Southern Great Xing Research Articles

Coupling Between Exhumation and Subduction: A Case Study From the Southern Great Xing'an Range, NE Asia

AbstractThe link between subduction and continental exhumation is explored using high‐resolution thermal histories from southern Great Xing'an Range (GXR), NE Asia and integrated with a regional low‐temperature thermochronology data synthesis from the NE Asian continental margin. The GXR thermal histories are constrained by multiple thermo‐, geochronometers (zircon, titanite, apatite U‐Pb, zircon, apatite (U‐Th)/He and apatite fission track). These data yield a large range in U‐Pb ages (292–119 Ma) with enhanced exhumation mainly during the early Cretaceous (ca. 155–110 Ma) in an extensional regime linked to roll‐back of the Paleo‐Pacific Ocean and consequent lithospheric thinning and delamination. Integrated with Cretaceous‐Cenozoic low‐temperature thermochronological data from the NE Asian continent margin, three regional phases of exhumation are recognized, which can be linked to changes in the geometry and kinematics of the subduction systems of the Paleo‐Pacific and Pacific oceans, demonstrating coupling between the subducting plate and the continental margin at active plate boundaries.

Petrogenesis and Tectonic Setting of Early Cretaceous A-Type Granite from the Southern Great Xing’an Range, Northeastern China: Geochronological, Geochemical, and Hf Isotopic Evidence

The southern Great Xing’an Range is located in the eastern Central Asian Orogenic Belt, where voluminous igneous rocks developed during the Late Mesozoic period. The east slope of the southern Great Xing’an Range has been the topic of numerous debates on the level of influence of the Mongol-Okhotsk and the Paleo-Pacific regimes in the Late Mesozoic period. Therefore, this area is a suitable region in which to study the temporal changes in magma sources and tectono-magmatic evolution. In this paper, whole-rock geochemical data, zircon U-Pb geochronology, and zircon Hf isotope studies were carried out on the granitoids in the east slope area of the southern Great Xing’an Range. LA-ICP-MS zircon U-Pb dating revealed the ages of four granitoid samples: 135.0 ± 0.6 Ma, 130.7 ± 1.4 Ma, 130.4 ± 1.0 Ma, and 127.6 ± 0.8 Ma, respectively. The Hf isotope values 176Hf/177Hf = 0.282751–0.283015, εHf (t) = +2.0~+11.5, and T2DM = 583~1442 Ma suggest that the magma was generated by partial melting of Meso- and Neoproterozoic accreted and thickened low crust. The whole-rock geochemical data implied that these granitoids are A-type granite and their formation is closely linked to the subduction of the Paleo-Pacific Ocean plate. These geochemical, isotopic, and geochronological data suggest that the Early Cretaceous magmatism in the east slope area of the southern Great Xing’an Range formed in an extensional back-arc tectonic setting associated with the slab roll-back of the Paleo-Pacific plate subduction.

Contribution discrepancy of two distinct wall rocks to wolframite mineralization from Dongshanwan quartz-vein tungsten deposit, Southern Great Xing’an Range, China

The Southern Great Xing’an Range is a significant polymetallic metallogenic belt in Northeast China. The ages of granite related to tungsten mineralization have been well quantified, however, the timing and mechanism of quartz vein-type wolframite deposition remain unclear. Therefore, our study focused on the Dongshanwan tungsten deposit, representing a typical wolframite-bearing quartz vein-type deposit in the Southern Great Xing’an Range. Quartz vein-type tungsten mineralization was mainly contained in the Early Cretaceous granite porphyry, with few exceptions in the Permian tuff. Representative wolframite samples were collected from intragranitic (Wol-I) and intra-tuff (Wol-II) quartz veins for wolframite U–Pb dating, electron probe microanalysis (EPMA), and trace elemental analysis. Wolframite U–Pb dating recognized an Early Cretaceous mineralization event at 139–141 Ma, consistent with the previous Dongshanwan granite’s ages (∼142 Ma) but much younger than tuff (∼260 Ma). All the wolframite samples belonged to the ferberite series (FeO/MnO = 4.0–6.9), which indicates a link to the highly fractionated granite. Wol-I showed high contents of Nb, Ta, Sc, and HREEs and a strongly negative Eu anomaly (0.02–0.29), while these elements in Wol-II were approximately one order of magnitude lower than in Wol-I and the Eu anomaly was highly variable (0.17–1.02). The redox characteristics reflected by the Eu anomaly of wolframite may correspond to the variations in oxygen fugacity. Based on petrology, geochemistry, and element mass migration, this study suggests that the granite porphyry and tuff in the Dongshanwan deposit contributed differently to the wolframite precipitation even if the ore-forming fluids were of a common magmatic-hydrothermal origin. The exsolved fluid reserved in the closed system interacts with granite to achieve continuous enrichment in Nb, Ta, Sn, and REEs and accepts external Fe supply from granite alteration to precipitate Wol-I. In contrast, the fluids in relatively open and non-granitic systems have lower Nb, Ta, Sn, and REEs than the former, and Fe supply depends on the alteration of tuff. The abundance of fluorite and the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of Y/Ho and Zr/Hf in the wolframite suggested that fluorine plays an important role in the migration and enrichment of tungsten and other elements during tungsten mineralization.

