Preliminary study on the characterization of geothermal fluids at Mount Jobolarangan (old Mount Lawu) western side and its implications for geothermal exploration

¹ Geological Engineering, Faculty of Engineering and Planning, Institut Teknologi Nasional Yogyakarta, Indonesia
² Universiti Teknologi Malaysia, Johor Bahru, Malaysia

Abstract

Mount Jobolarangan, also known as Old Lawu, is located on the southern side of Mount Lawu in Karanganyar, Central Java. This Research is crucial to understand the geothermal resource potential within it. The purpose of this study is to conduct a lithology and geochemical analysis of geothermal fluids to determine the characteristics of the fluids and their potential implications for geothermal exploration. The research method used is in the form of surface geological research, which is divided into field data analysis, petrography and geochemistry. The geochemistry method used in this research involves fluid (water and gases) geochemical sampling with AAS and XRF analysis. The study area contains andesite lava formed from volcanic activity that products by subduction with the temperature of magma forming in the range 1090°C - 1098°C. The geothermal manifestations in the study area are hot springs, which exhibit a bicarbonate fluid type. These geothermal fluids belong to the boundary zone between immature water and partial equilibrium, with a subsurface temperature ranging from 80°C to 120°C. The high magnesium content indicates that the geothermal fluid has been influenced by surface water and contact with surrounding rocks. The reservoir temperature is between 82°C and 86°C included in low-temperature geothermal system category.