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Gold (Au) deposits have formed in orogenic belts throughout Earth’s history. However, the upper temperature limits of orogenic Au vein formation are difficult to constrain because measurements made on fluid inclusions focus on intermediate to late-stage minerals (e.g., quartz and calcite) or are based on P-T estimates for the metamorphic mineral assemblages of the host rocks. We conducted a study of TiO2 polymorphs that are among the earliest minerals that grew in Au-bearing veins of the Dongyuan deposit, Jiangnan orogenic Au belt, South China. Based on Raman analyzes, we identified TiO2 polymorphs of anatase (with Raman peaks at 396, 515, and 638 cm−1), rutile (with Raman peaks at 235, 447, and 613 cm−1), and anatase–rutile intergrowths. Transmission electron microscope (TEM) confirmed the polymorphs identifying the [111] zone axis of anatase, [110] zone axis of rutile, and [111] and [111] zone axes of rutile–anatase intergrowths. The TiO2 polymorphs in the Dongyuan Au veins constrain a temperature range for early mineral precipitation in the veins of 450–550 °C. The results show that ore-forming fluids for this orogenic Au deposit emplaced in the shallow crust originated from deeper and hotter crustal levels (e.g., high-grade metamorphic rocks in the middle to lower crust).

Understanding soil erosion in the northeastern area of China with black soil is vital for protecting the natural environment and preserving food security. Although spatial and temporal studies of soil erosion have been conducted, further research is needed on the correlation between soil erosion and land use type changes. In this study, the soil erosion modulus is computed using RUSLE. The model that is most suitable to the research area was produced by contrasting three different approaches to estimating the rainfall erosion factor. The RUSLE based on the multi-year continuous high-density hourly average precipitation had the best performance of the bunch, with a MAPE of 15.49%, RMSPE of 7.99%, and R2 of 0.99. Based on this model, simulated soil erosion trends in the study region from 1980 to 2020 were examined, along with the link between soil erosion and land use change. The results showed that 40.47% of the overall erosion area is made up of cultivated land, and 97.83% of it is low erosion. The most severe soil erosion occurred on unused land, with moderate and above soil erosion occupying 48.93%. Since 2000, there has been an increase in the erosion of soil in the study region, which is primarily spatially represented in the rise in the soil erosion of forests in the central and northern mountainous areas. The study’s findings serve as a guide for land planning and the development of sustainable agriculture.

The Central Asian Orogenic Belt (CAOB) is among the world’s largest Phanerozoic accretionary collage systems and hosts one of the three best-known porphyry metallogenic domain. Relatively few Devonian porphyry Cu (±Au) deposits (such as Oyu Tolgoi, Lailisigao’er, Halasu, Yulekenhalasu, etc) have been found in the CAOB, and the geological characteristics, fluid evolution and metallogenesis of Devonian porphyry Cu deposits are still uncertain. In this work, we undertake a fluid inclusion and isotopic study of the Xiaotuergen Devonian porphyry Cu deposit and present a comprehensive analysis of the ore-forming fluids to better understood Devonian porphyry deposits in the CAOB. The Devonian porphyry copper (±gold) deposits in the CAOB formed during the Early and Late Devonian (366–412 Ma) and have two peaks (375 Ma and 405 Ma). The Xiaotuergen porphyry Cu deposit, located in the Altay orogenic belt, Xinjiang, NW China, is mainly hosted by an Early Devonian granodiorite porphyry. The ore-forming fluids of the main copper mineralization stages (II and III) in Xiaotuergen were characterized by high to intermediate temperatures (190–320°C) and low to intermediate salinities (3.5–15.7 wt.% NaCl eqv.), similar to those of other the Devonian porphyry copper (±gold) deposits in the CAOB (T = 120–500°C, salinities = 0–21.7 wt.% NaCl eqv. and 33.5–51.0 wt.% NaCl eqv.). The temperatures and salinities of the ore-forming fluids changed, and phase separation might have been one of the important factors in the precipitation of chalcopyrite and pyrite. The Devonian porphyry copper (±gold) deposits in the CAOB have similar hydrogen and oxygen isotope characteristics, and the ore-forming fluids were dominated by magmatic fluids, with some minor contributions from meteoric water. The coexistence of CO2-bearing fluid inclusions with aqueous fluid inclusions in stage III suggests that fluid phase separation occurred at pressures of 110 to 320 bar (depths of 0.4–1.3 km). The formation depths of the Xiaotuergen deposit are shallower than those of the Lailisigao’er Cu deposits (palaeodepths of 1.7–2.2 km). The total sulphur value in the Xiaotuergen deposit is +12.2‰, indicating that the sulphur could have originated from crust. The δ34SV-CDT values of the most Devonian porphyry copper (±gold) deposits in the CAOB are concentrated near 0 ± 7‰, indicating a homogeneous sulphur source and derivation of sulphur from deep-seated magmas.

