The Mineral Resource
Under 40 per cent of the Ok Tedi ore body remains to be mined between 2004 and mine closure in 2012.
The Ok Tedi ore body lies within Mt Fubilan and contains copper, gold and silver mineralisation. Gold production began at Ok Tedi in 1984 and the copper processing facilities were commissioned in 1987.
Phases of mining
Due to the presence of a copper-leached residual gold cap over the main ore body, mining was planned in three phases:
Initial phase
- Mining and processing of oxide gold ore from the gold cap.
Second phase
- Extraction and treatment of both sulphide copper and oxide gold ore.
Third phase
- Mining the main copper ore body, which includes porphyry and skarn ores. Both copper and gold are extracted from the ore body and sold as concentrates.
Regional geology
The major rock types in the region are continental margin marine sedimentary rocks (siltstones and limestones). Large-scale folds and thrust faults form the dominant structural features, with a large sheet of Darai Limestone thrust over siltstone in the mine area. The fold belt is developed along the southern margin of a transition zone between two major geologic provinces: the Australian Plate to the south and the Pacific Plate to the north.
The transition zone is also a region of rapid uplift and erosion dated from 2.6 to 0.7 million years.
The major rock types used for geologic modelling at the Ok Tedi mine are:
- Siltstone - the common waste rock surrounding the ore body
- Limestone - all waste, contains no economic mineralisation, but valuable neutralising capacity
- Monzonite - a major ore type, makes up the majority of economic mineralisation tonnage
- Monzodiorite - mostly waste grade Endo skarn - minor ore-grade mineralisation
- Skarn - generally ore-grade, accounts for an estimated 50 per cent of contained metal due to its high-grade nature
- Oxide Skarn - very minor ore type, and
- Thrust Zones - two major zones in the Taranaki and Parrots Beak thrusts, all waste material.
Production totals
At 31st December 2007, the Ok Tedi mine had produced 11,580,784 tonnes of copper concentrate containing 3,598,992 tonnes of copper metal and 8,771,026 ounces of gold metal. Between 1984 and 1990 it also produced 1,712,953 ounces of gold bullion.
Reserves
Ok Tedi's estimated proven and probable reserves as at 31 December 2006 were:·
- Proven reserves: 157 million tonnes at 0.88% copper and 1.14 g/t gold ·
- Probable reserves: 21 million tonnes at 0.76% copper and 1.29 g/t gold
The anticipated contained product is estimated to be around 4.5 billion pounds of copper and 7 million ounces of gold.