A geoenvironmental characterisation tool for the coreshed during early life-of-mine assessments

Defining the acid forming potential during the exploration stages of a mining project is critical for financial modelling and waste management planning. However, at such early stages, there are limited resources for evaluating the geoenvironmental characteristics of future waste materials. Considering this, a geoenvironmental logging code was developed and trialled using drill cores from a low-grade porphyry copper prospect in Northern Europe. Four drill holes were targeted with a focus on zones which were marginal or below economic grade. The logging code developed required that for each metre interval, a visual estimate of each sulfide present was recorded. As a conservative approach was adopted, the area (8.5 cm by 5.5 cm i.e., grain size card dimensions) recognised to contain the most sulfides, was assessed using the acid rock drainage index (ARDI). A geoenvironmental risk factor was calculated based on ARDI values scaled to the sulphide mineral abundance over the interval. To enhance the classification, results were plotted against sulphur assay values. As corresponding drill core pulps (< 75 µm) were available in this project, they were analysed using the ASTMD492-01(2007) paste pH method. Collectively, these cost-effective low-technology methods enabled the identification of high and low-risk waste zones and will allow the mine planners to start developing robust waste management strategies rightly guided by the deposit’s mineralogy and texture.