The Sarsuk polymetallic Au deposit is located in the Devonian volcano-sedimentary Ashele Basin of the Altay Orogenic Belt (AOB), Xinjiang. Mineralization in the deposit is confined to an area of 400 m long and 50–120 m wide, and occurs as dense massive, banded, disseminated, stockwork, and veinlet ore structures. Exhalative sedimentary, subvolcanic hydrothermal, and supergene periods have been distinguished. Although syn-depositional ores can be found, the main orebodies from this period have been eroded. Thus, the orebodies being mined are hosted mainly in a rhyolite porphyry subvolcanic intrusion within the volcanic conduit of a hydrothermal system. Electron microprobe analysis of the main ore minerals indicates that pyrite is the main Au-bearing mineral. The Au occurs mainly as either inclusions or in fissures in the form of tellurides, and is closely associated with Ag. Zn/Fe ratios of sphalerite vary from 11.37 to 251.36, with an average of 96.65, and the formation temperatures of chlorites are 155–206 °C, with an average of 175 °C. The compositions of sphalerite and chlorite indicate that the main mineralization occurred in a low- to moderate-temperature environment. Homogenization temperatures of fluid inclusions from ores of the main mineralization stage vary generally from 130 °C to 390 °C, with peaks at 140 °C, 190 °C, and 310 °C. Their corresponding salinities range from 3.0 to 10.0 wt.% NaCl equivalent, with densities from 0.56 to 1.03 g/cm3. The main mineralizing fluid of the deposit is characterized by high–low temperatures, moderate–low salinities, and moderate–low densities. The 3He/4He ratios of fluid inclusions in pyrite are 0.02 to 0.44 Ra, and the percentage of mantle-derived He ranges from 0.06% to 7.45%. 40Ar/36Ar ratios range from 319.6 to 458.5, and the percentage of 40Ar* varies from 7.53% to 35.55%. Both fluid characteristics and He and Ar isotope compositions suggest that the ore-forming fluids were a mixture of magmatic fluid and seawater. The CO2-rich fluids in the ores suggest that boiling occurred. The mixing of a high-temperature and high-pressure magmatic fluid with deeply circulating seawater caused a decrease in temperature, and phase separation in the ore-forming fluids. Thus, the precipitation of the most economically important ore materials was the result of this mixing process.

