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The Chinese Tianshan experienced large-scale transcurrent tectonics, synkinematic emplacement of ultramafic to felsic intrusions, and the formation of various mineral deposits during late Paleozoic accretionary orogenesis. The relationships among the spatial variation of deformation, the distribution of Permian orogenic Au and magmatic Ni-Cu sulfide deposits, and the kinematic evolution of crustal-scale shear zones, however, remain ambiguous. To address these ambiguities, the spatial variation in the degree of deformation in the Kanggur-Huangshan shear zone in the Chinese Tianshan was characterized using detailed structural measurements and zircon U-Pb and muscovite 40Ar/39Ar age data. The new structural data indicate that a prominent spatial variation exists in the style of deformation throughout the Kanggur-Huangshan shear zone; intense ductile deformation structures are dominant in the east, while brittle structures become progressively more dominant toward to the west. Zircon U-Pb and muscovite 40Ar/39Ar age data for syn- and postkinematic intrusions along the Kanggur-Huangshan shear zone indicate that dextral strike-slip shearing occurred between 279 Ma and 249 Ma. The spatial variation in the degree of deformation and exhumation along the Kanggur-Huangshan shear zone was potentially caused by regional differential uplift induced by the collision of the Tianshan and Beishan regions; this was likely responsible for the predominant occurrence of magmatic Ni-Cu sulfide deposits in the eastern portion of the Kanggur-Huangshan shear zone and orogenic Au deposits in the western portion. The identified spatio-temporal relationship between deformation and distribution of orogenic Au and magmatic Ni-Cu sulfide deposits is crucial to the future success of mineral exploration in the Central Asian orogenic belt.

Supplemental Text: Analytical methods. Supplemental Table S1: Zircon U-Pb age dating results. Supplemental Table S2: Argon step-heating data.

Volatilization is an important pathway of element transport in nature, and this process may be associated with stable isotope fractionation, which could be used to understand the elemental volatilization mechanisms. In this study, we report that evaporation of Sn(IV) chloride solution under experimental conditions (96 °C, 1 atmospheric pressure) results in significant loss of aqueous Sn(IV) and Sn stable isotope fractionation. The δ122/116Sn of the residue solution can increase by up to 0.50‰ (or a 0.33‰ increase in δ122/118Sn) after repeated evaporation, indicating preferential partitioning of isotopically light Sn species into the vapor phase during evaporation. The observed Sn loss and associated Sn isotope fractionation during the evaporation experiments can be described using a Rayleigh fractionation function, with a best-fitting isotope fractionation factor of −0.36‰ in Δ122/116Snvapor-aq (or −0.24‰ in Δ122/118Snvapor-aq). We also performed quantum mechanical calculations to assess the stability of different potential Sn(IV) species in aqueous and vapor phases, and derived the equilibrium Sn isotope fractionation factors between these Sn(IV) species. The calculation results suggest that the dominant gaseous species of Sn(IV), SnCl4, is isotopically heavier than the aqueous Sn(IV) species by 1.24‰–0.35‰ in δ122/116Sn (or 0.82‰–0.19‰ in δ122/118Sn) under equilibrium at 96 °C, which is opposite to the experimental results. Such contrast in the direction of Sn isotope fractionation implies that kinetic isotope fractionation, rather than thermodynamic equilibrium isotope fractionation, took place for SnCl4 in the evaporation experiments at 96 °C. The observed experimental data can be explained by a kinetic isotope fractionation model involving backward reaction of SnCl4 vaporization at the solution-vapor boundary. This study, in combination with a recent report of positive Δ122/116Snvapor-aq (or Δ122/118Snvapor-aq) factor during evaporation of SnCl4 at 150 °C (Wang et al., 2019a), suggests that Sn(IV) volatilization mechanisms may be different with and without fluid boiling. Combined laboratory experiments and quantum mechanical calculations on the isotopic effects of Sn(IV) chloride solution evaporation provide important constraints for understanding the rapidly accumulating Sn isotopes data from studies on Sn ore-forming processes, bronze metallurgy and archeology, and volatile elements in planetary processes.

