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[Display omitted] • Tourmaline in muscovite is of schorl type and tourmaline in barren and ore-bearing pegmatite are of oxy-schorl and fluor-elbaite. • Local fluid/melt composition may have influenced the tourmaline trace element compositions. • Fluid exsolution occurred in ore-bearing pegmatite with high Li contents. • B-isotope variation among tourmaline types linked to melt-fluid-tourmaline fractionation. The Bailongshan in the West Kunlun Orogen (northern Tibet) is a newly-discovered super-large rare-metal (Li-Rb(-Be-Ta-Nb)) pegmatite deposit. Tourmaline occurs widely in muscovite granites and pegmatites at Bailongshan, but comprehensive study is yet to be done on the geochemical evolution of tourmaline from the magmatic to the hydrothermal stages. Here, we present a systematic study of in-situ major, trace elemental and boron isotopic variations of tourmaline from Bailongshan deposit, and discuss the tourmaline genesis and how boron isotopes change during the magmatic to hydrothermal stage. Three types of tourmaline have been identified at Bailongshan deposit, including disseminated tourmaline in the muscovite granite, medium-coarse-grained euhedral tourmaline in the barren pegmatite, and multicolored medium-coarse-grained tourmaline in the ore-bearing pegmatite. EPMA and LA-ICP-MS geochemical analyses reveal that the tourmaline samples belong mainly to alkali group, with the tourmalines from the muscovite granite and the barren pegmatite falling into the schorl solid-solution series and the ore-bearing pegmatite falling into elbaite. There is a major chemical change from Fe-rich compositions with moderate Al in the Y-sites (muscovite granite and barren pegmatite) to Li-rich compositions with high YAl and relatively high F (ore-bearing pegmatite). Most trace element contents vary over several orders of magnitude with median concentrations of 0.1–10 μg/g. High concentrations are found for Ga, Zn, Be, Sc, Sn and Li (several tens to thousands of μg/g), whereas low concentrations (<0.1 μg/g) are found for V, Rb, U, Th, W, and Hf. The tourmalines from muscovite granite and barren pegmatite yielded δ11B = -8.9 to −7.5 ‰ and −8.7 to −6.0 ‰, respectively, whilst the tourmaline in the ore-bearing pegmatite show a wider δ11B range (-8.8 to −5.2 ‰). The B isotopic values indicate a source of the continental crust in a post-collisional setting. The estimated δ11B value of parental granitic magma is −10.0 ‰. The overlap in δ11B values between muscovite granite and barren pegmatite indicates a little isotopic fractionation between tourmaline and melt. Rayleigh fractionation results in the observed δ11B decrease from zone I (-6.9 ‰) to zone V (-8.0 ‰). After the barren-pegmatite-hosted tourmaline formation, the δ11B value of boron-rich magma would have been about −11.5 ‰. The intragrain δ11B variation of tourmaline in the ore-bearing pegmatite is 2.7 ‰, much larger than that from the other zones, indicating the rim of the tourmaline crystallized from fluid exsolved. We calculated the boron-isotope fractionation (between fluid and melt) to be 4.2–5.7 ‰ at 600–450 °C. Chemical variations in tourmaline are continuous in the muscovite granite and barren pegmatite, consistent with fractional crystallization, whereas the tourmaline from the ore-bearing pegmatite may have formed during the magmatic-hydrothermal transition. The boron isotopic variations could be attributed to fractionation between melt-tourmaline, melt-fluid and tourmaline-fluid and Rayleigh fractionation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Xuefengling lithium polymetallic deposit is a superlarge pegmatite deposit. • Micas and columbite-group minerals from the Xuefengling pegmatites magmatic-hydrothermal process similar with the Bailongshan pegmatites, they may have originated from the same parental magma chamber. • The Xuefengling pegmatites show lower degree of fractionation than the Bailongshan pegmatites. The Xuefengling rare metal pegmatite deposit is located in the West Kunlun orogenic belt, Northwest China. It is one part of the Bailongshan orefield, which is located 5 km southeast of the Bailongshan deposit, and it is composed of the Xuefengling, Xuepen, Longmenshan and Shuangya ore segments. The Xuefengling pegmatite and the Bailongshan pegmatite have similar zoning characteristics, and the pegmatite-hosted rare metal mineralization is approximately 206–213 Ma. On the basis of detailed observations and characterization of the textures and mineral assemblages of pegmatites in the Xuefengling deposit, four zones are identified: a quartz–spodumene (QS) zone, quartz–albite–muscovite (QAM) zone, quartz–albite–tourmaline (QAT) zone, and block albite–quartz pegmatite (BAQ) zone. We use the textures and major and trace element compositions of muscovite and columbite-group