Geology, Geochronology, and Hf and Pb Isotope Data of the Raul-Condestable Iron Oxide-Copper-Gold Deposit, Central Coast of Peru

Abstract

Raúl-Condestable is a >32 million metric ton (Mt) iron oxide-copper-gold (IOCG) deposit located on the Peruvian coast, 90 km south of Lima. The ore occurs as veins, replacement "mantos," and disseminations consisting of a chalcopyrite-pyrite-pyrrhotite-magnetite-amphibole mineral association. The geology of the studied area comprises a series of superposed volcanic edifices of Late Jurassic to Early Cretaceous age, which are part of a larger volcanic island to continental arc system. Particularly good exposures of the tilted host sequence allow the mapping of the Raúl-Condestable IOCG deposit in a nearly complete oblique cross section, from its associated volcanic edifice down to a paleodepth of about 6 km.U-Pb zircon ages indicate that in the deposit area felsic magmatic activity took place between 116.7 ± 0.4 and 114.5 ± 1 Ma, defining a new Raúl-Condestable superunit, the oldest so far, of the Peruvian Coastal batholith. This superunit is located west of the main part of the batholith and includes a dacite-andesite volcanic dome and a subvolcanic quartz-diorite porphyry sill-dike complex that were emplaced at 116.7 ± 0.4 and 116.4 ±0.3 Ma, respectively, followed by tonalite stocks and dikes emplaced between 115.1 ± 0.4 and 114.5 ± 1 Ma. All these rocks contain hornblende and/or biotite but no pyroxene and correspond to silica-and waterrich magmas following a calcic differentiation trend. Hf isotope data on zircons (εHf(115 Ma) = 5.2-7.5) and Pb isotope data on whole rock, combined with lithogeochemical results, suggest that magmas were generated by partial melting of the upper mantle, enriched through hydrous metasomatism and/or melting of subducted pelagic sediments. The lack of zircon inheritance suggests that there was no direct involvement of continental crust.The Raúl-Condestable IOCG deposit is connected in space and time with the magmatism of the Raúl-Condestable superunit. The mineralization was emplaced in the core of the dacite-andesite volcanic dome at a paleodepth of 2 to 3 km, surrounding two tonalitic intrusions formed at 115.1 ± 0.4 and 114.8 ± 0.4 Ma. The U-Pb age of hydrothermal titanite from IOCG veins at 115.2 ± 0.3 Ma indicates that the mineralization was coeval with (or more probably just followed) the emplacement of the tonalites. Re-Os geochronology on molybdenite did not yield reliable ages due to apparent Re loss. Copper ore is associated with a zoned alteration pattern, which surrounds the tonalite intrusions. It consists of a core of biotite alteration and quartz stockwork, †

Geochronology and geochemistry of igneous rocks in the Bailingshan area: Implications for the tectonic setting of late Paleozoic magmatism and iron skarn mineralization in the eastern Tianshan, NW China

“…However, the lack of inherited zircons in the dacite suggests that crustal contamination only played a minor role in the petrogenesis (De Haller et al, 2006).…”

“…14c-d), with a tectonic regime unambiguously dominated by back (intra)-arc basin-arc transition. These Central Andean batholiths are widely accepted to be dominantly generated by the remelting of isotopically juvenile crust (e.g., back-arc basin basaltic rocks) and mixing with minor mantle components during basin inversion (Atherton, 1990;Polliand et al, 2005;De Haller et al, 2006;Mišković and Schaltegger, 2009;Boekhout et al, 2012;Cochrane et al, 2014).…”

Spatial and temporal evolution of Liassic to Paleocene arc activity in southern Peru unraveled by zircon U–Pb and Hf in-situ data on plutonic rocks

“…A major part of the plutonic rocks from central and northern Peru (between 14 and 5°S) were emplaced between 90 and 65 Ma, with some intrusions around 117 and 100 Ma (De Haller et al, 2006;Mukasa, 1986a). In Chile, distinct episodes of pluton emplacement have also been described between 18°S and 56°S.…”

Mesozoic Iron Oxide Copper-Gold Mineralization in the Central Andes and the Gondwana Supercontinent Breakup

“…A direct connection between IOCG ore-forming processes and tholeiitic to calc-alkaline, subduction-related magmatism has been identified (Vila et al, 1996;Marschik and Fontboté, 2001;Rhodes and Oreskes, 1999;Sillitoe, 2003;de Haller et al, 2006). Although field evidence and more recent data from fluid inclusions and stable isotopes have confirmed that the intervention of nonmagmatic fluids, e.g., seawater or evaporite-derived basinal brines, may play an important role in the generation of Cu (-Au) mineralization (Ripley and Ohmoto, 1977;Ullrich and Clark, 1999;Ullrich et al, 2001;de Haller et al, 2002;Benavides et al, 2007;Chen et al, 2011).…”