The Altay Mountains within the Xinjiang region of northwestern China hosts major metallic ore deposits. Here we review the geological characteristics, metallogenic features and tectonic settings of these deposits. The metallic ore deposits in the Altay Mountains occur mainly within four regions: North Altay, Central Altay, South Altay and Erqis. We recognize seven types of metallic ore deposits in the Altay Mountains: VMS, submarine volcanogenic iron, magmatic, skarn, pegmatite, hydrothermal vein (Cu–Zn, Fe) and orogenic gold. Among these types, the VMS, pegmatite, orogenic gold and skarn deposits are the most common. Most of the rare metal pegmatite deposits are distributed in Central Altay, with only a few in South Altay. The VMS, submarine volcanogenic type iron and skarn-type deposits are distributed in South Altay, whereas the orogenic-type gold deposits are distributed in the Erqis Fault belt. The hydrothermal vein-type deposits occur in the Erqis Fault belt and Chonghu’er Basin in South Altay. Magmatic-type deposits are mostly in the Erqis Fault belt and Central Altay. Based on isotopic age data, the VMS, submarine volcanogenic-type Fe and skarn-type Cu, Pb, Zn, Fe mineralization occurred during Early–Middle Devonian (∼410–377 Ma), orogenic-type Au, magmatic-type Cu–Ni, and a small number of skarn-type Fe, hydrothermal vein-type Cu–Zn, pegmatite-type rare-metal deposits in Early–Middle Permian (293–261 Ma), pegmatite-type rare-metal deposits, few skarn-type Fe deposit in Early–Middle Triassic (248–232 Ma), and dominantly represented by pegmatite-type rare-metal deposits in Late Triassic–Early Jurassic (223–180 Ma). The metallic ore deposits in the Altay Mountains formed in various tectonic settings, such as the Early–Middle Devonian continental arc and oceanic island arc, Early–Middle Permian post-collisional extensional setting, and Triassic–Early Jurassic intracontinental setting.

The Xiaorequanzi Cu–Zn deposit is the first and only volcanogenic massive sulfide (VMS) Cu–Zn deposit discovered in the Carboniferous volcanic-sedimentary rock series of the East Tianshan, Xinjiang. The mineralization includes stratiform, stringer/stockwork, volcanic hydrothermal-related veinlet, and subvolcanic-related vein/veinlet. The exhalative sedimentary period contributed to the majority of the Cu–Zn resource and can be subdivided into three stages: (I) stratiform (Ia) and stringer/stockwork (Ib) mineralization is represented by layered, lenticular, tabular, vein, and irregular Cu–Zn–(Au) orebodies, (II) volcanic hydrothermal-related vein mineralization is defined by pyrite–quartz ± carbonate veinlets, and (III) subvolcanic-related vein/veinlet mineralization is associated with albitophyre and dacite porphyry. Fluid inclusions study reveals that the mineralizing fluids in stage I are characterized by moderate–low temperature (peak at 160–240 °C) and low salinity (peak at 5.0–10.0 wt% NaCl eqv.). The composition of He–Ar and H–O isotopes indicate that stage I mineralizing fluids were derived from deep-circulation seawater mixed with magmatic fluids accompanied by fluid mixing. Sulfides from stage I record a range of δ34S values between 3.7 and 7.8‰, suggesting that the mineralizing sulfur was derived from seawater sulfate and volcanic rocks by thermochemical sulfate reduction. The mineralizing fluids in stage II display low temperatures (peak at 140–180 °C) and low salinities (peak at 5.0–7.0 wt% NaCl eqv.), which could indicate continuous cooling of magmatic fluids and input of seawater accelerated the precipitation of pyrite in this stage. The mineralizing fluids in stage III are characteristic of bimodal distribution temperatures (peak at 160–220 °C and 240–280 °C) and salinity (peak at 6.0–8.0 wt% NaCl eqv. and 9.0–12.0 wt% NaCl eqv.). The composition of H–O isotopes indicate that stage III mineralizing fluids were derived from magmatic fluid mixed with seawater accompanied by fluid boiling. The δ34S values range from 1.5 to 4.0‰, implying a magmatic sulfur origin. Zircon U–Pb dating of mineralization-hosting tuff and dacite porphyry yielded ages of 354.5 ± 3.9 Ma and 341.9 ± 3.1 Ma, respectively. Combining the previous Re–Os and U–Pb ages of the deposit, we conclude that the Xiaorequanzi Cu–Zn deposit is spatially and genetically associated with the volcanic exhalative sedimentation at 352–357 Ma and subvolcanic intrusion at 342–345 Ma, respectively.

