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The Alastuo gold deposit, located in the Narati region of the Chinese West Tianshan, is a newly discovered gold deposit within the world-class Tianshan gold belt. The gold mineralization is hosted by an Early Carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal North Narati Fault. The deposit consists of auriferous alteration assemblages and minor vein ores. Field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz, chlorite, epidote, pyrite, and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation. The temperature range of gold precipitation is estimated to be 280–330 °C using chlorite geothermometry. Ten auriferous pyrite samples yielded a well-defined Re-Os isochron age of 325 ± 3 Ma and two sericite samples yielded plateau-like 40Ar/39Ar ages of 321.7 ± 3.0 Ma and 321.2 ± 2.8 Ma. These consistent ages suggest that the gold mineralization in the Narati region was emplaced in a transitional regime from subduction to continental collision between the Tarim block and Middle Tianshan terrane (325–310 Ma), rather than during the post-collisional stage as in most part of the Tianshan gold belt. Gold-bearing pyrite has an initial Osi value of 0.7 ± 0.1 and lead isotopes ratios of 17.897 to 18.723 for 206Pb/204Pb, 15.474 to 15.643 for 207Pb/204Pb, and 37.522 to 38.299 for 208Pb/204Pb, while samples of pyrite, galena, and sphalerite have 34SV-CDT of +1.9 to +7.8‰. The isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks. The mineralization styles, structural controls, metal and sulfur sources, and the timing of gold mineralization with respect to the orogenic event all suggest that the Alastuo gold deposit represents an orogenic type deposit. This newly recognized Carboniferous orogenic gold mineralization event calls for a re-evaluation of the gold metallogeny in the Middle Tianshan. [ABSTRACT FROM AUTHOR]

The End deposit is one of several uranium deposits in the Kiggavik area near the Proterozoic Thelon Basin, which is geologically similar to the Athabasca Basin known for its unconformity-related uranium deposits. The mineralization occurs as uraninite and coffinite in quartz veins and wall rocks (psammopelitic gneisses) in the sub-Thelon basement and is associated with clay- and hematite-altered fault zones. Fluid inclusions were studied in quartz cementing unmineralized breccias formed before mineralization (Q2), quartz veins that were formed before mineralization but spatially associated with uranite (Q4), and calcite veins that were formed after mineralization. Four types of fluid inclusions were recognized, namely liquid-dominated biphase (liquid + vapor), vapor-dominated biphase (vapor + liquid), monophase (vapor-only), and triphase (liquid + vapor + halite) inclusions. The first three types were found in Q2, whereas all four types were found in Q4 and calcite. The coexistence of these different types of inclusions within individual fluid inclusion assemblages is interpreted to indicate fluid immiscibility and heterogeneous trapping. Based on microthermometry, the fluids associated with Q2 are characterized by low salinities (0.4 to 6.6 wt%) and moderate temperatures from 148 to 261 °C, and the fluids associated with calcite show high salinities (26.8 to 29.3 wt%) and relatively low temperatures from 146 to 205 °C, whereas the fluids associated with Q4 have a wide range of salinities from 0.7 to 38.8 wt% and temperatures from 80 to 332 °C. Microthermometric and cryogenic Raman spectroscopic studies indicate that the high-salinity fluids in Q4 and calcite belong to the HO-NaCl-CaCl ± MgCl system, with some dominated by NaCl and others by CaCl. The fluid inclusions in Q2 are interpreted to be unrelated to mineralization, whereas those in Q4 and calcite reflect the mineralizing fluids. The fluid inclusion data are consistent with a genetic link of mineralization with basinal brines derived from the Thelon Basin. However, unlike the conventional deep-burial (>5 km) diagenetic-hydrothermal model proposed for the unconformity-related uranium deposits, the uranium mineralization in the End deposit is inferred to have formed in a shallow environment (probably <2 km), based on fluid immiscibility and low fluid pressures obtained in this study. The U-Pb age of uraninite (1295 ± 12 Ma) is interpreted to reflect isotopic resetting after the primary mineralization. [ABSTRACT FROM AUTHOR]

