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The Kaladawan Fe–Mo ore field (Altyn, Xinjiang) in Northwest (NW) China contains six deposits, with a total reserve of 60 Mt Fe and 10 Kt Mo metal. The orebodies are hosted in lower Paleozoic andesite, dacite, phyllite and marble with well-developed skarn alteration. The Kaladawan granites are newly U–Pb dated to be Early Ordovician (476.1 ± 3.3 Ma), largely coeval with the Fe–Mo mineralization (molybdenite Re–Os: 480.3 ± 3.2 Ma). The granites contain high SiO 2 , K 2 O and Al 2 O 3 , low TiO 2 , MgO and CaO, with high K 2 O/Na 2 O ratios (1.26–1.58) and A/CNK values (1.00–1.08), showing peraluminous high-K calc-alkaline affinity. The rocks are characterized by large ion lithophile element (LILE) and light rare earth element (LREE) enrichments and depletions of Sr, Ba, Nb, Ta, Ti and P, and with negative Eu anomalies. The rocks have initial 87 Sr/ 86 Sr ratios of 0.7066 to 0.7112 and e Nd ( t ) values of −1.4 to −1.1, with T DM2 (Nd) ages of 1.32–1.30 Ga. Zircon e Hf (t) values range from 2.9 to 6.4, with T DM2 (Hf) ages of 1.26–1.04 Ga. The new geochemical and isotopic data suggest that the Kaladawan granites are highly fractionated I-type, and likely formed by fractional crystallization of a magma that was derived from partial melting of a mixture of crustal and mantle materials. Deposits in the Kaladawan Fe–Mo field are skarn-type and may have occurred in an active continental margin, via the contact metamorphism and metasomatic reaction between granite-derived fluids and the wall rocks.

The Zankan iron deposit (Taxkorgan County, Xinjiang) is a recently discovered large Fe deposit in western China. The deposit is hosted in the Bulunkuole metamorphic complex in the Taxkorgan terrane of the West Kunlun Orogen. The ores are uniquely composed of magnetite, pyrite and anhydrite with variable contents, and show massive, disseminated and banded styles. The ores contain widely varying (Al2O3 + TiO2) (0.28–5.48 wt%), Zr (3.0–83 ppm) and Hf (

The Xinjiang Uygur Autonomous Region in NW China occupies around 1/6 of the total China land size, and contains components of both the Central Asian Orogenic Belt (CAOB) and Paleo-Tethyan Orogenic Belt (PTOB). The Paleozoic CAOB is situated in the northern and central parts of Xinjiang, whilst the Paleozoic-Mesozoic PTOB is mainly located in the southern part of Xinjiang. These orogenic belts were formed by the multiphase Paleozoic-Mesozoic terrane accretions and collisions enacted by the Paleo-Asian Ocean and Paleo-Tethys closure, a process that has also generated many well-endowed tectono-metallogenic belts. From north to south, these belts include the Chinese Altay, the Junggar, the Chinese Tianshan and the Kunlun, Alytn and Qimantage mountains. Since the late 1990s, especially in the past 10 years, many Au, Cu, Fe and Pb-Zn deposits have been discovered. These ore deposits commonly show clear but complex relationships with the orogenic processes. Detailed studies of these mineral systems and their associated magmatic-metamorphic events and structural deformation would significantly improve our understanding of the metallogenic evolution of the CAOB and PTOB in Xinjiang. The 33 papers presented in this special issue, which represents the first collective work of Xinjiang mineral resources in international journals, are aimed to convey the latest research findings on key Au, Cu, Fe-(Cu), Pb-Zn and other metal deposits in Xinjiang. It is our wish that this special issue could enhance our knowledge on the nature and evolution of the metallogenesis in the Xinjiang orogens, and reinforce the foundation for future mineral research and exploration.

Western Tianshan along the southwestern margin of the Central Asian Orogenic Belt is well-endowed with epithermal and porphyry Au deposits. The Kuruer Cu-Au deposit, recently discovered in the eastern part of Western Tianshan, was considered as a high sulfidation epithermal deposit. However, our geological, fluid inclusion and stable isotopic studies indicate that it actually formed in transition from high sulfidation to porphyry. The host rocks include the Dahalajunshan Formation volcanic and volcano-sedimentary rocks such as andesite, rhyolite, ignimbrite and tuff. Cu-Au mineralization mainly occurs as quartz-dominated stockworks or disseminations, with abundant pyrite and chalcopyrite and minor galena and sphalerite. Gold occurs as invisible phase in sulfides. Hydrothermal alteration includes a silicic core, surrounded by phyllic alteration and peripheral propylitic alteration. Based on field observations, paragenetic and crosscutting relationship, the mineralization process can be roughly divided into three stages. The early stage is characterized by the assemblage of quartz + pyrite + chalcopyrite while the middle stage contains quartz and chalcopyrite at absence of pyrite. The late stage is characterized by calcite ± quartz ± chlorite ± chalcopyrite veins. Fluid inclusions at the early stage are mainly liquid-rich aqueous and CO2-rich inclusions and minor vapor-rich aqueous and solid-bearing inclusions. Their homogenization temperatures and salinities can be up to 420 °C and 39 wt.% NaCl eq., respectively, indicating that the initial ore-forming fluids are high temperature, high salinity, H2O-CO2-NaCl systems. In the middle stage, there are only liquid-rich aqueous inclusions, with homogenization temperatures and salinities of 130–190 °C and 0.18 to 10.7 wt.% NaCl eq., respectively. Liquid-rich aqueous inclusions in the late stage display much lower temperatures and salinities, ranging from 110 to 130 °C and 0.18–2.7 wt.% NaCl eq., respectively. Obtained δDH2O and δ18OH2O values of quartz from the middle stage are −98 to −107‰ and −2.1 to 0.74‰, respectively. The δ34S values of 9 chalcopyrite samples range from −10.2 to −2.4‰, with an average of −4.1‰. We conclude that the initial ore-forming fluids are magmatic in origin, and further cooled and diluted by mixing with meteoric water. Intensive fluid boiling and mixing facilitated hydrothermal alteration and mineralization.

The Baiganhu W-Sn ore field in the northwestern area of the East Kunlun Orogen, NW China, contains three economically important W-Sn deposits, namely Kekekaerde, Baiganhu and Bashierxi. Timing of the W-Sn mineralization remains under debates due to lack of precise isotope dating directly conducted on ore minerals. We herewith report LA-MC-ICP-MS (laser ablation (multi-collector) inductively coupled plasma mass spectrometry) and ID-TIMS (isotope dilution thermal ionization mass spectrometry) cassiterite U−Pb ages for the Kekekaerde W-Sn deposit in the Baiganhu W-Sn ore field. The ID-TIMS cassiterite 206 Pb/ 238 U results yield a weighted mean age of 416 ± 1 Ma (95% confidence, MSWD = 0.8), and the LA-MC-ICP-MS analytical data give a 206 Pb/ 207 Pb– 238 U/ 207 Pb isochron age of 426 ± 13 Ma (95% confidence, MSWD = 0.1). These two ages are same within errors, suggesting that the mineralization in the Baiganhu W-Sn ore field occurred at ca. 416 Ma. These new ages and understandings are consistent with the previously reported zircon U−Pb ages of 430–420 Ma for the ore-bearing granites in the ore-field, and with the 40 Ar/ 39 Ar plateau ages of ca. 412 Ma for the hydrothermal muscovite from ore-bearing quartz veins and greinsenized granite. It shows that the granite magmatism and its associated hydrothermal mineralization resulted from the Caledonian Orogeny that accommodated the closure of the Proto-Tethys, followed by the continental collision between the Central Kunlun, Northern Kunlun terranes and the Qaidam Block.

