Distribution of Sr and Ca Isotopes in Fluids of Lahendong Geothermal Field

Abstract

Naturally occurring Sr and Ca isotopes can help to understand geochemical processes like mineral dissolution/precipitation and solute sources in geothermal systems. To test the potential of the two isotope systems, we conducted research in a high-temperature liquid-dominated system located in volcanic rocks in North Sulawesi (Indonesia). Fluids were collected from hot springs, shallow groundwater wells, geothermal production wells, and surface waters in the Lahendong area. The results of the investigations show that the Sr isotope compositions of the fluids vary with the source of solutes and differences in the 87Sr/86Sr ratio reflect geochemical differences of andesitic and basaltic rocks in the reservoir and at the surface. In contrast, the distribution of Ca isotopes in the fluids is largely affected by fractionation effects resulting from the precipitation of Ca-bearing mineral phases.