A Reconstructed Cretaceous Depositional Setting for Giant Volcanogenic Massive Sulfide Deposits at Tambogrande, Northwestern Peru
Lawrence S. Winter, Richard M. Tosdal, James M. Franklin, Peter Tegart, 2005. "A Reconstructed Cretaceous Depositional Setting for Giant Volcanogenic Massive Sulfide Deposits at Tambogrande, Northwestern Peru", Andean Metallogeny: New Discoveries, Concepts, and Updates, Richard H. Sillitoe, José Perelló, César E. Vidal
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The Cretaceous Tambogrande volcanogenic massive sulfide (VMS) deposits of northwestern Peru represent some of the largest Cu-Zn-Au-Ag bimodal-mafic VMS deposits in the world. There are currently three known deposits each with approximately 100 million metric tons (Mt) of massive pyrite-rich sulfide. The deposits are intimately associated with dacite lava dome complexes and were deposited within steep-sided basins on the sea floor. Reconstructed sea-floor paleogeomorphic models suggest that sulfide deposition was concentrated in the deepest parts of the basins. Sulfide deposition accompanied synvolcanic faulting and episodic dacitic and basaltic eruptions. A series of time-stratigraphic horizons are defined at the TG1 and TG3 deposits and mark stages in the development of the volcanic complex and massive sulfide bodies. There is only limited evidence for replacement of host rocks during formation of the Tambogrande deposits, in contrast to many other large massive sulfide deposits. The deposits at Tambogrande resulted from focused hydrothermal fluid flow along synvolcanic faults with deposition of sulfide minerals within deep and restricted basins. These depressions, the results of the structural and volcanologic setting, acted as efficient traps for sulfide deposition and were also important for the preservation of the sulfide masses as they acted to shield them from submarine oxidation and weathering. Steep basins and episodic bimodal lava eruptions are key geologic attributes of the depositional setting at Tambogrande and may be necessary for the formation of anomalously large VMS deposits in a volcanic-rock–dominated environment.
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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, Perú, Bolivia y Chile se encuentra definida por una gama de metales y estilos de mineralización, son los depósitos tipo pórfido de cobre y epitermal de oro los que dominan en el presente y continuarán prevaleciendo en el futuro. Los descubrimientos de los últimos 30 años, predominantemente en los Andes centrales y especialmente en Chile, han sido realizados mediante métodos geológicos rutinarios de campo, generalmente complementados satisfactoriamente por métodos geoquímicos. Se estima que esta situación difícilmente experimentará variaciones radicales en un futuro cercano. El único cambio destacable en esta historia evolutiva está dado por el aumento apreciable de descubrimientos de depósitos cubiertos, bajo cobertura pre o postmineral. A nivel andino, la capacidad predictiva de la geología conceptual ha tenido un impacto mínimo en el número total de descubrimientos, aunque se piensa que su uso debiera garantizar buenas perspectivas futuras. El presente artículo