GEOCHEMICAL INVESTIGATION ON JABOI MANIFESTATION, JABOI VOLCANO, SABANG, INDONESIA

Abstract

Geochemical studies have been conducted in the geothermal system of Jaboi manifestation, Sabang, Aceh. There are three sub-area of geothermal water sites in this area, that are production-injection wells of PT Sabang Geothermal Energy, Jaboi crater, and hot spring pond. The fumaroles were also found in the Jaboi crater. The mineral contents were analyzed by ion chromatography, alkalimetry, and spectrophotometry, the isotope was determined by Laser Absorption Spectrophotometer, while the gas contents were analyzed by Gas Chromatography-TCD. The obtained data were used to estimate the reservoir temperature by using geothermometers, FT-HSH diagram, and CH₄/CO₂-H₂/Ar diagram. The graphical analysis were also done to obtain chemical and physical characteristics. The water analysis showed that the reservoir temperatures were in range of 253.2-416.5 °C. The water types of production-injection wells, Jaboi crater and hot spring pond were chloride, sulphate and bicarbonate-sulphate mixtures, respectively. The fluid equilibria showed that only production well was mature water while the other sites were immature ones. The water composition source of production-injection wells and hot spring pond were marine sedimentary rocks, Jaboi crater JK1 and JK4 were magmatic gas, and Jaboi crater JK2 was hot rock. The water origin of production-injection wells were both magmatic and meteoric, Jaboi craters were magmatic water, and hot spring pond was meteoric water. The gas analysis in Jaboi crater fumaroles showed that the reservoir temperature were in range of 196.9-362.8 ºC, and the gas origin were earth’s crust. The reservoir temperatures showed a high-temperature geothermal system which is suitable for power plant.