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[Display omitted] • Variable Fe isotopic composition in metallic minerals controlled by multiple factors. • Magmas may be the main source providing iron to form the Beiya deposit. • Post-magmatism hydrothermal activities play a major role on leaching the metals out and transporting them to the mineralization area. The Beiya Au-base metal deposit in southwest China is characterised by a huge amount of iron associated with gold mineralization. The formation of the Beiya deposit is generally thought to be related to Tertiary potassic intrusion, as porphyry- and skarn-type mineralization are the two most important types of mineralization in the region. However, the lack of direct evidence to constrain the source of iron and gold as well as other metals makes it difficult to accurately conceptualise the ore genesis model. In this study, we report high-precision (0.03 ‰; 2sd) Fe isotope data on Fe-bearing minerals including magnetite, pyrite and chalcopyrite, and major igneous rocks exposed in the area, including monzogranite porphyry (MGP), mafic microgranular enclave (MME), lamprophyre and basalt. Magnetites have a wide range of δ Fe from 0.15 to 0.64 ‰, reflecting substantial isotopic fractionation at different mineralization stages. MMEs have heaviest Fe isotopic composition (0.35 ‰ to 0.88 ‰) compared to MGPs (0.19 ‰ to 0.48 ‰), lamprophyre (∼0.2 ‰) and basalt (∼0.0 ‰). A negative correlation between δ56Fe and TFe 2 O 3 is found for both MPGs and MMEs, which indicates the leaching of iron by hydrothermal fluids mobilizes light Fe and leaves behind isotopically heavy Fe in the remaining source rock. Fe isotopic compositions of MPG and MME overlap with those of magnetite, both of which are proposed to be the source of Fe in magnetite. The basalt has δ56Fe value of 0 ± 0.03 ‰, similar to those of global basalts, suggesting a negligible contribution to the formation of iron ores. Therefore, we propose that magmas parental to the MGP and MME may be the main source of iron to form the Beiya deposit; post-magmatism hydrothermal activities play a key role in leaching the metals out and transporting them to the mineralization area. [ABSTRACT FROM AUTHOR]

Recent marine mineral investigations in the South China Sea (SCS) have found increasingly significant abundances of Fe–Mn polymetallic crusts and nodules with variable substrates and nuclei. There is, however, no systematic and complete study of the SCS crusts and nodules. The lack of mineralogical and geochemical studies affects our explicit understanding of the mineralization characteristics and genesis of the crusts and nodules. In this study, we analyzed a set of SCS polymetallic crusts and nodules obtained from ten sites to determine their mineralogy, chemistry, and Fe and Os isotopes. The SCS crusts/nodules are composed predominantly of vernadite (δ–MnO 2 ) and amorphous Fe oxides/hydroxides. The nodules also contain minor todorokite. TEM imaging and electron diffractions show that the Fe–Mn minerals are nano–sized minerals with very poor crystallinity. Nitrogen adsorption/desorption analysis indicates an average specific surface area of 257.128 m 2 /g for the SCS crusts and nodules, and main apertures of 2–10 nm for their nanopores in the Fe–Mn minerals. It is noteworthy that the SCS crusts/nodules contain substantial amount of terrigenous detritus, suggesting that marginal sea–type Fe–Mn deposits are strongly influenced by terrigenous sedimentary input. Furthermore, geochemical analysis indicates that the SCS crusts/nodules have relatively lower Co (1482 ppm), Cu (556.2 ppm), Ni (3132 ppm), Mo (276.2 ppm), and Zn (598.3 ppm) compared to open oceanic crusts/nodules, but relatively high concentrations of REY (1647 ppm), PGE (234.0 ppb), Ba (1056 ppm), Pb (1878 ppm), Sr (995.9 ppm), Te (28.81 ppm), and Tl (67.87 ppm). Iron isotopic compositions suggest that the Fe sources of the SCS crusts/nodules may have been Fe dissolved in terrigenous (fluvial) inputs. Osmium isotopes indicate that the main ore–forming elements came directly from the ambient seawater, which was mainly influenced by terrigenous inputs, although there may have been mixing with minor mantle–derived signatures. Evidence from mineralogy, major element geochemistry, shale–normalized rare earth element (REE) patterns, and the Fe and Os isotopes suggest that the SCS crusts/nodules are mainly hydrogenetic, whilst the formation of some nodules may have been contributed by minor pore waters of their surrounding sediments. The SCS crusts/nodules had probably much higher growth rates (mean 19.20 mm/Ma) than most hydrogenetic Fe–Mn deposits in other open oceans, which are typical of marginal sea Fe–Mn deposits that contain sufficient supply of ore–forming terrigenous detritus. Grades of some critical metals of economic interest (notably Co, Cu, Ni, Mo, and Zn) are slightly lower in the SCS crusts and nodules than in the crust and nodules from Pacific prime mineralization zones. Concentrations of Mn, REY, Pt, Mo, Co, Te, and Bi, however, show relatively high concentrations relative to the continental crust. The SCS crusts and nodules could thus represent a strategic REE, Co and Pt resource, and will likely catalyse additional investigation of seabed resources in the South China Sea. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetite can be used to trace metal and fluid sources in iron oxide copper gold (IOCG) deposits using O, Fe, and Ti stable isotope geochemistry. • This is the first work to explore Ti isotope geochemistry in a hydrothermal system and in a mineral deposit. • Magnetite from the Ernest Henry IOCG deposit in Queensland, Australia exhibits magmatic O isotope signatures, but non-magmatic Fe isotope signatures, suggesting that much of the Fe in the deposit was sourced from the leaching of crustal rocks by magmatic-hydrothermal fluids. • Ti isotope signatures indicate that Ti was mobilized during the mineralization of the copper ore resulting in Ti isotope compositions that are more fractionated than what has been observed in magmatic systems. Iron oxide copper gold (IOCG) deposits are globally important sources of Cu; however, their origins remain poorly understood with respect to the metal and fluid sources involved in their formation. In this work, we utilize integrated Fe, Ti, and O isotopic data for magnetite to trace major metal and fluid inputs for the Proterozoic-aged Ernest Henry IOCG deposit—the largest known IOCG deposit in the Cloncurry District, Queensland, Australia. Magnetite separates from ore stage and pre-ore biotite-magnetite (bt-mgt) and magnetite-actinolite (mgt-act) alteration assemblages from Ernest Henry were analyzed for their O, Fe, and Ti isotope abundances, reported as δ18O (VSMOW), δ56Fe (IRMM-14), and δ49Ti (OL-Ti). Select magnetite samples were also analyzed for 17O (reported as Δ'17O 0.5305) and range from −0.118 to −0.056 ‰—suggesting evaporitic input. The δ18O values from ore stage (+1.57 to +7.36 ‰), bt-mgt (+0.34 to +5.68 ‰), and mgt-act (+1.68 to +2.10 ‰) samples are consistent with a magmatic-hydrothermal origin for ore and pre-ore mineralizing fluids at Ernest Henry; non-magmatic δ18O values > c. 5 ‰ may be explained through localized carbonate wall rock assimilation. Despite this, δ56Fe values for ore stage (−0.50 to +0.33 ‰), bt-mgt (−0.65 to +0.38 ‰), and mgt-act (−0.26 to +0.30 ‰) magnetite are generally isotopically lighter than the accepted range (c. +0.06 to +0.49 ‰) for igneous and magmatic-hydrothermal magnetite and exhibit a relatively large range of c. 1 ‰, suggesting Fe source mixing within the deposit. Ore stage magnetite δ49Ti (−1.64 to + 3.79 ‰; avg: +1.49 ‰; 2σ = 2.63 ‰) compositions are generally higher and more variable than either the bt-mgt (-0.44 to + 1.49 ‰; avg: +0.62 ‰; 2σ = 1.13 ‰) or mgt-act (+0.27 to + 1.89 ‰; avg: +1.05 ‰; 2σ = 1.56 ‰) and suggest that Ti isotope fractionation occurred due to differential mobility in the fluid. The data are best explained by models invoking both magmatic and non-magmatic metal and fluid input. Fluid flow channeled between the footwall and hanging wall shear zones introduced non-magmatic Fe that may have been leached from local mafic units by magmatic-hydrothermal fluids, resulting in neoformed and regeneratively replaced magnetite with magmatic δ18O, but non-magmatic δ56Fe values during pre-ore alteration. These fluids may have mixed with Fe-poor evaporitic fluids prior to magnetite formation. Later magmatic Fe and O contributions during ore stage mineralization resulted in magnetite with variable δ56Fe and irresolvable δ18O overprinting. Ernest Henry is the first known example of an IOCG deposit with a major leached metal component identified through metal stable isotope geochemistry. [ABSTRACT FROM AUTHOR]

• Gol-e-Gohar iron ore district is of Kiruna type. • Host rocks include meta-sedimentary rocks, meta-basalt and meta-granite. • O and Fe isotopes of magnetite indicate a magmatic-hydrothermal (high-T) origin. • The Gol-e-Gohar represents a disrupted fragment of the Kashmar-Kerman arcent. The Gol-e-Gohar iron ore district in the Sanandaj-Sirjan zone of south-western Iran comprises six major ore bodies. The largest deposit is Gol-e-Gohar No. 3 (Gohar-Zamin) with about 643 Mt @ 53.1% Fe. The host rocks in this district are Late Neoproterozoic meta-sedimentary rocks (para-gneiss, marble), meta-basalt (ortho-amphibolite), and I-type meta-granite (ortho-gneiss). The district is characterized by potassic-sodic (albite-K-feldspar), phyllic (muscovite) and propylitic (chlorite-calcite-dolomite-magnesite with pyrite) hydrothermal alteration, and massive and brecciated Kiruna-type magnetite ± apatite mineralization. There