Potential of Mine Waste Rock to Generate Acid Mine Drainage – A Case Study in South-Western Ghana

Abstract

Acid Mine Drainage (AMD) is one of the major threats confronting mining companies worldwide, due to the ability of the acidic water to contaminate water bodies and cause ecological destruction, adversely affecting flora and fauna even years beyond the mine life. South-western Ghana hosts two major gold belts, and these together have 10 large-scale mining companies, several small-scale mines, farms and other units and activities that cause land disturbances. The potential for these activities to promote AMD generation has brought about interest in studies on mapping out the sulphur-mineralised zones in south-western Ghana to document the acid generating potential of these areas and recommend remedial measures. This paper reports on some of the findings of on-going studies on AMD generation potential in south-western Ghana. Mineralogical studies showed that quartz accounted for about 75% while carbonates, feldspars, pyroxene, sericites and chlorites accounted for 25% of samples tested. The pyrite content was up to 5% and arsenopyrite, 1% of samples observed in polish section. All the samples: mine waste, mineralised waste and ore contained sulphides. The results from geochemical and Acid-Base Accounting (ABA) analysis passed 57% of the samples as non-sulphidic, 38% contained 1.6–4% sulphur, and 5% had 0.02–1.5% sulphur. Analysis of paste pH confirmed that about 80% of the samples were neutral to basic (i.e. pH 6.5–8.5). Further analysis using Net Neutralising Potential (NNP) and ratios of Maximum Neutralisation Potential to Acid Production Potential (NP:AP) placed 35% of the samples as having the potential to generate acid since the NNPs were negative, while the NP:AP had values less than 1. This 35% had the capacity to significantly deteriorate natural water quality. The study concludes that there is a significant potential for AMD generation in both mining and non-mining areas in south-western Ghana, and this calls for periodic monitoring and development of proactive neutralising strategies to arrest the situation.