Chemical and mineralogical properties of post-mining sites in two gold mining concessions in Ghana

Abstract

Mining companies adopt different post-mining management practices to rehabilitate mined sites to enhance environmental management and sustainability. The study assessed the chemical and mineralogical properties of some post-mining land management options from two gold mines in the Western Region of Ghana. Samples of waste rock (WR), mine tailings (MTs), mine soils and un-mined soils were analysed for soil pH, cation exchange capacity (CEC), exchangeable cations, soil organic carbon (SOC), total nitrogen (Ntotal), concentrations of some heavy metals (HMs) and mineralogy by ICP-AES and X-ray diffraction techniques. The results revealed pH values of 4.2-4.6 in un-mined soils and 4.6-5.4 in mine soils. The MTs and WR were alkaline due to CaCO3 (4.8-5.8 g kg-1). Virtually all the samples contained kaolinite, muscovite and quartz. The MTs contained ankerite, bobierrite, clinoclase and greenalite, which were not present in the WR. These minerals were most probably neo-formed out of the chemical constituents of the tailings and contamination during the disposal. Mine soils from three-year-old reclaimed mine site planted with oil palm had substantial SOC and Ntotal contents among all the post-mining sites which also reflected slightly on the CEC status. This showed the influence of soil management practices such as mulching, cover cropping with Pueraria phaseoloides, erosion control and fertiliser application. The HMs contents in the mine tailings occurred in the order of Pb > As > Cd and revealed relatively higher contents in the abandoned MTs compared to reclaimed ones but they were all in the range of those in uncontaminated soils elsewhere.