The Axi deposit is the largest low-sulfidation epithermal gold deposit in Chinese Western Tianshan, Central Asian Orogenic Belt. In this contribution, combined petrological observations, electron microprobe analysis (EMPA) and X-ray backscattered electron images (BSE) have been conducted on Fe-S-As minerals to reveal their textural and compositional evolution. Pyrite and arsenopyrite are ubiquitous. Their texture and composition show gradual changes with time. Four generations of pyrite can be identified, named Py1, Py2, Py3 and Py4 from early to late. The coarse-grained, euhedral to subhedral Py1 (mostly 100–300 μm) from the quartz-chalcedony stage is the earliest, and predates gold mineralization. Sometimes they contain silicate and arsenopyrite (Apy1) inclusions. Compositionally, they are enriched in Pb (up to 0.60 wt%), but depleted in As (0.06–7.61 wt%, mostly syn -mineralization feature. Subsequent Py3 occurs as very fine-grained disseminations of euhedral crystals (10–50 μm) in quartz-polymetallic sulfides stage and carbonate-quartz stage. They display clear oscillatory zoning and contain arsenopyrite (Apy3), sphalerite and Sb-Te mineral inclusions. Their Au content vary greatly from 0.02 wt% to 1.02 wt%, with corresponding As content varying from 0.07 wt% to 8.28 wt%. The post-mineralization Py4 crystals (30–5000 μm) mainly occur as foliated, sheaf, or radiaxial aggregates in carbonate-quartz stage. They have the lowest Au (with a mean value of 0.04 wt%), As (with a mean value of 0.32 wt%), Co (with a mean value of 0.04 wt%) and Ni (with a mean value of 0.04 wt%) concentrations, although dramatically high S contents (with a mean value of 52.72 wt%). Correspondingly, there are three generations of arsenopyrite: Apy1 (20–50 μm) and Apy3 (3–15 μm) mainly occur as inclusions in Py1 and Py3, respectively, whereas the latest Apy4 (

The Qiman Tagh W-Sn ore belt is located in the westernmost sector of the East Kunlun Orogen, NW China. It has been recognized as a unique W-Sn belt that formed in the early Paleozoic and related to closure of the Proto-Tethys. To understand the evolution of ore-forming fluids and its relationship with the tectonic setting of East Kunlun Orogen, we report the results obtained from fluid inclusion and H-O isotopic studies of ores and quartz veins for the Qiman Tagh W-Sn ore belt. Mineralization in Qiman Tagh includes four stages characterized by quartz-cassiterite-wolframite assemblage stage 1, quartz ± scheelite assemblage stage 2, quartz-polymetallic sulfides stage 3, and ore-barren veins stage 4. The former two stages are conducive to mineralization, while the latter two stages are less important. The fluid inclusions are distinguished between CO2-H2O (C-type) and NaCl-H2O (W-type) in composition, containing a trace of CH4, N2, C2H6, SO2, and CO32–. Cassiterite and quartz in stage 1, instead of wolframite, contain a great deal of C-type inclusions. All inclusions in minerals of stage 1 yield homogenization temperatures of 230.1–384.1 °C (peaking at 310–320 °C), with salinities lower than 14.76 wt% NaCl equiv. and bulk densities of 0.63–0.89 g/cm3. The stage 2 minerals contain both two types of inclusions, yielding homogenization temperatures of 183.4–335.9 °C (peaking at 280–290 °C), with salinities lower than 14.53 wt% NaCl equiv. and bulk densities of 0.66–0.97 g/cm3. Fluid inclusions in minerals of stages 3 and 4 are mainly W-type and homogenized at temperatures of 140.6–277.6 °C (peaking 210–220 °C), and 116.9–255.1 °C (peaking 160–170 °C), respectively. The H-O isotopic systematics shows that the fluids were dominated by magmatic water in stages 1 and 2, but by meteoric water in stages 3 and 4. Integrating all the geological and geochemical data, we conclude that the fluids forming the Qiman Tagh W-Sn ore belt evolved from granite-derived, CO2-rich and reducing, to meteoric water-dominated, CO2-poor and oxidizing. Fluid immiscibility, cooling and interaction with rocks are main mechanisms for metallic deposition.

Origin and accumulation process of gold in the metavolcanic-hosted orogenic gold deposits is still open to debate. Approximately fifteen gold-bearing deposits are hosted in the metamorphosed volcanics of the Chinese Altay Orogen, NW China. Among them, the representative Sarekuobu gold deposit, occurs as lodes in a Devonian volcanic-sedimentary succession that was deformed into a series of multiple overturned synclines and metamorphosed to (garnet)-biotite-chlorite schists. In previous studies, little attention has been paid to pyrite varieties and their in situ geochemistry to constrain their genetic understanding. Herein, five types of pyrite with distinct textures and mineral assemblages at Sarekuobu are divided into four generations based on the crosscutting and replacing relationship. The earliest pyrite (PyI) occurs as magnetite-pyrite parallel laminated layers comparable to those in VMS deposits, and some of its beddings are crosscut by PyⅡ that is scattered in foliation of the host greenschists and likely formed during syn-deformation. The colloidal PyIIIa and inclusion-rich PyIIIb are present in the same auriferous quartz veins continuously cutting across the PyⅡ-rich schists. It is notable that PyIIIb acts as the most important gold-bearing pyrite containing some micro-mineral inclusions such as visible gold and chalcopyrite. The final inclusion-poor PyⅣ with coarse and euhedral grains replaces or envelops all above three pyrite generation. The highest gold concentrations are presented in PyIIIa and PyIIIb by LA-ICP-MS spot analysis, with the maximum values up to 16 ppm and 426 ppm, respectively. In contrast to the substituted invisible Au nano-particles in lattice structures with time-resolved LA-ICP-MS signal parallel to Fe, the visible Au occurs as sizeable micro-inclusions in PyIIIb revealed by highly variable LA-ICP-MS signal spectrum. Further LA-ICP-MS trace element mapping show Au and other trace elements (e.g., Cu, Pb, Zn, Bi, Sb and Ag) are unevenly distributed in PyIIIb but barren in coexisting PyⅣ, in agreement with the microscopic textures of inclusion-rich PyIIIb and inclusion-poor PyⅣ. Another mapping displays these trace elements are homogeneously distributed along colloidal layers in PyIIIa but depleted in the coexisting PyI. Collectively, PyIIIb is believed to experience relatively longer-time crystallization co-precipitating with native gold and chalcopyrite, whereas PyIIIa is rapidly deposited from the same auriferous ore fluids without sufficient time for crystallization and captures some clay minerals and organic matters. In-situ δ34SV-CDT values of four pyrite generations by fsLA-MC-ICP-MS range from +2.34 to + 10.14‰, and gradually decrease from PyI (mean, +9.59‰), through PyⅡ (+8.67‰), PyIIIa (+6.16‰) and PyIIIb (+4.97‰), to final PyⅣ (+3.66‰). In combination with published sulfur isotope composition of host rocks (maximum, +18.7‰), the formation of the auriferous fluids and deposition of Au in pyrite at Sarekuobu might be attributed to the sulfur pathway of progressively enhanced thermal sulfate reduction (TSR) in the Devonian marine strata. Thus, two process including the Devonian seafloor sedimentation and Triassic orogeny-related metamorphism are critical for formation of the Sarekuobu gold deposit.

