Discovery of the Ujina Cu deposit, Collahuasi District, Chile

Abstract

The Collahuasi District of Chile, situated high in the Andean antiplano, approximately 4300m ASL, is a historic mining district. In 1990 the Collahuasi joint-venture (Falconbridge, Chevron, Shell), refocused its exploration efforts from exploring a small high-grade vein resource in the Rosario porphyry area to a more regional evaluation for primary and secondary Cu mineralization. As part of this process, an IP test survey, carried out on the property in 1979, was uncovered and recompiled. The new interpretation indicated that, unlike elsewhere in Chile, conductive cover and poor ground conditions were not problematic. Also, IP and resistivity response from this survey to known ore was clear-cut and suggested that IP was ideally suited to the terrain and the target. The ensuing 200 km IP/resistivity program not only defined the Rosario/La Grande porphyry system (710 mT @ 0.93% Cu) in its entirety, but also led to the discovery of a totally new resource, the Ujina deposit (1200 mT @ 0.8% Cu, including 126 mT of secondary enrichment), under 170 meters of ignimbrite cover.