Late Paleozoic large-scale transcurrent tectonics and synkinematic intrusions are prominent features in the Eastern Tianshan segment of the southwestern Central Asian Orogenic Belt. However, the spatial and temporal relationship between synkinematic intrusions and crustal-scale shear zones remains unclear. Here we report petrology, geochemistry, and geochronology of the Qiziltag pluton associated with the Kanggur-Huangshan Shear Zone (KHSZ) with a view to characterize the spatial and temporal relationship between synkinematic intrusions and large-scale transcurrent shearing. Field relations and zircon U-Pb ages indicate that the Qiziltag pluton was formed through two stages of magmatism, with earlier stage granitoids (gneissic biotite granite: 288.9 ± 1.9 Ma, biotite monzogranite: 291.5 ± 1.7 Ma, K-feldspar granite: 287.9 ± 3.1 Ma), and later stage bimodal intrusions (biotite quartz monzonite: 278.5 ± 1.8 Ma, gabbro: 278.1 ± 2.3 Ma). The earlier stage granitoids are high-K calc-alkaline, enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). Combined with their depleted isotopic compositions (εNd(t) = +6.29 to +7.48) and juvenile model ages (TDM2 = 450–610 Ma), we infer that the granitoids were derived from juvenile lower crust in a post-collisional tectonic transition (from compression to extension). The structural and temporal features indicate that the earlier stage (ca. 290 Ma) granitoids formed prior to the regional large-scale dextral strike slip. The later stage bimodal intrusions are dominated by biotite quartz monzonite as the felsic member and gabbro as the mafic component. The biotite quartz monzonite is high-K calc-alkaline with enriched LREEs and LILEs (e.g., Rb, Th, and U), and depleted HFSEs (e.g., Nb, Ta, and Ti), whereas the gabbro is subalkalic with depleted LREEs and HFSEs (e.g., Nb and Ta), resembling normal mid-ocean ridge basalt features. The bimodal intrusions show similar isotopic compositions (εNd(t) = +6.41 to +6.72 and εHf(t) = +9.55 to + 13.85 for biotite quartz monzonite; εNd(t) = +9.13 to +9.69 and εHf(t) = +4.80 to +14.07 for gabbro). These features suggest that the later stage (ca. 280 Ma) bimodal intrusions were derived from partial melting of depleted mantle and anatectic melting of lower crust materials induced by synchronous underplating of basaltic magma in a post-collisional extension. The structural features of the bimodal intrusions indicate that the later stage (ca. 280 Ma) magmatism was coeval with the development of the KHSZ. In conjunction with spatial and temporal evolution of magmatism and sedimentary records of Eastern Tianshan, we infer that transition between the northward closure of the North Tianshan Ocean and subsequent collision between the Central Tianshan Massif and the Qoltag Arc belt occurred at ca. 300 Ma.

