East Africa Metals has reported the final results of a comprehensive metallurgical test program completed for the Terakimti Oxide Gold Project in Ethiopia.
Column leach testwork achieved gold extractions up to 74.8% with rapid leach rates.
Column Leaching Testwork
The column testwork program was performed to evaluate the potential to utilize heap leaching for the extraction of gold and silver from the Terakimti oxide gold deposit. The column tests included two column leach tests at SGS Mineral Services ("SGS") metallurgical testing facility in Johannesburg, South Africa, and a third column test at McClelland Laboratories Inc. ("McClelland") in Reno, Nevada. SGS and McClelland are highly respected within the global minerals industry for their expertise in metallurgical testing.
Two separate column leach tests at SGS achieved gold extractions of 74.8% and 70.2%. Leach kinetics were rapid with gold extractions of 70% after 14 days and 56% after 15 days respectively. The third column leach test performed at McClelland achieved gold extraction of 73.0% with 70% extraction achieved at 28 days, further supporting the high extraction and good leach kinetics of the Terakimti oxide material. Silver extractions for the two SGS columns were 38.4% and 39.4% respectively and the McClelland column achieved silver extraction of 13.0%.
The two SGS column tests were performed on representative samples of Terakimti gold/silver oxide material crushed to 100% passing minus 16 mm (5/8 inch), a common crush size for heap leaching. The samples were composites of material collected from six metallurgical drill holes in order to represent the different major lithologies identified within the Terakimti oxide gold deposit.
The McClelland column test was performed on coarser oxide material crushed to 100% minus 38 mm (1.5 inch). The material for this test was collected from surface trenches and is considered representative of the near surface zone of the deposit however it may not be representative of the entire oxide deposit. The high level of gold extraction achieved in this test combined with very good leach kinetics, indicates the potential to utilize a coarser crush size for gold extraction at Terakimti.
Additional tests were performed by SGS to assess permeability, mechanical strength and the requirement for agglomeration of the oxide material for heap leaching. The results indicate good permeability and heap material strength, with agglomeration required to maintain permeability in the heap leach. The agglomeration rates applied in the testwork were within ranges typical for heap leaching of oxide gold deposits.
"We are very pleased by the metallurgical test results achieved for the Terakimti oxide and especially the excellent column test results. These positive results confirm that heap leaching technology is the preferred process for the Terakimti oxide gold deposit. The results of this comprehensive testwork program will provide a solid basis for the next stage of project development," stated Sean Waller, P.Eng., Chair of East Africa's Technical Development Committee.
Rock Hardness and Abrasion Tests
Additional testwork performed by SGS included the determination of Bond ball mill work indices and an abrasion index. Three Bond tests were completed generating work indices ranging between 5.5 and 8.7 kwh/t, confirming the Terakimti oxide is soft to very soft relative to other rock types. A single abrasion test generated a low abrasion index of 0.04, indicating this material will have very low abrasiveness. These results are positive as it indicates the oxide material will be relatively easy to crush and will result in low abrasion of crusher wear surfaces.
Kinetic Leach Testwork
The testwork program at SGS also included eighteen kinetic leach tests (bottle roll tests) on representative samples of Terakimti oxide material to assess gold and silver extractions. The resulting extractions at a grind size of 75% minus 75 microns averaged 77.8% for gold. Gold extractions for the five oxide lithologies ranged from 64.9% to 81.2%, with an average of 75.0%. The gold extraction for transition material was 91.4%. Silver extractions for the various lithologies ranged from 20.0% to 77.3%, with an average of 46.9%. The overall gold extractions achieved in the kinetic leach tests may be considered low when compared to typical oxide gold leach operations utilizing agitated leaching. Given that the column leach test extractions are only slightly lower than the kinetic leach extractions, the test results strongly support utilizing heap leaching for the Terakimti oxide gold deposit.
The results of this testwork program will be used to support ongoing evaluation and development of the Terakimti Oxide Gold Project, including plans to initiate a Preliminary Economic Assessment upon closing of the financing announced in East Africa's news release on November 2, 2016.