Subsurface Geology of the Nasuji- Sogongon Sector, Southern Negros Geothermal Field, Philippines

Abstract

A geological assessment of the Nasuji-Sogongon sector in the Southern Negros Geothermal Fi e ld, including salient features of the subsurface stratigraphy, lithology, alteration mineralogy, temperature, permeability and structure acquired from wells completed in this area as of February 1982, is discussed. Hydrothermal alteration zones are established based on the relative distribution and association of alteration minerals in cores and cuttings of the Nasuji-Sogongon wells. Fluid inclusion and alteration mineralogy temperatures compared with table rock temperatures indicate that the present sys has undergone considerable temperature decline but remains economically exploitable. Most of the production zones are confined within the plutonic body as recognized in SG-1, SG-2 and OK-6.