What is ZTEM seeing over these tropical porphyry deposits?

Abstract

A ZTEM survey over the Cobre Panama mine lease, which highlights the known porphyry copper deposits in the cluster, is credited with the discovery of a sixth deposit that has been included in the mine plan. The source of the ZTEM response is within the fresh rock below weathered saprolite and extends to a depth of many hundreds of metres, as does the orebody. The response is at least partly due to the sulphide content of the orebody, both pyrite and chalcopyrite. However, the sulphide percentage of all the deposits is quite low, to a maximum of 3% in significant volume. A shallow airborne TEM survey also detects a near-surface, fresh rock signature associated with the ZTEM response of each deposit. Thus the TEM response should probably be attributed in part to the associated alteration, mainly sericitic, and this will contribute to the intensity of the ZTEM signature as well. Inversion modelling in 2D and 3D indicates the ZTEM is detecting deeper parts of the orebodies, with the correct gross geometries, including the main sulphide mineralisation. These conclusions are supported by analysis of multiple deposits in the cluster.