Late Jurassic Haobugao granites from the southern Great Xing’an Range, NE China: Implications for postcollision extension of the Mongol–Okhotsk Ocean

Abstract The Mongolia-Okhotsk tectonic regime had a significant impact on the tectonic evolution of Northeastern (NE) China. However, there is no consensus on the role of this regime in the geological evolution of the Xing’an Massif during the late Mesozoic. This article presents the results of zircon U–Pb geochronology, whole-rock major and trace-element geochemistry, and zircon Hf isotopic compositions for granites in the Haobugao area of the southern Great Xing’an Range, NE China, to determine their petrogenesis, source, and tectonic setting. The zircon U–Pb ages indicate that the granites crystallized at 152.7 ± 0.5 Ma. The granites exhibit high SiO2 (70.75–73.19 wt%) and K2O + Na2O (8.00–8.65 wt%) contents and extremely low MgO (0.40–0.59 wt%) and TiO2 (0.24–0.33 wt%) contents. They belong to the metaluminous, high-K calc-alkaline, and ferroan series, with mostly right-inclined REE curves, flat heavy rare earth element patterns, high 10,000 Ga/Al ratios, and intensely negative Eu anomalies. The Zr/Hf ratios are 24.2–27.7, Nb/Ta ratios are 6.4–8.9, and Y/NbN ratios are >1.2. These characteristics suggest an A2-type granite affinity. The zircon εHf values of the rocks range from +5.62 to +9.12, corresponding to T DM2 values of 621–906 Ma, indicating that juvenile materials in the Neoproterozoic may be a source of these granites. Geochemically, these Late Jurassic A2-type granites are similar to those from post-collision extension settings. The primary magma was likely derived from the partial melting of a delaminated region of the lower crust.

Petrogenesis of the Mesozoic granitoids from the Yuanlinzi Sn-Cu deposit, Northeast China: Implications for Cu-rich Sn mineralization

Granite-related hydrothermal Sn deposits are commonly expected to contain little or no Cu because Cu and Sn have markedly different geochemical properties. However, examples of Sn deposits rich in Cu are well-known in many Sn belts worldwide. So far, the magmatic processes of ore-related rocks and genesis of Cu-rich Sn deposits remain controversial. The newly discovered Yuanlinzi Sn-Cu deposit is located in the southern Great Xing’an Range (SGXR), Northeast China. It is a typical Cu-rich Sn deposit in the SGXR. This contribution reports new cassiterite and zircon U-Pb ages, geochemical compositions, and Sr-Nd isotopic data for the granitoids in the Yuanlinzi deposit to decipher the genesis of Cu-rich Sn deposit. Cassiterite U-Pb dating reveals that the Sn mineralization at Yuanlinzi was formed at ∼ 138 Ma. Zircon U-Pb dating of the granitoids yielded two age clusters: Early Triassic (247.6–246.3 Ma) for the granodiorite, and Early Cretaceous (145.3–141.9 Ma) for the granites, including K-feldspar granite (145.3 ± 0.5 Ma), granite porphyry (143.6 ± 0.9 Ma), fine-grained granite (142.8 ± 1.1 Ma) and albite granite (141.9 ± 1.3 Ma). The Early Cretaceous granites have geochemical affinities for A-type granites, for example, A/CNK = 0.98–1.07, high TFeO/(TFeO + MgO) ratios, total alkali (Na2O + K2O), and Ga/Al ratios. The Early Triassic granodiorite have relatively low (87Sr/86Sr)i values of 0.7034–0.7041, whereas the Early Cretaceous granite has slightly variable and higher (87Sr/86Sr)i values, varying from 0.7020 to 0.7065. The Early Triassic granodiorite and Early Cretaceous granites have similar bulk-rock εNd (t) values and TDM2 ages, ranging from + 1.89 to + 3.53 and 732 to 845 Ma, respectively. The geochemical data and Sr-Nd isotopes indicate that the Early Cretaceous granites were derived from partial melting of the juvenile middle-upper crust. This study further suggests that the 145.3–141.9 Ma granites are associated with back-arc extension environment during the low-angle subduction of Paleo-Pacific plate. In addition, the whole-rock and zircon compositions show that the Cu-Sn magma is characterized by relatively oxidized and less evolved features compared to the Cu-poor Sn deposits in the region. The rapid increase of oxygen fugacity of the latest episode of the Early Cretaceous magma is supposed to have initiated by the injection of mafic magma, which supported the Cu source for the deposit. Our studies suggest that the Cu-bearing mafic magma/fluid injection plays a key role on the formation of Cu-rich Sn deposit.

