Cyanide from gold mining and its effect on groundwater in arid areas, Yanqul mine of Oman

The use of cyanide (CN), which is characterized by volatility, toxicity and high odor, in gold mining is scarcely addressed in the literature and remain controversial. Environmentalists oppose CN usage as it potentially poses serious environmental threats, whereas economic and mining geologists are in favor of its usage for its extracting capacity and economic feasibility. The present study investigates the possible dispersion of CN into groundwater resources caused by a gold mine (ca. 15 years old) located in the arid area of Yanqul, North Oman. The gold is hosted in gossan deposits associated with ophiolitic rocks and sulfide deposits. Sodium cyanide is mixed with 0.5 m³ of water and then added to a tonne of crushed ore rock to extract 6 g of gold mineral. The final residues are dumped in engineered, lined and uncovered tailing dams. Subsequent to rainfall water draining the mine plateau flows along the wadies and percolates into the shallow Quaternary alluvium aquifer. Hence, groundwater samples were collected from 16 piezometers adjacent to and around the mine. The samples were analyzed for CN using the revised phenolphthalin method and they all show CN concentration below the detection limit (5 ppb). The samples were also analyzed for heavy metals to investigate the potential of CN complexation. Most of heavy metals indicated very trace concentration. The absence of CN in groundwater is attributed to volatilization of CN (converted to HCN), lined dam structure, high evapotranspiration rate and deeper water table. This finding is consistent with the historical CN analysis in the groundwater and solid wastes. It can be pointed out that within few years of operation well engineered tailing dams can provide safe structure preventing CN-groundwater pollution in arid areas. Potential threats to the air and soil are not addressed in this article.