The Chemistry of Geothermal Fluids in Indonesia and Their Relationship to Water and Vapour Dominated Systems

As part of the initial assessment of the geothermal power potential of Indonesia an electronic model, (IGSEP), Mahon, (1987), was developed to prioritise the most favourable resources and determine the least cost development scenarios for generating geothermal electricity. The model was tested and assessed using data from 100 different geothermal prospects in the country. This involved researching and collating the scientific information and in particular reviewing the chemistry of discharge fluids. These chemical relationships are discussed in reference to the formation of water dominated geothermal systems and, in some cases, their subsequent evolution to vapour dominated systems. There is also a close relationship between active volcanism and meteoric-derived geothermal fluids. The unique geographical location of many Indonesian geothermal systems at high elevations of 1500-2000 m.a.s.l has lead to a characteristic set of chemical compositions in the shallow and deeper fluids associated with the individual