Petrogenesis and implications for tin mineralization of the Beidashan granitic pluton, southern Great Xing'an Range, NE China: Constraints from whole-rock and accessory mineral geochemistry

The Beidashan pluton, consisting of quartz monzonite in the northeast and biotite granite in the southwest, is a representative granitic intrusion in the southern Great Xing'an Range. To investigate its petrogenesis and relationship with tin mineralization, whole-rock and accessory minerals (zircon and apatite) geochemical analyses were carried out. The quartz monzonite mainly belongs to high-K calc-alkaline strongly peraluminous granite, and the biotite granite is high-K calc-alkaline weakly peraluminous granite. Zircon U-Pb dating indicates a younger age for the biotite granite (138 Ma) than the quartz monzonite (140 Ma). The zircon Hf and apatite Nd isotopic compositions of the quartz monzonite (εHf(t) = 5.2 to 9.1 and εNd(t) = −1.1 to 1.3) and those of the biotite granite (εHf(t) = 5.6 to 8.0 and εNd(t) = −0.9 to 1.0) are indistinguishable, implying that they were derived from the same sources. Modeling results using apatite Nd isotope data show that they were from a mixing source of the Xilinhot Group and mantle-derived basaltic melt. Whole-rock and apatite trace elements reveal that the granitic magma mainly experienced fractional crystallization of amphibole, biotite, plagioclase, K-feldspar, apatite, and monazite from the quartz monzonite to the biotite granite. Mineralogical, whole-rock geochemical, and apatite trace element data indicate that the Beidashan pluton has an I-type granite affinity. A crystal mush model was proposed accounting for the composition gap between these two granites (e.g., SiO2, Al2O3, and Ba), in which the biotite granite represents the highly fractionated interstitial melt extracted from the crystal mush system whereas the quartz monzonite is the residual crystal mush consisting of the cumulate crystals and trapped interstitial melt. The melt was extracted when the crystallinity of the crystal mush reached about 33–37%, and the residual crystal mush trapped about 38–46% interstitial melt. Both Ce anomalies in zircon and Eu anomalies in apatite imply reducing conditions. The calculated values of oxygen fugacity for the Beidashan pluton range from −19.3 to −15.7, and most of them are lower than the fayalite-magnetite-quartz (FMQ) oxygen buffer. Apatite in the Beidashan pluton has high F (2.35–3.61%) and low Cl (0–0.41%) concentrations, which are similar to those of Sn-W deposits worldwide. The Sn contents of apatite increase from the quartz monzonite (mean 0.30 ppm) to the biotite granite (mean 1.09 ppm), suggesting that magma evolution is important for the enrichment of Sn in the melt.

Provenance, Sedimentary Environment, Tectonic Setting, and Uranium Mineralization Implications of the Yaojia Formation, SW Songliao Basin, NE China

The SW Songliao Basin is an extremely significant part of the giant sandstone uranium metallogenic belt in northern China. The Yaojia Formation is the most significant ore-bearing layer in the region. However, the poorly constrained sedimentology of the Yaojia Formation has substantially hindered the understanding of the basin and the exploration of uranium deposits within it. To determine the sedimentology, provenance, and tectonic setting of the Yaojia Formation in the study area, we conducted petrography, whole-rock geochemical analysis, and electron probe research. Based on the results of the study, it appears that the Yaojia Formation sandstone is predominantly composed of lithic sandstone and feldspar lithic sandstone. Uranium exists in two forms: as independent minerals and as adsorption uranium. Pitchblende is the most common independent uranium mineral, with small amounts of coffinite also occurring. The ratios of Sr/Ba, V/(V+Ni), V/Cr, Ni/Co, and (Cu+Mo)/Zn of the samples indicate that the Yaojia Formation was deposited in a sub- to oxygen-rich freshwater environment with a moderately stratified bottom water body and smooth circulation. The geochemical characteristics of the Yaojia Formation sandstones imply that they are primarily derived from felsic igneous rocks in the upper continental crust in active continental margin and continental island arc environments. According to geochemistry and previous detrital zircon U-Pb chronology studies, the Mesozoic and Late Paleozoic felsic igneous rocks of the southern Great Xing’an Mountains are the principal sources of the Yaojia Formation in the SW Songliao Basin. Besides providing sediments for the study area, the uranium-rich felsic igneous rocks in the source areas also represent a long-term, stable, and ideal source of uranium, suggesting substantial potential for uranium exploration in the study area.