The Nuoerte Basin in northern Altay contains numerous mineral discoveries, including the Xiaotuergen porphyry Cu, Kumasu VMS Pb–Zn, and Hongshanzui orogenic Au deposits. This deposit, newly discovered by the 4th Geological Team of XJBGMR – the Xiaotuergen porphyry Cu deposit – is mainly hosted along the contact zone between the granodiorite porphyry and the Nuoerte Formation volcanic-sedimentary rocks. Disseminated, veinlet, veinlet-disseminated, and stockwork Cu mineralization occur in the granodiorite porphyry. Wall-rock alteration styles include mainly potassic (K-feldspar and biotite), silicic, carbonate, sericite, pyrite, chlorite, and epidote alterations. In this study, we used LA-ICP-MS zircon dating for the various rock types in the Xiaotuergen Cu ore district. The tuff at the periphery of the ore district has been newly dated to be ca. 411 Ma. This, together with stratigraphic correlation, suggests that the local stratigraphy is the Lower Devonian Nuoerte Formation, rather than the Lower Carboniferous Hongshanzui Formation as previously assumed. The ore-hosting granodiorite porphyry, quartz porphyry, biotite monzogranite, and granite porphyry are dated to be ca. 405 Ma, 400 Ma, 398 Ma, and 397 Ma, respectively. This constrains the Cu mineralization to be slightly younger than 405 Ma, and indicates that they may have belonged to the same Early Devonian intrusive event. Magmatism at Xiaotuergen had recommenced in the Late Devonian, as represented by minor granite porphyry dikes (ca. 370 Ma) intruding the ore-hosting granodiorite porphyry.

The Qiaxia Fe–Cu deposit is located on the southern Altay margin, Xinjiang, China, and is hosted in the submarine volcanic–sedimentary rocks of the Lower Devonian Kangbutiebao Formation. Ore genesis of the Qiaxia deposit plays an important role on understanding the metallogenesis of submarine volcanic-hosted Fe deposits. In the Qiaxia deposit, stratiform and podiform Fe orebodies are conformable with host sequence strike, whereas lenticular Cu mineralization is closely related to skarn. Wall-rock alteration is dominated by silicification with minor skarn (actinolite, chlorite, diopside, and tremolite). Based on field evidence and petrographic observations, the paragenesis of the Qiaxia deposit includes the following three periods: (1) a volcanic–sedimentary period characterized by the formation of barite and Fe orebodies; (2) a magmatic–hydrothermal period with the formation of skarn-type Cu mineralization; and (3) a regional metamorphism period. The volcanic–sedimentary period shows moderate temperature and moderate- to low-salinity fluids with compositions of predominantly K+, Cl−, and SO42− in the liquid phase and H2O, CO2, and N2 in the gaseous phase. By contrast, the regional metamorphism period reveals high- to moderate-temperature and high- to low-salinity fluids and compositions of predominantly Na+, K+, Cl−, and SO42− in the liquid phase and H2O, CO2, N2, CH4, and C2H6 in the gaseous phase. The H–O isotopic compositions suggest that the volcanic–sedimentary period involved both magmatic fluids and seawater, while the fluids of the regional metamorphism period were derived from a mixture of metamorphic water and deeply circulated meteoric water. Sulfur isotope analysis shows that sulfur of volcanic–sedimentary period is mainly formed from thermochemical sulfate reduction of seawater sulfate, while sulfur of the magmatic–hydrothermal period reveals a mantle-derived source. The metamorphic quartz diorite yields a zircon U–Pb age of 398.9 ± 6.2 Ma (MSWD = 0.31). Combining with the available data, we conclude that the Fe orebodies formed from 413 to 399 Ma. The geological and geochemical evidence presented in this paper suggest that the Qiaxia deposit was initially a volcanic–sedimentary Fe deposit, which was overprinted by a later skarn Cu mineralization, and finally underwent greenschist-facies metamorphism.