Orogenic gold deposits are one of the most important gold deposits in the world. However, it is controversial that orogenic gold deposits are only generated at subduction-accretion or both in collisional setting. The Altai Orogen experienced a complex subduction accretion–collision history, including magmatism and metamorphism, and forming giant gold deposits. The Tokuzbay gold deposit consists of quartz vein ores and disseminated ores hosted in dikes. The ore bodies are controlled by secondary shear zone of the NW-, NNW-trending Ma’erkakuli Fault and occurred in meta-sediments, i.e., meta-sandstone and phyllite of Devonian Altai Formation, and diorite dikes and granite porphyritic dikes. Wall rock alteration is represented by silicification, pyritization, and muscovite alteration. The ores are restricted by ductile and brittle deformation in the shear zone. Large amounts of native gold and auriferous tellurium were precipitated during a transition from ductile to brittle regime. These characteristics indicate that the Tokuzbay gold deposit is an orogenic gold deposit in the Altai Orogen. The zircon LA-ICP-MS U-Pb ages of the ore-bearing granite porphyritic dikes and diorite dikes are 390 ± 2.5 Ma (MSWD = 0.87) and 378 ± 4 Ma (MSWD = 0.21), respectively, indicating that the magmatic rocks were emplaced during subduction of the Paleo Asian Ocean beneath Altai Orogen. Muscovite samples associated with gold from the auriferous quartz vein and disseminated ores hosted in diorite dikes returned Ar-Ar ages of 292.7 ± 1 Ma (MSWD = 1.3) and 293.9 ± 1.2 Ma (MSWD = 0.7), indicating that gold mineralization in quartz vein is synchronized with disseminated ores. The gold mineralization is restricted to the Early Permian and overlaps with the collision between Altai Orogen and Junggar Plate. The ore-hosting magmatic rocks related to subduction are more than 100 million years earlier than the ore-forming events. Combined with the regional tectonic evolution and the shear characteristics of the gold district, it is well proved that sinistral shearing trigged by the collision of Junggar Plate and Altai Orogen contributed to gold mineralization of the Tokuzbay deposit. Considering the Altai gold deposits in Kazakhstan, it is revealed that Permian collision between Junggar Plate and Altai Orogen triggered a large number of orogenic gold mineralization.

Orogenic gold deposits are the most important gold resource in the world. It is controversial whether their ore-forming fluids were sourced from metamorphic dehydration of the crust or the mantle. The Tokuzbay gold deposit is a typical orogenic-type gold deposit in the Central Asian Orogenic Belt , providing a case for discussing the source of ore-forming fluids. The auriferous quartz veins are fault-controlled and occur mainly in metamorphic sediments of Devonian Altai Formation and minor in diorite dikes, forming three ore types, i.e., quartz vein, altered metamorphic sediments and altered diorite dikes. We studied the Sr–Nd–Pb isotope characteristics of the ore sulfides, and magmatic and metamorphic rocks from the Tokuzbay gold deposit, and thereby discuss the source of the ore-forming fluids. The 87Sr/86Sr ratios of meta-sediment hosted ores scatter between 0.709474 and 0.715238, and ISr (292 Ma) values range from 0.706570 to 0.714045. The diorite dikes hosted ores show more restricted 87Sr/86Sr ratios ranging from 0.706963 to 0.711519, and ISr (292 Ma) values ranging from 0.706777 to 0.710612. The wall rocks of the Altai Formation have ISr (292 Ma) values of 0.711778 and 0.714409, which are higher than ore sulfides. This indicates that the ISr (292 Ma) values of initial ore-forming fluids that interacted with the Altai Formation are no higher than 0.706777, which is the lowest ISr (292 Ma) value for disseminated ores. The calculated (143Nd/144Nd)i ratios and eNd (292 Ma) values for meta-sediment hosted ores range from 0.511882 to 0.512464, and −7.4 to 4.0, respectively. The calculated (143Nd/144Nd)i ratios and eNd (292 Ma) values for diorite dike hosted ores vary from 0.512293 to 0.512562, and from 0.6 to 5.9, respectively. The meta-sediments of Altai Formation show eNd (292 Ma) values ranging from −6.8 to −4.4 with an average of −5.8, which are lower than those of ore sulfides. This indicates that the eNd (292 Ma) values for the fluids that interacted with the wall rocks cannot be lower than 4.5, which is the average value for disseminated ores. The calculated (208Pb/204Pb)i, (207Pb/204Pb)i, and (206Pb/204Pb)i values of ore sulfides are 37.796–38.989, 15.512–15.707, 17.988–18.100, respectively. The wall rocks of the Altai Formation show relatively higher (206Pb/204Pb)i ratios, indicating that the ore-forming fluid that interacted with the Altai Formation are not higher than 17.988, which is the lowest values of sulfides from disseminated ores. Based on the Sr–Nd–Pb isotope data, we suggest the possible ore-forming fluids should have lower ISr (292 Ma) values, higher eNd (292 Ma) values, and lower (206Pb/204Pb)i values compared to the those of ore sulfides and were possibly sourced from a source compositionally similar to the diorite dikes in addition to wall rocks of Altai Formation. Combining with the regional metamorphism and tectonic evolution , we suggest that the ore fluids have originated from the metamorphic dehydration of sediments of Altai Formation in the South Altai during the collision between Altai Orogen and Junggar Plate.

Classification algorithms were constructed based on pyrite trace elements using two machine learning methods, support vector machine (SVM) and artificial neural network (ANN), to discriminate the genesis of pyrites sampled from sedimentary rock, orogenic and volcanic hosted massive sulfide (VHMS) deposits. The classifiers were trained with a dataset including published trace element compositions of 2104 pyrite samples from 92 mineral deposits or stratigraphic units. Cross validations were conducted to evaluate the performances of the classifiers on unknown samples, using a variant of the k-fold method. Each time, all pyrite samples from one of the 92 deposits/strata were set aside as the testing set, and the classifiers were trained with samples of the remaining 91. Then, the performances of the classifiers were evaluated based on whether it can correctly determine the genesis of testing deposit/stratum. The circulation was repeated 92 times for each one of the deposits/strata in the dataset, and 91 of them were correctly classified by the SVM-based classifiers, and 90 by the ANN-based. The trained classifiers were then applied to reveal the genesis of the Jiashengpan Zn-Pb deposit, which is characterized by two stages of pyrite formation: early-stage fine-grained massive and late-stage coarse-grained hydrothermal pyrite. The trained algorithms show that the early-stage is compositionally similar to sedimentary pyrite, while the late-stage has affinity to those from orogenic deposits, consistent with geological and geochemical features revealed by previous studies. This study sheds light on the power of machine learning in decoding the geochemical data of pyrite, which can well record the history of ore formation.

The large Yueyang Ag-Au-Cu deposit is commonly regarded as a low-sulfidation epithermal deposit in the Zijinshan orefield, Fujian Province, southeastern China. The Ag-Ag-Cu orebodies hosted in the Zijinshan granitic batholith are mainly stratoid and lens in shape, and controlled by a series of NW-trending listric faults with shallow dip angles. Four mineralization stages are recognized on the basis of mineral assemblage, ore fabrics, and crosscutting relationships of the ore veins, namely: pre-ore (pyrite + sericite + quartz ± chlorite), main Cu (chalcopyrite + pyrite + sericite + quartz ± bornite), main Ag-Au (Ag and Au minerals + pyrite + quartz + adularia ± calcite ± apatite ± chalcopyrite ± galena ± sphalerite) and post-ore (quartz ± chalcedony ± calcite) stages. Fluid inclusions (FIs) in the deposit include aqueous liquid-rich (WL-), aqueous vapor-rich (WV-), and minor carbonic (C-) and daughter mineral-bearing (S-) type ones. WL-subtype is the main inclusion type in the Yueyang deposit, accounting for more than 90% in proportion in each stage. Minor WV-subtype inclusions occur in both the main Cu and Ag stages, while the C-type and S-type ones are only observed in the main Cu stage. Fluid inclusion and H-O isotope study indicated that the ore-forming fluid of the main Cu stage is primarily magmatic vapor, which further underwent fluid boiling and mixing with meteoric water, while the ore-forming fluid of the main Ag stage is meteoric water-dominated, and the precipitation of silver and gold was mainly resulted from fluid boiling and the precipitation of other sulfides. On the basis of the aforementioned geological, fluid inclusion and stable isotope studies, we proposed a two-stage model for the Yueyang deposit, including a magmatic vapor-related porphyry type Cu mineralization and meteoric water-related low-sulfidation epithermal Ag-Au-Cu mineralization, although the porphyry Cu mineralization is very limited in scale. The mineralization and exhumation depths of the Yueyang deposit are estimated to be 448‒527 m and 18‒97 m, respectively. By comparison with the exhumation depths of other deposits in the Zijinshan orefield, it is suggested that more epithermal deposits could be found in the southwest of the orefield due to less uplift and exhumation therein.