Geochronology and Geochemistry of Early Cretaceous A‐type Granites in Central–Eastern Inner Mongolia, China: Implications for Late Mesozoic Tectonic Evolution of the Southern Great Xing'an Range

AbstractThe southern Great Xing'an Range is the most critical Sn‐polymetallic metallogenic belt in northeast China. However, the tectonic setting of the Early Cretaceous magmatic‐metallogenic “flare‐up” event remains uncertain. This paper presents an integrated study on the occurrence, petrology, zircon U‐Pb ages, whole‐rock geochemistry, and in situ zircon Hf isotopes for Wenduerchagan granites of Xi Ujimqin Banner, central‐eastern Inner Mongolia. These granites consist primarily of granite porphyry (with ages of 137 ± 1 Ma and 138 ± 1 Ma) and (porphyritic) alkali feldspar granite (with an age of 141 ± 2 Ma), corresponding to the early Early Cretaceous. They are A‐type granites characterized by high silicon, alkali, and TFeO/MgO contents while being depleted of Ba, Nb, Ta, Sr, P, and Ti. They show right‐dipping trend rare‐earth element distribution characteristics with negative Eu anomalies (Eu/Eu* = 0.01–0.20) and weak heavy rare‐earth element fractionation ((Gd/Yb)N = 0.77–2.30). They demonstrate homogeneous zircon Hf isotopic compositions (positive εHf(t) values from +5.3 to +7.1 and young two‐stage Hf model ages of 851–742 Ma) and high zircon saturation temperatures (av. 810°C). These geochemical characteristics indicate that Wenduerchagan granites originated from the partial melting of juvenile crust under high‐temperature and low‐pressure conditions. Wenduerchagan granites most likely formed in a post‐collisional compression‐extension transition regime caused by the closure of the Mongol–Okhotsk Ocean, when combined with regional geology. Such a transition regime can probably be attributed to the upwelling of the asthenospheric mantle caused by the break‐off of a subducted Mongol–Okhotsk oceanic slab. Upwelling asthenospheric mantle provided sufficient energy and favorable tectonic conditions for magmatism and mineralization of the Early Cretaceous.

The origin of high-silica granites and rare metal mineralization: Insights from geochemistry and U-Pb-Sr-Nd-Hf-O isotopes of Early Cretaceous granitoids in the southern Great Xing’an Range, NE China

The origin of high-silica granites and rare metal mineralization: Insights from geochemistry and U-Pb-Sr-Nd-Hf-O isotopes of Early Cretaceous granitoids in the southern Great Xing’an Range, NE China

Age, Fluid Inclusion, and H–O–S–Pb Isotope Geochemistry of the Superlarge Huaaobaote Ag–Pb–Zn Deposit in the Southern Great Xing’an Range, NE China

The superlarge Huaaobaote Ag–Pb–Zn deposit is located on the western slope of the southern Great Xing’an Range (SGXR). The deposit includes four ore blocks, namely, ore blocks I, II, III, and V. Except for the no. I orebody of ore block I, which is hosted in the contact zone between the Carboniferous serpentinized harzburgite and the Permian siltstone, the other orebodies all occur as veins controlled by faults. The mineralization process at the deposit can be divided into four stages: cassiterite–arsenopyrite–pyrite–quartz stage (stage I), cassiterite–chalcopyrite–pyrite–freibergite–arsenopyrite–pyrrhotite–quartz stage (stage II), sphalerite–galena–jamesonite–stibnite–freibergite–silver mineral–quartz–calcite–chlorite stage (stage III), and argentite–pyrargyrite–pyrite–quartz–calcite (stage IV). Cassiterite U–Pb dating of the Huaaobaote deposit yielded ages of 136.3–134.3 Ma, indicating that the deposit formed in the Early Cretaceous period. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich FIs, have been distinguished in the quartz vein and sphalerite. The homogenization temperature during the four stages gradually decreases, with temperatures of 302–340 °C for stage I, 267–304 °C for stage II, 186–273 °C for stage III, and 166–199 °C for stage IV, respectively. The salinity (wt% NaCl eqv.) at stages I, II, III, and IV is 3.7–6.6, 0.2–4.5, 0.2–5.0, and 0.4–1.6, respectively, indicating that the ore-forming fluid is characterized by low salinity. The δ18Owater and δD values of the ore-forming fluid range from −11.9‰ to 7.9‰ and −168‰ to −76‰, respectively, indicating that the ore-forming fluid was dominantly derived from a mixture of magmatic and meteoric water. The calculated δ34SH2S values range from −3.6‰ to 1.2‰, indicating that the sulfur mainly came from granitic magma. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of sulfides are in the ranges of 18.195–18.317, 15.509–15.667, and 37.965–38.475, respectively, implying that the ore-forming material was mainly derived from felsic magma that may be formed by the partial melting of orogenic materials. Fluid mixing, cooling, and immiscibility were the three primary mechanisms for mineral precipitation in the Huaaobaote deposit.

