Application of Mineral Deposit Concepts to Geothermal Exploration

Abstract

The recognition that epithermal and porphyry mineral deposits are the fossil equivalents of geothermal systems has led to the successful application to mineral exploration of principles learnt in the development of geothermal systems for energy extraction. Similarly, technology developed for mineral exploration can be successfully applied to geothermal exploration. Low sulphidation epithermal gold deposits are found mainly in highly permeable tensional structures within dilational jogs. Recognition of this structural pattern in active systems allows targeting of geothermal wells into open tensional structures. High sulphidation epithermal gold deposits produced by acid, condensed, magmatic volatiles have a wider gangue mineral suite than unmineralised alteration produced by acid oxidised steam condensates. Recognition of these gangue minerals allows identification of alteration by different types of acid fluids in active systems allowing adoption of appropriate strategies for dealing with them when developing the system. Porphyry deposits have large concentric alteration zones. Identification of these zones in an active geothermal system can point to the identification of low-grade Cu-porphyries at depth that still retain fracture permeability that presents prime deep targets for geothermal wells.