| Abstract |
The geophysical model of Mt. Labo geothermal field, based on the results of the regional gravity and magnetotelluric (MI)surveys, indicates a geothermal reservoir centered beneath the Mabahong Labo thermal ground. The heat source of the present hydrothermal system is provided by a cooling intrusive body mapped as a gravity high, associated with the Mt. Labo volcanic activity. The geothermal fluids circulate along factures within the low-density reservoir rocks of the Susung Dalaga Formation. This reservoir rock shows relatively high resistivity values of 30 to 40 ohm-m. Directly overlying the resistive reservoir, occurring between -1000 m to -1500 m, is a thick alteration halo formed within the basal unit of the Labo Volcanics (Lbu). The predominantly hydrous, low-temperature clay minerals which compose the alteration halo give low resistivity values of 1 to 4 ohm-m. Outjflow of hot fluids to the south-southwest, which possibly feeds the thermal springs at Kilbay and Alawihaw, may be channeled along the thinning low resistivity Lbu. The geophysical model also shows a possible separate hydrothermal system in the west associated with a relatively shallower intrusive body, also defined by positive gravity values. ThIs intrusion, which could be related to the cluster of volcanic domes located south of Bakilid Fault, may provide the heat that drives the hot Vrings at Kilbay anddlawihaw. It could also be possible that the Kilbay and Alawihaw springs originate from both systems. Based on the interpretation of the gravity and MT data, wells LB-ID and LB-SD lie closest to the intrusive, LB-3D and LB-4D are located in the center of the resource, while LB-2D and LB-6D lie along the margin or outside of the resource. The size ofthis resource, as defined by the 5 ohm-m MT low resistivity anomaly, is about 10 sq. km. |