Triassic magmatism has been increasingly identified in the Eastern Tianshan and played a crucial role in the tectonic evolution of the Tianshan Orogenic Belt. The petrogenesis and geodynamic setting of the Triassic magmatism, however, are poorly constrained. In this study, we integrate new field and petrological observations, zircon U Pb ages and Hf isotopic compositions, and whole-rock geochemical data for the microgranular enclaves (MEs) and their host Triassic Tianhu granitoids to investigate their origin and the tectonic regime of the Eastern Tianshan during the Triassic. Based on zircon U Pb geochronology, the Tianhu granitoids and MEs have indistinguishable Early Triassic crystallization ages of 247.1 ± 1.8 Ma, 249.5 ± 2.0 Ma, and 251.0 ± 3.2 Ma. The MEs in the Tianhu granitoids are typically sub-rounded to ellipsoidal in shape. They contain abundant acicular apatite, plagioclase that has been partially resorbed, and megacrysts of feldspar and quartz. They are characterized by high Mg# (50–52), positive eHf(t) values of 3.41–5.83, and young one-stage Hf model ages, all of which are indicative of crystallization from mantle-derived melts. The host Tianhu granitoids, which belong to I-type granites, contain higher SiO2 contents (68.3–69.8 wt%) and lower Mg# (38.3–45.4) than the MEs, are metaluminous (A/CNK = 0.97–0.98), and are characterized by high eHf(t) values of 2.26–5.46 and young two-stage Hf model ages. These geochemical characteristics indicate that the Tianhu granitoids and the MEs likely formed through mixing between mafic and felsic magmas. The mafic magma was originally derived from partial melting of a depleted mantle source, and subsequently evolved via fractional crystallization and modification by the felsic magma. In contrast, the felsic magma was generated by partial melting of the juvenile continental lower crust. The Tianhu granitoids would likely form in an intracontinental extensional environment, in which upwelling of the asthenospheric mantle led to partial melting of the lithospheric mantle to form the mafic magmas. And the felsic magmas were produced by partial melting of the deep juvenile crust with a heat source either from the ascending mafic magmas or the upwelling asthenospheric mantle along the thinned orogenic lithosphere. In either case, there would be significant Triassic crust–mantle interaction in the Eastern Tianshan and its adjacent Beishan area. This interaction was responsible for the formation of widespread Triassic granites and related ore deposits in this intracontinental region.

The Huangshandong Ni–Cu sulfide deposit is the largest magmatic sulfide deposit in the Huangshan–Jing’erquan mafic–ultramafic belt in the Eastern Tianshan; it was overprinted by post-magmatic hydrothermal fluids, and metamorphosed and deformed as a result of regional ductile shearing. Ore-forming elements were remobilized as a result of post-magmatic hydrothermal fluid flow, but the extent of this remobilization is still unclear. In this contribution, detailed mineralogical–textural characteristics of silicates and base-metal sulfides in different types of ores in the Huangshandong Ni–Cu sulfide deposit were integrated with spatially resolved trace-element compositions of olivine, serpentine, pyrrhotite, pentlandite, and chalcopyrite to identify the metals that were mobilized, the scale and quantity of metal remobilization, and the phases into which the mobilized metals were incorporated. Based on varying degrees of serpentine and talc alteration, three different types of ores are identified – weakly serpentinized magmatic ores, which are most representative of the primary magmatic mineralization, strongly serpentinized and deformed ores, and talc-altered ores. The cracks consisting of serpentine and magnetite in weakly serpentinized magmatic ores caused by the expansion of olivine during serpentinization; this, serpentine is enriched in ore-forming metals (e.g., Ni, Co, Cu) relative to olivine. The expansion cracks extend from olivine to sulfides also enriched in ore-forming metals, suggesting that some metals were mobilized from olivine during serpentinization. Based on the higher Ni content of secondary pyrrhotite compared to primary pyrrhotite, it is suggested that base-metal sulfides in the primary, weakly serpentinized ores were dissolved and reprecipitated in the strongly serpentinized and deformed ores from metal-rich fluids that interacted with olivine.

