Mine waste management at Ok Tedi mine, Papua New Guinea: A case history

The Ok Tedi mine commenced production in 1983 and is currently milling ore at a nominal rate of 83,000 tpd. The mine is located in unstable mountainous terrain which experiences extremely high rainfall of over 10 m per annum, and where conventional approaches to storage of waste rock and tailings are unacceptable from a risk-cost-benefit perspective. Apart from a brief period at start up, the mine adopted riverine tailings disposal until mid 1998 when, due to increasing concerns over environmental effects, trial storage of some of the waste, predominantly sand, was commenced. Mine derived sand is trapped within a dredged slot and delivered to the storage site at a nominal rate of 20 mtpa via a conventional cutter suction dredge which operates in the Ok Tedi River near the village of Bige about 100 km downstream of the mine site. An extensive study of all practical sites in the mountainous terrain near the mine was made prior to selection of the floodplain storage site. The chosen site has challenging foundation conditions ranging from lowland swamp to weathered tropical clay. The paper discusses the background to selection of the site and the construction of the dredged sand storage scheme in the context of a high rainfall, weak foundation, seismically active environment. Results of performance monitoring of the sand storage area are presented.