Depressurization as a Strategy for Mining Ore Bodies with an Active Geothermal System

Abstract

The Lihir Gold Mine in Papua New Guinea is a world-class open pit gold mine that contains an active geothermal system. Temperatures within the ore bodies are up to 200°C and this presents a major constraint to mining operations and creates the potential for geothermal hazards including hydrothermal eruptions. For mining to be feasible, it is necessary to depressurize and cool down the hot rocks of the pit to safe levels.

Drilling of steam relief wells ahead of mining is the primary method used to achieve depressurization. At the Lienetz pit where bench temperatures reach 130°C, the steam relief wells have been effective in lowering pressures and temperatures. This allowed conventional mining operations to proceed and also mitigates the risk of hydrothermal eruptions during mining.

Mining is advancing into the Kapit area where temperatures of up to 200°C and fluid pressures of up to 15 bars are expected. The strategy considered for this area is to depressurize the ore body to induce seawater encroachment to cool down the ore body. The challenge in this area is to achieve depressurization and cooling of the ore body without significantly affecting the deeper geothermal reservoir supplying steam to the mine’s 56 MWe geothermal power plant.