The Tianshan is one of the largest gold provinces on Earth and hosts several giant gold deposits, while most giant gold deposits are distributed in the western and central segments of the Tianshan (i.e., the Western Tianshan) but not in Chinese Tianshan. Thus, the differences for metallogenesis of gold deposits between the Western and Chinese Tianshan attract intensive interest but remain ambiguous. Here we present sericite 40Ar/39Ar ages and S–Pb isotope compositions of pyrite from the Kanggur gold deposit, the largest shear zone-related gold deposit in the Chinese Tianshan. By integrating new sericite 40Ar/39Ar plateau ages (262.71 ± 2.95 Ma and 263.40 ± 2.94 Ma) with previous geochronological results, three peaks in gold mineralization are identified for the entire Tianshan: an early peak at ca. 330 Ma during which time subduction–accretion-related porphyry-type and orogenic gold deposits formed, a middle peak at ca. 290 Ma during which time post-collisional magmatism-related orogenic gold deposits formed in a collisional compressional to post-collisional extensional environment, and a late peak at ca. 260 Ma during which time strike–slip shear zone-related orogenic gold deposits formed in a post-collisional extensional environment. The sulfur (δ34SV-CDT of −1.0 to +2.5‰ for pyrite from ores and −1.9 to +2.6‰ for pyrite from wall rocks) and lead (18.199–18.231 for 206Pb/204Pb, 15.585–15.624 for 207Pb/204Pb, 38.104–38.229 for 208Pb/204Pb for pyrite from ores, and 18.176–18.244 for 206Pb/204Pb, 15.583–15.611 for 207Pb/204Pb, 38.090–38.205 for 208Pb/204Pb for pyrite from wall rocks) isotope compositions of pyrite indicate that the metals in gold deposits throughout the Tianshan were sourced from different reservoirs. In the Western Tianshan, the ore-forming metals for the deposits southwest of longitude 70°E were mainly sourced from upper crustal reservoirs, whereas those east of longitude 70°E were mainly sourced from lower crustal reservoirs. In the Chinese Tianshan, however, the ore-forming metals were dominantly sourced from lower crustal and/or mantle reservoirs. These different reservoirs were likely responsible for the distinct characteristics of the gold deposits located in the Western and Chinese Tianshan.

The return of widespread banded iron formation (BIF) deposition during the Neoproterozoic Era after a more than one-billion-year hiatus appears to be a hallmark of the Neoproterozoic, and may be indicative of critical changes in the Earth’s environmental and tectonic conditions. However, consensus on the Fe sources and origin of Neoproterozoic iron formations (NIFs) remains elusive. Here we present new petrographic and geochemical data from the newly discovered Shalong NIF from the Central Tianshan block in order to constrain the iron source and elucidate the origin and depositional conditions of the NIF. The major and trace element composition of the Shalong NIF indicates that it is a relatively pure chemical sediment with a low detrital input. Rare earth elements and Y patterns (REY) exhibit seawater-like signature such as depletion in light REEs (LREEs) and enrichment in heavy REEs (HREEs). The weak positive Eu anomalies (Eu/Eu∗ = 1.11–1.31) and consistent chondritic Y/Ho ratios of 25 to 29 (average 26) suggest a predominant influx of low-temperature hydrothermal fluids. The geochemistry of the Shalong NIF also supports a predominant hydrothermal iron source characterized by low-temperature hydrothermal fluids. The lack of negative Ce anomalies, as well as weak positive Eu anomalies, and positive and variable δ56Fe values (−0.09‰ to +1.28‰) in the Shalong NIF indicates partial Fe2+ oxidation in a relatively large dissolved iron marine basin under oxygen-limited conditions. The Shalong NIF deposition likely took place on the slope of an extensional oceanic basin in a low energy environment. The Shalong NIF has a close association with metamorphized- bimodal volcanic rocks and predominant hydrothermal iron source. Combined with no sign for any glacial influence and depositional age prior to the global Sturtian glaciations, we suggest that the Shalong NIF is a non-glaciogenic Neoproterozoic iron formation in association with volcanic and hydrothermal activity. Our results, in conjunction with previous studies, suggest that glacial events are not essential or necessary for the origin of all the NIFs. Instead, hydrothermal activity seems to be a more important controlling factor for the build-up of ferruginous basins and subsequent iron oxidation events in the Neoproterozoic leading to the sudden recurrence of NIFs.

