The application of hydrogeochemical and stable isotope data to decipher the origin and evolution of hot springs in the Rawadanau Basin, Indonesia

Abstract

The emergence of hot springs is usually associated with hydrothermal prospects. This paper discusses the certainty of the nature, type, and origin of the hot springs found in the Rawadanau Basin, Indonesia. The approach in this study is to use hydro-chemical characteristics and stable isotopes. Besides measuring field data, laboratory analyzes were also carried out - hydrogeochemical analysis including cations and anions and stable isotopes analyses. Twenty-one hot springs have been reported. The temperature varied from 31.2 to 54.6 °C; the pH was 6.8 and 7.7, and EC was between 1099 and 4460 μS/cm. There are three water types of Mg-Ca-HCO3-Cl, Mg-Ca-HCO3 in the northern, and Na-Cl in the southern. Chloro-alkaline indices implied that ion exchange and reverse ion exchange influenced the hydrogeochemistry of hot springs. The δ18O and δ2H values varied between -8.6 to -4.6‰ (δ18O) and from -57.0 to -32.4 ‰ (δ2H), lay to the local meteoric water line, indicating that the thermal waters are meteoric local in origin and originated from precipitation. The hot springs in the study area originate from meteoric water and interact with geothermal fluids from confined aquifers that flow to the surface through fractures and faults. The reservoir temperature approach 150 °C is based on chalcedony; and the reservoir depth is about 1.1 km.