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The large-scale Dahongliutan hematite-rich Fe deposit in the Tianshuihai terrane (Western Kunlun orogenic belt), Xinjiang, northwestern China, contains proven Fe ore reserves exceeding 100 Mt at an average grade of 35 wt.% Fe(t) (maximum 53 wt.%). The deposit is hosted in the Neoproterozoic Tianshuihai Group, a suite of neritic, siliciclastic and sedimentary carbonate rocks subjected to greenschist-facies metamorphism. The Fe orebodies are laminate, stratoid, lenticular and interlayered with marbles and schists. Ore minerals mainly contain hematite, with minor siderite and limonite and rare sulfides, whereas gangue minerals mainly comprise quartz, dolomite, ankerite, calcite, muscovite and chloritoid. Most Fe ores display lepidoblastic, blastopsammitic, crystalloblastic and metasomatic textures with massive or banded structures. Based on mineral assemblages, the Fe ores are divided into four types, namely: (1) Quartz–hematite; (2) Quartz–dolomite–calcite–muscovite–hematite; (3) Quartz–ankerite–hematite; (4) Quartz–siderite–hematite. Zircon U–Pb analyses on the marbles and schists yielded a Neoproterozoic age (Ediacaran; 593 ± 7 Ma), whereas those on the ore-intruding medium-grained porphyritic biotite-quartz monzonite, medium to fine grained biotite-quartz monzonite and metagabbro yielded Cambrian–Early Ordovician ages (i.e., 484.5 ± 2.7, 527.9 ± 2.8 and 532.3 ± 3.1 Ma), which altogether constrain the ore formation to the Late Neoproterozoic to Early Cambrian (532–593 Ma). In addition, the 163 detrital zircon analyses on the Dahongliutan marble and schist define five major age populations, namely: 2561–2329, 2076–1644, 1164–899, 869–722 and 696–593 Ma. Provenance studies show that the detritals at Dahongliutan were mainly sourced from the North Kunlun and Tianshuihai terranes. Comparison with typical BIF deposits in the world, we infer that the deposit belongs to Neoproterozoic (Ediacaran) BIF-related sedimentary metamorphic type iron deposit and resembles Superior-type BIF, probably reflecting the recurrence of anoxic ferruginous conditions in the Neoproterozoic–Early Cambrian deep sea. [ABSTRACT FROM AUTHOR]

The Bailongshan pegmatite deposit is a newly discovered super-large Li–Rb–(Be–Ta–Nb) rare-metal deposit in the West Kunlun orogenic belt, northwest China. Fifty-two rare-metal orebodies (50–1230 m long by 1.5–157 m wide) have been discovered by detailed field surveying, making up a metallogenic field that is larger than 8250 × 400 m. The deposit is estimated to have ore reserves of more than 5.06 million tonnes (t) Li 2 O, 160,020 t BeO, 316,200 t Rb 2 O, 40,060 t Nb 2 O 5 , and 10,750 t Ta 2 O 5. Pegmatite dikes are zoned around a granodiorite batholith, ranging from barren through orebodies rich in Be, Nb, Ta, Rb, and Li with increasing distance from the batholith, similar to the classical model of a zoned Li–Ce–Ta (LCT)-type pegmatite. LA–ICP–MS analyses of coltan and zircon yield 206Pb/238U ages of 208.1 Ma and 212.3 Ma, respectively, representing the emplacement ages of the pegmatites and granodiorite. These data indicate a temporal link between the emplacement of the granodiorite batholith and rare-metal mineralization in the pegmatites, and that the Bailongshan rare-metal pegmatites are temporospatially related to the granodiorite batholith. The Bailongshan pegmatites and other rare-metal pegmatite deposits in the West Kunlun orogenic belt likely make up a >600-km-long Li metallogenic belt, and further exploration for rare-metal pegmatites should be focused on the area adjacent to Late Triassic granitoid plutons in the belt. This belt likely extends to the East Kunlun and West Sichuan rare-metal belts, forming the >2000-km-long, Late Triassic West Kunlun–Songpan–Garzê rare-metal metallogenic belt. • The Bailongshan deposit is a newly discovered superlarge Li-Rb-(Be-Nb-Ta) pegmatite deposit. • The Bailongshan Li-rich pegmatites (ca. 208 Ma) is closely related to the granodiorite batholith. • Further exploration of Li-rich pegmatite should be around the Late Triassic granitoids. • We highlight a huge "West Kunlun–Songpan-Ganzê rare-metal pegmatite metallogenic belt" occurs. [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]

Granitic pegmatites are considered significant host rocks for the rare metal deposits. However, the enrichment mechanisms for the rare metal elements (e.g., Li, Be, Nb and Ta) remain debated. Here we report the whole-rock and mineral (e.g., muscovite and spodumene) major, trace elements and Li isotopic compositions of the Bailongshan granitic pegmatites in the West Kunlun, NW Tibet, to address this issue. The Bailongshan pegmatites (hosting a super-large Li–Rb polymetallic deposit) are composed of Li-poor and Li-rich pegmatites. The Li-poor pegmatites display high δ7Li values in the whole rock (2.30–4.94‰) and muscovite (2.22–7.55‰). In contrast, the Li-rich pegmatites show low δ7Li values in the whole rock (−1.89 to 0.35‰), muscovite (−3.39 to 4.49‰) and spodumene (−2.83 to 1.87‰). These results, together with the variations of the elements, suggest that the Li-poor and Li-rich pegmatites were produced by the melt-fluid separation during the late stage of granitic magma evolution. This means that the Li-poor pegmatites were formed in a H 2 O-poor silicate-rich melt system, while the Li-rich pegmatites were generated in a H 2 O-rich silicate-poor melt (supercritical fluid) system. The melt-fluid separation can lead to significant Li isotope fractionation, with 7Li enriched in the strongly-bonded residual silicate melt, and 6Li preferring to weaker hydrated bonds in the fluid. Alternatively, the Li-rich pegmatites enriched in 6Li could have been induced by preferential accumulation of the faster-diffusing 6Li in the supercritical or near critical fluid. The Li-rich pegmatites experienced extensive crystal-fluid interaction in a relatively closed magmatic-hydrothermal system, which resulted in the leaching and reprecipitation of ore-forming elements, but produced restricted Li isotope fractionation. The exsolved supercritical fluid is more enriched in alkali-, fluxing components (Li, Rb, Cs, P and F) by the continuous interaction with the residual silicate melt. Therefore, the supercritical fluid exsolution plays an important role in the Li isotope fractionation and rare metal mineralization. • First report of Li isotopic composition of Bailongshan pegmatites. • Significant Li isotope fractionation between Bailongshan Li-poor and Li-rich pegmatites. • Li isotope fractionation during melt-fluid separation. • Implications for the rare metal mineralization. [ABSTRACT FROM AUTHOR]