South China Block (SCB) is the area including the Yangtze Craton and the Huanan Orogen where scattered Precambrian terranes are usually regarded as segments of Cathaysia Land. It is the third most important molybdenum metallogenic province in China, next to the Qinling-Dabie area and Northeast China, containing 29 Mo-only or Mo-dominated, 9 W-Mo(-Sn-Bi) and 8 Cu-Mo deposits. These 46 deposits are located mainly in: (1) the Lower Yangtze River Belt of the northeastern Yangtze Craton, (2) the Northern Jiangnan Orogenic Belt that is generally considered a Meso-Neoproterozoic magmatic arc complex accreted onto the southeastern margin of the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt characterized by local exposures of Proterozoic metamorphic terranes and the more widespread Sinian (Uppermost Proterozoic) to Triassic sedimentary sequences, and (4) the Southeast Coastal Volcanic Belt characterized by Yanshanian andesitic to felsic volcanic rocks. Their genetic types are dominated by porphyry and skarn mineral systems, with only a few quartz-vein systems. The orebodies form veins, lens, cylindrical shapes, pipes, or irregular in shape, usually controlled by faults at various scales and volcanic-subvolcanic complexes. The host-rocks are variable in lithologies, including granites, porphyries, volcanic breccias and tuffs, clastic sediments and carbonate rocks, but the high-grade orebodies are usually hosted in carbonate-shale sequences. Hydrothermal mineralization processes can be generally divided into four stages, from early to late, they are (1) K-feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-polymetallic sulfide stockworks, and (4) quartz-carbonate-fluorite veinlets. Fluid-rock interaction as exemplified by wallrock alteration evolved from K-silicate alteration (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alteration, with skarn alteration typically occurring in skarn-type mineral systems. Hydrothermal mineral assemblages vary between two end-members, namely the dry system formed by CO2-rich fluids and marked by quartz, K-feldspar, fluorite, carbonate and epidote, and the wet system mainly originated from CO2-poor fluids and composed of biotite, sericite and chlorite. The ore-forming fluids are magmatic in origin and show high-temperature and high-salinity. The melt-fluid systems forming Cu-Mo deposits are more oxidizing than those forming the W-Mo or Mo deposits, as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions. The Cu-Mo deposits are related to the I-type granitic rocks (adakite-like), whereas the W-Mo and Mo-only systems are related to granitic rocks of S- or A-types, although all of them show high K contents. Available isotope ages show that the Mo and Mo-bearing deposits were predominantly formed in the early Yanshanian Orogeny (170–134 Ma), followed by the late Yanshanian Orogeny (110–92 Ma) and the Caledonian Orogeny (450–410 Ma). The Caledonian Mo-mineralization has been observed only in the Wuyi-Yunkai Orogenic Belt and related to the collision between the Yangtze Craton and the pre-Devonian Huanan Orogen or terranes separated from the Cathaysia Land, linked to the assembly of the Gondwana supercontinent. The Early Yanshanian mineralization affected the entire Huanan Orogen and the eastern Yangtze Craton, and resulted from the syn- to post-collisional tectonism following the closure of eastern Paleo-Tethys. The Late Yanshanian Mo deposits mainly occur in the Southeast Coastal Volcanic Belt and the southeastern margin of the Wuyi-Yunkai Orogenic Belt, and are related to the westward subduction of the Paleo-Pacific plate. The skarn-type mineral systems generally show lower Re contents than the porphyry-type deposits in a same tectonic unit, suggesting that carbonate host-rocks have lower Re contents than the causative porphyries. The Re contents in molybdenites from porphyry or porphyry-skarn Cu-Mo systems are > 50 ppm, mainly > 100 ppm, suggesting a source significantly contributed by the mantle; whereas the Re contents in molybdenites from the Mo-only or W-Mo-dominated deposits are

The Waifangshan Mo-quartz vein cluster occurs at the northernmost margin of the Qinling Orogen. The orebodies occur as quartz veins and are controlled by low-angle faults. We identify three hydrothermal stages, characterized by veinlets of quartz–pyrite, quartz–molybdenite–pyrite–chalcopyrite–galena–sphalerite, and quartz–carbonate assemblages, respectively. The early-stage quartz veins were structurally-deformed, brecciated, and filled by non-deformed middle- or late-stage veinlets, suggesting that the mineralization is associated with a tectonic transition from compression to extension. Five molybdenite separates from the Zhifang Mo deposit yield individual Re–Os ages from 241.2 ± 1.6 to 247.4 ± 2.5 Ma, with a weighted mean age of 243.8 ± 2.8 Ma. Individual Re–Os isotope ages of four molybdenite samples from the Badaogou Mo deposit range from 238.9 ± 2.1 to 255.8 ± 2.2 Ma, with a weighted mean age of 246 ± 10 Ma. Four analyses of molybdenite separates from the Xiangchungou Mo deposit yield individual Re–Os isotope ages of 243.8 ± 8.8 to 247.7 ± 4.4 Ma, with a weighted mean age of 246.0 ± 1.1 Ma. All of these data yield a weighted mean age of 241.9 ± 1.9 Ma, coeval with the accretionary orogeny. We thus conclude that the Waifangshan Mo-quartz veins formed during a transition from continental arc to back-arc setting. The Waifangshan Mo-quartz veins share similar geological, geochemical and geochronological features with the orogenic-type systems. We propose that the Waifangshan Mo-quartz veins are an orogenic-type Mo mineralization, and possibly represent the deepest member in the crustal continuum model of the orogenic-type mineral systems. The molybdenite samples from the Mo-quartz veins in the Waifangshan area have low Re contents (1.457 to 39.16 ppm), suggesting a continental crust-dominated source.

Northeast (NE) China lies in the eastern sector of the Central Asian Orogenic Belt (CAOB) that connects with the Circum-Pacific Orogenic Belt in the east, and accommodates multistage magmatism, crustal growth and mineralization. In this region 69 Mo-only or Mo-dominated and 9 Cu-Mo deposits have been discovered, including 65 deposits ranking medium-size (> 10 Kt Mo metal) or larger in tonnage and containing a total resource of 10.5 Mt Mo metal. Six giant and seventeen large deposits have total reserves of 6.7 and 3.1 Mt Mo, respectively. These deposits occur in the areas surrounding the Songliao Basin, including the northern margin of the North China Craton, the Great Hingan Range and the Ji-Hei Fold Belt, and have been formed during Paleozoic and Mesozoic tectono-magmatic events. All the Mo-only or Mo-dominated deposits were formed in the Mesozoic, postdating the closure of the Paleo-Asia Ocean, and in a series of pulses around 250–200 Ma, 200–160 Ma, 160–130 and