Metallogeny and exploration indicators of Sn and Ag deposits in the Southern Great Xing'an Range, China: Application of knowledge-driven CoDA based on geology and geochemistry

There have been recent breakthroughs in exploration for tin (Sn) and silver (Ag) mineral resources in the Southern Great Xing'an Range, making this region a world-class Sn and Ag metallogenic area. However, thick surface coverage and hidden deposits make exploration difficult, and conventional geological and geochemical prospecting methods have severely limited efficacy. In order to further extract geological and geochemical information on the basis of the existing research, to serve the regional mineral exploration, the knowledge-driven CoDA method is used to identify geochemical associations for inferring matallogenic information. Meanwhile, the fractal C-A model is used to determine geochemical anomalies, the catchment basin geochemical method is used to delineate anomaly boundary. Especially, the data-driven CoDA method is employed for comparison analysis with the knowledge-driven one. As a result, seven groups of compositional balances are proposed and verified, and geological bodies closely related to Sn and Ag mineralization are identified. These occurred in Dashizhai Formation strata, being calcareous rocks and granites, especially A-type granite, which is most closely related to mineralization. Meanwhile, Sn and Ag mineralization areas were identified and found to be consistent with known deposits. Finally, this paper proposes a novel model of regional porphyry Sn–Cu metallogenic systems and delineates exploration targets for Ag–Zn–Pb–Cu deposits and Sn–polymetallic deposits based on the analysis of catchment basins.

Geological characteristics and genesis of the Late Carboniferous extremely thick slate in the Shuangjianzishan Ag-Pb-Zn district, southern Great Xing’an Range, NE China: constraints on metallogenesis and tectonic setting

The Shuangjianzishan super-large Ag-Pb-Zn deposit is situated in the southern Great Xing’an Range (SGXR), which is part of the eastern Central Asian Orogenic Belt (CAOB) and the northeastern Xing’an-Mongolia Orogenic Belt (XMOB). The host rock of this deposit is the Dashizhai Formation, characterized by a widely distributed, extremely thick slate in the Shuangjianzishan basin. Petrographically, the slate contains secondary minerals such as secondary quartz, biotite, sphalerite, pyrite, galena, and chalcopyrite, in addition to primary quartz, feldspar, and rock fragment. The whole-rock geochemical analysis indicates that the slate was deposited in an oxygen-deficient shale basin, influenced by calcium-rich volcanic ash and magmatic-hydrothermal fluids. The mineralogical characteristics of sulfide minerals and the in-situ sulfur isotopic composition of pyrites suggest that the sulfide minerals were likely formed before the primary metallogenic epoch, indicating pre-enrichment of metals. The color variation from black to green observed in the drilling core of the slate is attributed to differences in feldspar content, with the denser “black” slate marking the metallogenic horizon. Based on previous research, it is inferred that the slate is a product of the post-orogenic extensional tectonic setting of the XMOB in the Late Carboniferous, and it underwent alteration by epithermal magmatic-hydrothermal fluids during the Mesozoic metallogenic episode.

Insights into the formation of Shihuiyao Ta-Nb deposit in southern Great Xing'an Range, NE China: Evidence from chronology and fluid inclusion