minerals from the Xuefengling pegmatite to illustrate both the existing state of rare elements and the origin of the Xuefengling pegmatite. Our results show that from Li-poor (QAM and QAT zones) to Li-rich pegmatites (QS zone), the K/Rb and K/Cs ratios of muscovite gradually decrease from 41.6 to 10.9 and 2276 to 208, respectively, and the Mn# values of columbite-group minerals increase from 0.35 to 0.49, which are similar to the progressive evolution trend identified in Bailongshan pegmatites. However, the lower K/Rb and K/Cs ratios of muscovite from the Xuefengling pegmatites than those from the Bailongshan pegmatites indicate that the Xuefengling pegmatites may have formed from the lower degrees of fractional crystallization of the same parental magma chamber, leading to the Bailongshan ore-field pegmatites gradually strengthening their evolution from east to west. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mineralization age of the Akesayi deposit is Middle Miocene. The Akesayi deposit is a skarn-type iron ore related to the diorite porphyrite. • Miocene skarn Fe mineralization events in West Kunlun have good prospective foreground and potential. The Akesayi deposit, located in the eastern part of the Tianshuihai terrane of the Western Kunlun Orogenic Belt, Xinjiang, China, is a recently discovered medium-sized magnetite deposit containing approximately 51 million tons of ore with an average grade of 41 wt%. This deposit is hosted by skarns at the contact between monzonitic granite, diorite porphyry, and medium to low-grade metamorphic clastic rocks of the Permian Huangyangling Group. The ore types include banded, disseminated, and massive ores. The metallogenic process can be divided into prograde skarn, retrograde skarn, oxide, quartz-sulfide, and carbonate stages. The metallic minerals include magnetite and pyrite, and the gangue minerals include olivine, garnet, hedenbergite, hornblende, actinolite, biotite, cummingtonite, chlorite, quartz, and calcite. The zircon U–Pb dating of biotite adamellite intrusion and schist together constrains the formation age of the host rocks in the Akesayi Fe deposit to 217–272 Ma. Rb–Sr dating of eight garnet samples yields an isochron age of 12.41 ± 0.31 Ma, which is almost identical to the 12.56 ± 0.50 Ma age obtained via Sm–Nd dating of eight garnet samples. Furthermore, zircon U–Pb dating yields ages of 12.76 ± 0.12 Ma and 12.37 ± 0.18 Ma for diorite porphyry and monzonitic granite near the Fe orebodies, respectively. The initial Sr isotopes of garnet ((87Sr/87Sr) i = 0.710901) prove that the diorite porphyrite ((87Sr/87Sr) i = 0.709283) is related to skarn mineralization. Thus, the Akesayi deposit is a skarn-type iron ore related to the middle Miocene diorite porphyry. The mineral assemblage indicates the extensive development of manganese-skarn in the Akesayi mining area. The manganese content of host rocks of the deposit is low, and the source of manganese in the skarn may mainly come from the hydrothermal fluids associated with Miocene diorite porphyry emplacement. The compositional variations between the cores and rims of single garnet grains and different stages of tephroite indicate the concentration characteristics of the hydrothermal system, particularly manganese content, which evidently changed during hydrothermal activity. The endmembers of garnet and pyroxene suggest that the ore-forming environment transformed from a relatively reduced acidic environment to an alkali-rich, high-oxygen fugacity environment. The widely developed chlorine-rich amphiboles and biotite indicate that the hydrothermal fluids were rich in chlorine and may have been related to the diorite porphyrite intrusion near the ore bodies. The iron mineralization of the Akesayi deposit is analogous to the Gangdese Miocene porphyry–skarn polymetallic mineralization, which occurred during the Miocene in a post-collisional tectonic setting. Considering the series of Miocene intrusives discovered in West Kunlun, we propose that Miocene skarn Fe mineralization events occurred in West Kunlun, and that this area has great prospecting potential. [ABSTRACT FROM AUTHOR]

