Gold mining in West-Africa is associated with a variety of geological settings, comprising both underground and open-pit operations. Often underground operations follow the open pit phase as deeper lying ores are mined and the ore transitions to a less oxidised form. These operations have one thing in common; high concentrations of arsenic minerals (mainly arsenopyrite) associated with the gold deposits. This arsenic regularly reacts and dissolves into the water circuits during processing and from mine workings and residue deposits. The more mine operators increase gold recovery from these orebodies (methods to increase recovery from arsenic containing ore) the higher the tendency for arsenic to enter into solution. The high arsenic concentrations (dissolved As > 0.1 mg/L) along with the high rainfall associated with the region, makes water quality, and discharge management, a challenging task. Arsenic is both a toxin and a carcinogen, recognised as one of the most serious inorganic threats to drinking water on a global scale as well as to aquatic ecologies that accumulate arsenic. Water contaminated with arsenic and discharged into the environment is a liability and a risk to mining operations and surrounding communities. This paper considers case studies from six gold mines in Cte dIvoire, Liberia, Mali and Senegal, as relevant to the methods tested and implemented to prevent, manage and mitigate soluble arsenic issues. Groundwater and surface water impacts are discussed. This paper will present the geochemical investigations on the sources and solubility of arsenic, discuss how these predictions match actual measured results, the utilisation of tools such as water and salt balances to fully understand the planned mine systems and the transport of the contaminant. Mitigation and management options are presented as well as the stability and longevity (post-closure) of the management options. Leach test results will be presented as well as the management/mitigation methods tested including ferric and ferrous iron dosage, enhanced natural arsenic precipitation and accumulation by using naturally available material (ferricrete), passive treatment through constructed wetlands, conventional water treatment plants and arsenic stabilisation.
CITATION:van Coller, A A and Trusler, G E, 2019. Arsenic management in gold mine water circuits: West-African case studies, in Proceedings World Gold 2019, pp 244258 (The Australasian Institute of Mining and Metallurgy: Melbourne).