is also boron (B) metasomatism, manifested as tourmaline blastesis. Gol-e-Gohar magnetite contains Mg, Ca and Si up to the percent range, V and Ti in the 100s ppm level, and low Cr, Co, Ni in the tens of ppm range, typical of skarn or IOCG mineralization. The oxygen isotope composition of magnetite is 4.9 ± 0.7‰ δ18O (n = 9) and the iron isotope composition is 0.49 ± 0.05‰ δ56Fe (n = 17). These data suggest that the magnetite ore formed from a magmatic-hydrothermal (high-T) fluid in equilibrium with a granitic source. The hydrothermal carbonate inclusions in late pyrite have δ11B values of 20.3 ± 2.4‰, indicating the imprint of fluids which interacted with the Early Cambrian marine country rocks of the district, such as limestone and/or evaporites. The Gol-e-Gohar iron ore district shows several similarities to the Bafq iron district, located about 400 km to the north, and seems to be a disrupted member of the Kashmar-Kerman arc. [ABSTRACT FROM AUTHOR]

• Fe and Sr isotope study of both dolomite-related and serpentinite-related nephrite. • Fe in serpentinite-hosted is from serpentinite, and in dolomite-hosted from granite. • Progressive rise of δ56Fe and δ57Fe from marble, towards nephrite. • Progressive rise of δ56Fe and δ57Fe from ophiolitic serpentinite, towards nephrite. • Sr isotopes and structural data suggest involvement of two age groups of granites. Nephrites belonging to both the dolomite-related and serpentinite-related genetic types, from the Złoty Stok deposit, and Jordanów Śląski and Nasławice prospects in the Ślęża Ophiolite, respectively, were analyzed for Fe and Sr isotope compositions. These deposits in the Central Sudetes (SW Poland), are unusually situated relatively close to each other. This study is a first attempt to perform combined Fe and Sr isotope study of nephrites. Our results show that Fe in the Fe-As-Au-bearing skarn samples from Złoty Stok (2.77–7.00 wt% Fe, δ56Fe +0.07 to +0.14‰, and δ57Fe +0.12 to +0.21‰), to which the dolomite-related nephrite belongs, is not inherited from the host dolomitic marbles (ca. 0.4 wt% Fe; δ56Fe −0.08 to −0.07‰, and δ57Fe −0.12 to −0.09‰), but derived from the nearby, ca. 340 Ma granite intrusion (2.64–5.64 wt% Fe). In contrast, iron in the serpentinite-related nephrites (2.06–3.88 wt% Fe, δ56Fe +0.41 to +0.45‰, and δ57Fe +0.59 to +0.66‰) was likely inherited from host serpentinites (5.27–4.81 wt% Fe), rather than metasomatically derived from adjacent granite intrusions (0.13–0.45 wt% Fe). Moreover, both the marble transformation into a dolomite-related nephrite (and Fe-As-Au-bearing skarn), and the abyssal serpentinite – through ophiolite – towards serpentinite-related nephrite transformation, are accompanied by a progressive increase of δ56Fe and δ57Fe. This increase is regardless of changes in the bulk Fe content, increasing during the dolomite-related nephrite formation, and decreasing during serpentinite-related nephrite formation. This phenomena may be caused by one of the below listed factors, or combinations: a) preferential incorporation of heavy iron by tremolite and diopside; b) preferential incorporation of the heavy iron in the Fe3+-bearing phases, crystallizing during nephrite formation; c) preferential incorporation of the heavy Fe from migrating granite-derived fluids (positive fractionation between aqueous Fe-bearing fluid, and tremolite/diopside); d) positive isotope fractionation between dolomite/antigorite precursor, and newly formed amphibole/clinopyroxene; e) change of the Fe oxidation state. Furthermore, Fe in the rock-forming tremolite from the serpentinite-related nephrites is isotopically heavier than Fe in tremolite from the dolomite-related ones. In contrast to the iron, the isotopic composition of strontium, combined with its content and structural evidence, suggest multiple sources for this element. In the case of the dolomite-related nephrite (ca. 3–4 ppm Sr; initial 87Sr/86Sr = 0.7085), Sr inheritance from the host-dolomitic marble (ca. 90 ppm Sr; initial 87Sr/86Sr = 0.7081), as well as its derivation from intrusions of both the syn- to late-tectonic, ca. 340 Ma granites (ca. 400–440 ppm Sr), and post-tectonic ~305 Ma granites (86.4 ppm Sr), is suggested. In the case of the serpentinite-related nephrite (6.3–61.7 ppm Sr; initial 87Sr/86Sr 0.7037 to 0.7081), the situation is similar, i.e., Sr in the most primitive samples tends to be sourced from ophiolitic rocks (up to 2.4 ppm Sr in serpentinite), whereas in the more evolved types, it was likely delivered from the adjacent, ca. 340 Ma partially rodingitized granites (8.8–102.6 ppm Sr), as well as ~305 Ma granites (ca. 80 ppm Sr). Moreover, these granites caused the fluid-flow, responsible for Sr-bearing clinozoisite vein formation; these veins are likely related with nephrite formation, and with a metallic mineralization. [ABSTRACT FROM AUTHOR]