The recently discovered Sanjiaowo Sn deposit is located in eastern Guangdong, SE China. The Sn mineralization, hosted in granite porphyry and the Lower Jurassic Jinji Formation low-grade metamorphic wall rocks, is considered to be granite-related. Zircon U–Pb dating of the granite porphyry yielded concordant ages of 140.5 ± 1.4 Ma, which is consistent with the cassiterite U–Pb age of 139.8 ± 5.0 Ma, indicating a temporal link between the emplacement of granitic plutons and Sn mineralization. The granite porphyry samples are weakly peraluminous and show an A-type geochemical signature with high Na 2 O + K 2 O (7.19–8.51 wt.%), REE (261–308 ppm), Zr + Nb + Ce + Y (353–476 ppm) contents, FeO T /MgO (0.93–0.99), and Ga/Al (2.65–3.42) ratios. They display bulk rock initial 87 Sr/ 86 Sr of 0.7110 to 0.7165, εNd(t) of −5.90 to −4.04, and zircon εHf(t) values from −8.36 to −4.16 with Mesoproterozoic T DM2 ages for both Nd and Hf isotopes. Detailed elemental and isotopic data suggest that the Sanjiaowo Granite porphyry belongs to the A 2 -subtype and were formed by partial melting of a crustal source of Mesoproterozoic overall residence age with minor input of mantle materials. The low calculated zircon Ce 4+ /Ce 3+ (6.5–81.2) and Eu N /Eu N ∗ (0.05–0.24) ratios demonstrates that the Sanjiaowo granitic magma had a low oxygen fugacity, which may have facilitated the Sn enrichment and played a key role in the Sn mineralization. Lead isotopes indicate that there is no difference for 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios between the granite porphyry and the sulfide minerals from the orebodies. Moreover, the sulfur isotopic compositions for the sulfides (pyrite and pyrrhotite: δ 34 S = −1.6–1.0‰, average = −0.32) is similar to magmatic δ 34 S, but different from the δ 34 S in the Jinji Formation strata. Consequently, these data favor of a magmatic-hydrothermal origin for the Sn mineralization in the Sanjiaowo deposit. Integrating new and published data on the tectonic evolution, we suggest that the granite porphyry and associated Sn mineralization in the Sanjiaowo deposit formed in a back-arc extensional environment at ∼141 Ma, related to the rollback of the paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Neoproterozoic (593–532 Ma) Dahongliutan banded iron formation (BIF), located in the Tianshuihai terrane (Western Kunlun orogenic belt), is hosted in the Tianshuihai Group, a dominantly submarine siliciclastic and carbonate sedimentary succession that generally has been metamorphosed to greenschist facies. Iron oxide (hematite), carbonate (siderite, ankerite, dolomite and calcite) and silicate (muscovite) facies are all present within the iron-rich layers. There are three distinctive sedimentary facies BIFs, the oxide, silicate–carbonate–oxide and carbonate (being subdivided into ankerite and siderite facies BIFs) in the Dahongliutan BIF. They demonstrate lateral and vertical zonation from south to north and from bottom to top: the carbonate facies BIF through a majority of the oxide facies BIF into the silicate–carbonate–oxide facies BIF and a small proportion of the oxide facies BIF. The positive correlations between Al 2 O 3 and TiO 2 , Sc, V, Cr, Rb, Cs, Th and ∑REE (total rare earth element) for various facies of BIFs indicate these chemical sediments incorporate terrigenous detrital components. Low contents of Al 2 O 3 (<3 wt%), TiO 2 (<0.15 wt%), ∑REE (5.06–39.6 ppm) and incompatible HFSEs (high field strength elements, e.g., Zr, Hf, Th and Sc) (<10 ppm), and high Fe/Ti ratios (254–4115) for a majority of the oxide and carbonate facies BIFs suggest a small clastic input (<20% clastic materials) admixtured with their original chemical precipitates. The higher abundances of Al 2 O 3 (>3 wt%), TiO 2 , Zr, Th, Cs, Sc, Cr and ∑REE (31.2–62.9 ppm), and low Fe/Ti ratios (95.2–236) of the silicate–carbonate–oxide facies BIF are consistent with incorporation of higher amounts of clastic components (20%–40% clastic materials). The HREE (heavy rare earth element) enrichment pattern in PAAS-normalized REE diagrams exhibited by a majority of the oxide and carbonate facies BIFs shows a modern seawater REE signature overprinted by high-T (temperature) hydrothermal fluids marked by strong positive Eu anomalies (Eu/Eu ∗ PAAS = 2.37–5.23). The low Eu/Sm ratios, small positive Eu anomaly (Eu/Eu ∗ PAAS = 1.10–1.58) and slightly MREE (middle rare earth element) enrichment relative to HREE in the silicate–carbonate–oxide facies BIF and some oxide and carbonate facies BIFs indicate higher contributions from low-T hydrothermal sources. The absence of negative Ce anomalies and the high Fe 3+ /(Fe 3+ /Fe 2+ ) ratios (0.98–1.00) for the oxide and silicate–carbonate–oxide BIFs do not support ocean anoxia. The δ 13 C V-PDB (−4.0‰ to −6.6‰) and δ 18 O V-PDB (−14.0‰ to −11.5‰) values for siderite and ankerite in the carbonate facies BIF are, on average, ∼6‰ and ∼5‰ lower than those (δ 13 C V-PDB = −0.8‰ to + 3.1‰ and δ 18 O V-PDB = −8.2‰ to −6.3‰) of Ca–Mg carbonates from the silicate–carbonate–oxide facies BIF. This feature, coupled with the negative correlations between FeO, Eu/Eu ∗ PAAS and δ 13 C V-PDB , imply that a water column stratified with regard to the isotopic omposition of total dissolved CO 2 , with the deeper water, from which the carbonate facies BIF formed, depleted in δ 13 C that may have been derive from hydrothermal activity. Integration of petrographic, geochemical, and isotopic data indicates that the silicate–carbonate–oxide facies BIF and part of the oxide facies BIF precipitated