Investigation of old waste dump composition of lean gold-bearing ores from the Golden Pride Project (GPP) mining operation in Nzega district, Tanzania

Abstract

The search for alternative sources of useful minerals is a pressing issue. One such possible source is the processing of lean gold-bearing ores, which previously did not seem feasible to exploit for subsoil users, leading to their disposal in off-balance ore dumps. Processing these resources becomes economically viable as gold prices rise and processing technologies improve over time. This paper presents the elemental and mineralogical composition of lean gold-bearing ore dumps from the Golden Pride Project (GPP) mining operation in Tanzania’s Lihendo district. This area contains an old dump of lean gold-bearing ores, weighing approximately 1.4 million tons. Extracting valuable components from lean mineral raw materials is a current priority. Sampling was conducted to study the dumps. Boreholes were drilled to a depth of 1 m, covering a total sampling area of 20 ha; 18 samples, each averaging 3 kg in weight, were collected. The results of X-ray fluorescence analysis (XRF) indicated the presence of Fe, S, Si, Ca, Ca, Mn, Cu, Al, Cr, Ti, As, and Ag in the collected samples. X-ray diffraction (XRD) analysis revealed that the main minerals in the dumps are muscovite, kaolinite, quartz, montimorillonite, and goethite. The average gold grade in the selected samples is 0.72 g/t. Studies of the grain-size distribution and gold distribution by grain-size classes after ore grinding demonstrated that the majority of gold (74%) is in the −75 μm class. In the initial mineral material of the dumps, the share of the +30-50 mm grain-size class is 81%. The paper proposes potential methods for processing lean dumps of gold-bearing ores. One such methods involves crushing the dump material, separating the −75 μm class, and subjecting it to direct leaching or leaching using “carbon-in-pulp” technique. Heap leaching appears to be the most promising method for extracting gold from such dumps in terms of technical and economic feasibility. Positive experience has been reported in applying this process to ores of similar mineralogical type.