Great Boulder Resources has “fantastic result” from testing of Mulga Bill gold samples
Wed Jan 15 2025
Great Boulder Resources Ltd (ASX:GBR) has fielded very high gold recoveries of up to 98.7% in gravity recovery and cyanide leach testing of a range of samples from the 568,000-ounce Mulga Bill deposit of the flagship Side Well Gold Project in WA. The recoveries, which were described by the company as “excellent” and included high gravity recovery, were achieved with only moderate cyanide consumption.Samples were selected to represent all mineralisation styles from weathered material to fresh rock, including areas with copper grades up to 6,483ppm copper.
De-risking milestone
This metallurgical test-work represents an important de-risking milestone in the development of the 668,000-ounce Side Well project.
It means the project's "engine room", the Mulga Bill deposit, is amenable to conventional gravity recovery and cyanide leaching processing methods similar to those used by neighbouring gold mills.
“This is a fantastic result for the Side Well Project and for Great Boulder shareholders," Great Boulder’s managing director Andrew Paterson said.
"The results of our metallurgical test-work demonstrate that Mulga Bill leached extremely effectively and is therefore amenable to standard cyanide leaching. This means it can be processed through a conventional gold plant or any of the existing gold plants in the Meekatharra region.
“Hugely important”
“This is a hugely important outcome, as it removes one of the last remaining questions around potential mine development at Side Well.
"Mulga Bill has the majority of gold ounces known to date so it will always be the engine room of any mining operation here, and hence we’re extremely pleased and excited with this outcome.”
Test-work was completed by Independent Metallurgical Operations Ltd (IMO) and was designed to look at gravity and cyanide leach recoveries of gold over various grind sizes between 150 µm and 75 µm, with leach durations to a maximum of 48 hours.
Five sample parcels were chosen from recent RC drill spoils at Mulga Bill and these are representative of the full range of mineralisation styles and oxidation states within the conceptual open pit shell, from low-grade oxide material to high-grade fresh gold mineralisation and lower-grade gold-copper mineralisation.
The proportion of cyanide-soluble copper was low, with low cyanide-soluble chalcopyrite being the dominant copper mineral in four of the five sample parcels.
By testing a range of different ore styles, the test-work was also designed to consider whether the presence of copper minerals, primarily malachite (in the weathered horizon) and chalcopyrite (in the fresh rock) would negatively impact cyanide consumption and/or gold recovery.
The results from four of the five parcels were extremely positive, with high gold recoveries and low levels of cyanide-soluble copper. Low cyanide-soluble chalcopyrite was the dominant copper mineral in the four parcels.
This means that copper levels within the Mulga Bill deposit will not unduly affect gold recoveries or cyanide consumption, particularly in the supergene and fresh mineralisation zones.
The test results obtained conclusively demonstrate that Mulga Bill is amenable to industry-standard cyanide leaching and can be successfully processed at any of the existing gold mills in the Meekatharra region.
Low levels of cyanide-soluble copper and excellent leach characteristics seen in four of the five sample types demonstrate that copper is not a constraint to development at Mulga Bill.
The fifth sample, which was expected to show the worst outcome, returned an extremely positive gold recovery of 96.3% with moderate cyanide consumption.
Additional test work is now being considered to optimise the metallurgical flowsheet with results expected to demonstrate that lower-recovery ore types can be easily and effectively managed by blending with nearby high-grade supergene zones.
In the next stage, IMO will run a series of reagent optimisation tests to examine the effect of varying cyanide concentration levels while keeping the grind size constant.
Subsequent tests will look to further optimise blend characteristics by testing higher levels of cyanide-soluble copper to find the maximum permissible cyanide-soluble level.
To discuss the latest company newsflow, including the metallurgical test-work results from the Mulga Bill deposit and the ongoing drilling activities at the Side Well Gold Project, Great Boulder will hold a live webinar tomorrow.
Source: https://www.proactiveinvestors.com.au/