in a near-shore, oxic and shallow water environment, whereas a majority of the oxide and carbonate facies BIFs deposited in anoxic but Fe 2+ -rich deeper waters, closer to submarine hydrothermal vents. High-T hydrothermal solutions, with infusions of some low-T hydrothermal fluids, brought Fe and Si onto a shallow marine, variably mixed with detrital components from seawaters and fresh waters carrying continental landmass and finally led to the alternating deposition of the Dahongliutan BIF during regression–transgression cycles. The Dahongliutan BIF is more akin to Superior-type rather than Algoma-type and Rapitan-type BIF, and constitutes an additional line of evidence for the widespread return of BIFs in the Cryogenian and Ediacaran reflecting the recurrence of anoxic ferruginous deep sea and anoxia/reoxygenation cycles in the Neoproterozoic. In combination with previous studies on other Fe deposits in the Tianshuihai terrane, we propose that a Fe 2+ -rich anoxic basin or deep sea probably existed from the Neoproterozoic to the Early Cambrian in this area. [ABSTRACT FROM AUTHOR]

[Display omitted] • Garnets from Bailongshan deposit are magmatic in origin. • The composition of garnets from Bailongshan deposit mainly depends on the competing effects of coexisting minerals. • Garnet is a potential exploration indicator for rare-metal mineralization in Bailongshan deposit. The Bailongshan deposit is a newly-discovered super-large lithium polymetallic pegmatite deposit. Garnets occur widely in muscovite granites and pegmatites at Bailongshan, but comprehensive study is yet to be done on the geochemical evolution of garnet from the magmatic to the hydrothermal stages. Here, we present a systematic study of in-situ major and trace elemental variations of garnet from Bailongshan, and discuss the geochemical behaviors during magmatic to hydrothermal stage and the mineral indicator of large-scale mineralization of rare metal. Three types of garnet have been identified at Bailongshan, including disseminated garnet in muscovite granite (Grt I), medium-coarse-grained garnet in barren pegmatites (Grt II), and medium-grained euhedral-subhedral garnet in ore-bearing pegmatites (Grt III). EPMA and LA-ICP-MS geochemical analyses reveal that the garnet belong to almandine-spessartine solid-solution series. The garnets have varied REE contents (∑REE = 3.64～382 ppm), and HREE-enrichment, negative Eu anomalies, and LREE below or close to their detection limits. Grt III has higher Mn and Zn, but lower Fe, Y and HREE than those of Grt I and Grt II. The contents of Li, Zr, Hf, Nb and Ta increase from Grt I to Grt II, but decrease abruptly to Grt III. During the evolution of granitic magma, the increasing magma fractionation and fluid-phase accumulation and the crystallization of zircon lead to the continuous decrease of Y and HREE contents from Grt I to Grt III, and the gradual decrease of Y and HREE contents from core to rim of garnet crystals. In the quartz-albite-spodumene pegmatites, the crystallization of spodumene and columbite-group minerals removes Li, Nb and Ta from the melt, which significantly reduces the contents of these elements in garnet. The crystallization of spessartine-rich garnet is a reflection of a high degree of melt evolution at low pressure which facilitates the formation of LCT type pegmatite deposit. The Zr/Hf and Y/Ho ratios also indicate that magma fractionation degree and fluid activity increase from muscovite granites to barren-pegmatites and ore-bearing pegmatites, The combination of some major (e.g., Fe and Mn) and trace elements (e.g., Li, Ta, Nb, Sc and HREE) signatures, as well as the Zr/Hf, Y/Ho ratios in garnets can indicate the magma fractionation degree and the crystallization of some ore minerals (e.g., spodumene and columbite-group minerals), and may be a potential exploration indicator for rare-metal mineralization. [ABSTRACT FROM AUTHOR]

• Akesayi magnetite was occurred mainly during the retrograde skarn and oxide stages. • Akesayi comprises of banded (BO), disseminated (DO), primary (MO-1) and secondary massive (MO-2) magnetite. • Variable magnetite compositions controlled by multiple factors. • Magnetite compositions in skarn deposits are more variable than previously thought. The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite. Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18O V-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18O V-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO 2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought. [ABSTRACT FROM AUTHOR]

