Column Leaching Testwork
Ethiopia – The column testwork programme was performed for East Africa Metals to evaluate the potential to utilise 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 metallurgical testing facility in Johannesburg, South Africa, and a third column test at McClelland Laboratories in Reno, Nevada.
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 East Africa Metals’ 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 programme will provide a solid basis for the next stage of project development,” states Sean Waller, Chair of East Africa’s Technical Development Committee.