The Geophysical Response of the Tupinda Cu-Au-Mo Porphyry Prospect, Tabar Islands, Papua New Guinea

Abstract

The Tupinda porphyry prospect is located in the Tabar Islands Group of Papua New Guinea (PNG), approximately 80 km NW of the supergiant Lihir epithermal gold deposit (43 Moz Au). Geophysical data over the prospect include airborne magnetics and radiometrics, ground pole-dipole induced polarization and resistivity, gradient array induced polarization, petrophysics, and airborne time domain electromagnetics. All geophysical datasets clearly identify the footprint of the porphyry body and associated alteration system. The magnetic data show a central high representing the magnetite altered potassic core surrounded by a circular zone of low response indicative of magnetite destructive alteration. The radiometric data show a discrete potassium anomaly overlapping the magnetic anomaly. The pole-dipole IP data display a resistive chargeable zone coincident with the magnetic anomaly. Mid to late time airborne EM data exhibit a broad sub-circular resistor coincident with the mapped limits of the alteration system. Field mapping and drilling of the prospect are consistent with the geophysical data. Outcropping potassic alteration is observed at the location of the magnetic and radiometric anomalies. Drill core shows widespread disseminated sulphide mineralization consistent with the chargeable response observed in the IP data. Predominantly fresh felsic lithologies intersected in the drilling concur with the resistor measured in the airborne EM data. A more complex relationship exists between grade (Au and Cu) and magnetic susceptibility, with some areas displaying a good correlation and other demonstrating a more cryptic relationship which may be a function later overprinting geological events.