High-resolution numerical modelling of a marine mine tailings discharge in Western Norway

Abstract

Waste from mining operations includes mine tailings, a slurry of fine-grained mineral particles and processing chemicals that remains after the desired compounds have been extracted from the ore. In some cases, the method of disposal is to place tailings into the marine environment; this is known as Submarine Tailings Placement (STP). To understanding the environmental impact of releasing large amounts of mine tailings into the marine system, multiple processes must be well characterised, including those relating to the transport and fate of the disposed material. We applied a set of high-resolution models for wind, hydrodynamics, and sediment transport to simulate a submarine mine tailings discharge in a Norwegian fjord. The transport model includes processes to account for the effect of flocculation on mine tailings transport and fate. We calculated the mean tailings sedimentation rate in the fjord, which is closely related to the environmental footprint of the STP. Comparisons with measurements of winds, currents, turbidity, and sedimentation rates were made to evaluate the model, and we found overall reasonable agreement. We investigated discharge scenarios during 2013 and identified a strong wind event around November 17, which caused increased particle dispersal. The increased mixing caused by the strong winds were seen in elevated turbidity measurements, as well as increased modelled suspended sediment concentration.