• Elevated U concentrations (up to 266 ppm) were found in the Lala IOCG ores. • Uraninite, uranothorite, polycrase and coffinite were recognized. • Uranium was initially enriched with Cu, Mo, Th and REE at ca. 1086 to 1053 Ma. • U and Mo were remobilized and re-enriched together at ca. 888 to 828 Ma. Elevated uranium concentrations have been reported in many IOCG deposits, but detailed information about the occurrences of uranium minerals and their relationships with other minerals remains scarce, which hinders understanding of the mineralization mechanisms and the nature of the association of these metals. This paper reports a new case of uranium enrichment in an IOCG system, the Lala Cu-Fe deposit in the Kangdian region, SW China. Whole-rock analyses of ores and barren rocks yielded highly variable U concentrations ranging from 0.76 to 266 ppm. Uranium shows a strong positive correlation with Mo, broadly positive correlations with Cu and ΣREE, and a vague, negative correlation with Th. Four uranium minerals, uraninite [UO 2 , uranothorite [(Th,U)SiO 4 , polycrase [(Y,Ca,Ce,U,Th)(Ti,Nb,Ta) 2 O 6 , and coffinite [U(SiO 4) 1-x (OH) 4x , were identified. The uraninite is divided into two phases: phase 1 (Ur1) characterized by corroded or irregular crystal shapes, and phase 2 (Ur2) showing well-developed, subhedral to euhedral crystal shapes. Ur1 is interpreted to be formed in the primary Cu – Fe – Mo – REE – U mineralization, together with the bulk of Cu and other metal sulfides, as well as other U and REE minerals, including uranothorite, polycrase, bastnäsite and xenotime, and accompanied by K-alteration (K-feldspar and biotite). Ur2 is interpreted to be formed in a secondary hydrothermal event characterized by introduction of fluorite and carbonates, in which U and Mo, and to lesser extent Cu and REE, were remobilized, while Th remained relatively stable. The primary mineralization is inferred to have taken place in a period from ca. 1086 to 1053 Ma based on previous Re-Os geochronology, and the secondary mineralization (remobilization) likely took place from ca. 888 to 828 Ma, as suggested by uraninite chemical ages obtained in this study and other published geochronological data. These ages correspond to tectonomagmatic events taking place in generally extensional environments, in the western margin of the Yangtze Block during the Meso- to Neoproterozoic time. The Lala Cu-Fe deposit represents a new case of IOCG deposits with U (and REE) enrichment, the economic potential of which warrants further examination. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights: • The Arqiale deposit is a distal skarn Zn-Pb deposit. • Regional magmatism and mineralization age are consistent at ca. 340 Ma. • S-Pb isotope compositions suggests the ore-forming materials were derived from a magmatic source. • There is significant potential for skarn Zn-Pb deposits associated with Late Paleozoic magmatic intrusions in Western Tianshan. Abstract The Arqiale deposit, located in the southern Yili Block of Western Tianshan, Xinjiang, China, is a newly discovered large Zn-Pb deposit with a resource of approximately 10 million tons ore grading 9.65% Zn+Pb, and a certain amount of Cu and Ag. The Zn-Pb orebodies are tabular and lentoid in shape, developed along SW-striking and NW-dipping interlayer structures between the Lower Carboniferous Akeshake (mainly carbonate rocks) and Dahalajunshan (mainly volcanic rocks) formations. Garnet and pyroxene-rich skarn, formed in the early (prograde) stage of skarnization, occurs only locally as lenses within skarn bodies enriched in actinolite, tremolite, ilvaite, biotite, epidote, chlorite, calcite, quartz and fluorite, which were formed in the retrograde stage. Metallic minerals comprise sphalerite, galena, chalcopyrite, pyrite, and hematite. They mainly occur as disseminations, patches and massive ores, replacing retrograde skarn minerals and crosscut by later stage quartz and calcite veinlets. There is a general trend of increasing Cu contents and decreasing Zn/Pb ratios from the upper and south portion to the lower and north portion of the orebody. Rb-Sr dating of seven sphalerite samples yielded an isochron age of 339.5 ± 2.7 Ma, which is almost identical to the 341.8 ± 2.5 Ma age obtained from Sm-Nd dating of eight actinolite samples. Furthermore, zircon U-Pb dating yielded an age of 343 ± 6 Ma for a gabbro-diorite stock that is located about 600 m south of the Zn-Pb orebody. The age data indicate that the mineralization and retrograde skarnization were contemporaneous, and they are likely related to a magmatic intrusion of similar age which may be linked to the gabbro-diorite stock. Thus, although the direct causative