part of a group of five priority areas for follow-up exploration, prompted by the discovery in March of high-grade porphyry copper-gold mineralisation at Boda-Kaiser by Alkane Resources (ASX: ALK).
Rock chip assays from Greenobbys returned up to 9.5 grams per tonne gold, 215g/t silver and 745 parts per million bismuth.
Zones of quartz and potassium feldspar veins were shown to contain an array of pathfinder metals, particularly bismuth (up to 754ppm), molybdenum (up to 519ppm) and tellurium (up to 40ppm).
Boda South returned up to 0.1% copper, 2g/t silver and 40ppm bismuth.
Priority areas
Impact said two of the other priority areas – Apsley and Spicers Creek – are believed to have significant porphyry copper-gold potential due to the presence of characteristics commonly seen around global alkaline systems such as Cadia-Ridgeway and Boda.
Apsley has been ranked as the most prospective and is currently the subject of a detailed soil geochemistry survey with results expected in August.
All five priority areas have undergone detailed airborne magnetic and radiometric surveying with final data expected next month.
Wuuluman Granite
Greenobbys lies a few kilometres east of Boda South and covers the variably magnetic western margin of the potassium-rich Wuuluman Granite.
It is associated with an “unusually large array” of pathfinder metals – including selenium-thallium-antimony-arsenic-lead-barium and tungsten, as well as the rare metals indium and rhenium.
Impact said Greenobbys contained a new style of mineralisation for the area, suggestive of a telescoped epithermal gold-silver system driven by cooling of host granite, the margin of which extends over many strike kilometres on the company’s acreage and has not been previously explored.
Boda South
The undrilled Boda South prospect covers the faulted southern contact of the Boda intrusive complex, host to Alkane’s Boda-Kaiser mineralisation.
It is believed to contain the characteristics required to potentially host a significant porphyry copper-gold deposit, such as copper-bearing Ordovician shoshonites with weak to moderate copper assays of up to 0.1% with the content increasing as the rocks become more potassium-rich.
Follow-up exploration
The Greenobbys and Boda South results – combined with those from Apsley and Spicers Creek – support the potential for the Commonwealth project to host significant porphyry copper-gold and intrusion-related epithermal gold-silver deposits.
Impact managing director Dr Mike Jones said the rock chip assays exceeded the company’s expectations and will require follow-up exploration.
“This has further confirmed and enhanced our belief that our extensive ground holdings in the prolific Lachlan Fold Belt have the potential to host major porphyry copper-gold as well as other possible styles of intrusion-related mineral deposits such as the newly-recognised epithermal gold-silver mineralisation at Greenobbys,” he said.
“Incredibly, none of these prospects have been drilled and we will be doing the necessary work to get them to drill-ready status as rapidly as we can,” Dr Jones added.
Arkun project
Earlier this month, Impact announced it had significantly expanded its ground position at its new Arkun project in the emerging nickel-copper-platinum-metal-group province of south-west Western Australia.
The project sits between the towns of York and Corrigin and was first identified as an area of anomalous nickel-copper-gold in publicly-available regional geochemistry data sets.
Impact’s ground expansion was prompted by Anglo American’s lodgement of exploration licence applications covering 10,130sq km directly surrounding three sides of Arkun’s acreage.
Anglo’s applications – which comprise one of the largest holdings by a single company in WA – were lodged shortly after Impact disclosed it had made applications for the five tenements making up the Arkun project.
Positive endorsement
Dr Jones said Anglo’s presence in the region will be a positive endorsement of the emerging nickel-copper-platinum group elements province, backed by recent discoveries at Julimar (Chalice Gold Mines, ASX: CHN) and Yarawindah (Cassini Resources, ASX: CZI).
“We believe it is also a direct recognition of the importance of the proposed mobile belt in this part of the state, which we interpret to be a deep structure that may have tapped the mantle and allowed nickel-copper and platinum group metals to migrate into the crust,” he said.
“Such deep structures are critical components to the formation of major deposits like Nova-Bollinger and the recent discovery at Mawson,” Dr Jones added.
He said the company is completing reconnaissance work along roads and tracks to move Arkun forward while waiting for statutory drilling approvals at its wholly-owned Broken Hill nickel-copper-platinum group elements project.