Space-Time Relationships of Some Porphyry Cu-Au, Epithermal Au, and Other Magmatic-Related Mineral Deposits in Northern Peru
Donald C. Noble, César E. Vidal, Jose Perelló, Rodríguez P. Omar, 2005. "Space-Time Relationships of Some Porphyry Cu-Au, Epithermal Au, and Other Magmatic-Related Mineral Deposits in Northern Peru", Andean Metallogeny: New Discoveries, Concepts, and Updates, Richard H. Sillitoe, José Perelló, César E. Vidal
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A 40Ar/39Ar age of 16.94 ± 0.34 Ma on hypogene alunite from the La Virgen sedimentary and volcanic rockhosted Au deposit and new ages of 16.06 ± 0.11 to 15.58 ± 0.12 Ma on porphyry Cu-Au deposits at Minas Conga confirm the existence of early Miocene and earliest middle Miocene mineralization in the eastern part of the Miocene metallogenic belt of northern Peru. A new K-Ar age of 15.3 ± 0.3 Ma for the Magistral porphyry-skarn Cu-Mo deposit extends the belt of known early and middle Miocene deposits southeast of La Virgen. A 40Ar/39Ar age of 20.02 ± 0.15 Ma is reported for a late intrusive phase at the Michiquillay porphyry Cu deposit.
A 40Ar/39Ar plateau age of 15.61 ± 0.12 Ma on alunite from the San Pedro Sur zone at the La Zanja epithermal Au district is consistent with the location of the district within the middle Miocene Quiruvilca-Pierina subbelt of the Miocene metallogenic belt. 40Ar/39Ar mineralization ages of 20.79 ± 0.10 and 21.78 ± 0.11 Ma have been obtained on mineral deposits of the Malvas and Huinac districts in the Cordillera Negra to the south. Together with a published age of 18.7 ± 0.6 Ma on the Churropampa Au prospect in the eastern part of the Cordillera Negra and a new Re-Os age of 18.15 ± 0.06 Ma on the Pachagón porphyry Cu-Ag prospect northeast of Trujillo, an early Miocene mineral activity in the western part of the metallogenic belt is indicated. The new ages show that clearly magmatically related mineralization was formed at the same latitudes in both the eastern and western parts of the Miocene metallogenic belt during early Miocene and earliest middle Miocene times.
The deposits of the giant Yanacocha Au district, which were formed at about 11 Ma, are younger than deposits to the west and to the east. Deposits of the Hualgayoc district to the north, which have yielded mineralization ages from 12.4 ± 0.4 to 14.4 ± 0.2 Ma, may overlap in time with those of Yanacocha. These districts, which are located within large coeval volcanic fields, could reflect a younger episode of magmatic activity of late middle Miocene age.
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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