Succession of Laramide Magmatic and Magmatic-Hydrothermal Events in the Patagonia Mountains, Santa Cruz County, Arizona

摘要

This investigation of the space-time progression of magmatism and hydrothermal activity in the Patagonia Mountains of southern Arizona is based on field and paragenetic relationships, and on U-Pb and ~(40)Ar/~(39)Ar geo-chronology of igneous and hydrothermal minerals. The Patagonia Mountains consist of Precambrian, Paleozoic, and Mesozoic sedimentary, granitic, and volcanic rocks, Laramide volcanic rocks, and a core of Laramide intrusions that comprise the Patagonia Mountains batholith. Laramide igneous rocks and adjacent Paleozoic and Mesozoic rocks contain significant porphyry Cu-Mo deposits, Mo-Cu breccia pipes, Ag replacement deposits, and numerous other Cu-Pb-Zn-Ag replacement and vein deposits. Ages of igneous and hydrothermal minerals from 20 U-Pb and 52 ~(40)Ar/~(39)Ar determinations define four magmatic and magmatic-hydrothermal events that formed the batholith and altered parts of it and adjacent rocks; cumulatively the events span at least 16 m.y., from -74 to 58 Ma. The oldest event of this succession includes the 74 Ma Washington Camp stock and spatially associated Cu-Pb-Zn-Ag replacement deposits in Paleozoic carbonate rocks of the Washington Camp-Duquesne district. Eruption of 73 to 68 Ma volcanic rocks in the northern part of the range was the next youngest event, which coincides temporally with replacement and vein deposits in Paleozoic carbonate rocks at the Flux mine (-71 Ala). An event at 65 to 62 Ala is marked by emplacement of small-volume quartz monzonite, granodiorite, and diorite intrusions, formation of the Ventura breccia deposit in Jurassic granite at 65 to 64 Ala, and formation of other Pb-Zn-Ag-Cu replacement and vein deposits (-62 Ma; Blue Nose and Morning Glory). The Red Mountain porphyry Cu-Mo system is hosted by -62 Ma granodiorite and Laramide volcanic rocks (73-68 Ma) at the northern end of the batholith. It includes a deep, chalcopyrite-bornite resource (-60 Ma) that is associated with potassic and sericitic alteration and a near-surface chaleocite-enargite resource (60 Ala) that is associated with advanced, supergene-enriched argillic alteration.