Prediction of acid rock drainage from automated mineralogy: the computed acid rock drainage (CARD) risk grade

An accurate understanding of acid forming potential can be gained based on a detailed knowledge of mineralogy. However, most mineralogical techniques require careful sample preparation, are expensive and require dedicated expertise to interpret the output data. Considering this, geochemical techniques are often preferred for use in acid rock drainage (ARD) prediction studies, but are not without limitations. Therefore, a new methodology is required which collects and uses mineralogical data in a manner which is rapid, low-cost, statistically valid, and simple to process. We addressed this by developing the computed acid rock drainage (CARD) risk grade tool. This involves: i) MLA/QEMSCAN analyses; ii) processing of XMOD and BSE data to produce congruent whole sample images; iii) image fusion to calculate surface area; iv) calculation of the CARD risk ratio; and v) classification of CARD risk ratios (from extreme risk to very-low risk).

The CARD risk grade tool was tested on a mineralogically diverse suite of samples (n= 135). CARD risk grade values were compared to static ARD data, and showed it to be of greater accuracy in classifying acid forming characteristics. Based on this, the CARD risk grade protocol is applicable as a domaining technique.