The Emperor Gold Mining Company (EGM) is situated on the verge of the Tavua Caldera on the island of Viti Levu in Fiji. Based on the most recent data, the Vatukoula gold mine has a gold resource of some 3.8 million ounces at 9g/t, currently being minded at over 110,000 ounces of gold annually.
There have been previous studies conducted regarding water temperature, which indicate that the temperatures increase with depth based on a geothermal gradient of 3°C per 100m. Consequently at a depth of 400m, the temperature is 40°C as compared to the surface temperature of around 28°C. Temperatures of the water at R1 are around 48°C but are over 55°C at the Philip Shaft. As a result of the hot groundwater inflows, the underground air temperatures reach to about 35-40°C. The heat has to be counteracted as the legislations indicate that workplace should be evacuated if the WB temperature exceeds 34°C. There are additional constraints to ventilation. The hot groundwater flows generate hot and humid working conditions.
The present strategies to control the groundwater inflows are by utilising underground boreholes and practising cover drilling and grouting. Some of the possible recommendations include major aquifer identification, prevention of open water flow in drives, improvements to the present dewatering strategies, and installations of piezometers. Apart from these, the more generic approach include insulation of pipelines, installation of chilled water service, installations of submersible pumps, careful planning development levels to be ahead of production levels for enhanced depressurisation and dewatering, considerations to thermal insulation of rock surfaces, and the usage of air movers.
It is always advisable that further feasibility studies are undertaken prior to selection of any of the strategies.