intrusion has not been identified, the Arqiale deposit can be classified as a distal skarn deposit. The δ34S V-CDT values of 26 ore sulfide samples range from −7.1‰ to +1.3‰ with an average of −1.5‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 25 ore sulfide samples range from 18.266 to 18.880, 15.577 to 15.668 and 38.068 to 38.720, respectively, which are similar to the Early Carboniferous intrusions of the Wusun Range and partly overlap with the volcanic rocks of the Dahalajunshan Formation, and are different from the carbonate rocks of the Akeshake Formation. Based on these data, we propose that the Arqiale deposit formed from magmatic-hydrothermal fluids emanated from a concealed magmatic intrusion which may be located beneath the northern and deep part of the deposit. Much of the metals and sulfur may have been derived from the magmatic intrusions, although some of them may have also been extracted from the volcanic rocks underlying the deposit. The results of this study indicate that there is a great potential of finding more skarn Zn-Pb mineralization in Western Tianshan, where numerous Early Carboniferous arc-related intrusions with similar ages as the Arqiale deposit, in relation to the subduction of the Southern Tianshan Oceanic plate underneath the Yili-Central Tianshan Block, were emplaced into or beneath carbonate rocks. [ABSTRACT FROM AUTHOR]

The Qunjsai copper deposit in West Tianshan, Xinjiang, NW China, with a reserve of 7.5 million metric tons of ore grading 0.57 wt% Cu, is characterized by mineralization occurring as sparsely disseminated chalcopyrite, bornite and chalcocite in a diabase dike. The deposit is different from most magmatic-hydrothermal Cu deposits in that the mineralization is mostly constrained to the dike and is not associated with extensive wall rock alteration. On the other hand, the deposit differs from typical orthomagmatic deposits in that it lacks significant Ni and PGE mineralization. Zircon grains from a diabase sample yield a weighted 206 Pb/ 238 U age of 289.9 ± 1.4 Ma, which is broadly coeval with the Re–Os isochron age of 307 ± 10 Ma from six Cu concentrate samples (mixture of bornite+chalcopyrite+chalcocite with an average Cu grade of 29%), suggesting that they are coeval. Petrochemical studies suggest that the diabase dikes in the Qunjsai area were derived from a subduction-related, fluid-metasomatized sub-continental lithospheric mantle, with assimilation of crustal materials in a post-collisional extensional setting. Measured δ 34 S (−3.8 to 0.8‰ CDT) and lead isotopes of sulfides, as well as initial 187 Os/ 188 Os ratios of Cu concentrates (0.42 ± 0.19) are consistent with the notion that the sulfur and metals were derived from a mantle source and were contaminated by crustal components. The flat patterns of mantle-normalized chalcophile element diagrams are comparable with those from typical orthomagmatic Ni–Cu sulfide deposits. Based on these data, we propose that the Qunjsai deposit is of orthomagmatic origin, the depletion of Ni and PGE, being due to source rocks originally rich in Cu and to segregation of a Cu-rich sulfide melt from a Ni-rich sulfide melt. This orthomagmatic mineralization was followed by hydrothermal alteration (mainly chlorite and epidote alteration) by magmatic fluids, which may have introduced additional amounts of Cu and S and reworked the magmatic sulfides. [ABSTRACT FROM AUTHOR]

The Dabate deposit is a porphyry Cu–Mo deposit located in the Sailimu Block, northern Chinese Tien Shan. The deposit shows a clear separation of Cu and Mo mineralization, with Cu mineralization occurring along the edge of the rhyolitic porphyry, and Mo mineralization in the inner part of the rhyolitic porphyry. Sm-Nd isotopic analyses of six fluorite samples from the Cu sulfides–fluorite veins yield an isochron age of 298.1 ± 5.0 Ma, and Re-Os isotopic analyses of four molybdenite samples from the molybdenite–quartz veins yield an isochron age of 299.6 ± 3.2 Ma. These geochronological data and accompanying geologic evidence indicate that the Cu and Mo mineralization belongs to the same hydrothermal system and are closely related to the rhyolitic porphyry, which has a youngest zircon 206 Pb/ 238 U age of 297.3 ± 8.0 Ma. Rare earth element (REE) and fluid inclusion studies were carried out for fluorite in the Cu ores. The fluorite related to Cu mineralization have high ΣREE (63.4–216.9 ppm) and show generally similar REE patterns with the rhyolitic porphyry, suggesting that the fluid of Cu mineralization is closely related to the