Great Boulder Resources Ltd (ASX:GBR) has reported remarkable results from its recent metallurgical testing at the Mulga Bill deposit, part of the flagship Side Well Gold Project in Western Australia. The company recorded gold recoveries of up to 98.7% through gravity recovery and cyanide leach testing across a range of samples, a performance that was described as “excellent” by the company.
The tests included a variety of samples from different mineralisation styles, ranging from weathered material to fresh rock. These samples represented the full spectrum of the deposit’s mineralisation, including areas with copper grades as high as 6,483ppm. The results also indicated high gravity recovery with only moderate cyanide consumption.
Key Milestone for the Side Well Project
This milestone marks a crucial step in de-risking the development of the 668,000-ounce Side Well Project. The successful recovery rates from Mulga Bill, the project’s primary deposit, indicate that the gold can be processed through conventional methods such as gravity recovery and cyanide leaching. These are the same methods used at nearby gold mills, enhancing the project’s potential for smooth development.
Andrew Paterson, Managing Director of Great Boulder, expressed his enthusiasm about the results: “This is a fantastic result for the Side Well Project and for Great Boulder shareholders. The metallurgical test-work has shown that Mulga Bill leached extremely effectively, making it amenable to standard cyanide leaching. This means we can process the gold at conventional gold plants or any existing mills in the Meekatharra region.”
A Significant Step in Mine Development
Paterson emphasized the importance of these results, noting that they remove one of the last remaining uncertainties regarding the potential for mine development at Side Well. Since Mulga Bill contains the majority of known gold ounces, it is expected to be the core source for any future mining operations at the site.
“This is a hugely important outcome, as it addresses one of the final questions around the project’s feasibility,” Paterson said. “We are extremely pleased and excited with this result.”
Details of the Test Work
The metallurgical test-work, completed by Independent Metallurgical Operations Ltd (IMO), involved gravity and cyanide leach testing at various grind sizes (150 µm to 75 µm) and leach durations of up to 48 hours. The samples selected for the test came from recent reverse circulation (RC) drilling at Mulga Bill, covering a range of mineralisation types and oxidation states within the proposed open-pit shell.
The tests also examined whether the presence of copper minerals—such as malachite in the weathered zone and chalcopyrite in the fresh rock—would adversely affect cyanide consumption or gold recovery. Notably, the proportion of cyanide-soluble copper was low, with chalcopyrite being the dominant copper mineral in four out of the five sample parcels.
Encouraging Results Across Most Samples
The test results were overwhelmingly positive. Four of the five sample parcels demonstrated high gold recoveries and low levels of cyanide-soluble copper, confirming that the copper content at Mulga Bill will not negatively impact gold recovery or cyanide consumption, particularly in the supergene and fresh mineralisation zones.
The fifth sample, although expected to yield less favorable results, still returned a strong gold recovery of 96.3% with moderate cyanide consumption. This further underscores the deposit’s potential.
Optimising Future Testing
Looking ahead, Great Boulder plans to conduct additional tests to further optimize the metallurgical flowsheet. These will include reagent optimisation studies to assess the impact of varying cyanide concentrations while maintaining consistent grind sizes. The next phase of testing will also focus on managing ore blends, particularly to determine how to effectively combine lower-recovery ore types with high-grade supergene material.
The results from this stage of testing are expected to demonstrate that gold recovery can be maximized by blending different ore types, further enhancing the project’s economic potential.
In conclusion, the successful metallurgical results represent a significant de-risking step for the Side Well Gold Project, confirming its potential for efficient and cost-effective processing.
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