GBM finds a promising processing path for Twin Hills gold

Flotation recovers up to 99% of Twin Hills gold

GBM Resources Limited (ASX:GBM) has found a potentially attractive processing route for its Twin Hills Gold Project, with initial rougher flotation tests recovering between 92.0% and 99.0% of gold from composite samples drawn from the 309 and Lone Sister deposits. The strongest result came from 309 at a 45-micron grind, where 99.0% of gold reported to a rougher concentrate.

The result is notable for the relatively small amount of material carrying the recovered gold. At the coarser 75-micron grind, 98.9% of 309’s gold reported to 8.7% of the original feed mass, while Lone Sister recovered 92.0% of gold into 4.8% of feed mass. Those concentrates graded 18.0 grams per tonne gold at 309 and 26.0 grams per tonne at Lone Sister.

The testwork arrives as GBM advances a project whose resource growth case has been supported by recent drilling beyond the existing resource envelope. The company has reported an existing Twin Hills Mineral Resource of approximately 1.0 million ounces, within a broader Drummond Basin portfolio containing about 1.84 million ounces.

Lone Sister leaching performs, while 309 remains difficult

Flotation was not the only encouraging signal. Forty-eight-hour carbon-in-leach bottle-roll tests at Lone Sister returned gold extractions of 87.3% at a 75-micron grind and 88.8% at 45 microns, results GBM said were consistent with historical investigations.

The 309 results were materially less settled. Current CIL extractions ranged from 25.2% to 47.5%, below historical gravity and CIL results of 92.8% to 96.4% from selected 309 composites. GBM said the current tests did not include gravity separation, while variability in repeat assays and differences between assayed and calculated head grades suggested coarse or unevenly distributed gold may have affected sample representivity.

The company also pointed to 309’s low arsenic content of 88 parts per million as providing little indication of significant arsenic-associated refractory mineralisation. However, elevated organic and graphitic carbon, variable gold mineralogy and possible carbon-related effects remain relevant to the leaching response.

Flowsheet choice still depends on follow-up work

GBM’s initial flotation tests used a conventional reagent scheme with limited optimisation. Finer grinding to 45 microns did not materially improve rougher recovery at either deposit, and produced lower concentrate grades and higher mass pulls than the 75-micron tests. The next phase will examine reagent selection, cleaner flotation and concentrate upgrading.

Further work will also test gravity recovery, whole-ore CIL and leaching of flotation concentrates, with particular attention on reconciling the current 309 results with historical outcomes. The samples came from 81 intervals across four Lone Sister drill holes and five 309 holes, and were designed as an initial assessment rather than a full representation of deposit-wide variability.

That distinction matters. The reported flotation figures are rougher recoveries before cleaning and concentrate treatment, so they are not final plant recoveries. GBM has not selected a preferred processing flowsheet, and the commercial significance of the results will depend on whether strong recovery can be reproduced across different geological domains while producing a saleable concentrate or an efficient leach feed.