The Kanggur gold polymetallic deposit, located in the western segment of the Kanggur–Huangshan Shear Zone (KHSZ) of the Chinese North Tianshan, is the largest shear zone-controlled gold polymetallic deposit in this region. The gold mineralization is hosted by Early Carboniferous volcanic rocks of the Yamansu Formation, which is predominantly composed of andesite, dacite, and tuff. In this contribution, we present U–Pb age data and Hf isotopes of zircon from wall rocks associated with mineralization in the Kanggur deposit, as well as whole-rock geochemistry of the wall rocks with the goal of characterizing the petrogenesis of the deposit, and the sources of the ore-forming materials. Our new LA–ICP–MS zircon age data indicate that the wall rocks formed at ca. 340 Ma in the Early Carboniferous (andesite at 338.0 ± 1.7 Ma, dacite at 338.1 ± 2.2 Ma, rhyolite 332.4 ± 2.8 Ma, and granite porphyry at 342.6 ± 1.9 Ma). These wall rocks are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; e.g., U, K, and Pb), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). Based on the lack of ancient crustal basement rocks in the Qoltag Arc, the lithological assemblage of andesite–dacite–rhyolite, the presence of chert, and the enrichment of andesite and dacite in Na2O (3.35–6.89 wt%) relative to K2O (0.67–2.42 wt%), it is inferred that the Early Carboniferous volcanic wall rocks of the deposit formed in an oceanic arc setting. Considering the similar isotopic compositions of andesite, dacite, rhyolite, and granite porphyry (eNd (t) = −0.12 to 0.64 and eHf(t) = 6.05 to 8.96 for andesite, eNd(t) = 1.01 to 3.02 for dacite; eNd(t) = 4.20 to 4.91 and eHf(t) = 11.02 to 13.79 for rhyolite, and eNd(t) = 1.65 to 2.13 and eHf(t) = 4.70 to 6.80 for granite porphyry) and juvenile Hf model ages (TDM1 = 610 to 730 Ma for andesite, TDM2 = 460 to 640 Ma for rhyolite, and TDM2 = 910 to 1050 for granite porphyry), it is suggested that the primary magma from which the andesite and dacite crystallized was derived from partial melting of metasomatized mantle wedge, whereas, the magma from which the rhyolite and granite porphyry crystallized was derived from partial melting of juvenile lower crust. The bulk S isotope composition (δ34SV-CDT) of these wall rocks varies from −0.8 to 8.7‰ (average of 4.8‰), with the S isotope composition of the andesite and rhyolite being similar to that of pyrite in mineralized rock. The bulk Pb isotope composition of these wall rocks ranges from 17.561 to 18.258 206Pb/204Pb, 15.535 to 15.602 207Pb/204Pb, and 37.593 to 38.118 208Pb/204Pb, with the Pb isotope composition of andesite being similar to that of pyrite from gold-bearing ores in the Kanggur deposit. The high abundance of sulfides in the wall rocks, and the similar S–Pb isotope compositions of ores and andesite suggests that the ore-forming materials were likely derived from the andesite wall rocks.

The Dajingou gold deposit is one of the typical gold deposits in the Quruqtagh metamorphic terrane, north of the Tarim Craton. The deposit mainly comprises gold-bearing quartz veins hosted in Precambrian metamorphic rocks and structurally controlled by the subsidiary faults and ductile shear zone. To determine the age of gold mineralization in the Dajingou deposit, a single sericite 40Ar/39Ar age of 829.4 ± 4.8 Ma (MSWD = 0.57) and hydrothermal zircon weighted average U–Pb ages (812 ± 15 Ma, MSWD = 3.2) from auriferous quartz veins were obtained in this study, indicating that mineralization occurred in the mid-Neoproterozoic (ca. 0.83 Ga), corresponding to regional metamorphism of the Tarim Craton, termed the Tarim orogeny. The Dajingou deposit is the first Precambrian gold deposit identified in North Xinjiang, NW China. The δ18O and δD of quartz ranges from 14.7‰ to 15.9‰ and −104‰ to −75‰, respectively; the calculated δ18OH2O of the fluids ranges from 0.9‰ to 5.0‰. This suggests that the ore-forming fluids in the Dajingou gold deposit were derived from dehydration of metamorphic rocks during regional metamorphism, with a subsequent input of meteoric water. Based on its similarities with typical orogenic gold deposits, the Dajingou deposit is proposed to be an orogenic gold deposit formed during the mid-Neoproterozoic Tarim orogeny in the Tarim Craton.