The Dabie Shan in central East China is a collisional orogenic belt suturing the North China and Yangtze blocks. It was formed by Jurassic-Early Cretaceous continental collision , following the Triassic closure of the northernmost paleo-Tethyan Ocean. In the area, at least ten porphyry Mo systems have been discovered, including two giant ones, with a total reserve of > 3 Mt Mo metal. The porphyry-type Mo mineralization mainly occurred during 156–110 Ma, in the post-collisional extension setting. The location of Mo deposit is controlled by NW- and NNE-trending faults, mostly in the south of the Gui-Mei Fault suturing the North China and Yangtze blocks. Mo mineralization is generally associated with the Yanshanian high-K calc-alkaline metaluminous-peraluminous granitic intrusions, with orebodies being located in the intrusions and/or host-rocks. The hydrothermal ore-forming process generally includes four stages, with the initial ore-forming fluids being featured by high temperature, high salinity and CO 2 -rich. Geochemical signatures indicate that the ore-causative magmatism in the Dabie Shan mainly originated from either the northern or southern Dabie complex, but mixed with the Precambrian rocks of the North China block, except for the Tianmugou porphyry system which shares more similar geological and geochemical characteristics with the porphyry Mo deposits in eastern Qinling Orogen. We also develop a scissor-style intracontinental subduction model to interpret the differences in spatial distribution, geneses, and geochemical and geological characteristics between the Mo deposits in Dabie Shan and Qinling Orogen. In our model, the basement of the North China Block southwardly underthrusted beneath the Dabie Shan, possibly along the Gui-Mei Fault; whilst the basement of the Yangtze Block northwardly underthrusted beneath the Qinling Orogen; and the inferred Minggang-Xinyang fault zone served as a dextral strike-slip fault zone in the North China Block, but acted as a sinistral transpressional fault zone within the orogenic area. Compared to the subduction- or Endako- and rift- or Climax-types of porphyry Mo deposits, the porphyry Mo deposits in the Dabie Shan are unique because of their crustal source for the magma and ore-forming materials, and as such are assigned to the Dabie- or collision-type. Hence we develop a new global tectonic model for porphyry Mo deposits of three types, showing their genetic tectonic settings .

The Great Hingan Range is located in the eastern sector of the Central Asia Orogenic Belt, and is the second important Mo province in China, next to the Qinling–Dabie orogenic belt. Previous studies concluded that all the Mo deposits (Mo-only or Mo-dominated polymetallic) in the area were formed in the Mesozoic, and related either to the syn- to post-collisional setting following the closure of the Paleo-Asia Ocean, or to the westward subduction of the Pacific plate. However, the fluids forming the giant Diyanqin'amu porphyry Mo deposit in the area disagree with the features of collision-type Mo deposits, but accord with those of the subduction- or continental arc-type. The Mo mineralization is hosted in the Late Jurassic volcanic rocks and genetically related to the buried porphyritic granite and aplitic granite. Two porphyritic granite samples yield LA-ICP-MS zircon weighted mean 206 Pb/ 238 U ages of 158.7 ± 0.8 Ma (MSWD = 0.64, 2σ) and 158.0 ± 0.9 Ma (MSWD = 0.38, 2σ), respectively. The aplitic granite yields a zircon U–Pb weighted mean 206 Pb/ 238 U age of 156.9 ± 1.1 Ma (MSWD = 0.48, 2σ), slightly younger than the porphyritic granite. Seven molybdenite samples from the ores yield Re–Os isotope ages of 156.1 ± 2.2 to 158.1 ± 4.3 Ma. These ages constrain that the Diyanqin'amu Mo system was formed in the period of 159–156 Ma. The granites at the deposit have high contents of SiO 2 , K 2 O and Al 2 O 3 , and low contents of TiO 2 , MgO and CaO, showing a peraluminous high-K calc-alkaline affinity. These granites and the host volcanic rocks are characterized by enrichment of K, Rb, U, Pb, Th and LREE, and depletion of Nb, Ta, Ti and HREE, with negative Eu anomaly, which are similar to magmatic rocks in the Andean arc. Zircon grains from the granites show positive e Hf ( t ) values of 4.2–9.0, with T DM2 (Hf) ages of 0.63–0.94 Ga. These geochemical data imply that the granites at Diyanqin'amu are highly fractionated I-type, formed in a continental arc generated by the southeastward subduction of the Mongol–Okhotsk oceanic plate.

Northwest China, covering northern Xinjiang, northern Gansu and westernmost Inner Mongolia, mainly includes Junggar Basin and its surrounding mountains such as Chinese Altay, Junggar, Chinese Tianshan and Beishan. It lies at the junction of Siberia, Tarim and Kazakhstan plates, and is a key sector of the Central Asian Orogenic Belt (CAOB), characterized by multistage Phanerozoic continental growth. Herein at least nine Mo-only or Mo-dominated, fourteen Cu-Mo, two W-Mo and one Be-Mo deposits have been discovered. These 27 deposits occur in Altay, West Jungar, West Tianshan, East Tianshan and Beishan areas, and have been formed during accretionary or collisional orogenies. The majority of the deposits are porphyry type, followed by the skarn and quartz vein types. The orebodies occur mainly as veins, lens, pods in the positions from inner intrusions through contact zones to the hostrocks distal to causative intrusions. The host-rocks are variable in lithologies, including granites, porphyries, volcanic breccias and tuffs, and sedimentary rocks. Outward from orebodies to hostrocks, the wallrock alteration is zoning from potassic (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alterations, with skarn specifically occurring in skarn-type systems. Hydrothermal mineralization generally includes four stages, from early to late, represented by (1) potassic feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-polymetallic sulfide stockworks, and (4) quartz ± carbonate ± fluorite veins or veinlets. The ore-forming fluids were initially magmatic in origin and shew high-temperature and high-salinity, containing daughter mineral- and/or CO2-bearing fluid inclusions; and eventually evolved to low-temperature, low-pressure, low-salinity and CO2-poor meteoric water. The porphyry Mo deposits can be further subdivided into two subtypes, i.e., Dabie- and Endako-types. The Endako-type Mo deposits, e.g., Suyunhe and Hongyuan, together with all the Cu-Mo systems, were formed in the Palaeozoic subduction-related magmatic arcs. The Dabie-type porphyry Mo deposits, represented by giant Donggebi and Baishan, together with the Mo-only, Mo-dominated and W-Mo or Be-Mo deposits were formed in syn- to post-collisional tectonic setting, with isotope ages ranging 260–213.2 Ma, with the Kumutage skarn-type Mo system being an exception aged 319 Ma. The Dabie-type porphyry Mo deposits are characterized by the CO2-bearing fluid inclusions that cannot be observed in the Endako-type porphyry Mo systems. The Re contents in molybdenites from porphyry and porphyry-skarn Cu-Mo systems are mainly > 100 ppm, suggesting a source significantly contributed by the mantle; whereas the Re contents in molybdenites from the Mo-only or W-Mo deposits are mainly

The large Zankan iron deposit is hosted in the pre-Devonian Bulunkuole metamorphic complex within the Taxkorgan terrane, West Kunlun Orogen, southwestern China. The deposit is unique for its mineral association of magnetite, pyrite and anhydrite in variable proportions, forming disseminations, banded and massive ores. Magnetite grains from the ores show variable contents of many elements, such as Mg (182–1167 ppm), Al (198–2691 ppm), Ti (898–1677 ppm), V (112–8468 ppm), Mn (821–4695 ppm), Co (7–26 ppm), Ni (1–29 ppm), Zn (5–45 ppm), and Ga (20–62 ppm). The high Al, Ti and V contents are interpreted to result from relatively reduced, Al–Ti-rich seafloor hydrothermal activities. The magnetite coexisting with sulfide has lower Co concentrations (7.8–13 ppm) than those not coexisting with sulfides (Co = 22–26 ppm). Compositional variations of magnetite possibly related to oxygen fugacity, temperature and coexisting minerals. The δ 56 Fe values in magnetite range from − 0.3 to 0.5‰, suggesting a changing hydrothermal precipitation environment. The Fe isotope fractionation between pyrite and magnetite (△δ 57 Fe py-mag ) range 0.2–1.1‰, implying a high-temperature crystallization (≥ 236 °C). The δ 56 Fe ratios in pyrite range 0.6–0.8‰, higher than the coexisting magnetite. Such a negligible variation of positive δ 56 Fe values indicates that the pyrite possibly originated from a slow precipitation or a transformation from FeS (mackinawite), which was induced by the rise of atmospheric oxygen at ~ 0.6 Ga. Integrating the data obtained from the studies including regional geology, ore geology, magnetite composition and Fe isotope geochemistry, we conclude that the Zankan Fe deposit was formed from an Early Cambrian seafloor hydrothermal system developed in a volcanic arc caused by southward subduction of Proto-Tethyan plate.

