Sediment arsenic hotspots in an abandoned tailings storage facility, Gold Ridge Mine, Solomon Islands

Gold mining of arsenopyrite ore bodies result in waste tailings that contain elevated levels of arsenic. Disposal of these wastes in a Tailings Storage Facility (TSF) represents a substantial environmental risk if not properly managed. The Gold Ridge mine on Guadalcanal, in the Solomon Islands was abandoned from 2014 to 2018, leaving the TSF with little ongoing environmental management. Surface water quality monitoring observed a threefold increase in surface water arsenic concentrations over a 6-month period when no mining operations were occurring. This study aimed to investigate bottom sediments as the source of elevated concentrations of arsenic in the surface waters of the TSF during mine closure. This was achieved by analysing arsenic concentrations in the surface water, sediment porewaters and by quantifying sediment arsenic flux as dissolved oxygen availability declined. It was evident that bottom sediments of the TSF were the potential source of arsenic, having an average arsenic concentration of 437.9 mg kg(-1). In addition, average sediment porewater arsenic concentrations across the TSF were 1.07 mg L-1, with a large central zone of highly elevated concentrations peaking at over 17 mg L-1. Long term sediment core incubations demonstrated arsenic effluxes from all sites monitored under both oxic and hypoxic conditions, ranging from 0.72 mg m(-2) day(-1) to 7.01 mg m(-2) day(-1) respectively. These results suggest that arsenic hotspots within the TSF have the capability to contribute to increased arsenic concentrations in surface waters. Management of mine TSF's should consider these geochemical interactions that can occur in abandoned sites. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Gold mining activities can lead to arsenic contamination in waste tailings, posing environmental risks if not managed properly. This study found that sediments in the tailings storage facility may contribute to elevated arsenic concentrations in surface waters during mine closure. Geochemical interactions in abandoned mine sites should be considered for effective management of tailings storage facilities.