The medium-tonnage Sarsuk polymetallic Au deposit is located in the Devonian volcanic–sedimentary Ashele Basin of the south Altay Orogenic Belt (AOB), Northwest China. Within the deposit, the rhyolite porphyries and diabases are widespread, emplaced into strata. The orebodies are hosted by the rhyolite porphyries. We studied the petrography, geochemistry, and Sr–Nd–Hf isotopes of the rhyolite porphyries and diabases, in order to understand the petrogenesis of these rocks and their tectonic significance. They display typical bimodality in geochemistry compositions. The diabases are characterized by SiO2 contents of 44.84–59.77 wt.%, high Mg# values (43–69), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb and Ta, low (87Sr/86Sr)i (0.706687–0.707613) values, positive eNd(t) (4.8–6.8) values, and positive and high eHf(t) (7.15–15.19) values, suggesting a depleted lithosphere mantle source that might have been metasomatized by subduction-related ...

The Early–Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu–Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U–Pb geochronology, geochemistry, and Sr–Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U–Pb ages of 402 ± 6 Ma and 403 ± 2 Ma. The dacites are calc-alkaline, and characterized by high Na 2 O/K 2 O ratios (3.6–9.3), and high Mg# values (47–63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive e Nd ( t ) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe–Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66–73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive e Nd ( t ) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction.

The Laoshankou Fe–Cu–Au deposit is located at the northern margin of Junggar Terrane, Xinjiang, China. This deposit is hosted in Middle Devonian andesitic volcanic breccias, basalts, and conglomerate-bearing basaltic volcanic breccias of the Beitashan Formation. Veined and lenticular Fe–Cu–Au orebodies are spatially and temporally related to diorite porphyries in the ore district. Wall–rock alteration is dominated by skarn (epidote, chlorite, garnet, diopside, actinolite, and tremolite), with K–feldspar, carbonate, albite, sericite, and minor quartz. On the basis of field evidence and petrographic observations, three stages of mineralization can be distinguished: (1) a prograde skarn stage; (2) a retrograde stage associated with the development of Fe mineralization; and (3) a quartz–sulfide–carbonate stage associated with Cu–Au mineralization. Electron microprobe analysis shows that garnets and pyroxenes are andradite and diopside-dominated, respectively. Fluid inclusions in garnet yield homogenization temperatures (T h ) of 205–588 °C, and salinities of 8.95–17.96 wt.% NaCl equiv. In comparison, fluid inclusions in epidote and calcite yield T h of 212–498 and 150–380 °C, and salinities of 7.02–27.04 and 13.4–18.47 wt.% NaCl equiv., respectively. Garnets yield values of 6.4‰ to 8.9‰ δ 18 O fluid , whereas calcites yield values of − 2.4‰ and 4.2‰ δ 18 O fluid , and − 0.9‰ to 2.4‰ δ 13 C PDB , indicating that the ore-forming fluids were dominantly magmatic fluids in the early stage and meteoric water in the late stage. The δ 34 S values of sulfides range from − 2.6‰ to 5.4‰, indicating that the sulfur in the deposit was probably derived from deep-seated magmas. The diorite porphyry yields LA–MC–ICP–MS zircon U–Pb age of 379.7 ± 3.0 Ma, whereas molybdenites give Re–Os weighted mean age of 383.2 ± 4.5 Ma (MSWD = 0.06). These ages suggest that the mineralization-related diorite porphyry was emplaced during the Late Devonian, coincident with the timing of mineralization within the Laoshankou Fe–Cu–Au deposit. The geological and geochemical evidence presented here suggest that the Laoshankou Fe–Cu–Au deposit is a skarn deposit.

