COLOMBIA - GREYSTAR RESOURCES of Vancouver has successfully applied bio-oxidation pre-treatment to sulphide ore from its Angostura gold-silver project. When it is followed by cyanidation, gold recovery rates from the treated ore were 92% and 86%.
Colorado-based Little Bear Laboratories did the bio-oxidation testing on two Angostura sulphide samples. The first sample, which graded 1.51 g/t Au (and yielded 42% gold recovery by cyanidation without bio-oxidation), showed an increase to 92% gold extraction after 92% bio-oxidation. Gold extraction by cyanidation of the second sample, grading 3.64 g/t Au, increased from 39% without bio-oxidation to 86% after 90% bio-oxidation.
Both samples were readily bio-oxidized in stirred reactor batch tests with nominally 150 mesh material at 10% solids at 36-37C, Greystar explained. The gold extraction increased with the extent of oxidation, and it is anticipated that milling the ore more finely would probably increase the rate and extent of pyrite bio-oxidation, likely resulting in even higher gold recovery. Silver extractions for the unoxidized samples were 85% and 69%, respectively and did not increase with bio-oxidation. This amenability testing program is considered the first step in the potential evaluation of the Angostura sulphide mineralization to whole-ore bio-oxidation or bio-oxidation of flotation concentrate.
The Angostura project is only 35 km from Bucaramanga, a city of 700,000. The deposit contains indicated resources of 166.4 million tonnes grading 1.3 g/t Au and inferred resources of 83.3 million tonnes grading 1.6 g/t Au.
The latest technical report is available at www.GreystarResources.com.