Geochemistry of the Lihir Geothermal Field, Papua New Guinea.

Abstract

The Lihir mine is located on Lihir Island, Papua New Guinea and is currently one of the largest epithermal gold mines in the world. The mine is situated inside an active geothermal system. A number of wells have been drilled and discharged to reduce underground pressures to enable open pit mining to proceed. Recently, a 6 MW generator has been installed, and a further larger, power plant is planned for early 2005.
Deep deviated wells (>1000 m depth) have been used to lower pressures in the deep reservoir, while more shallow (500-600 m), vertical wells have been utilised to reduce pressures in the upper formations. Temperatures of the fluid range from 230-270 C. The fluids that are discharged have very high total dissolved solids content (>100,000 ppm) and are unusual because of the very high sulfate concentrations (>30,000 ppm). The sulfate concentrations indicate equilibrium with anhydrite, which is pervasive in the rocks. Calcite scaling occurs in many wells, and antiscalant dosing is reasonably successful. Although the geothermal field is situated adjacent to the sea, isotope analyses indicate that the geothermal fluid has a magmatic and meteoric water component. The meteoric water component is not reflected in the argon concentrations in the gas analyses.