The application of ZTEM to porphyry copper-gold exploration

Abstract

The ZTEM airborne EM system was introduced into commercial service by Geotech Ltd. in late 2007. ZTEM is unlike any other commercial EM system in that it relies on the measurement of natural occurring EM fields in the Afmag frequency range of 25-720 Hz. As a result of using natural EM fields that pass through the earth as plane waves, the ZTEM system response shares similarities and important differences to traditional inductive source EM systems such as VTEM or MegaTEM, used extensively by the minerals industry to explore for targets of high conductance. While ZTEM can detect discrete conductors like inductive systems, it also responds to bulk changes in resistivity and conductivity gradients that often characterize geological contacts or structures. One important deposit style that typically lacks a discrete conductivity response are porphyry copper-gold deposits, such as commonly found in many locations around the circum Pacific region. The present study will examine the ZTEM responses for several porphyry deposits in light of other exploration data including drilling, mapped geology and other forms of airborne and ground geophysics