Environmental Studies of Mine Wastes - Case Study of a Gold Mine in North Sulawesi

SS4: Environmental Studies of Mine Wastes

This paper was presented in Vancouver, Canada in 2003.

Heavy-metal contamination of reef sediment and coral skeletons from submarine tailings disposal at a gold mine, Buyat Bay, North Sulawesi, Indonesia

Edinger, E.N., Geography and Biology Departments, Memorial University, St. John's, NL, A1B 3X9, eedinger@mun.ca; Siregar, R.P., Indonesian Forum for the Environment (WALHI), Jl. Tegal Parang Utara No. 14, Jakarta, 12790, Indonesia, Glynn, T., School of Resource and Environmental Studies, Dalhousie University, Halifax, NS, B3H 4A6

Tailings from the Newmont Minahasa Raya gold mine are dumped in seawater at 75 m depth approximately 1.5 km from the shore in Buyat Bay, North Sulawesi, Indonesia. Despite treatment prior to disposal, the tailings contain high concentrations of Hg, As, and Sb, and tailings-water Hg concentrations far exceed Indonesian environmental regulations. Tailings dumping has caused health concerns among the local villagers, who are mostly dependent on artisanal fishing in the bay and on adjacent fringing reefs for their dietary protein. Blood sampling in 2000 showed that 95% of villagers had blood As concentrations above tolerance values, and 65% had blood Hg concentrations above tolerance values. The mine contends that Hg contamination is largely derived from artisanal mining operations using Hg amalgamation in the nearby Totok River. To compare the relative importance of different potential sources of heavy-metal contamination, we sampled water, sediments, and coral skeletons from the end of the tailings pipe, two local rivers and river mouths, and a series of fringing reefs at increasing distance from the end of the tailings pipe. Bottom sediments and corals were collected in June 2002 using a hand-operated grab sampler, and massive Porites lobata corals were collected using SCUBA. Whole-sediment metals concentrations were determined by ICPMS following complete dissolution in HF, and whole-sediment Hg concentrations were determined by cold-vapour AAS. Trace-metal concentrations in coral skeletons were determined by laser-ablation ICPMS. Sediment collected at the end of the tailings pipe has a distinctive dark red colour, and has As, Hg, and Sb concentrations many times higher than background levels for local terrigenous sediment, including mine runoff. Arsenic concentrations in all sediments collected in Buyat Bay far exceed legal limits under Indonesian fisheries regulations. Fluvial sediments, including mine runoff, primarily deliver metals of lesser toxicity, such as Ti, Fe, Cr, Co, and Cu. Molybdenum, Ag, and Cd contamination is associated with both industrial mine tailings and artisanal mining using Hg amalgamation. Elemental ratios suggest that tailings are the primary vector of toxic metal contamination on fringing reefs between Buyat and Totok bays. These patterns suggest that submarine disposal of tailings in Buyat Bay may pose significant health threats to local residents.