Investigation of Hydrologic and Geochemical Properties of an Unsaturated Waste Rock Pile at Key Lake, Saskatchewan

Waste rock is any rock that must be removed to gain access to the ore at a mine. Waste rock piles at mine sites often rest above the water table, which exposes the rock to oxygen, and promotes the oxidation of sulfide minerals releasing sulfuric acid, metals and heat. Water flow through unsaturated waste rock and its role in geochemical processes is not well understood. The objective of this work was to identify spatial relationships between hydrologic and geochemical properties of waste rock. A 12-meter high waste rock pile was deconstructed and sampled during the summer of 2000. Approximately 175 samples were collected to assess the physical properties of matric potential, volumetric water content, and grain-size distribution and the geochemical properties of temperature, paste pH, pore-water chemistry, mineralogy, and bulk rock chemistry. In addition, we characterized weathering using selective extractions that target the weathering products that contain sulfur and iron. We discuss the influence of fluid flow paths, gain-size distribution, mineralogy and sample volume on the characterization of waste rock weathering.