Great Boulder Resources Ltd (ASX:GBR) has received encouraging results from the initial metallurgical tests conducted on a sample of high-grade drill chips at the Mulga Bill prospect within the Side Well Gold Project in Western Australia.
Notably, the results indicate positive gold recoveries from gravity separation followed by leaching, with more than 62% of gold recovered in the gravity circuit, indicating coarse, free-milling gold.
Looking ahead, this testwork is an important first step in considering the future potential for economic extraction of gold from the Mulga Bill deposit, helping to determine typical gold recovery parameters.
“High percentage of gravity-recoverable gold”
GBR managing director Andrew Paterson said: “These initial indications from metallurgical work on RC chips are very positive, particularly the very high percentage of gravity-recoverable gold and the apparent coarse nature of the gold.
“Obviously we’re also pleased to note Mulga Bill appears to be amenable to standard cyanide leach extraction as expected, with no indications of any refractory mineralisation.”
Testwork
A parcel of mineralised RC drill chips was collected from two high-grade intersections and submitted to Independent Metallurgical Operations Pty Ltd (IMO) to examine gravity gold recovery and cyanide leach characteristics.
The parcel grade assayed 39.47g/t gold and leach tests were conducted at grind sizes of 150 μm, 106 μm and 75 μm.
Highlights from the IMO’s tests include the following findings:
- Gravity gold recoveries were very high, averaging 62.5%. This result indicates a high portion of the gold present is coarse gravity recoverable gold.
- Assays of the parcel indicate very low levels of common deleterious elements including tellurium, arsenic and antimony and there is no indication of a refractory component to gold mineralisation.
- Overall recoveries ranged from 87.2% to 88.0% after a 48-hour leach time and independent of grind size. Leaching kinetics suggest that slow-leaching coarse gold is present, potentially recoverable with increased cyanide.
- A fourth leach test is now underway to see if increased cyanide concentrations at 150 μm will improve overall recovery to more than 90%.
Forward plan
Diamond drilling at Mulga Bill is ongoing and regional AC drilling is complete, with remaining assays from 2021 RC and AC holes expected to be received during March.
Paterson adds: “IMO are now running another leach test to determine whether the high tail grade is due to undissolved coarse gold remaining in this high-grade sample, which may be recovered by increasing the cyanide dosage.
“We will also be doing more tests in future using different mineralisation styles, including samples of diamond core to gather more comprehensive data on potential milling characteristics.”