Balboa

Authors: Jean Legault, Chris Wijns, Carlos Izarra, and Geoffrey Plastow
Reviewer: Seogi Kang, Douglas Oldenburg, and Lindsey J. Heagy

Prelude

This case history describes the inversion of ZTEM airborne EM and magnetic data over the porphyry copper-gold camp at Cobre Mine, Panama. Data collected as part of this case history were flown in the summer of 2010. This case history was adapted from the expanded abstract “The Balboa ZTEM Cu-Mo-Au porphyry discovery at Cobre Panama”.

Abstract

This paper describes the ZTEM airborne EM and magnetic inversion results over the porphyry copper-gold camp at Cobre Panama. We focus on the discovery of the blind Balboa deposit in 2010; this is the first documented blind discovery attributed to the ZTEM system. Balboa is the westernmost of six porphyry copper-gold deposits that make up Cobre Panama. It escaped detection in 40 years of exploration that relied primarily on soil geochemistry, airborne magnetics and drilling. ZTEM was flown in the summer of 2010 to see if it could detect resistivity variations related to porphyry systems hidden in a region of dense jungle, difficult to access, and covered by a thick (20-30 m) conductive saprolite layer The ZTEM survey detected all of the known porphyry systems, including Balboa, based on anomalous conductive responses. Our study presents the geophysical survey results at Cobre Panama and is supported by 2D-3D ZTEM and magnetic inversions that appear to validate the survey evidence. 2D synthetic modeling appears to confirm the detectability of the weakly conductive Balboa orebody below 30 m of saprolite cover.