The Lihir Open Pit Gold Mine Revisited

Abstract

In a previous workshop (White et al. 2000) we described initial modelling of the geothermal system and groundwater in the vicinity of the open pit Lihir gold mine. This mine pit is planned ultimately to reach more than 200 metres below sea level and is being dug into an active geothermal system with some of the area to be mined at boiling-point for depth conditions. Cooling and depressurisation of the geothermal resource associated with the gold mineralisation is an essential part of the mining operation. Previous modelling was based on data from eight deep, deviated geothermal wells completed during 1999 and information from the shallower mineral exploration wells drilled and tested in the 1980's.

Currently the mine is over 150 meters deep and more than 30 geothermal wells, a number of steam relief and pumped dewatering wells have been drilled. Two power stations have been built to provide a total of 36 MW of electricity for use in the gold refining process. The new geothermal drilling has shown the productive reservoir beneath the mine pit to be fracture dominated with a low effective porosity, partially isolated from the shallow reservoir.

This system provides a number of challenges to the modeller with coupling between the groundwater, the sea and the geothermal system all being important and the need to take account of the changing surface topography as the mine pit is deepened.