Ascertaining the acid mine drainage potential of a mineral concession in south-western Ghana

Acid Mine Drainage (AMD) poses a myriad of problems in communities where mining of sulphide-containing ores takes place. Thus current environmental practice requires that samples be tested for their AMD potential before mining commences. In connection with this, samples from a gold concession in south-western Ghana have been investigated for AMD generation potential using Acid-Base Accounting (ABA) techniques. Mineralogical studies indicated that the ore zones were conglomerate whereas the country rock was quartzite. There were also intrusives of mafic dykes (doleritic). Quartz was the main mineral with composition above 75%, and minor minerals included feldspars, sericite, chlorite, mica, and pyrite. Geochemical analysis and ABA showed that 57% of the samples did not contain sulphide minerals, 38% had sulphur content of 0.01%, and 4% had between 0.02 - 0.03% sulphur. The paste pH of 228 samples out of 230 (99.1%) was above 6.0 with an average of 7.5, implying that these are not likely to generate AMD. The Net Neutralising Potential (NNP) values of 3% of the samples were negative and the ratios of Maximum Neutralisation Potential to Acid Production Potential (NP:AP) were less than 1 confirming the possibility of AMD generation. A proactive strategy was developed to contain the possible environmental hazards of this 3%.