The Panulcillo and Teresa de Colmo copper deposits: two contrasting examples of fe-ox Cu-Au mineralization from the Coastal Cordillera of Chile

The Coastal Cordillera of Chile hosts several world-class FeOx CuAu deposits, including Candelaria, Mantos Blancos, Manto Verde, and El Soldado. Despite this comparatively little has been published on Chilean FeOx CuAu systems. This paper presents observations from two small Chilean FeOx CuAu deposits of Lower Cretaceous age; Panulcilio and Teresa de Colmo.

Panulcilio is a pseudo-stratiform FeOx CuAu / Skarn deposit located within the metamorphic aureole of a monzodioritic intrusive. Chalcopyrite, bornite, pyrite and pyrrhotite occur with calcic amphibole as disseminations and microveinlets in K-feldspar-albite-silica altered meta-andesites, magnetite-albite-scapolite rich mcta-andcsites and in overlying garnet skam.

Teresa de Colmo is a multiphase hydrothermal - tectonic breccia deposit associated with the emplacement of a leucodioritic stock. Chalcopyrite and pyrite is associated with albite and chlorite alteration and has been incorporated in a specularite-matrix breccia that cuts andesitic volcanic and sedimentary country rocks.

Although both deposits show many similarities, such as the presence of abundant Fe-oxides, Cu sulphides, strong pervasive sodic alteration and a spatial relationship to differentiated intermediate intrusives, they also show many significant differences. While Panulcilio appears to have formed in a semi-ductile regime and has abundant potassic alteration, amphibole and magnetite, Teresa de Colmo seems to have formed in a brittle regime, lacks potassic alteration, and has chlorite and specularite.

We consider these variations to be inherent in the FeOx CuAu family of deposits, and suggest that they do not reflect different ore-forming processes but rather changes in oxygen and sulphur fugacities, chemical equilibria, temperature and tectonic regime due to differing host rocks and levels of emplacement.