The Yulekenhalasu porphyry copper deposit is located in the Kalaxiange'er metallogenic belt in northern Junggar, China. We present the results from zircon U–Pb geochronology, and geochemical and Sr–Nd–Hf isotope analyses of the granitoids associated with the ore deposits with a view to constrain their petrogenesis and tectonic setting. The granitoids consist of quartz diorite, diorite porphyry, porphyritic monzonite, and quartz porphyry, emplaced at 382, 379, 375–374, and 348 Ma, respectively, which span Late Devonian to early Carboniferous ages. The ore-bearing intrusion is mainly diorite porphyry, with subordinate porphyritic monzonite. The Late Devonian intrusions are characterized by SiO2 contents of 54.5–64.79 wt.%, Na2O contents of 3.82–8.24 wt.%, enrichment in Na, light rare-earth elements (LREEs), and large ion lithophile elements. They also display relative depletion in Y, Ba, P, Nb, Ta, and Ti, and weak negative Eu anomalies (δEu = 0.6–0.87). The early Carboniferous quartz porphyry is characterized by high SiO2 content (72.26–73.35 wt.%), enrichment in LREEs, K, and Sr, and relative depletion in Y (10.82–12.52 ppm) and Yb (1.06–1.15 ppm). The Late Devonian and early Carboniferous granitoids are characterized by positive eNd(t) values (5.2–10.1, one sample at − 1.9), positive eHf(t) values (7.46–18.45), low (87Sr/86Sr)i values (0.70363–0.70476), and young crustal residence ages. These data indicate that the sources of the granitoids were mainly mantle-derived juvenile rocks. Geochemical and Nd–Sr–Hf isotopic data demonstrate that the Late Devonian granitoids formed in an oceanic island arc, and they were formed from different sources, among which the mineralized diorite porphyry might have originated from a mixed slab-derived and mantle wedge melt source. The early Carboniferous quartz porphyry was likely emplaced in a mature island arc environment, and was probably derived from juvenile crust.

The Qiaoxiahala Fe–Cu–Au deposit located in Fuyun County at the northern margin of Junggar Terrane in China is hosted by Middle Devonian tuffaceous sandstones, marbles, tuffs, basalts, and andesites of the Beitashan Formation. The Cu and most Fe orebodies are stratiform, podiform, or lenticular, and are spatially and temporally related to diorite porphyry dykes in the ore district. The deposit is associated with epidote, chlorite, garnet, diopside, K-feldspar, quartz, and carbonate wall-rock alteration. On the basis of field evidence and petrographic analysis, three stages of mineralization can be distinguished: (1) a prograde skarn stage; (2) a retrograde stage associated with the development of Fe mineralization; and (3) a quartz–sulfide–carbonate stage associated with Cu–Au mineralization. H2O–NaCl and H2O–CO2–(± CH4/N2)–NaCl fluids are present in fluid inclusions in quartz and calcite. These fluids show peak Th of 200–320 °C and salinities of 1.23–13.72 wt.% NaCl equiv. Stable isotope analysis of quartz and calcite yielded values of − 141‰ to − 93‰ δD, 8.1‰ to 15.8‰ δ18OSMOW, − 0.7‰ to 9.6‰ δ18Ofluid, and − 3.9‰ to − 2.7‰ δ13CPDB, indicating that the ore-forming fluids were mainly magmatic fluids, with some contributions from meteoric water. The δ34S values of pyrite and chalcopyrite range from − 4.3‰ to 2.9‰, indicating that the sulfur in the deposit was probably derived from deep-seated magmas. Zircon U–Pb dating (206Pb/238U) of the diorite porphyry yielded a weighted mean age of 377.6 ± 1.4 Ma (MSWD = 0.20), whereas the molybdenite yielded a Re–Os isochron age of 375.2 ± 2.6 Ma (MSWD = 1.4). These geochronological data suggest that the mineralization-related diorite porphyry was emplaced during the Late Devonian, coincident with the timing of mineralization within the Qiaoxiahala Fe–Cu–Au deposit. The geological and geochemical evidence presented here suggests that the Qiaoxiahala Fe–Cu–Au deposit is related to late-stage magmatic–hydrothermal activity of the diorite porphyry, and shares a number of similarities with the IOCG deposits.