• Two pulses of magmatic-hydrothermal fluid are documented in Taoxihu deposit. • The first pulse of fluid is H 2 O-CO 2 -NaCl system and the second one is H 2 O–NaCl. • Fluid immiscibility is responsible for the precipitation of Sn during the first pulse. • The oxidizing process due to the influx of meteoric water accounts for the precipitation of Sn during the second pulse. The Taoxihu deposit is a newly discovered Sn-polymetallic deposit in eastern Guangdong, SE China. The mineralization is related to an Early Cretaceous, highly fractionated I-type granite porphyry. The ore-forming process is divided into six stages, i.e., garnet (stage I), quartz–fluorite–biotite (stage II), quartz–biotite–cassiterite–sulfides (stage III, main mineralization), quartz vein with minor sulfides and cassiterite (stage IV), quartz–K-feldspar–biotite–cassiterite–sulfides (stage V), and quartz–K-feldspar–chlorite–sulfides (stage VI). Fluid inclusion study shows that the hydrothermal fluids from stage II (salinity = 5.9 to 13.2 wt%, and T h = 302 to 382 °C) to stage IV (salinity = 0.2 to 5.9 wt%, and T h = 275 to 315 °C) are of H 2 O–CO 2 –(CH 4)–salt composition and show a trend of systematically decreasing temperature and salinity from early to late stages. In contrast, the fluids in stage V (salinity = 6.5 to 13.9 wt% and T h = 223 to 343 °C) and stage VI (salinity = 6.0 to 11.8 wt%, and T h = 140 to 300 °C) are of the H 2 O–salt compositional system, and demonstrate also a trend of decreasing temperature and salinity with time, representing a distinct hydrothermal event. H–O isotope data indicate that these two different fluid systems are all initially of magmatic origin. In view of the almost identical cassiterite U–Pb ages of stage III (139.7 ± 1.1 Ma) and stage V (139.8 ± 1.6), the two hydrothermal events are interpreted to represent two pulses of magmatic fluid releasing from the same magma chamber. The first pulse is characterized by an initially single-phase CO 2 -bearing magmatic fluid that was subsequently subject to unmixing or phase separation in relation to hydraulic fracturing and decompression, which lead to the main phase mineralization, whereas the second pulse is the release of residual, CO 2 -free magmatic fluid, which mixed with meteoric water and resulted in the second phase of mineralization. [ABSTRACT FROM AUTHOR]

• Continental and hydrothermal Fe both contributed into the Dahongliutan BIF. • <65% of aqueous Fe2+ occurred oxidation at Dahongliutan. • Conversion of a small amount of Fe(OH) 3 to siderite occurred via DIR process. • DIR play an important role involved in Neoproterozoic BIF genesis. Unlike most Neoproterozoic BIFs in which Fe occurs almost exclusively in hematite, the Late Neoproterozoic Dahongliutan BIF uniquely contains Fe oxides (hematite), Fe–rich carbonates (siderite and ankerite) and Ca–Mg carbonates (calcite and dolomite). The diversification of minerals presents a unique opportunity to constrain the biotic and/or abiotic pathways for the precipitation of Fe–bearing minerals involved in Neoproterozoic BIF genesis. Here, we present integrated Fe, Nd and C compositions of hematite, Fe–rich carbonates, bulk–rock various facies BIFs, silicified calcic marbles and schists from the Dahongliutan BIF. These data suggest that the aqueous Fe2+ with light δ56Fe (~−1.60‰) at Dahongliutan was sourced from mixed continentally derived Fe (δ56Fe ~ −2‰) that was mobilized by microbial dissimilatory Fe reduction (DIR) and hydrothermally sourced Fe (δ56Fe ~ 0‰) from MORB systems. Lower than 65% of this dual–source mixed Fe occurred oxidation and formation of Fe(OH) 3 via limited atmospheric O 2 , and/or anaerobic photosynthetic Fe2+ oxidation. The majority of these poorly crystalline Fe(OH) 3 precipitates undergo dehydration and recrystallization to eventually bury as hematite with light δ56Fe (averaging −0.15‰). δ56Fe (~−0.11‰) and δ13C V-PDB (−4.00‰ to −6.60‰) of the siderite suggest that conversion of a small amount of Fe(OH) 3 into siderite occurred via near–complete reduction by DIR. This DIR process is coupled to the oxidation of organic C, in which the ratio of HCO 3 − derived from oxidation of CH 2 O (HCO 3 − org) to total HCO 3 − (HCO 3 − total) = 1/4. Petrographic evidence (the common occurrence of hematite inclusions in the siderite and ankerite), coupled with mineral chemistry, support a model that some siderite transform into ankerite with consistent δ56Fe (~−0.11‰) and δ13C V-PDB values (−4.20‰ to −5.40‰). In summary, our results demonstrate that DIR play an important role in Neoproterozoic BIFs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ore-forming fluid is a mixture of magmatic fluid and meteoric water. • The ore-forming fluid was derived mainly from crustal source, with minor proportions of mantle source input (<4.28%). • Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit. The Tashan deposit is hosted and genetically associated with the highly fractionated A-type granite porphyry formed at ca. 138 Ma. Its Sn metallogenic processes can be subdivided into three stages: biotite–K-feldspar–cassiterite (stage I, main Sn mineralization), quartz–cassiterite (stage II), and chlorite–sulphides (stage III). Fluid inclusion study indicates that the hydrothermal fluids from stage I (salinity = 5.2–12.8 wt%, and T h = 303–376 °C) through stage II (salinity = 2.7–10.9 wt%, and T h = 236–313 °C) to stage III (salinity = 1.7–8.5 wt%, and T h = 192–262 °C) are of H 2 O–CO 2 –salt composition and its temperature and salinity from early to late stages tend to decrease. The H and O isotopes of quartz from stage II and stage III show δD water values in the range of –66.7 to –60.5‰ and –52.8 to –39.6‰, and δ18O (‰) values in the range of 6.7 to 7.3‰ and 5.8 to 6.9‰, respectively, suggesting contributions of both magmatic fluids and meteoric water. Inclusion-trapped fluids in stage II pyrite show 3He/4He, He mantle (%), and 40Ar/36Ar values of 0.07–0.35 Ra, 0.76%–4.28%, and 302.6–309.0, respectively, indicating that the metallogenic fluids were derived mainly from crustal sources, with minor proportions of mantle source input (<4.28%), consistent with the magma sources of the granite porphyry. Lead isotopes indicate that there is no difference for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios between the sulfide minerals from the orebodies and the fertile granites parental to Sn mineralization in Eastern Guangdong, indicating a magmatic Pb origin. Sulfur isotopic values obtained from sulfides are in the range of –4.5‰ to 0.4‰ (average, –1.7‰), implying an initially of magmatic origin with some contamination of sedimentary sulfur through the interaction with sedimentary rocks of Jinji Formation (–6.67 to –2.41‰). Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dominant Fe sources at Kukeate were derived from mixed seawater and low-T hydrothermal fluids (<200 °C). • There exists a dynamic redoxcline, which separated shallow oxygenated waters and deep, reducing, Fe2+-rich waters at Kukeate. • The abiotic oxidation of Fe2+ to Fe3+ via free O 2 could have occurred at Kukeate. • The Kukeate IF provides evidence for episodic anoxic ferruginous deeper water conditions during the early Silurian. Phanerozoic iron formations (IFs) provide a unique opportunity to understand both the contemporaneous chemical composition and redox state of seawater where they precipitated. However, the absence of detailed reports of Phanerozoic IFs inhibits a robust understanding of their depositional conditions and dominant Fe sources. Here, we describe a hematite- and siderite-rich IF from Kukeate hosted within lower Silurian submarine siliciclastic and carbonate sedimentary succession in NW China. The chemical composition of our analysed samples is dominated by high TFe 2 O 3 and variable SiO 2 contents, with low Al 2 O 3 , TiO 2 , Sc, Nb, Th, and Zr concentrations, indicating an authigenic origin. Distinct depletion in LREE relative to HREE, super-chondritic Y/Ho ratios, and slightly positive Gd anomalies, are diagnostic for derivation from surface seawater. The lack of strong positive Eu anomaly, along with coupled Fe and O isotopic characteristics for the hematite, point to a significant low-T hydrothermal input. Slightly negative to no Ce anomalies, weakly negative to mildly positive Eu anomalies, homogeneous δ56Fe values (near zero), and large positive δ13C V-PDB excursions, together suggest that there exists a dynamic redoxcline, which separated oxic surface water and ferruginous deeper water conditions, where dissolved Fe2+ in deep, reducing, Fe-rich hydrothermal fluids, was oxidized and precipitated as Fe(OH) 3 in shallow oxygenated seawater, leading to the formation of hematite. Accordingly, the occurrence of Kukeate IF suggests intermittent ferruginous deeper water conditions during the early Silurian. [ABSTRACT FROM AUTHOR]

• The studied BIF deposits were formed in the Early Cambrian (516–520 Ma). • The studied BIF deposits were formed in a back-arc basin. • High- to low-T hydrothermal fluids, seawater and minor clastic input all contribute to the studied BIF deposits. • The studied BIF deposits formed in a stratified seawater column. Large amounts of magnetite-rich banded iron formation (BIF) deposits, located in the Western Kunlun orogenic belt (WKOB), are hosted within the greenschist- to amphibolite-facies metamorphosed Bulunkuole complex. The iron (Fe) orebodies of these BIF deposits are interlayered with biotite-quartz schist and amphibolite, indicating that they are temporally closely associated. Analyses of the contents and ratios of major and trace elements indicate that the protoliths of the amphibolite should be basalt and andesite. LA-ICP-MS U-Pb dating of zircons from three representative amphibolite samples suggests that the studied BIF deposits were formed in the Early Cambrian (516–520 Ma). Based on regional geology and geochemistry of the amphibolite, we propose that these BIF deposits were formed in a back-arc basin setting. A wide range of Ce and Eu anomalies for Fe ores indicate that the studied BIF deposits were formed in both oxygenated surface seawater and deeper suboxic to anoxic seawater. Linking the tectonic setting with geochemical characteristics of bulk-rock Fe ores, we propose Fe and Si are predominantly seafloor-derived, with pulsed contribution of high- to low-T hydrothermal fluids that were closely associated with the extension of back-arc basin. In addition, we postulate that periodically upwelled metalliferous hydrothermal fluids were subsequently oxidized by surface seawater and mixed with detrital components, which ultimately led to the rhythmic precipitation of the Fe-rich and Si-rich layers. [ABSTRACT FROM AUTHOR]

