Geological Controls on Thermal Manifestation Occurences in Batu Gede and Batu Kapur, Subang Regency: A Preliminary Result

Abstract

Batu Gede and Batu Kapur are administratively located in Subang Regency, West Java, precisely in the northern part of Tangkuban Perahu Geothermal Working Area. Characteristics of the manifestations in Batu Gede and Batu Kapur are generally bicarbonate neutral pH warm springs and their location exposed in the foot of Tangkuban Perahu Volcano. Despite the similar chemical characteristic of those two manifestations, there is a significant characteristic difference between them. Spring with low pH with the pungent smell emerges in the Batu Gede not far from neutral pH bicarbonate warm spring. The aim of this research is to determine control of the occurrence and relationship of manifestation in both areas by conducting geological mapping. Surface manifestations are controlled by a geological process associated with primary and secondary permeability. Both manifestations emerge dominantly in the control of fault as a secondary permeability. Primary permeability also controls the occurrence of manifestations but not significant. Batu Gede manifestations are dominantly controlled by overstepping structure, while Batu Kapur are dominantly controlled by intersections between structures. Based on high content of SO4-2, acid pH, and the presence of sulfur, the acid manifestation might be correlated with magmatic activity beneath Batu Gede's manifestation.