Shihuiyao is a typical granite-type Ta-Nb deposit in the southern Great Xing'an Range (SGXR), Northeast China. The ore field is comprised of several granitic intrusions that were emplaced into the Early Permian Linxi Formation during the Late Jurassic (ca. 145 ∼ 150 Ma). The main Ta-Nb mineralization (stage 1–2) is found within the leucogranite, with minor identified in the porphyritic granite in the deposit. Four distinct stages in the metallogenic process can be identified: weakly mineralized magmatic stage (stage 1), strongly mineralized magmatic stage (stage 2), post-magmatic hydrothermal stage (stage 3) and low-temperature hydrothermal stage (stage 4). Cassiterite samples collected from stage 2 were dated to be 147 ± 3.5 Ma and 147.7 ± 1.9 Ma, providing evidence for the latest Jurassic Ta-Nb metallogenic event at Shihuiyao. To acquire a more profound comprehension of the properties and behaviors of the fluids, fluid inclusions within quartz, albite, amazonite and fluorite were analyzed among all stages. The results showed that the Shihuiyao fluid inclusions were relatively homogeneous and predominantly comprised liquid-rich inclusions, with occasional occurrences of CO2-type, vapor-rich type, and solid-type inclusions. From stage 1 to stage 4, the temperature of the ore-forming fluids decreased gradually, while the salinity showed increasing during stage 4, which indicates a possible contribution from surrounding strata sourced fluids. Raman analysis of the inclusions at each stage revealed that the vapor components were primarily H2O, CO2, and CH4, with additional N2 and CH4 appearing in the late stage, pointing to mixing between the metallogenic fluids and the surrounding strata source materials. Notably, the simultaneous occurrence of liquid-rich and solid-type inclusions under low pressure conditions (0.6 ∼ 1.5 km) in the early ore-forming stage (stages 1–2) suggests a fluid boiling process. We argue that the fluid boiling and rapid chemical quenching of the granitic melt play a crucial role in changing the physicochemical conditions of the ore-forming fluids, ultimately resulting in the enrichment and precipitation of niobium and tantalum. The fluid mixing and intense water–rock interaction in the late stages (stages 3–4) may have also contributed to the minor mineralization.Drawing upon our investigations utilizing petrographic features and composition analysis of individual fluid inclusions, we have prognosticated on the Sn mineralization potential within the Shihuiyao deposit. Our results indicate the Shihuiyao granites are comparable to the tin granites worldwide. Genesis of cassiterites is linked to both magmatic and hydrothermal processes, exsolution from tin-rich fluids (up to 233 ppm) and interaction with country rocks attribute to the probable economic tin mineralization. Consequently, the Shihuiyao deposit has been noteworthy prospectively for further tin mineralization.

Petrogenesis of Shihuiyao Rare-Metal Granites in the Southern Great Xing’an Range, NE China

Shihuiyao Rb–Nb–Ta-rich granites from the Late Jurassic period are newly discovered rare-metal-bearing granites found in the southern Great Xing’an Range, NE China. Further research of these granites may contribute to better understanding the petrogenesis of rare-metal granites and their associated mineralization mechanisms. The granites are high-silica (SiO2 = 73.66–77.08 wt%), alkali-rich (K2O + Na2O = 8.18–9.49 wt%) and weakly to mildly peraluminous with A/CNK values (molar ratios of Al2O3/(CaO + Na2O + K2O)) ranging from 1.06 to 1.16. High differentiation indexes (DI = 95–97) and low P2O5 contents demonstrate that Shihuiyao rocks are low-P and peraluminous rare-metal granites. Mineral chemistry and whole-rock geochemistry can be used to obtain the following lithological sequence: zinnwaldite granite, muscovite–zinnwaldite granite, amazonite-bearing granite and amazonite pegmatite. The effect of the rare-earth element tetrad; low K/Rb (18.98–32.82), Nb/Ta (2.41–4.64) and Zr/Hf (5.99–8.80) ratios; and the occurrence of snowball-textured quartz suggest that extreme magmatic fractionation might be the key factor that causes Rb–Nb–Ta enrichment.

Composition and evolution of ore-forming fluids in the Sansheng porphyry W-Mo deposit, Inner Mongolia, NE China: Evidence from LA-ICP-MS analysis of fluid inclusions

