Geothermal Surface Alteration and Water Chemistry: an Updated Geochemical Data in Gunung Endut Geothermal Area, Banten, Indonesia

Abstract

Gunung Endut in Java Island is one of the prospected geothermal area to expand geothermal capacity in Indonesia. With limited scientific data in Gunung Endut, the aim of study is to complete scientific data to build an updated conceptual model. This study focuses on the association of surface alteration and water chemistry at Gunung Endut Geothermal Working Area, Banten, Indonesia. Water chemistry were analysed from surface manifestations had pH values of 6.8 – 7.6 indicating SO4-HCO3 water type. Surface alteration were also collected from the surrounding area of Gunung Endut. Alteration mineral assemblage groups were laid out based on its surface intensity. Montmorillonite, dickite and chlorite predominated around distal-proximal area of Gunung Endut. Alteration factors can be driven by the mobility of ions, the protolith physical properties, fluid type circulating in the near surface, and water chemistry and topography. The type of altered clay mineral assemblage, the richness of Na, K, and Mg indicates an intense fluid-rock interaction, promoting rock leaching and altering both protolith composition and mineralogy.