The Xiaobaishitou W (–Mo) deposit is located in the eastern segment of the Central Tianshan, northwestern China. The deposit represents a skarn system distributed in the contact zones of biotite granite and crystalline limestone of the Mesoproterozoic Kawabulag Group. The Xiaobaishitou deposit is characterized by a typical calc-silicate mineralogy dominated by garnet, diopside and wollastonite, with minor epidote, tremolite, actinolite, chlorite, quartz, fluorite and calcite. The prograde and retrograde skarns are characterized by garnet–clinopyroxene–wollastonite and epidote–tremolite–actinolite–chlorite, respectively, intruded and replaced by mineral assemblages of scheelite–cassiterite–magnetite, quartz–sulfides and calcite–quartz–fluorite in younger order. Six molybdenite samples from the deposit yielded Re − Os isotope model ages ranging from 239.7 ± 3.6 Ma to 251.4 ± 3.6 Ma. The zircon crystals from biotite granite and Mo-mineralized granite yield weighted 206Pb/238U age of 242 ± 1.7 and 240.5 ± 2.1 Ma, respectively. Both the zircon U − Pb and the molybdenite Re − Os ages obtained in this study fall in a narrow span of 242–240 Ma, which suggest that the Xiaobaishitou W (–Mo) system was formed in the Triassic. The Re contents of the molybdenites range from 40.33 to 64.67 ppm, suggesting that the ore-forming materials were derived mainly from continental crust together with the involvement of minor mantle components. Combined with the 87Sr/86Sr ratios of tungsten-bearing quartz veins from other studies, which scatter between 0.707153 and 0.709877, demonstrating mixing between two end-member isotopic compositions of crust and mantle. It can be concluded that the Indosinian Xiaobaishitou deposit was formed in a tectonic transition from collisional crust shortening and thickening to post-collisional extension and thinning.

Isotope dilution thermal ionization mass spectrometry (ID-TIMS) and laser ablation inductively coupled plasma mass spectrometry (LA–ICP-MS) are two popular analytical methods used to constrain the age of minerals, including cassiterite. Compared to ID-TIMS, the LA–ICP-MS analytical method is often favoured due to its simple analytical procedure and sample preparation, although the methodology constantly needs modification. Our recent paper on dating cassiterite from the Baiganhu W-Sn ore field in NW China based on LA–MC-ICP-MS and ID-TIMS methods has received a response from Dr. Leonid A. Neymark (2017). Definitely, Neymark is appreciated, and his suggestions are helpful to improve the methodology of cassiterite U–Pb geochronology. Based on a discussion on the cassiterite U–Pb dating method, we re-confirm the validity of the cassiterite U-Pb ages for the Baiganhu W-Sn ore field. The initial non-radiogenic 204Pb used in the U-Pb isochron approach can be replaced by the non-radiogenic 207Pb, because the radiogenic 207Pb decayed from 235U can be ignored in cassiterite with a high Pb content. Therefore, the cassiterite U-Pb isochron yields an age similar to that obtained from T-W concordia for the same sample, testifying the validity of the cassiterite 238U/207Pb–206Pb/207Pb isochron method.

The Kalatag Cu–Zn–Au district contains a number of economically important Cu deposits in eastern Tianshan in Xinjiang, NW China. Due to the lack of precise mineralization ages, the metallogenesis of this area has long been a matter of debate. In this study, chalcopyrite Re–Os isotope methods are used to date the South Meiling Cu–Zn and Hongshi Cu deposits in the eastern part of Kalatag area. The South Meiling Cu–Zn deposit is hosted in volcanic-sedimentary rocks of the Late Ordovician to Early Silurian Daliugou Formation. The deposit consists of two parts: a concordant massive sulfide ores and discordant vein-type ores located in the footwall strata. The principal ore minerals are pyrite, chalcopyrite, sphalerite, minor tetrahedrite, galena and pyrrhotite. Gangue minerals include quartz, sericite and barite, and minor chlorite, plagioclase and carbonate minerals. The Hongshi Cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of Daliugou Formation. The orebodies are associated with quartz veins and controlled by subsidiary faults of the Kalatag fault. The ore-forming process can be divided into the early, middle and late stages and is characterized by quartz–pyrite, quartz–chalcopyrite–pyrite and quartz–carbonate–gypsum veins, respectively. Re–Os analyses of chalcopyrite from the South Meiling Cu–Zn deposit yield an isochron age of 434.2 ± 3.9 Ma and initial 187Os/188Os ratio of 0.647 ± 0.098 (MSWD = 0.59). Re–Os analyses of chalcopyrite from the Hongshi Cu deposit yield an isochron age of 431.8 ± 2.7 Ma and initial 187Os/188Os ratio of − 0.165 ± 0.075 (MSWD = 0.77). Since chalcopyrite is the primary copper mineral, we interpret these isochron ages as the timing of Cu mineralization, based on field geology and petrographic evidence. These results suggest that the Re–Os ages presented here provide, for the first time, a direct constraint on an early Paleozoic Cu mineralization event of the eastern Tianshan Orogen. The high initial 187Os/188Os ratios (0.647 ± 0.098) ratio of ~ 434 Ma chalcopyrite from the South Meiling deposit suggest that the metal was sourced from a two end-member mixing of crust and mantle materials. Moreover, we propose that the VMS mineral system and hydrothermal vein system of the Kalatag district were related to the south-dipping subduction of the Kalamaili oceanic plate during the Late Ordovician–Silurian.

The Xiaguan Ag–Pb–Zn orefield (Neixiang County, Henan Province), hosting the Yindonggou, Zhouzhuang, Yinhulugou and Laozhuang fault-controlled lode deposits, is situated in the Erlangping Terrane, eastern Qinling Orogen. The quartz-sulfide vein mineralization is dominated by main alteration styles of silicic-, sericite-, carbonate-, chlorite- and sulfide alteration. Major Ag-bearing minerals are freibergite, argentite and native Ag. The deposits were formed by a CO2-rich, mesothermal (ca. 250–320 °C), low-density and low salinity ( The δ18OH2O values change from the Early (E)-stage (7.8–10.8 ‰), through Middle (M)-stage (6.0–9.4 ‰) to Late (L)-stage (− 1.5–3.3 ‰), with δD values changing from E-stage − 95 to − 46 ‰, through M-stage − 82 to − 70 ‰ to L-stage − 95 to − 82 ‰. δ13CCO2 values of the ore fluids in the E- and M-stage quartz vary between 0.1 ‰ and 0.9 ‰ (average: 0.3 ‰); δ13CCO2 values of L-stage FIs are − 0.2–0.1 ‰ in quartz and − 6.8 ‰ to − 3.5 ‰ in calcite. The H–O–C isotopic data indicate that the initial ore fluids were sourced from the underthrusted Qinling Group marine carbonates, and were then interacted with the ore-hosting Erlangping Group metasedimentary rocks. Inflow of circulated meteoric water may have dominated the L-stage fluid evolution. Sulfur (δ34S = 1.9–8.1 ‰) and lead isotopic compositions (206Pb/204Pb = 18.202–18.446, 207Pb/204Pb = 15.567–15.773 and 208Pb/204Pb = 38.491–39.089) of sulfides suggest that the ore-forming materials were mainly sourced from the ore-hosting metasedimentary strata. The stepped heating sericite 40Ar/39Ar detection suggests that the mineralization occurred in the Middle Jurassic to Early Cretaceous (ca. 187 − 124 Ma). Considering the regional tectonic evolution of the Erlangping Terrane, we propose that the Xiaguan Ag–Pb–Zn orefield was formed in a continent–continent collisional tectonic regime, in accordance with the tectonic model for continental collision, metallogeny and fluid flow (CMF).

