Great Boulder Resources Ltd (ASX:GBR) has recovered up to 99.7% gold during the second round of metallurgical testing at its Mulga Bill prospect, part of the Side Well gold property in WA.
Recently, the explorer tested high-grade drill chips from the gold target, carrying out three leach tests to examine the effect of grind size on gold recovery.
All three tests achieved similar recoveries — around the 87.2% to 88% mark — but a fourth test this week upped the gold recovery to 99.7% thanks to an increase in cyanide concentration.
What’s more, the test sample generated a strong residual (or tails) grade of 0.1 g/t, meaning very little gold is left in the waste material.
Independent Metallurgical Operations Pty Ltd (IMO), which completed all four tests at the prospect, will carry out further testing to better understand the other mineralisation styles at Mulga Bill.
The big picture
Speaking to what he called “a fantastic result”, Great Boulder managing director Andrew Paterson said: “Achieving an overall gold recovery of 99.7% on a high-grade sample is excellent, but only leaving 0.1g/t in the tail is sensational.
“For this test, IMO increased the maintained cyanide level from 300 to 400 parts per million and used a coarse grind size of 150 micrometres, which was enough to improve gold recovery from 87.7% to 99.7%.
“This is another step in our understanding of Mulga Bill, and we will be doing more comprehensive metallurgical studies on other mineralised zones and on drill core over the next few months.”
What’s next?
Down the line, GBR’s test-work program will examine the metallurgical characteristics of other mineralisation styles at Mulga Bill.
This includes lower-grade zones and areas with significant chalcopyrite (copper) and associated gold mineralisation, building on Great Boulder’s understanding of the prospect’s overall metallurgy.
Collecting mineralised samples from the Mulga Bill drill core will also help GBR complete physical testing, thereby determining the crushing and grinding parameters of different mineralisation styles.