Magnetotellurics (MT) Resistivity Signature of a Geothermal Prospect with Au-Cu Mineralization in Surigao del Norte, Philippines

Abstract

Magnetotelluric (MT) soundings were conducted in the Mainit geothermal prospect in Surigao del Norte, Philippines. This area is located in a highly mineralized district of Surigao del Norte, Philippines with abundant deposits of Au and Cu. The survey was concentrated within and around the Quaternary volcanic domes of Paco-Maniayao Volcanic Complex (PMVC). Based on the generated models, surface high resistivity values of 100-700 ohm-m were mapped within the central region of PMVC covering a maximum thickness of around 500 m. This can be associated with the younger units of the Paco-Maniayao Volcanics. The thick low resistivity layers with values of ≤15 ohm-m in the western portion of the model reflect the sedimentary deposits such as sandstone, siltstone and, more generally, clays belonging to the Tugunan Formation. Extensive outcrop of Tugunan sedimentary rocks are found as patches in the central lowlands and along the slopes of Malimono Mountains in the west and northwest of PMVC. Modeled sections show that this low resistivity layer extends to a thickness of greater than 3000 m in the west and tapers off towards the east. The increased resistivity to the east of PMVC with values of more than 40 ohm-m is related to the intrusive rocks of the older Mabuhay Volcanics. These intrusive bodies have outcrops following a NNW-SSE trend and are associated with mineral occurrences such as porphyry Au-Cu deposits found in the central region i.e. Boyongan and Bayugo mineral districts and other areas northeast of PMVC. The intrusive body is believed to be a remnant of a waning and old geothermal environment which also led to epithermal mineralization in the area.