The Caixiashan giant carbonate-hosted Zn–Pb deposit (~ 131 Mt@ 3.95% Zn + Pb) formed by replacement of dolomitized marble, with stratiform massive and breccia bodies is located near the base of the Proterozoic Kawabulake Group limestone and marble. It is one of the largest carbonated-hosted massive sulfides Zn–Pb ore deposits in Northwest China to have been discovered in recent years. Abundant pyrite occurs in dolomitized marble, along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock. Locally, colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite. The sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena, with less pyrite than the earlier stage, and minor pyrrhotite. Galena occurs as small veins cutting the early-formed sphalerite. Dolomite and calcite are the main gangue minerals that co-precipitated with these sulfides. Tremolite and quartz alteration commonly overprints the orebodies. According to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies, three stages are recognized at Caixiashan, i.e., syn-sedimentary pyrite (stage I), pyrite alteration, sphalerite–carbonate and galena–pyrite–carbonate (stage II-1, stage II-2 and stage II-3, respectively) and magmatic/metamorphic reworking (stage III). Calcite and quartz crystals are important host minerals among the three hypogene stages (stages I–III, although quartz mainly occurred in stage III). Stage I contains only aqueous inclusions (W-type), which were homogenized from 110 to 236 °C (main range of 138–198 °C and average at 168 °C; main range = average ± σ) and the salinities are from 0.5 to 16.5 (main range of 5.1–15.1 with average of 10.1) wt.% NaCl eqv. In the pyrite alteration of stage II-1 the W-type fluid inclusions homogenized from 175 to 260 °C (main range of 210–260 with average of 235) and the salinities range from 8.5 to 22.4 (main range of 16.7–20.1 with average of 18.4) wt.% NaCl eqv. In the main Zn–Pb mineralization stage (stage II-2–3), four types of fluid inclusions were identified an aqueous phase (W-type), a pure carbon phase (PC-type), a carbon phase containing (C-type) and mineral bearing inclusions (S-type). The W-type fluid inclusions of stage II-2–3 homogenized at 210 to 370 °C (main range of 253–323 and average at 270) and the salinities range from 5.9 to 23.1 (main range of 13.3–20.3 with average at 16.8) wt.% NaCl eqv.; C-type homogenized at 237 °C to 371 °C and the salinities range from 6.4–19.7 wt.% NaCl eqv.; S-type fluid inclusions homogenized at 211 to 350 °C and daughter minerals melted between 340 and 374 °C during heating, indicating a salinity range of 42 to 44 wt.% NaCl eqv. PC-type fluid inclusions with homogenization temperatures of CO 2 phase show large variation from 7.4 °C to 21.2 °C. Laser Raman analyses show that CH 4 , CO 2 and SO 4 2 − coexist in the main mineralization stage fluids. The magmatic/metamorphic reworking stage only contains W-type fluid inclusions which yield homogenized between 220 and 360 °C (main range of 251–325 and average at 288), with salinities ranging from 1.7 to 23.0 (main range of 14.3–20.0 and average at 18.8) wt.% NaCl eqv. The textural features, mineral assemblages and fluid geochemistry suggest that the Zn–Pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal (Zn, Pb and Fe) enriched stratiform orebodies. Subsequent rapid precipitation of sulfides was triggered by sulfate (SO 4 2 − ) thermal reduction with the CH 4 preserved in sedimentary rocks and early stage I pyrite bodies. This process occurred at moderate temperatures ( ca . 270 °C). Higher-temperature magmatic hydrothermal alteration overprinted the orebodies, but only provided a minor contribution to the mineralization.

Tourmaline is widespread in the Baiganhu W–Sn deposit, Xinjiang Province, NW China. In this study, electron microprobe analysis reveals that tourmaline in the Baiganhu deposit belongs to the alkali and X-site group with low Ca and moderate X site vacancy, all beyond the confines of schorl–dravite series, with Na/(Na + Ca) and Fe/(Fe + Mg) ratios ranging from 0.769 to 0.965 and 0.518 to 0.822, respectively. In chemical discrimination diagrams, the tourmaline samples plot in the fields of Li-poor granite, associated with Al-saturated metapelites and metapsammites. The tourmaline cores are depleted in Mg, Ca, Ti, but enriched in Al and Fe compared to the rims. Substitution mechanisms for the compositional variations are dominantly due to MgFe− 1, □Al(NaFe)− 1, □Al(NaMg)− 1, and AlO(Fe− 1(OH))− 1 exchange vectors. The δ11B values of the tourmalines range from − 12.9 to − 7.9‰, with a slight variation between cores and rims, which reflect a common boron source, and also indicate that the tourmaline crystallized during a single magmatic-hydrothermal event related to monzogranite. Tourmaline is a valuable prospecting indicator of W–Sn mineralization.

The Jinwozi deposit is the most economically important gold (Au) deposit in the Beishan Orogen (Eastern Xinjiang, NW China). The Au orebodies occur as quartz veins or altered lodes in the Jinwozi Formation clastic rocks and the Jinwozi granite. The age, detrital source and tectonic setting of the Jinwozi Formation, however, have not been well understood. In this paper, we reported new LA–ICP MS detrital zircon U–Pb ages and Lu–Hf isotopes of ore-hosted clastic rock of the Jinwozi Formation. Detrital zircons from three samples yield 334 U–Pb ages varied from 330 to 2598 Ma, showing complex detrital sources. The youngest detrital zircon population suggests that the Jinwozi Formation deposited no earlier than 330 Ma in the Late Carboniferous or Permian. The majority of the detrital zircons (291 out of 334) have ages between 330 and 533 Ma, suggesting a dominant Paleozoic detrital source. Much of these age data (282 out of 334) range from 470 to 370 Ma, broadly coeval with the zircon U–Pb ages of the Jinwozi granite. Zircon Hf isotope data also implicate their similar origin to the Jinwozi granite. The source rocks, as well as the Jinwozi granite, may have formed in the Early Paleozoic Caledonian Orogeny, during which the supercontinents of Gondwana and Laurasia assembled. This orogeny process may have provided plenty of detritus for the clastic rocks of the Jinwozi Formation. Precambrian detrital zircon ages from the Jinwozi Formation cluster around 2400–2600 Ma, 1800–2100 Ma, 800–1300 Ma, which corresponds to the supercontinent assembly events of Kenor, Columbia and Rodinia, respectively. The age populations of 2200–2300 Ma and 600–660 Ma are possibly related to the breakup of Kenor and Rodinia supercontinents. This understangding is supported by zircon Hf isotope data.

The Qiangma gold deposit is hosted in the > 1.9 Ga Taihua Supergroup metamorphic rocks in the Xiaoqinling terrane, Qinling Orogen, on the southern margin of the North China Craton. The mineralization can be divided as follows: quartz-pyrite veins early, quartz-polymetallic sulfide veinlets middle, and carbonate-quartz veinlets late stages, with gold being mainly introduced in the middle stage. Three types of fluid inclusions were identified based on petrography and laser Raman spectroscopy, i.e., pure carbonic, carbonic-aqueous (CO 2 –H 2 O) and aqueous inclusions. The early-stage quartz contains pure carbonic and CO 2 –H 2 O inclusions with salinities up to 12.7 wt.% NaCl equiv., bulk densities of 0.67 to 0.86 g/cm 3 , and homogenization temperatures of 280−365 °C. The early-stage is related to H 2 O–CO 2 ± N 2 ± CH 4 fluids with isotopic signatures consistent with a metamorphic origin (δ 18 O water = 3.1 to 5.2‰, δD = − 37 to − 73‰). The middle-stage quartz contains all three types of fluid inclusions, of which the CO 2 –H 2 O and aqueous inclusions yield homogenization temperatures of 249−346 °C and 230−345 °C, respectively. The CO 2 –H 2 O inclusions have salinities up to 10.9 wt.% NaCl equiv. and bulk densities of 0.70 to 0.98 g/cm 3 , with vapor bubbles composed of CO 2 and N 2 . The isotopic ratios (δ 18 O water = 2.2 to 3.6‰, δD = − 47 to − 79‰) suggest that the middle-stage fluids were mixed by metamorphic and meteoric fluids. In the late-stage quartz only the aqueous inclusions are observed, which have low salinities (0.9−9.9 wt.% NaCl equiv.) and low homogenization temperatures (145−223 °C). The isotopic composition (δ 18 O water = − 1.9 to 0.5‰, δD = − 55 to − 66‰) indicates the late-stage fluids were mainly meteoric water. Trapping pressures estimated from CO 2 –H 2 O inclusions are 100−285 MPa for the middle stage, suggesting that gold mineralization mainly occurred at depths of 10 km. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO 2 -rich to CO 2 -poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ 18 O water values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Qiangma gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic−Early Cretaceous continental collision between the North China and Yangtze cratons.

