The results showed heap leach amenability, with 95.8% gold recovery at a coarse crush size on an oxide sample, above the 80% modelled in a July preliminary economic assessment.
"More significantly, the testwork on fresh (sulphide) samples shows that CIL processing will likely be very effective, with 86.8 % gold recovery at attractive grind sizes," CEO Steven Poulton said.
He said Altus had commissioned Mining Plus UK to update Diba's PEA, using the higher oxide recoveries and broadening to model CIL processing, to incorporate the current sulphide resource of an indicated 33,600 ounces and 153,000oz inferred.
The July PEA had outlined initial capex of US$20 million and an after-tax NPV10 of $81.3 million and IRR of 469%, based on the oxide ounces alone.
"The significantly enhanced recoveries and addition of the sulphide resource should add considerable economic value to the project," Poulton said.
Privately-held La Mancha holds a cornerstone 35% interest in the company following a February investment.
Altus had £7.4 million (US$9.6 million) in cash, according to a presentation this month.
Its shares (AIM: ALS) closed up 14% yesterday to 61p, a three-fold increase on a year ago, capitalising it about £38 million (US$49 million).