Gold and base metals explorer Great Boulder Resources (ASX:GBR) has set an exploration target for intrusive-related copper-silver mineralisation at the Mulga Bill prospect within its Side Well Gold Project.
The company reports it will be targeting 8-10 million tonnes at grades of between 0.2% and 0.4% copper and between 3 grams per tonne (g/t) and 6g/t silver, for 16,000-40,000 tonnes of contained copper and 770,000-1.93 million ounces of contained silver.
This exploration target was generated by retrospectively assaying 90 drillholes completed from 2021 to present for multiple elements, with intervals selected using portable X-ray fluorescence (pXRF) data and visual observations.
The company says it is still working to refine this definition and gain a greater understanding of the mineral system responsible for the known gold endowment at Mulga Bill, Ironbark, and other mineralised targets seen in surface geochemistry along the Ironbark trend.
Great Boulder reports there are likely at least 2 mineralising events at Side Well, with the first being the early intrusive-related pulse of copper-gold-silver mineralisation and associated pathfinders, while the second is a later remobilisation of gold into ‘high-grade’ orogenic positions like those discovered at Ironbark.
It appears the gold remobilisation event may also have remobilised ‘higher-grade’ copper mineralisation grading between 0.5% to 1% into these domains.
Great Boulder says the data will be incorporated into a combined Mineral Resource Estimate (MRE) in the future, which will enable the interpolation of each component based on individual variography. This approach will allow the ‘high-grade’ gold lodes to be modelled separately, as they are in the current MRE, without artificially smearing gold values into the surrounding ‘low-grade’ areas.
Additionally, copper and silver have not been estimated within the MRE gold lodes. The company reports future resource estimation will consider the various orientations of mineralisation and domain the different mineralisation styles appropriately.
Commenting on the exploration target, Great Boulder Resources Managing Director Andrew Paterson says: “We have been working on this process for several months, identifying copper-rich intervals in the pXRF data in and around the gold lodes and resubmitting those examples for base metal analysis. We’ve now compiled a significant data set which underpins the exploration target expectations.
The exploration target doesn’t include gold because there are 2 different populations of gold data within Mulga Bill: the high-grade cross-cutting veins contrast with bulk-tonnage low-grade gold mineralisation within the copper sulphide lodes, so we are treating both styles of mineralisation separately at this stage.
“This work demonstrates Mulga Bill has potential for significant Cu-Au-Ag endowment in addition to the high-grade gold structures”
Once the gold, copper, and silver data is compiled into a formal resource estimate, we will be able to quantify the different styles of mineralisation. This work demonstrates Mulga Bill has potential for significant Cu-Au-Ag endowment in addition to the high-grade gold structures. This could be a significant value-add for an eventual production scenario.”
Great Boulder reports copper-gold-silver lodes are proximal to the subvertical gold lodes and ‘higher-grade’ shallow dipping gold lodes modelled during the 518,000-ounce MRE.
Highlight assays from within the copper-gold-silver zones include 21MBRC017 with 55m @ 0.75% Cu, 2.72g/t Au, and 7.6g/t Ag from 100m; 22MBRC067 with 57m @ 0.49% Cu, 5.07g/t Au, and 16.7g/t Ag from 96m; and 22MBRC003 with 31m @ 1.11% Cu, 1.72g/t Au, and 18.8g/t Ag from 82m.
Great Boulder Resources is an ASX-listed mineral exploration company with a portfolio of ‘highly prospective’ gold and base metals assets in Western Australia, including the Side Well, Whiteheads, and Wellington projects.
The Side Well Gold Project lies in the Murchison gold field near Meekatharra and hosts an inferred MRE of 6.192 million tonnes @ 2.6g/t Au for 518,000 ounces.
Write to Harry Mulholland at Mining.com.au
Images: Great Boulder Resources Ltd