The Taoxihu deposit (eastern Guangdong, SE China) is a newly discovered Sn polymetallic deposit. Zircon U-Pb dating yielded 141.8 ± 1.0 Ma for the Sn-bearing granite porphyry and 145.5 ± 1.6 Ma for the biotite granite batholith it intruded. The age of the granite porphyry is consistent (within error) with the molybdenite Re–Os isochron age (139.0 ± 1.1 Ma) of the Sn mineralization, indicating a temporal link between the two. Geochemical data show that the granite porphyry is weakly peraluminous, contain high Si, Na and K, low Fe, Mg, Ca and P, and relatively high Rb/Sr and low K/Rb values. The rocks are enriched in Rb, Th, U, K, and Pb and depleted in Ba, Sr, Ti and Eu, resembling highly fractionated I-type granites. They contain bulk rock initial 87 Sr/ 87 Sr of 0.707371–0.707730 and εNd(t) of −5.17 to −4.67, and zircon εHf(t) values from −6.67 to −2.32, with late Mesoproterozoic T DM2 ages for both Nd and Hf isotopes. This suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of Mesoproterozoic overall residence age with minor mantle input. δ 34 S CDT values of the Taoxihu chalcopyrite and pyrite range from 0.1 to 2.1‰ (average: 0.9‰), implying a dominantly magmatic sulfur source. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios of the Taoxihu sulfide ores are 18.497–18.669, 15.642–15.673 and 38.764–38.934, respectively, indicating a mainly upper continental crustal lead source with minor mantle contribution. The highly fractionated and reduced (low calculated zircon Ce 4+ /Ce 3+ and Eu N /Eu N ∗ values) nature of the ore-forming granitic magma may have facilitated the Sn enrichment and played a key role in the Sn mineralization. We propose that the ore-forming fluids at Taoxihu were of magmatic-hydrothermal origin derived from the granite porphyry, and that both the granite porphyry and the Sn mineralization were likely formed in an extensional setting, possibly related to the subduction slab rollback of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The recently discovered Jinkeng deposit, located in eastern Guangdong Province, SE China, is a granite-related cassiterite–sulfide-type Sn–Cu–Pb–Zn deposit in the Cathaysia Block. Zircon U–Pb dating of the biotite granite and fine-grained granite associated with the deposit yielded concordant ages of 144.7 ± 0.8 Ma and 141.1 ± 1.3 Ma, respectively. These ages are consistent, within error, with the molybdenite Re–Os isochron age of 139.3 ± 2.5 Ma for the deposit, indicating a temporal link between the emplacement of granitic plutons and polymetallic Sn mineralization. Combined with the regional mineralization ages, we propose that the 145–135 Ma interval represents another significant period of Sn–W mineralization in southern China, in addition to those already recognized. The biotite granite and fine-grained granite have similar geochemical characteristics; both are weakly peraluminous, high-K and calc-alkaline, containing abundant Si, Na, and K, and low concentrations of Fe, Mg, Ca, and P. Compared to primitive mantle and unfractionated granitoids, they are enriched in Rb, Th, U, K, and Pb, have relatively high Rb/Sr and low K/Rb values, are depleted in Ba, Sr, and Ti, and have prominent negative Eu anomalies (δEu = 0.05–0.19), characteristic of highly fractionated I-type granites. Zircons from these granites have ε Hf (t) values ranging from − 9.2 to − 3.3, and Hf model ages (T DM2 ) of 1776–1406 Ma, suggesting that the granites formed by the partial melting of Proterozoic basement material, and contain a minor mantle-derived component. Highly fractionated and reduced ( f O 2 below NNO) magma facilitated the enrichment of Sn. Existing knowledge on the tectonic evolution of this region and new data from this study, indicate that the granites and associated Sn mineralization in the Jinkeng deposit formed in an extensional environment at ~ 140 Ma, likely related to the rollback of the paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The newly discovered Dadaoshan Sn deposit is located in the eastern Guangdong Sn–W province, coastal SE China. The Sn mineralization, hosted in Jurassic porphyritic granite and the Lower