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

Abstract

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 geochronology 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 Ma). An event at 65 to 62 Ma 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 Ma, 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 chalcocite-enargite resource (60 Ma) that is associated with advanced, supergene-enriched argillic alteration.The youngest event includes the Sunnyside porphyry Cu-Mo system and a Cu-Mo breccia deposit at Red Hill (Four Metals mine), both of which formed in large-volume quartz monzonite, granodiorite, quartz monzonite porphyry, and quartz feldspar porphyry (~61-59 Ma). Similar to the Red Mountain system, the Sunnyside system consists of a deep chalcopyrite resource that occurs in ~60 to 59 Ma quartz feldspar porphyry, and a near-surface, slightly younger (~59-58 Ma) enargite-chalcocite-tennantite resource that occurs in quartz feldspar porphyry, quartz monzonite porphyry, and Mesozoic rocks. The Red Hill Cu-Mo breccia deposit is hosted by large-volume quartz monzonite, granodiorite, and quartz monzonite porphyry (~61-59 Ma). Discrepancies between field and paragenetic relationships and some analytic ages at Sunnyside and Red Hill preclude precise dating of mineralization stages, and may reflect disturbance of isotope systems by multiple, co-spatial to j...

Fate of the lower lithosphere during shallow-angle subduction: The Laramide example

“…Meanwhile, magmatism swept inboard, forming ca. 75-55 Ma granitic stocks and associated copper mineralization in the transition zone (Coney and Reynolds, 1977;Vikre et al, 2014). We suggest that the combination of magmatism and crustal thickening-related radiogenic heating precipitated Latest Cretaceous-early Cenozoic zircon growth in dislodged arclogite.…”

“…Our new results indicate that studied arclogitic xenoliths are coeval with the 1 GSA data repository item 2019368, field observations, sample descriptions, analytical methods, and zircon U-Pb data, is online at www.geosociety.org/datarepository/2019. SCB and, with the exception of a small proportion (<10% of analyzed grains) of Latest Cretaceous-early Cenozoic grains, are older than Arizona porphyry copper deposits (Vikre et al, 2014;Chapman et al, 2018;Fig. 2).…”

“…3 and 4). In Late Jurassic time, group 1 (i.e., amphibole-rich arclogite) xenoliths began forming as a mafic keel to continental arc magmas xenoliths with pluton ages from the Mojave Desert (Barth et al, 2008;Wells and Hoisch, 2008;Needy et al, 2009;Chapman et al, 2018) and the CPTZ (Vikre et al, 2014;Tosdal and Wooden, 2015;Chapman et al, 2018). N-number of analyzed samples; n-number of analyzed grains.…”

“…160-140 Ma) and Late Cretaceous (90-70 Ma) arc plutonic assemblages with relatively small amounts of Mesozoic to Neoproterozoic metasedimentary rocks (Wells and Hoisch, 2008;Barth et al, 2008;Needy et al, 2009;Chapman et al, 2018 Repository Fig. DR1 1 ; e.g., Vikre et al, 2014;Tosdal and Wooden, 2015;Chapman et al, 2018). Hence, Latest Cretaceous-early Cenozoic and Early-Middle Jurassic xenolith zircon ages, readily distinguishable from Late Cretaceous and Late Jurassic ages expected from the Mojave Desert, may point to a SW Arizona origin.…”

Porphyry Copper Potential of the United States Southern Basin and Range Using ASTER Data Integrated with Geochemical and Geologic Datasets to Assess Potential Near-Surface Deposits in Well-Explored Permissive Tracts

“…A database of 690 deposits, prospects, and occurrences was compiled in a geographic information system for this study. Primary data sources included the USGS Mineral Resources Data System (USGS, 2016), a database maintained by the Arizona Geological Survey (Richard et al, 2002;Vikre et al, 2014), and numerous journal articles and websites (App . Table A2).…”