Unveiling the composition and evolution of ore-forming fluids in porphyry W-Mo mineralization systems is key to understanding their formation processes, but detailed quantitative studies are still limited. The Sansheng porphyry W-Mo deposit (17,285 t WO3 @ 0.569 % and 24,361 t Mo @ 0.226 %), located in southern Great Xing’an Range W belt, NE China, is characterized by quartz vein- and veinlet-disseminated-type W-Mo ore bodies mainly hosted in the cupolas of Early Cretaceous granitic intrusion. In this study, we provide an elaborate study that integrates detailed petrographic, laser Raman, microthermometric, and LA-ICP-MS analyses of fluid inclusions (FIs) to reconstruct the fluid evolution history of the Sansheng W-Mo mineralization system and to bridge the aforementioned knowledge gap. Four stages of hydrothermal veins are identified: stage 1 is the dominant stage of W mineralization, and characterized by the development of wolframite, quartz, K-feldspar, muscovite, and minor amounts of molybdenite; stage 2 is the main stage of Mo mineralization, and featured with the mineral assemblages of molybdenite, quartz, sericite together with minor amounts of pyrite; stage 3 involves Cu-Pb-Zn mineralization, and is characterized by the occurrence of polymetallic sulfides, quartz, and sericite; and stage 4 is dominated by barren carbonate-quartz veins. In wolframite and quartz, the FIs are classified as liquid-rich two-phase (L-type), vapor-rich two-phase (V-type), and pure vapor mono-phase FIs (PV-type) in types. Microthermometric results reveal decreasing homogenization temperatures in primary FIs from stages 1 to 4. Stage 1 fluids are characterized by high homogenization temperatures (320–420 ℃), moderate salinities (7.9–14.8 wt% NaCl equiv.), highly variable W contents (17–7251 ppm) and constant Mo contents (22–288 ppm). FIs in wolframite and coexisting quartz share similar homogenization temperatures and salinities, suggesting that they were formed concurrently. Stage 2 fluids have similar salinities (7.0–13.9 wt% NaCl equiv.) to stage 1 fluids but lower homogenization temperatures (250–340 ℃), and contain highly variable Mo contents (21–11176 ppm) and low W contents (5–23 ppm). Stage 3 fluids display moderate homogenization temperatures (220–300 ℃) and low salinities (3.1–10.1 wt% NaCl equiv.). The contents of W and Mo in stage 3 fluids decrease dramatically, marking the termination of W-Mo mineralization. Stage 4 fluids are characterized by moderate homogenization temperatures (200–270 ℃), low salinities (0.2–5.0 wt% NaCl equiv.), and the lowest contents of W (1–4 ppm) and Mo (8–16 ppm). All stage fluids contain high concentrations of B and Mn, and high ratios of Li/Na, K/Na, Rb/Na, Ba/Na, Pb/Na, and Zn/Na, similar to magmatic-hydrothermal fluids in composition and against typical basinal brines. In addition, they also have high Rb/Sr and low K/Rb ratios, which are equivalent to those of the Sansheng ore-bearing granite. In combination with the constant Cs/(Na + K) and Cs/Rb ratios of all stage FIs, we propose that the multistage hydrothermal fluids originated from a common source–the highly evolved and geochemically uniform Sansheng granitic magma, and that the derivation of ore-forming fluids was a continuous fluid exsolution process. Fluid boiling and fluid-rock interaction are collectively responsible for the deposition of wolframite and molybdenite, while the role of fluid cooling may be subordinate. The meteoric water began to enter the hydrothermal system in stage 3, and fluid cooling and dilution due to the fluid mixing process played a critical role in the deposition of Cu-Pb-Zn sulfides. Our findings highlight the significance of in-situ FI analyses in revealing the composition and evolution of multistage fluids in porphyry W-Mo deposits, which is critical for elucidating detailed ore-forming processes of intrusion-related W-Mo mineralization systems in NE China and globally.

Geochemical characteristics of the Middle–Late Permian sedimentary rocks in the southern Great Xing'an Range, NE China, and their constraints on the closure time of the Paleo Asian Ocean (Eastern Segment)

The Late Paleozoic sedimentary environment in the southern Great Xing'an Range in Northeast (NE) China, and the timing of the final closure of the Paleo Asian Ocean between the North China Craton and combined NE China blocks have been controversial for a long time, affecting and restricting the exploration and development of new area and new strata in the North Area in China. In order to reconstruct the structural-sedimentary evolution history of the southern Great Xing'an Range during the Middle to Late Permian, and to explore the closure time of the Paleo Asian Ocean (Eastern Segment), in this paper, the sedimentary characteristics and tectonic background of the Middle–Late Permian sedimentary rocks from well MKD1 are systematically analyzed by using elemental and organic geochemistry methods. The results show that the Middle Permian sedimentary records in well MKD1 show typical marine sediments, while the Late Permian sediments change significantly to clastic rocks deposited in the marine–continental transitional environment. The provenances of the Middle Permian rocks are mainly intermediate and felsic igneous rocks from continental active margin and oceanic island arc tectonic setting, related to the northern accretion complex, and the Songnen Block and partially arc magmatic rock. The source materials of the Late Permian rocks are mainly felsic rocks and some intermediate igneous rocks from the continental arc and active margin, related to the northern accretion complex, the arc magmatic rock and the Songnen Block. Depositional discontinuity after the Late Permian, regional lackness of the Early Triassic strata, sedimentary environment variation, tectonic setting and provenance location discrimination of the Middle–Late Permian rocks comprehensively reveal that the Paleo Asian Ocean (Eastern Segment) possibly closed in the late Late Permian. Finally, we propose a structural-sedimentary evolution pattern of the southern Great Xing'an Range during the Middle to Late Permian.