Jurassic Jinji Formation sedimentary wall rocks, is considered to be granite-related. In this study, the porphyritic granite was LA–ICP–MS zircon U–Pb dated to be 153.2 ± 1.2 Ma, consistent with the syn -mineralization molybdenite Re–Os age of 152.6 ± 1.8 Ma. The porphyritic granite samples are weakly peraluminous (A/CNK = 1.0–1.1) and high-K calc-alkaline. The rocks contain high SiO 2 (72.9–75.6 wt%), moderate Rb/Sr (5–9) and low ΣREE (136–223 ppm). They are enriched in F, Li, Rb and Sn, depleted in Ba, Sr, P, Zr, Th, Nb and Y, and have distinct negative Eu anomalies (δEu = 0.09–0.18), suggesting that the porphyritic granite is highly fractionated I-type granite. The calculated initial 87 Sr/ 86 Sr (0.711582–0.715173), relatively low ɛ Nd (t) (−9.48 to −8.54; T DM2 = 1638–1814 Ma), and the zircon ε Hf (t) (−14.2 to −5.1; two-stage model ages = 1528–2103 Ma) all suggest that the granite was mainly crustal-derived with little mantle input. Sulfur isotopic compositions for the sulfides (arsenopyrite and chalcopyrite: δ 34 S = −1.1 to 1.4‰, average = −0.1) imply a dominantly magmatic sulfur source. The calculated zircon Ce 4+ /Ce 3+ and Eu N /Eu N ∗ ratios of the Dadaoshan granite range from 1.0 to 112 (mean = 31.7) and from 0.04 to 0.37 (mean = 0.14), respectively, indicating a low oxygen fugacity for the magma. The reducing and highly fractionated nature of the Dadaoshan granitic magma may have played a key role in the Sn mineralization. It was previously argued that the Jurassic Sn–W mineralization and its causative magmatism were largely confined in the South China interior, e.g., the Nanling Range. Our new data suggest that the Late Jurassic Sn–W mineralization and its causative magmatism actually extended to the SE China coastal area. The Dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle-derived magmas in an extensional environment. Regional extension may have been related to the west-directed, flat-slab subduction and delamination of the Paleo-Pacific (Izanagi) plate beneath the South China block. Another suite of Early Cretaceous Sn–W-bearing granitic rocks in eastern Guangdong may have mainly been crustal-derived with minor mantle input, and likely occurred under back-arc extensional setting led by the Paleo-Pacific subduction rollback. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mineralization at Tashan is related to the granite porphyry, and both of them formed at ca. 138 Ma. • The granite porphyry is an A-type granite mainly produced from partial melting of crust with minor contribution of mantle materials. • Both the granite porphyry and the mineralization formed in an extensional setting induced by slab roll-back. The medium-sized Tashan Sn deposit, mainly hosted in the Tashan granite porphyry, is located in eastern Guangdong, Southeast China. Zircon U–Pb dating of the granite porphyry yielded a concordant age of 138.0 ± 1.1 Ma, which is consistent with the cassiterite U–Pb age of 138.0 ± 2.3 Ma from the Sn ores, indicating a temporal link between the emplacement of granitic pluton and Sn mineralization. The contents of Fe3+, Fe2+, and Mg2+ in biotite, low calculated zircon Ce4+/Ce3+ of 4.4–71.6, low Eu/Eu* ratios of 0.06–0.35, and low whole-rock Fe 2 O 3 /FeO of 0.04–0.13 of the granite porphyry reveals its low oxygen fugacity, which may have facilitated the Sn enrichment during magma evolution and played a key role in the Sn mineralization. Low K/Rb (150–175, aver. = 160), Nb/Ta (7.3–8.2, aver. = 7.8), and Zr/Hf (23.2–25.1, aver. = 23.9) values were observed for the granite porphyry, indicating its high fractionation and probable interaction with an aqueous fluid phase to some extent. The reduced and highly fractionated features and high F and Sn contents of the granite porphyry thus indicate it is a typical Sn-fertile granite. The granite porphyry is weakly peraluminous and belongs to high-K calc-alkaline type. The rocks are characterized by high SiO 2 , K 2 O + Na 2 O, F, and Zr + Nb + Ce + Y (360–410 ppm) contents; and 10000 Ga/Al (2.31–3.06) ratios and low CaO, MgO, TiO 2 , and P 2 O 5 contents; Rb, Cs, Th, and U enrichment; and Ba, Sr, Zr, Ti, and P depletion, exhibiting an A-type affinity. Moreover, the rocks display whole rock initial 87Sr/86Sr values of 0.70927–0.71218, εNd(t) of − 6.5 to − 6.3, and zircon εHf(t) values from − 5.7 to − 1.5 with Mesoproterozoic T DM2 ages for both Nd and Hf isotopes, indicating their formation by partial melting of a crustal source of Mesoproterozoic overall residence ages with minor input of mantle materials. By integrating new and published data on tectonic evolution, we suggest that the granite porphyry and associated Sn mineralization in the Tashan deposit that was formed in a back-arc extensional environment started before ∼ 141 Ma, related to the rollback of the paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]