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The Naozhi deposit of northeast China comprises intermediate-sulfidation epithermal-style veins and subeconomic, porphyry-style Cu mineralization hosted by dioritic to granitic plutons, which formed at ca. 130 Ma. These intrusive phases were fed by magmas that ponded at mid- to upper-crustal levels and were finally emplaced at < 0.6 kbar based on amphibole geobarometry. The magmas were moderately oxidized (∆NNO − 0.35 to 2.21; with NNO being the nickel–nickel–oxide buffer) and water-rich (mostly > 4 wt. %), and likely experienced a relatively prolonged evolution in the shallow crust rather than at depth. Magma devolatilization and fluid exsolution at shallow-crustal levels lead to decreases in both oxygen fugacity (log ƒO2 − 10.96 to − 14.13) and water content (6.53 to 2.26 wt. %) at < 2.5 kbar pressures. Thermochronological data of zircon and apatite, thermal history modeling, and geological preservation record complex time–temperature histories of the mineralized intrusive rocks, from the cooling of the parent magma itself through burial by younger volcanic rocks to protracted erosion with time. It is estimated that < 2 km of pre-mineralization material was removed from the top of the Naozhi magmatic–hydrothermal system from the Early Cretaceous to present. A 108 ± 2 Ma volcanic event possibly tilted the hydrothermal system, but buried the ores, protecting them from extensive erosion. [ABSTRACT FROM AUTHOR]

The Talate ore field is located in the Abagong polymetallic metallogenic belt of the Altay Orogen, NW China. Lenticular ore bodies occur in the Kangbutiebao Formation, a package of intermediate-felsic marine volcanic rocks and terrigenous clastic sedimentary-carbonate rocks. Skarn alteration (mainly garnet) is present in both ore and wall rocks, especially the carbonate rocks. The mineral assemblages and cross-cutting relationships of veins allow the alteration and mineralization process to be divided into four stages. From early to late, these are the early skarn (E-skarn), the late skarn with quartz-magnetite veins (QM), the quartz-sulphide (QS) and the quartz-carbonate (QC) assemblages. Quartz crystals are important gangue minerals in the latter three stages, in which four distinct compositions of fluid inclusions are identified based on petrography, microthermometry and laser Raman microspectroscopy, namely aqueous inclusions (W-type), pure CO2 inclusions (PC-type), CO2-rich inclusions (C-type) and daughter mineral-bearing inclusions (S-type). Microthermometric data and laser Raman analyses show that the quartz crystals from the QM stage contain all four inclusion types, with the W-type being predominant. Homogenization temperatures range between 271 and 426 °C. The salinities of the W- and C-type fluid inclusions range from 0.5 to 22.4 wt.% NaCl eqv., whereas the S-type fluid inclusions in the QM stage range from 31 to 41 wt.% NaCl eqv. Daughter minerals in the fluid inclusions include halite, sylvite, pyrite and calcite. Quartz from the QS stage (main mineralization stage) contains the W-, C- and PC-type inclusions, which are homogenized at temperatures of 204-269 °C, with salinities of 0.2-15.6 wt.% NaCl eqv. Only W-type fluid inclusions have been identified in the QC stage. These yielded homogenizing temperatures of 175-211 °C and salinities of 1.1-9.9 wt.% NaCl eqv. The C-type fluid inclusions of the main (QS) mineralization stage yield trapping pressures of 107-171 MPa, corresponding to a depth of 4-6 km. The sulphur isotope values (−1.7‰ and −6.6‰) imply that the QS stage may not be directly associated with the early skarn (−7.4‰) and quartz-magnetite stages (−4.8‰ and −5.0‰), though the QS stage is probably dominated by magmatic-hydrothermal fluids. 40Ar/39Ar isotope plateau ages of 227.6 and 214.1 Ma for biotite separated from the QM and QS stages are significantly younger than the host Kangbutiebao Formation ( ca. 410 Ma). The Talate Pb-Zn(-Fe) deposit is interpreted to be an unusual skarn-type system formed in a continental collision orogeny. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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The Mesoproterozoic 1108–1105 Ma Osler Group, a 3 km thick succession of basaltic flows and sedimentary units on the north shore of Lake Superior, is among the oldest expressions of the Midcontinent Rift. Basal sediments of the Simpson Island Formation (new name) deposited by braided fluvial systems record westward transport of debris eroded from local Archean and Proterozoic rock units. Strata deposited by this fluvial system are intercalated with, and overlain by, ocean-island basalt (OIB)-like basalts, which become increasingly contaminated up section (εNd(1100Ma) = +0.3 to –5.3). The light rare-earth element (LREE) enriched (La/Smn = 1.5–3.9) and heavy REE (HREE) fractionated (Gd/Ybn = 1.5–3.7) subaerial flows are divisible into two units that correlate with other sections of the Osler Group to the east, but simple correlations with more distant sequences are difficult. The volcanic rock dominated portion of the succession is overlain by a thin (25 m thick) conglomerate–sandstone assemblage representing southeast progradation of an alluvial fan in a semi-arid climatic setting. Clast lithologies and geochemistry indicate no extra-rift detritus was delivered from the hinterland of the fan. Various lines of evidence in both volcanic and sedimentary rocks support a scenario where early, pre-1108 Ma, subsidence along a north–south axis from the western arm of the rift to the Nipigon Embayment was replaced by subsidence along the east–west rift axis between 1108 and 1105 Ma. [ABSTRACT FROM AUTHOR]

Protracted magma storage in the deep crust is a key stage in the formation of evolved, hydrous arc magmas that can result in explosive volcanism and the formation of economically valuable magmatic-hydrothermal ore deposits. High magmatic water content in the deep crust results in extensive amphibole ± garnet fractionation and the suppression of plagioclase crystallization as recorded by elevated Sr/Y ratios and high Eu (high Eu/Eu*) in the melt. Here, we use a novel approach to track the petrogenesis of arc magmas using apatite trace element chemistry in volcanic formations from the Cenozoic arc of central Chile. These rocks formed in a magmatic cycle that culminated in high-Sr/Y magmatism and porphyry ore deposit formation in the Miocene. We use Sr/Y, Eu/Eu*, and Mg in apatite to track discrete stages of arc magma evolution. We apply fractional crystallization modeling to show that early-crystallizing apatite can inherit a high-Sr/Y and high-Eu/Eu* melt chemistry signature that is predetermined by amphibole-dominated fractional crystallization in the lower crust. Our modeling shows that crystallization of the in situ host-rock mineral assemblage in the shallow crust causes competition for trace elements in the melt that leads to apatite compositions diverging from bulk-magma chemistry. Understanding this decoupling behavior is important for the use of apatite as an indicator of metallogenic fertility in arcs and for interpretation of provenance in detrital studies. [ABSTRACT FROM AUTHOR]