rhyolitic porphyry. The slight LREE-depletion and Ce-depletion of fluorite relative to the rhyolitic porphyry may be due to preferential partitioning of HREE into the fluid in neutral to weak alkaline conditions and to mixing with meteoric water which is characterized by Ce-depletion. Three types of fluid inclusions were recognized in the fluorite from the Cu sulfides–fluorite veins: liquid–vapor (LV-type), CO 2 -bearing (C-type) and solid mineral-bearing (S-type). The LV-type inclusions have homogenization (vapor to liquid) temperatures from 175 to 328 °C and salinities of 0.4∼14.9 wt% NaCl eqv. (mode at 0∼8 wt% NaCl eqv.), and is of H 2 O + NaCl composition. The C-type inclusions have homogenization (vapor to liquid) temperatures from 206 to 279 °C and salinities of 1.6∼8.5 wt% NaCl eqv., and is of H 2 O + CO 2  + NaCl + CH 4 composition. The S-type inclusions have partial homogenization (vapor to liquid) temperatures of 173–233 °C and salinities of 1.2–7.9 wt% NaCl eqv., and is of H 2 O + NaCl composition. The solid particle in S-type inclusions did not change during heating up to 550 °C, indicating that the solid is not daughter mineral and the S-type inclusions are actually the same as the LV-type inclusions. The LV-type inclusions have microthermometric attributes similar to those typically found in the late stages of porphyry deposits, whereas the C-type inclusions have similar compositions as the inclusions in the Mo ores as documented in previous studies at Dabate. The presence of both LV-type and C-type inclusions suggests that the Cu mineralization may be related to mixing between meteoric water and magmatic fluids, as is also indicated by the REE of fluorite. Comparing with data from Mo ores reported in previous studies, it is suggested that the Mo-stage fluids were more reduced and acidic and Mo mineralization may be mainly related to fluid pressure decrease and immiscibility, whereas the Cu-stage fluids were more oxidized, neutral to weakly alkaline and Cu mineralization may be mainly controlled by mixing and cooling. The vapor phase produced by fluid immiscibility in the deep area may have carried Cu, As, Ag, HF, CO 2 and migrated to the outer part of the porphyry, precipitated Cu sulfides, arsenopyrite and fluorite by mixing with meteoric water from the country rocks. Whereas the liquid phase produced by fluid immiscibility at depth may have carried Mo, NaCl and migrated to the middle-west part of the rhyolitic porphyry, become immiscible and precipitated molybdenite. [ABSTRACT FROM AUTHOR]

Located in the southeastern margin of the Yangtze Block and generally interpreted as the Neoproterozoic collisional product of the Yangtze with the Cathaysia Blocks of South China, the Jiangnan Orogenic Belt (JOB) contains a number of gold (Au) (-polymetallic) ore deposits and mineral showings, mostly hosted by Neoproterozoic low-grade metamorphic volcaniclastic and sedimentary rocks. The mineralization styles mainly include auriferous quartz veins and disseminated mineralization in altered mylonite and cataclasite that are developed along shear zones, fracture zones and inter- or intra-formational fault zones closely related to regional folding and shearing deformation. Three gold mineralizing epochs are recognized in the JOB. The ca. 423–397 Ma mineralization was associated with the early Paleozoic tectonothermal event(s), which induced widespread emplacement of Silurian S-type granites, low-grade metamorphism and enrichment of gold in the Neoproterozoic rocks (i.e., forming Au source beds). The second Au mineralization epoch, occurring at ca. 176–170 Ma (Jurassic), was related to the subduction of the Paleo-Pacific plate beneath the South China continental margin. The third and most important Au mineralization epoch took place at ca. 144–130 Ma (early Cretaceous), when a Basin-and-Range tectonic pattern was developed, characterized by NE–NNE-trending strike-slip faults, granitic domes and metamorphic core complexes (MCC), and basins filled with red bed lithologies. C, H, O, He-Ar, S and Pb isotopic and fluid-inclusion data suggest that the ore fluids were predominantly metamorphic and/or magmatic, with variable input of mantle-derived fluids and the progressive involvement of meteoric waters in the later stages of mineralization. Ore materials were mostly contributed by the Neoproterozoic source beds, plus a possible contribution from mantle- or magma-derived components. The Au (-polymetallic) deposits in the JOB, particularly those formed in the early Cretaceous, share many geological and geochemical features with the orogenic-type and Carlin-type deposits. In the context of tectonic evolution of South China, the gold mineralization in the JOB may be considered an “intracontinental reactivation type”, characterized by synchronous development of Au–polymetallic mineralization, reactivation of stuctures developed in Neoproterozoic metamorphic rocks, and widespread granite emplacement in the late Mesozoic. [ABSTRACT FROM AUTHOR]

