Investigation and Documentation of Acidic Mining Exploration Drill Cuttings at the Pebble Copper– Gold Mineral Prospect, Southwest Alaska

During the Pebble copper-gold-molybdenum (Cu-Au-Mo) deposit discovery drilling, drilling waste was directly disposed of on the landscape or passed through unlined sumps prior to disposal. The ore and host rock are high in sulphides, which are weathered by metal leaching to sulfuric acid. Oxidized cuttings were visually noticeable and verified to have a pH of 2.7-4.3 by laboratory and field research. Cu and Mo reached or were at the high end of the natural history at these locations. Cu was within the range of 545 mg / kg to 4865 mg / kg, with one exception. At all sites with drill cuttings on the soil, dead vegetation was observed. There has also been observed dead vegetation on Covers of sump rock, unrelated to drilling waste. Places where vegetation had not been preserved were between the ages of four and thirteen. The possible surface and groundwater effect has not been determined. It could lead to better site management to understand the source and nature of damage from cuttings. In order to determine the rate of chemistry shifts, drill cuttings sump contents require more sampling and whether groundwater downgradient from sumps is being affected. Finally, more research should be carried out to determine if sulfidic drill waste accumulated in isolated bodies of water, such as glacial kettles, is having an effect. In order to ensure clean control samples, testing sites should be examined before and after drilling.

Author (s) Details

David M. Chambers,
Center for Science in Public Participation, Bozeman, MT 59715, USA.

Dr. Kendra Zamzow,
Center for Science in Public Participation, Chickaloon, AK 99674, USA.

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