The Donggou Mo deposit in the eastern Qinling area, China, is a giant porphyry system discovered based on a targeting concept by using the tectonic model for collisional orogeny, metallogeny and fluid flow (CMF model). Mo mineralization is associated with the Donggou aluminous A-type granite porphyry and was formed during the Early Cretaceous in a tectonic regime of continental extension. The orebodies mainly occur as numerous veinlets in the host-rocks. Hydrothermal ore-forming processes include at least three stages, characterized by veinlets of (1) quartz + K-feldspar + minor molybdenite, (2) quartz + molybdenite ± beryl and (3) quartz + carbonate + fluorite. Three types of fluid inclusions (FIs) are distinguished in quartz and beryl in stages 1 and 2, i.e., aqueous (W-type), carbonic–aqueous (C-type) and solid-bearing (S-type), with only aqueous FIs observed in stage 3 minerals. S-type FIs contain variable daughter minerals including halite, chalcopyrite, calcite and an unidentified transparent crystal, but only halite can dissolve during heating. Halite-bearing S-type FIs are mainly homogenized by halite dissolution at 182–416 °C, corresponding to salinities of 30.9–49.2 wt.% NaCl equiv.; minor halite-bearing S-type FIs are homogenized to liquid at 190–360 °C via vapor disappearance, with salinities of 29.1–36.2 wt.% NaCl equiv. Other FIs in minerals of stages 1, 2 and 3 are homogenized at temperatures of 341–550 °C, 220–440 °C and 125–225 °C, with salinities of 8.0–18.3, 5.3–16.8 and 0.5–7.3 wt.% NaCl equiv., respectively. The estimated minimum trapping pressures are up to 141 MPa in stage 1 and up to 81 MPa in stage 2, respectively, corresponding to an initial mineralization depth of no less than 5 km. The quartz in veinlets yields δ 18 O values of 8.5–10.0‰, corresponding to δ 18 O H 2 O values of − 2.9 to 5.9‰, while the δD H 2 O values of fluid inclusions range from − 59 to − 82‰. These data suggest that the ore fluids forming the Donggou deposit changed from high-temperature, high-salinity, CO 2 -rich magmatic to low-temperature, low-salinity and CO 2 -poor meteoritic fluids via boiling and mixing, resembling those of other magmatic–hydrothermal systems in Qinling Orogen and Dabie Shan. This supports the notion that the porphyry systems generated in a post-collisional tectonic setting were initially CO 2 -rich, as indicated by abundant C-type and CO 2 -bearing S-type fluid inclusions.

The genesis of polymetallic deposits in southern Altay, NW China has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic-type mineralization. The Dadonggou Pb–Zn deposit occurs as NW-trending veins in the Devonian Kangbutiebao Formation volcanic-sedimentary sequence in the Kelan basin, southern Altay. A set of integrated zircon U–Pb and biotite 40Ar/39Ar geochronological data were applied to constrain the forming ages of the ores and their country rocks. Three samples of host volcanic rocks yielded weighted mean 206Pb/238U ages of 397.1 ± 4.5 Ma, 391.7 ± 3.6 Ma and 391.1 ± 4.2 Ma, respectively, indicating that the Kangbutiebao Formation was deposited in a Devonian back-arc basin. Two biotite samples separated from the Pb–Zn-containing quartz veins yielded 40Ar/39Ar plateau ages of 205.9 ± 2.1 Ma and 204.3 ± 2.2 Ma, respectively, which represent the age of the Pb–Zn mineralization that is attributed to the closure of the Kelan back-arc basin and the Late Triassic orogeny. Combining the available geological and geochronological data, this contribution outlines the successive evolution from the development of a Devonian back-arc basin to the Late Triassic post-subduction orogeny, and proposes that the Dadonggou Pb–Zn deposit is an epigenetic orogenic-type deposit placed in the Late Triassic orogeny.

The giant Dongshengmiao Zn–Pb–Cu deposit is located in the Langshan district, northern China. The ores are hosted within a Proterozoic rift sequence, which underwent lower greenschist facies metamorphism and shear deformation during development of Early Cretaceous intraplate orogenic belt. Northwest-dipping thrust faults, which share similar orientations and dip angles with the orebodies, are well developed in the mining area. Syngenetic stratabound sulfides were formed during the Proterozoic rifting event, but syngenetic ore textures have seldom been preserved except for some pretectonic fine-grained pyrite. Petrological observation, 39 Ar/ 40 Ar geochronology, combined with previous isotopic and fluid inclusion studies indicates that significant Zn–Pb–Cu remobilization took place as a result of thrust faulting associated with metamorphic devolatilization of ore-hosting rocks at ca. 136 Ma, coeval with the intraplate orogeny and regional crustal shortening. Sulfides were redistributed in shear structures or along grain boundaries of ore-hosting carbonates, and Fe-rich carbonates were ideal sites for Zn–Pb–Cu precipitation.

The 1.85 Ga Longmendian Mo deposit in East Qinling is the oldest Mo system recognized in China. It is unique for three reasons: (1) quartzofeldspathic orebodies are away from any intrusion or fault, (2) it is closely associated with migmatitic rocks, and (3) it has remarkably high Re content in molybdenite (504 to 1660 ppm). The origin of the deposit is poorly constrained. In the Longmendian deposit, strong Mo mineralization is always associated with hydrothermally altered migmatitic amphibolites. To probe into ore genesis, detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore-barren rocks. Four compositional types of fluid inclusions are observed, including CO 2 ± CH 4 (PC-type), CO 2 –H 2 O (C-type), daughter mineral-bearing (S-type) and H 2 O–NaCl (W-type). Quartz in mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions. Measurements of immiscible inclusion assemblages in the ores constrain the Mo-mineralization temperatures and pressures to be 225–390 °C and 114–265 MPa, respectively. Primary fluid inclusions in barren migmatitic gneisses are dominated by S-type, and minor of C- and PC-types which are identical to those in the leucosome of migmatitic amphibolites. These inclusions yield lower homogenization temperatures than those in the mineralized mesosome and melanosome of migmatitic amphibolites, suggesting that the ore-causative, injected melts should have higher temperatures and originated from depths. Such features of the ore-forming fluids indicate that the Longmendian deposit was a migmatitic-hydrothermal system caused by high-temperature melt injection. This interpretation can also be supported by the observations below: (1) tourmaline is abundant in melanosome, but absent in mesosome; (2) the consistent quartzofeldspathic composition of leucosome is independent of mesosome; (3) leucosome in migmatitic amphibolite crosscuts each other; (4) halite-bearing fluid inclusions are prevalent in studied samples, which is the feature of granitic rocks, instead of the scenarios of in situ migmatites; and (5) the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting, but higher than those obtained from barren migmatitic rocks.