The Wangu gold deposit in northeastern Hunan, South China, is one of many structurally controlled gold deposits in the Jiangnan Orogen. The host rocks (slates of the Lengjiaxi Group) are of Neoproterozoic age, but the area is characterized by a number of Late Jurassic–Cretaceous granites and NE-trending faults. The timing of mineralization, tectonic setting and ore genesis of this deposit and many similar deposits in the Jiangnan Orogen are not well understood. The orebodies in the Wangu deposit include quartz veins and altered slates and breccias, and are controlled by WNW-trending faults. The principal ore minerals are arsenopyrite and pyrite, and the major gangue minerals are quartz and calcite. Alteration is developed around the auriferous veins, including silicification, pyritic, arsenopyritic and carbonate alterations. Field work and thin section observations indicate that the hydrothermal processes related to the Wangu gold mineralization can be divided into five stages: 1) quartz, 2) scheelite–quartz, 3) arsenopyrite–pyrite–quartz, 4) poly-sulfides–quartz, and, 5) quartz–calcite. The Lianyunshan S-type granite, which is in an emplacement contact with the NE-trending Changsha-Pingjiang fracture zone, has a zircon LA-ICPMS U–Pb age of 142 ± 2 Ma. The Dayan gold occurrence in the Changsha-Pingjiang fracture zone, which shares similar mineral assemblages with the Wangu deposit, is crosscut by a silicified rock that contains muscovite with a ca. 130 Ma 40 Ar– 39 Ar age. The gold mineralization age of the Wangu deposit is thus confined between 142 Ma and 130 Ma. This age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of NE-trending extensional faults, the emplacement of Late Jurassic–Cretaceous granites and the formation of Cretaceous basins filled with red-bed clastic rocks in northeastern Hunan, which forms part of the Basin and Range-like province in South China. EMPA analysis shows that the average As content in arsenopyrite is 28.7 atom %, and the mineralization temperature of the arsenopyrite–pyrite–quartz stage is estimated to be 245 ± 20 °C from arsenopyrite thermometry. The high but variable Au/As molar ratios (>0.02) of pyrite suggest that there are nanoparticles of native Au in the sulfides. An integration of S–Pb–H–O–He–Ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks, possibly driven by hydraulic potential gradient created by reactivation of the WNW-trending faults initially formed in Paleozoic, with possible involvement of magmatic and mantle components channeled through regional fault networks. The Wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic, epithermal and Carlin-type gold deposits, and may be better classified as an “intracontinental reactivation” type as proposed for many other gold deposits in the Jiangnan Orogen. [ABSTRACT FROM AUTHOR]

Our recent geochronological study on the Taldybulak Levoberezhny gold deposit in Kyrgyz Northern Tien Shan (KNTS) received critical comments by Boris Trifonov (2016) regarding the age of dikes and its relationship with gold mineralization at the deposit. In this contribution, based on a re-evaluation of our published data, together with new geochronological, geochemical and Sr–Nd–Hf isotopic data, the age of gold mineralization, magmatic and tectonic events and the relationship between dikes and mineralization at the deposit, it is proposed that the Taldybulak Levoberezhny gold deposit is a product of long-lived magmatic-hydrothermal system with multiple stages of gold mineralization from Cambrian to late Carboniferous–early Permian. [ABSTRACT FROM AUTHOR]

