José Perelló

Andean Metallogeny: New Discoveries, Concepts, and Updates

A variety of metals and deposit types define the metallogeny of the Andes from Colombia through Ecuador, Peru, and Bolivia to Argentina and Chile, although porphyry copper and epithermal gold deposits undoubtedly predominate and will continue to do so. Discoveries over the last 30 yrs or so, predominantly in the central Andes and especially Chile, have been made using routine, field-based geologic and complementary geochemical methods, a situation that is considered unlikely to change radically in the foreseeable future. The only clearcut evolutionary change is the increased number of deposits being discovered beneath pre- and postmineral cover. The predictive capacity of conceptual geology has had minimal impact on the Andean discovery record but is thought to offer much promise for the future. This introductory article selects mineralization styles and relationships as well as some broader metallogenic parameters as simple examples of geologic concepts that may assist exploration. Emphasis is placed on porphyry copper ± molybdenum ± gold and high-, intermediate-, and lowsulfidation epithermal gold ± silver deposits, although reference is also made to several carbonate rock-hosted precious and base metal deposit types and styles as well as subvolcanic tin, volcanogenic massive sulfide, and slate-belt and intrusion-related gold deposits. Particular emphasis is placed on the potential for exceptionally high grade porphyry copper, porphyry gold, epithermal gold, and subvolcanic tin deposits. Deposits resulting from the oxidation, enrichment, and chemical transport of copper and zinc and mechanical transport of gold and silver during supergene weathering are also briefly highlighted. Si bien la metalogenia de los Andes de Colombia, Ecuador, Peru, Bolivia y Chile se encuentra definida por una gama de metales y estilos de mineralizacion, son los depositos tipo porfido de cobre y epitermal de oro los que dominan en el presente y continuaran prevaleciendo en el futuro. Los descubrimientos de los ultimos 30 anos, predominantemente en los Andes centrales y especialmente en Chile, han sido realizados mediante metodos geologicos rutinarios de campo, generalmente complementados satisfactoriamente por metodos geoquimicos. Se estima que esta situacion dificilmente experimentara variaciones radicales en un futuro cercano. El unico cambio destacable en esta historia evolutiva esta dado por el aumento apreciable de descubrimientos de depositos cubiertos, bajo cobertura pre o postmineral. A nivel andino, la capacidad predictiva de la geologia conceptual ha tenido un impacto minimo en el numero total de descubrimientos, aunque se piensa que su uso debiera garantizar buenas perspectivas futuras. El presente articulo

Reply to discussions of “Age of the Zambian Copperbelt” by Hitzman and Broughton and Muchez et al.

We thank Hitzman and Broughton (2017) and Muchez et al. (2017) for their anticipated interest in our paper, which, based on 15 Re-Os ages for molybdenite intimately associated with Cu-bearing sulfide minerals from seven deposits and prospects throughout the Zambian part of the Central African Copperbelt, shows that there was a major Cu mineralization event during the Lufilian collisional orogeny (Sillitoe et al. 2017). These ages supplement and further support 12 Re-Os molybdenite dates reported previously from the Domes region in the northwestern part of the Zambian Copperbelt (Sillitoe et al. 2015). Both Hitzman and Broughton and Muchez et al. assemble evidence in defense of their Central African Copperbelt models, which assign important roles to Cu-bearing sulfide formation during sediment diagenesis, in conformity with the longstanding paradigm for sediment-hosted stratiform Cu deposits worldwide (Brown 1981; Hitzman et al. 2005). Nonetheless, Muchez et al. concede that the arenite-hosted deposits, exemplified by Mufulira, as well as the ubiquitous vein-hosted sulfide mineralization throughout the Zambian Copperbelt are Lufilian in age but insist that there was also an earlier syndiagenetic Cu introduction event to generate the weakly or non-metamorphosed shale-hosted deposits. In contrast, Hitzman and Broughton reiterate their previous opinion (Selley et al. 2005; Hitzman et al. 2012) that molybdenite was formed exclusively during a late-stage veining event, as reemphasized by their facetious re-titling of our paper. Both discussions cite selected geological features, sulfide textures, and geochronological results to support syndiagenetic Cu introduction. Many of the points raised were already discussed by Sillitoe et al. (2017) and it would be redundant to repeat the same arguments here. Nonetheless, it is worth reemphasizing several key points as well as