Characterization of potential Cu-Au mineralization using electrical resistivity and induced polarization methods: a case study in Eastern Labo, Bicol, Philippines

Electrical resistivity and induced polarization (ER-IP) surveys were carried out in Eastern Labo, Bicol, Philippines, to assess the potential Cu-Au mineralization in pyroclastic-covered areas. An electrical resistivity tomography method with a dipole-dipole array was used, and the L1 norm (robust) inversion approach was employed to generate the 16 2D ER-IP models. The analysis of the resistivity and chargeability classified the underlying lithology into eight zones. Zones from C to F are the potential mineralized zones, while Zones A and B (Labo Volcanic Complex) and Zones G and H (Tumbaga Formation and Tamisan Diorite) are the non-mineralized zones. Zone C, represented by low chargeability (<15 mV V-1) and intermediate resistivity (15-100 ohm-m) values, is characterized by a high concentration of disseminated sulfide minerals (e.g. chalcopyrite). Zone D has a chargeability range comparable to Zone C but higher resistivity (>100 ohm-m), which might be due to silicification. Zone E corresponds to the oxide zone with concentrated sulfide minerals along clayey, weathered, fractured areas; it has moderate to high chargeability (>15 mV V-1) and low resistivity (<15 ohm-m) signatures. Zone F has a similar resistivity range to Zone E but has lower chargeability (<15 mV V-1) values. The interpreted underlying lithological units were confirmed using borehole data. Because of the extensive occurrence of high chargeability zones with moderate resistivity anomalies, potentially mineralized areas for further investigation (e.g. drilling) were identified in the north-eastern portion of the study area.