The Hongshan Cu-polymetallic deposit is located in the southern Yidun arc in southwestern China, where both subduction-related (Late Triassic) and post-collisional (Late Cretaceous) porphyry–skarn–epithermal mineralization systems have been previously recognized. In this study, two distinct magmatic events, represented by diorite porphyry and quartz monzonite porphyry, have been revealed in the Hongshan deposit, with zircon SHRIMP U–Pb ages of 214 ± 2 Ma and 73.4 ± 0.7 Ma, respectively. The 73 Ma age is comparable to the Re–Os ages of 77 to 80 Ma of ore minerals from the Hongshan deposit, indicating that the mineralization is related to the Late Cretaceous quartz monzonite porphyries rather than Late Triassic diorite porphyries. The Late Triassic diorite porphyries belong to the high-K calc-alkaline series and show arc magmatic geochemical characteristics such as enrichment in Rb, Ba, Th and U and depletion in HFSEs, indicating that they were formed during the westward subduction of the Garzê–Litang Ocean. In contrast, the Late Cretaceous quartz monzonite porphyries show shoshonitic I-type geochemical characteristics, with high SiO 2 , K 2 O, LILE, low HREE, Y and Yb contents, and high LREE/HREE and La/Yb ratios. These geochemical characteristics, together with the Sr–Nd–Pb isotopic compositions (average ( 87 Sr/ 86 Sr) i = 0.7085; ε Nd (t) = − 6.0; 206 Pb/ 204 Pb = 19.064, 207 Pb/ 204 Pb = 15.738, 208 Pb/ 204 Pb = 39.733) suggest that the quartz monzonite porphyries originated from the partial melting of the ancient lower crust in response to underplating of mafic magma from subduction metasomatized mantle lithosphere, possibly triggered by regional extension in the post-collisional tectonic stage. The S isotopic compositions (δ 34 S V-CDT = 3.81‰ to 5.80‰) and Pb isotopic compositions ( 206 Pb/ 204 Pb = 18.014 to 18.809, 207 Pb/ 204 Pb = 15.550 to 15.785, and 208 Pb/ 204 Pb = 38.057 to 39.468) of ore sulfides indicate that the sulfur and metals were derived from mixed mantle and crustal sources. It is proposed that although the Late Triassic magmatic event is not directly related to mineralization, it contributed to the Late Cretaceous mineralization system through the storage of large amounts of sulfur and metals as well as water in the cumulate zone in the mantle lithosphere through subduction metasomatism. Re-melting of the mantle lithosphere including the hydrous cumulate zone and ancient lower crust during the post-collisional stage produced fertile magmas, which ascended to shallow depths to form quartz monzonite porphyries. Hydrothermal fluids released from the intrusions resulted in porphyry-type Mo–Cu ores in and near the intrusions, skarn-type Cu–Mo ores in the country rocks above the intrusions, and hydrothermal Pb–Zn ores in the periphery. [ABSTRACT FROM AUTHOR]

The Taldybulak Levoberezhny gold deposit, located in the eastern part of the Kyrgyz Northern Tien Shan, is hosted in highly deformed Precambrian schist and gneisses that have undergone intense quartz, carbonate, fuchsite and tourmaline alterations. Gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages, orebody geometries, and the occurrences of Au-bearing minerals. Negative thermal ionization mass spectrometry Re–Os isotopic analyses of five Au-rich pyrite samples from the early stage yielded an isochron age of 511 ± 18 Ma. Zircon sensitive high-resolution ion microprobe U–Pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 Ma, while a weighted mean 206 Pb/ 238 U age of 414.6 ± 6.8 Ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz–tourmaline–gold formation. The pyrite 187 Os/ 188 Os (initial) ratio of 0.132 ± 0.011, together with γ Os values varying from 0 to + 14, indicate a major mantle component for the source of Os and by inference ore metals, which may be linked to the ophiolite suite of the Kopurelisai Complex in the Taldybulak Levoberezhny area. Considering the geodynamic setting of the Kyrgyz Northern Tien Shan during the early Paleozoic, we suggest that Cambrian mineralization of the Taldybulak Levoberezhny deposit can be attributed to a subduction-related setting, probably associated with the earliest accretion of the Northern Tien Shan. [ABSTRACT FROM AUTHOR]

Abstract: The Tulasu basin is an important epithermal Au mineralization district in western Tianshan in northwestern China. Geochemical and geochronological studies of the volcanic host rocks (the Dahalajunshan Formation) and associated intrusive rocks, particularly the enrichment of large-ion lithophile elements and depletion of high field strength elements, suggest that the Tulasu basin was located in a magmatic-arc setting from Late-Devonian to Early-Carboniferous, associated with the southward subduction of the North Tianshan Ocean beneath the Kazakhstan–Yili plate. Geologic and geochemical characteristics of the Au Cu–polymetallic deposits in the Tulasu basin suggest that the mineralization is related to the Late-Devonian to Early-Carboniferous arc magmatism, and is mainly of epithermal nature, including both the adularia–sericite type (Axi, Tawuerbieke and