Metallurgical testwork for Nusantara Resources' Awak Mas Gold Project in South Sulawesi, Indonesia, has demonstrated improved metallurgical recoveries. The Whole of Ore leach tests have returned gold recoveries ranging from 92% to 98% compared to the 85% to 91% recoveries in the previous flotation-leach tests.
Nusantara commissioned Minnovo Pty Ltd to assist with the management of the metallurgical testwork program for the Awak Mas definitive feasibility study (DFS) with a focus on optimising gold recoveries.
The project’s process flowsheet was previously extensively studied on the basis of gold flotation with carbon in leach (CIL) treatment of reground sulphide concentrate.
Nusantara’s current DFS has initially focused on opportunities for improved recoveries and economic outcomes through the use of Whole of Ore CIL leaching.
The Phase 1 testwork, involving a 75 micron grind with gravity separation of coarse gold followed by leaching for 24 hours, has been completed on representative samples from five of the seven ore domains. The samples were from three of the five domains in the Awak Mas deposit and from the Salu Bulo and Tarra deposits.
Gold extractions of greater than 92% within a 24-hour leach time are reported, with less than 1.5% additional gold recovered for a 48-hour leach time.
Pending further testwork, an overall gold recovery in the range of 90% to 94% is expected for the project across all domains using this flowsheet.
The testwork has also reported low to moderate consumption rates for lime and cyanide, and low levels of deleterious elements. These results combined with low-cost grid power and previous assessments of moderate grindability, support previous estimates of low processing costs in the range of US$8 to US$10/tonne.
Given the improved gold recovery, simplified process flowsheet and low processing costs, the project DFS will now focus on fully developing Whole of Ore CIL Leach processing infrastructure. The program will now be expanded to identify gaps and bring the metallurgical testwork to DFS standard using previous drill core and samples from the drilling program currently in progress.
Nusantara’s CEO and managing director Mike Spreadborough said, “These metallurgical results represent a significant breakthrough for the planned development of Awak Mas.
"Previous testwork focused on flotation and CIL treatment due to the higher power cost involved in alternative process routes. The availability of low cost grid power has removed a major hurdle for the project, allowing the consideration of Whole of Ore CIL treatment. The results indicate potential for significant improvements to the overall project economics.”