GBM Resources (ASX:GBM) will optimise flotation and test cyanide leaching at its Twin Hills Gold Project in Queensland after rougher flotation recovered 92–99% of gold.
Independent consultant Core Resources completed initial testwork on composite samples from the 309 and Lone Sister deposits within the Drummond Basin.
Four rougher flotation tests at grind sizes of 75 and 45 microns each recovered more than 90% of the gold.
At 75 microns, Lone Sister returned 92% of gold into 4.8% of the feed mass, grading 26 grams per tonne gold (Au). The 309 deposit returned 98.9% into 8.7% of the feed mass, grading 18g/t Au.
Finer grinding to 45 microns delivered no material gain in recovery and produced lower concentrate grades and higher mass pulls.
Carbon-in-leach (CIL) bottle roll tests extracted 87.3–88.8% of gold at Lone Sister, consistent with historical work. At 309, extractions reached only 25.2% at 75 microns and 47.5% at 45 microns, well below historical results of 92.8% to 96.4% from gravity and CIL testing.
The company says assay variability and coarse gold may affect sample representivity. The 309 composite contains 88 parts per million (ppm) arsenic, giving little indication of refractory mineralisation.
Elevated organic and graphitic carbon is present, with activated carbon added to the tests to limit preg-robbing.
The next phase will focus on reagent selection, concentrate cleaning, gravity recovery at 309, mineralogy, and leaching of flotation concentrates. The company has not yet selected a processing flowsheet. Twin Hills hosts a mineral resource of about 1 million ounces of gold.
CEO Daniel Hastings says the work provides a base for further testing.
“Our immediate priority is to build on the flotation performance and undertake further leaching investigations to establish the most effective recovery methods for Twin Hills,” Hastings adds.
GBM Resources is an Australian explorer advancing a district-scale portfolio of epithermal gold projects in Queensland’s Drummond Basin.
Write to JC Villarba at Mining.com.au
Images: GBM Resources