Tabei) and alunite–kaolinite or acid–sulfate type (Jingxi–Yelmend and Tieliekesayi). However, some evidence of porphyry-type mineralization has also been found, including the presence of mineralized porphyry enclaves in volcanic rocks hosting the Tawuerbieke Au prospect, and the development of porphyry-style Cu mineralization overprinted by vein-type mineralization at Kexiaxi. Considering the magmatic-arc setting that is favorable for both epithermal and porphyry types of mineralization, and the development of such mineralization systems in other parts of western Tianshan and the Altaid Belt (e.g., Uzbekistan, Kazakhstan and Kyrgyzstan), we suggest that major porphyry Cu Au deposits may have been developed in the Tulasu basin, probably beneath or adjacent to known epithermal Au mineralization. [Copyright &y& Elsevier]

Magmatism associated with plate subduction and collision plays an important role in crustal growth during the evolution of the Earth, but the detailed mechanisms regarding how magmatism contributes to the vertical growth of the crust remain unclear, in part due to controversies on the petrogenesis of intermediate-felsic rocks. In the Central Asian Orogenic Belt (CAOB), although it has been recognized that both pre-existing crustal component and juvenile mantle-derived melt played a role in the crustal evolution of the orogens, the mechanics of how they contributed to vertical crustal growth remain uncertain. This study presents new geochronological, major and trace element geochemical, and Nd–Hf isotopic data for the Late Paleozoic intermediate-felsic volcanic rocks of the northern Yili terrane, Western Tianshan Orogen, with the aims to constrain the petrogenesis of the andesitic magma and to offer new insights into the deep interaction processes between crustal- and mantle-derived magmas. According to zircon U–Pb dating, trace element and isotopic compositional data, these volcanic rocks can be divided into two groups. Group 1 rocks (365–375 Ma) have relatively low whole-rock ε Nd (t) values (−4.2 – −1.6) and display high contents of Th (11.8–20.4 ppm), U (2.7–5.1 ppm), Nb (14.1–36.7 ppm) and Ta (1.1–3.1 ppm) that suggest they were derived from the partial melting of pre-existing crust. Group 2 rocks (346–349 Ma) show REE and trace elemental patterns typical of subduction-related calc-alkaline volcanic rocks with relatively high whole-rock ε Nd (t) values (−1.89 – +2.4), and with variable zircon Hf isotopic values (ε Hf (t) = +1.9 – +13.5) that can be attributed a juvenile crust with variable input of mantle material. Hf–Nd isotopic decoupling of the group 2 rocks suggests a replenishment by more mafic magmas. Samples from the entire Yili terrane show an increasing trend in ε Nd (t) values with younger ages that suggest an increasing involvement of melted juvenile crustal rocks. Overall, these results suggest a crustal evolutionary scenario in which: 1) pre-existing crustal components were melted and ascended to the upper crust (group 1) during the southward subduction of the Junggar-North Tianshan ocean in the early stage; and, 2) a later stage in which newly input mantle material solidified to form new arc crust that was also melted by basaltic underplating and that was probably associated with the rollback of the Junggar oceanic slab. This two-stage crustal growth model seems to be an efficient process for vertical crustal growth during the formation of an accretionary orogen. • The DVF volcanic rocks are divided into two groups according to their ages and source rocks. • Underplating of mantle-derived magmas was associated with rollback of Junggar oceanic slab. • Two-stage crustal growth model works well for accretionary orogenic process. [ABSTRACT FROM AUTHOR]

• The volcanism and mineralization from both the Yelimodun and Tulasu basins are coeval. • The ore-forming fluids were mixtures of magmatic and meteoric waters. • The metals and S were sourced from the magmatic fluids and hosting volcanic rocks. • The Xiaoyuzan Au deposit is an intermediate-sulfidation epithermal mineralization. • Concealed porphyry Cu-Au mineralization may occur underneath the Xiaoyuzan area. The Tulasu and Yelimodun volcanic basins are two important Au districts in the northwestern Chinese Western Tianshan. Two large Au deposits have been discovered in the Tulasu basin, whereas only small-sized Au deposits and prospects, including the Xiaoyuzan deposit, were found in the Yelimodun basin. The purpose of this study is to examine the genesis of the Xiaoyuzan deposit and its implications for further exploration