Magnetotellurics-Derived Resistivity Model of the Dauin Geothermal Prospect, Southern Negros, Central Philippines

Abstract

Success of modular power plant development and economic considerations revived interest in the Dauin Geothermal Prospect. This prompted a recent geophysical reinvestigation of the area using magnetotellurics (MT). The MT survey delineated two regions of shallow occurring high-resistivity (>50. 100 º?-m) overlain by a zone of low resistivity (í? 10 º?-m), one of which centers beneath Lagunao Dome, and another beneath Mt. Talines and Cuernos de Negros. The former, a larger anomaly, is related to the Palinpinon geothermal system at the Southern Negros Geothermal Production Field (SNGPF), while the latter, a smaller anomaly, is thought to define a separate geothermal system, referred to as the Dauin prospect. The high-resistivity anomalies are associated with high temperature but low conductivity mineral alteration products (illite, epidote, chlorite, etc.) that dominate most geothermal systems. The low-resistivity (í?10 º?-m) layer is associated with clay hydrothermal alterations (smectite and illite-smectite) that normally occur at regimes of intermediate temperatures (~70¿¼C). The resistivity model supports the idea of two geothermal systems separated by a zone of high-sulfidation. This high-sulfidation zone coincides with the region of intermediate resistivity likely defined by the Malingin Fault, which also separates the two high-resistivity anomalies. A single heat source possibly fuelling the two systems at deeper levels, however, is not discounted.