Extraction of Gold and Silver from Geothermal Fluid

Abstract

Gold and silver scaling deposits were discovered in the surface pipework from New Zealand geothermal fields (Brown, 1986). Approximate calculations for the well BR22 at Broadlands/Ohaaki showed that the deep aquifers contained about 1.5 mg/tonne of gold and 8.0 mg/tonne of silver. With these concentrations, it was felt worthwhile to investigate the possibility of commercial extraction of gold and silver from those geothermal fields which had been developed. At the Kawerau geothermal field, the surface concentrations of gold and silver are found to be higher than at Broadlands, consequently it was decided to construct a small pilot plant at Kawerau. The key element in the commercial recovery of the available gold and silver is the ease of extraction from the geothermal fluid. Because the concentrations are so low, the extraction must be very cheap and efficient. At BR22, it was observed that the gold and silver was very efficiently deposited as a result of a large pressure drop. This paper describes five experimental runs in the Kawerau pilot plant.