The Altay orogenic belt of Kazakhstan hosts a world-class polymetallic copper volcanogenic massive sulfide (VMS) metallogenic belt, and the eastern margin of this belt extends into the southern Chinese Altay. The Ashele Basin is located at the western end of the Chinese Altay and borders Kazakhstan. The basin hosts the large Ashele copper–zinc deposit, which is a typical VMS deposit and the largest deposit in the Ashele Basin, and it hosts the subvolcanic-hosted medium-sized Sarsuk polymetallic gold deposit. Both of these deposits are hosted in the Ashele Formation volcanic sequence. The Ashele copper–zinc orebodies are stratabound orebodies located between basalt and tuff units, and were formed during exhalative sediment deposition; in comparison, the Sarsuk gold–copper–lead–zinc orebodies are hosted by rhyolite porphyry that contains disseminated, veinlet, and veinlet–stockwork ore that formed during intrusion of the rhyolite porphyry. This study presents new zircon LA–MC–ICP–MS U–Pb analyses of six volcanic and subvolcanic units, and dikes associated with the Sarsuk and Ashele deposits. The ore-bearing rhyolite porphyry, diabase dike, basalt, tuff, and dacite porphyry samples analyzed during this study yielded ages of 382.0–382.8, 381.7, 388.2, 387.0, and 379.4 Ma, respectively. These data indicate that the Ashele Formation formed during the Early–Mid-Devonian (375–402 Ma), whereas the Ashele copper–zinc deposit formed during the Middle Devonian (388–387 Ma) and the Sarsuk polymetallic copper–gold deposit formed during the latest Middle Devonian (382 Ma). Inherited zircons within the six samples analyzed during this study yielded U–Pb ages of 618–2294 Ma, suggesting the presence of Precambrian crystalline basement within the Altay orogenic belt.

The Xiaotuergen deposit is the first porphyry Cu deposit to be identified in the northern Xinjiang Altay, Northwest China. Voluminous granitoids comprising granite porphyry, granodiorite porphyry, biotite monzogranite, and quartz porphyry are present in the ore district. Granodiorite porphyry hosts the main Cu mineralization, in disseminated, veinlet, veinlet-disseminated, and stockwork forms. The Xiaotuergen intrusions are weakly metaluminous to peraluminous calc-alkaline to alkaline granitic rocks, and exhibit typical subduction-related geochemical signatures comprising light rare earth element (LREE) enrichment, high field strength element (HFSE) depletion, and low Sr/Y and La/Yb ratios. They are depleted in Nb–Ta–Ti, P, and Eu–Sr, yield moderate Mg# values (41.10–55.38), and show negative but near-zero eNd(t) values (−2.0 to −0.1) and variable positive eHf(t) values (+1.52 to +11.08). Geochemical constraints indicate that the Xiaotuergen granitoids are highly evolved I-type granites which were derived from strong fractional crystallization of a parental magma, mixed with materials derived from partial melting of both subducting oceanic sediments and the overlying mantle wedge. The Xiaotuergen granitoids are products of the same tectono-magmatic activity as that which produced the synchronous magmatic rocks of the Xinjiang Altay, having been formed in a continental arc setting during the early Devonian. The Xiaotuergen ore-bearing porphyries are identified as the shoshonite series, rather than the adakite series. Mantle-derived contributions played a crucial role in the formation of magmas with Cu and S contents that were high enough to produce economic mineralization. The mature arc environment and long-lived magmatism provided favorable conditions for the development of porphyry Cu mineralization.