through geological, geochronological, geochemical and mineralogical studies of the host rocks and ores. The orebodies are mineralized veins and veinlets and are structurally controlled by NW- and NNW-trending faults within the Lower Carboniferous Dahalajunshan Formation volcanic rocks (DF). Sulfides are abundant (10–20 vol%) in the ores and consist of pyrite, sphalerite, galena, chalcopyrite and minor tetrahedrite. Electron microprobe analysis (EMPA) indicates that pyrite and sphalerite are both auriferous. Three ore-forming and alteration stages were distinguished: (I) quartz-pyrite stage with silicification and propylitization, (II) quartz-polysulfide stage with silicification and phyllic alteration, and (III) quartz-carbonate stage with carbonatization. The mineralization age is constrained to 357–331 Ma by a LA-ICP-MS U-Pb age of 357.3 ± 4.0 Ma for zircon from the ore-hosting tuff and the unconformably overlying Lower Carboniferous Aqialehe Formation containing fossils of the Visean period. The zircons from the tuff have highly positive ε Hf (t) values ranging from 5.9 to 10.1, indicating a magma source of depleted mantle with limited crustal contribution. The values of δ18O H2O-VSMOW calculated from δ18O quartz and δD H2O-VSMOW measured from fluid inclusions of stage II quartz range from −4.0‰ to −2.9‰ and −117‰ to −109‰, respectively. The values of δ13C CO2 calculated from δ13C cal and δ18O H2O calculated from δ18O cal range from −1.6‰ to −1.4‰ and −9.8‰ to −2.7‰, respectively. The in-situ δ34S values range from 2.6‰ to 3.7‰ for pyrite and 2.7‰ to 4.1‰ for sphalerite, respectively. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of pyrite vary from 18.196 to 18.253, 15.564 to 15.642, and 38.063 to 38.300, respectively, similar to those of ore-hosting DF and granites from the Tulasu-Yelimodun volcanic belt. The above geochemical characteristics suggest that the ore-forming fluids were mixtures of magmatic and meteoric waters, and the metals and sulfur may have been derived partly from magmatic fluids generated from the hidden causative intrusions and partly from the hosting volcanic rocks. These, together with high sulfide abundance and development of sulfide assemblages representing intermediate-sulfidation state, suggest that Xiaoyuzan is an intermediate-sulfidation epithermal Au deposit. Considering the limited erosion for the Au mineralization within the interior of Yelimodun basin and close spatio-temporal relationship between intermediate-sulfidation and porphyry mineralization, it is inferred that there may be concealed porphyry Cu-Au mineralization underneath the Xiaoyuzan deposit and its vicinity. [ABSTRACT FROM AUTHOR]

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

The Hetai goldfield, located in the southern segment of the Qinzhou Bay-Hangzhou Bay Juncture Orogenic Belt (QHJB), is the largest concentration of gold deposits in Guangdong Province, South China. The gold mineralization is hosted within the late Neoproterozoic to early Paleozoic Yunkai Group and strictly confined to mylonite (ductile shear) zones. The nature of the structural control of mineralization, in particular the role of ductile versus brittle deformation and their ages, which remain unclear despite numerous previous studies, are examined in this paper through an integrated study of geochronology and mineralogy. Lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism, but the majority of the ores are associated with brittle deformation features. In combination with macroscopic and microscopy observations on shear fabrics, LA-ICP-MS U-Pb dating on zircons of hydrothermal origin from mylonites suggests that the Hetai goldfield was subjected to two shearing events: an early sinistral ductile shearing at ca. 240 Ma, and a late dextral ductile-brittle shearing at ca. 204 Ma (Indosinian). These ages are ca. 90–30 Ma older than the previously published gold mineralizing ages of ca. 175–152 Ma (Yanshanian), suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation. This inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite (ca. 350–290 °C), chlorite (ca. 260–230 °C), and sphalerite (ca. 230–170 °C) intergrown with native gold, which are considerably lower than that for the ductile deformation (500–300 °C or higher). Based on these data, we propose that the gold mineralization in the Hetai goldfield predominantly occurred during the Yanshanian event, and only minor gold mineralization and associated sulfidation took place during the earlier Indosinian ductile deformation. [ABSTRACT FROM AUTHOR]