Problems With Acid Rock Drainage Predictions at the Ekati Diamond Mine, Northwest Territories, Canada

摘要

The Ekati Diamond Mine is located on permafrost terrain in Canada's Northwest Territories. The mine rock consists of: 1. diamond-bearing and barren kimberlite; and 2. surrounding waste rock such as granite. The kimberlite occurs in several vertical 'pipes' that are, or will be, mined using open pits. Early predictions of drainage chemistry at Ekati identified the potential for ARD due to sulfide oxidation from both waste rock and kimberlite. This was surprising for the kimberlite, because neutralisation potentials (NP) are typically hundreds of kg CaCO_3 equivalent/t. However, subsequent testwork showed that substantial portions of the NP 'disappeared' quickly, apparently due to the unusual non-carbonate mineralogy. In any case, additional predictive work concluded much of the rock was benign and there would be no ARD. Shortly after mining started, ARD appeared from both the waste rock and kimberlite, although a few years passed before the company and its consultants recognised that at least some of the acidic water was ARD. Numerous other processes have been put forward as possible explanations for the remaining acidic drainage, although none have been either confirmed or eliminated. Because: 1. the causes of the ARD and acidity are not known; 2. no causes have been eliminated and more have been added; 3. drainage chemistry was not predicted accurately; and 4. future mining will encounter similar rock. I believe the Ekati Diamond Mine needs high-level assistance to understand current chemistry and to avoid problems with future drainage. Organisations like INAP, MEND3, and universities could provide this assistance.