In this review, we describe the geological characteristics and metallogenic–tectonic origin of Fe deposits in the Altay orogenic belt within the Xinjiang region of northwestern China. The Fe deposits are found mainly within three regions (ordered from northwest to southeast): the Ashele, Kelan, and Maizi basins. The principal host rocks for the Fe deposits of the Altay orogenic belt are the Early Devonian Kangbutiebao Formation, the Middle to Late Devonian Altay Formation, with minor occurrences of Lower Carboniferous and Early Paleozoic metamorphosed volcano-sedimentary rocks. The principal mineral-forming element groups of the deposits are Fe, Fe–Cu, Fe–Mn, Fe–P, Fe–Pb–Zn, Fe–Au, and Fe–V–Ti. The Fe deposits are associated with distinct formations, such as volcanic rocks, skarn deposits, pegmatites, granite-related hydrothermal vein mineralization, and mafic pluton-related V–Ti-magnetite deposits. The Fe deposits are most commonly associated with volcanic rocks in the upper Kangbutiebao Formation, in the volcano-sedimentary Kelan Basin, and in skarn deposits at several localities, including the lower Kangbutiebao Formation in the volcano-sedimentary Maizi Basin, and the Altay Formation at Jiaerbasidao–Kekebulake region. Homogenization temperatures of fluid inclusions in the prograde, retrograde and sulfide stages of the skarn type deposit are mainly medium- to high-temperature (cluster between 200 and 500 °C), medium-temperature (cluster between 200 and 340 °C) and low- to medium temperature (cluster between 160 and 300 °C), respectively. Ore fluids in the sedimentation period in the volcano-sedimentary type deposit are characterized by low- to medium temperature (with a peak around 190 °C), low to moderate salinity (3.23 to 22.71 wt.% NaCl equiv). Ore fluids in the pegmatite type deposit are characterized by low- to medium temperature (with a peak at 240 °C), low salinity (with a peak around 9 wt.% NaCl equiv). An analysis of the isotopic data for Fe deposits from the Altay orogenic belt indicates that the sulfur was derived from several sources, including volcanic rocks and granite, as well as bacterial reduction of sulfate from seawater. The present results indicate that different deposit types were derived from various sources. The REE geochemistry of rocks and ores from the Fe deposits in the Altay orogenic belt suggests that the ore-forming materials were derived from mafic volcanic rocks. Based on isotopic age data, the timing of the mineralization can be divided into four broad intervals: Early Devonian (410–384 Ma), Middle Devonian (377 Ma), Early Permian (287–274 Ma), and Early Triassic (c. 244 Ma). The ore-forming processes of the Fe deposits are closely related to volcanic activity and the emplacement of intermediate and felsic intrusions. We conclude that Fe deposits within the Altay orogenic belt developed in a range of tectonic settings, including continental arc, post-collisional extensional settings, and intracontinental settings.

In this review, we describe the geological characteristics of porphyry copper deposits in Junggar region, Xinjiang, and place these into their metallogenic–tectonic context. These porphyry copper deposits are mainly found in four metallogenic belts: (1) a Late Silurian to Early Devonian Cu–Mo metallogenic belt in the Qiongheba area; (2) the Late Devonian Kalaxiange’er Cu metallogenic belt; (3) the Early Carboniferous Xilekuduke–Suoerkuduke porphyry-skarn Cu–Mo metallogenic belt; and (4) the Late Carboniferous Baogutu porphyry Cu metallogenic belt. The ages of mineralization can be divided into three broad intervals

The Altay orogenic belt (AOB), situated in the middle part of the Central Asian Orogenic Belt (CAOB), is one of the most important metallogenic belts in China. The Kangbutiebao Formation is a Late Paleozoic stratigraphic unit that hosts many important iron and Pb–Zn deposits. The Kangbutiebao Formation consists of intercalated volcanic and sedimentary rocks that have undergone regional greenschist to lower amphibolite facies metamorphism, and mainly outcrops in three NW-trending fault-bounded volcano–sedimentary basins, including the Maizi, Kelang, and Chonghuer basins. SHRIMP analyses of zircons from three metarhyolites of the Kangbutiebao Fm. in the Kelang Basin yield weighted mean 206 Pb/ 238 U ages of 412.6 ± 3.5 Ma, 408.7 ± 5.3 Ma and 406.7 ± 4.3 Ma, respectively, which can be interpreted as the eruption age of the Kangbutiebao silicic volcanic rocks in the Kelang Basin. These ages indicate that the Kangbutiebao Formation was formed during the Late Silurian to Early Devonian. They also demonstrate that the deposits hosted in the Kangbutiebao Formation were formed after 412–407 Ma. They play a key role in understanding the Paleozoic tectonic evolution and metallogenesis of the southern margin of the Chinese AOB.