Cost-effective means for identifying acid rock drainage risks: Integration of the geochemistry-mineralogy-texture approach and geometallurgical techniques

Best practice for acid rock drainage (ARD) risk assessment still relies solely on the geochemical properties of sulfidic rocks and mineral processing products, despite the fact that a rock’s tendency to produce acid also depends on mineralogy and texture. Consequently, there are a plethora of geochemical tests routinely utilised by the mining industry to predict ARD formation. Due to limitations associated with these tests and their relatively high costs, analysis of recommended best practice sample numbers is rarely achieved, reducing the accuracy of waste management plans. Our research addressed this through examining the application of geometallurgical data for predicting acid formation, and led to the identification of potential environmental geometallurgy indicators. Samples obtained from an iron-oxide copper gold deposit were subjected to the geochemistry-mineralogy-texture (GMT) approach, an improved methodology for classifying acid forming potential. GMT results were compared against geometallurgical and assay data sets to evaluate: • relative carbonate content measurements (measured by HyLogger) and identify how these could be used to calculate effective acid neutralising capacity • mineral hardness (measured by EQUOtip) to determine application of this data for calculating lag-time to acid formation • opportunities to automate the acid rock drainage index (ARDI) using classified images produced by a GEOTEK logger and automated microscopy. Links between the GMT approach and geometallurgical data sets were identified. Classified mineralogy data has application at stage one, HyLogger and EQUOtip at stage two and computerbased ARDI evaluations of classified images at stage three. Through such integration, ARD characterisation costs can be reduced, with value added to geometallurgical data sets. Furthermore, deposit-wide ARD domaining is possible, and acquisition of total-orebody knowledge more likely. Through adoption of this environmental geometallurgy approach, a better informed waste management plan can be formulated, allowing for best practice ARD sampling in a more costeffective manner.