Geometallurgical Analysis of Ore for Enhanced Comminution and Leaching

Abstract

Many gold processing plants are experiencing challenges as mining pits are becoming deeper, rocks are getting harder and more complex polymetallic and refractory ores are being encountered. The variations in the characteristics of ores lead to deviations from the established parameters, and these affect gold extraction efficiency. This paper presents a study where geological characteristics of the ore types from some mining pits were used to ascertain the influence of ore blends in optimising the performances of comminution and leaching circuits. To achieve this, mineralogical,  comminution, gravity recoverable gold and leaching  investigations were conducted on  fresh and weathered ore samples and their blends. Mineralogical study showed that the main rock types associated with the mine pits were dolerite, phyllites, conglomerates and sandstone. The established and dominant minerals were quartz, plagioclase and traces of pyrite. Tellurides were present in dolerite. The Crushability Work Indices of the rocks were between 30 and 37 KWh/t, which are generally higher than the maximum design value of 31.9 kWh/t, and this situation will pose throughput challenges in that section. The Bond Ball Mill Work Indices of the blends tested were between 16.4 kWh/t and 9.6 kWh/t and a blend ratio of 85% fresh and 15% weathered was found to have a Bond Ball Work Index almost equal to the design value of 14 kWh/t. With gold assays of 2.5 g/t for dolerite, 2.1 g/t for phyllite, 3.7 g/t for sandstone and 3.4 g/t for conglomerate, the gravity recoverable gold was in the order of sandstone 36% > phyllite (31.5%) > dolerite (29.5%) > conglomerate (18%). The overall gold recoveries were in the sequence of conglomerate (95%), sandstone (94%), phyllite (92%) and dolerite (87%). The low cyanide amenability of dolerite was due to the presence of gold and silver tellurides (AuTe₂) and ((Au,Ag)Te₂). This information can be utilised in developing a proactive plant operations strategy for an operating plant in order to ultimately manage the plant and enhance achievement of set targets.