Evaluating the Acid Mine Drainage Potential at Abosso Goldfields Limited (AGL), Ghana

Occurrence of Acid Rock Drainage (ARD) affects both plants and animals that are present in a drainage system. In some base metal and coal mining environments, the presence of sulphide minerals especially pyrite and their exposure to oxygen and water may trigger Acid Mine Drainage (AMD). Evaluation of the potential for acid generation is therefore very important in any mine setting where sulphide minerals exist. Results of two Acid-Base Accounting (ABA) studies conducted at Abosso Goldfields Limited (AGL) on 120 rock and tailings samples reveal that on average, total sulphide values in rocks are low, with 83 % less than 0.20 %. More than 95 % show Neutralisation Potential Ratio (NPR) of 2 and above, indicating the presence of excess neutralising capacity in the rocks and tailings to prevent acid generation. Also, more than 93 % of the samples possess long-term acid neutralisation because their Neutralisation Potentials (NP) are more than 10 and their total sulphide are less than 0.1 %. Average up- and down-stream measurements of pH were respectively 6.55 and 6.74 while for TSS (Total Suspended Solids), the values were respectively 14.9 mg/l and 7.2 mg/l, indicating improved water quality after passing through the mine. Although these figures show very high NP’s, the presence of less than 7% samples with the potential to generate acidity necessitates that AMD monitoring should continue, especially in meta-sedimentary and siltstones to ensure acid generation does not arise during mining.