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The Panulcillo and Teresa de Colmo Copper Deposits; Two Contrasting Examples of Fe-Ox Cu-Au Mineralisation from the Coastal Cordillera of Chile.
by
David Hopper & Arturo Correa, Rio Tinto Mining and Exploration Limited, Chile.

in - Porter, T.M. (Ed), 2002 - Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC        Publishing, Adelaide, v. 1, pp 177-189.

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ABSTRACT

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

Panulcillo is a pseudo-stratiform FeOx Cu-Au / 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 meta-andesites and in overlying garnet skarn.

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 Panulcillo 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 Cu-Au 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.

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