In Situ LA-ICP-MS of Zoned Garnets from the Huanggang Skarn Iron–Tin Polymetallic Deposit, Southeastern Mongolia, Northern China

The Huanggang deposit is the most important and largest skarn Fe–Sn polymetallic deposit in the Southern Great Xing’an Range of Northeast China. Cassiterite, magnetite, and other metal minerals are related to the garnets within skarn systems. The zoned garnets from various skarn stages are able to record numerous geological and mineralizing processes including variations in physicochemical conditions and hydrothermal fluid evolution. In this contribution, we present the mineralogy, systematic major, trace, and rare earth element (REE) concentrations of zoned garnets from the Huanggang Fe–Sn polymetallic skarn deposit. The in situ analytical results of garnets in the prograde skarn stage from andradite core (Grt I) to grossular rim (Grt II) reveal that core sections were formed from a fluid that was generally LREE-rich, with relatively high ∑REE, high LREE/HREE ratios, and weak negative Eu anomalies, whereas rim sections were crystallized from a fluid that was typically HREE-rich, with relatively low ∑REE, low LREE/HREE ratios, and obviously negative Eu anomalies. The garnets of the retrograde skarn stage from Fe3+-rich andradite core (Grt III) to andradite rim (Grt IV) demonstrate that the core sections have a flat trend with high ∑REE and obvious negative Eu anomalies, whereas rim sections were formed from a fluid with relatively low ∑REE, HREE-rich and obviously negative Eu anomalies. The garnets from the prograde skarn stage principally display relatively lower U and higher Y and F concentrations than those from the retrograde skarn stage. Based on optical and textural characteristics, REE patterns, Eu anomalies, and trace element variations in zoned garnets, it can be shown that, during skarn formation, Huanggang hydrothermal fluids shifted from near-neutral pH, oxidizing conditions, and high W/R ratios with relatively low LREE/HREE ratios characteristics to acidic, reducing conditions, and low W/R ratios with relatively high LREE/HREE ratios characteristics. We infer that variations in fluid compositions and physicochemical conditions may exert major control on formation and evolution of garnets and skarn hydrothermal fluids.

Spatial–temporal influence of the Mongol–Okhotsk and Palaeo–Pacific tectonic systems in NE China: Evidence from geochronological and geochemical data of felsic rocks in the east‐Central Jilin Province and southern Great Xing'an Range

The temporal and spatial extents of the Palaeo–Pacific and Mongol–Okhotsk tectonic systems, which together dominated the Mesozoic tectonics of NE China, still remain unclear. Here, we present new zircon U–Pb ages, isotopic analyses and whole‐rock major‐ and trace‐element data for felsic rocks from west and east Songliao Basin to explore the above question. The granites in Shancheng area formed between 176 and 164 Ma and have εHf(t) values of −22.09 to −7.59 with a TDM2 age range of 3622–2336 Ma. The granites are dominated by adakites and I‐type granite whose primary magma is derived from a thickened ancient crust. The rhyolites in Wushijiazi area formed between 151 and 141 Ma and have εHf(t) values of 3.34–12.38 with a TDM2 age range of 517–1328 Ma. They are A‐type granite and have a flat rare‐earth‐element (REE) pattern with obvious negative Eu anomalies, suggesting they were derived from partial melting of lower crustal rocks. The above findings indicate that the middle–late Jurassic granite in the Shancheng area formed in a compression setting related to the subduction of the Palaeo–Pacific Plate beneath the Eurasian continent and the Late Jurassic to early Cretaceous rhyolites in Wushijiazi area formed in an extensional setting related to the collapse of the Mongol–Okhotsk belt. In combination with regional geologic data, we conclude that the Palaeo–Pacific tectonic system mainly affected the east side of Songliao Basin, while the Mongol Okhotsk tectonic system mainly affected the Erguna Block, through the GXAR to the northern margin of the North China Craton (NCC).

Cassiterite geochemistry and U–Pb geochronology of the Shihuiyao Rb–(Nb–Ta–Be–Sn) deposit, Northeast China: Implication for ore‑forming processes and mineral exploration

The Shihuiyao giant Rb deposit in association with Nb–Ta–Be–Sn occurs within the Southern Great Xing’an Range tin belt known for its Sn, W, Cu, Ag, and base-metal deposits. The trace element compositions of four types of cassiterites hosted in the granite, greisen, unidirectional solidification texture (UST) quartz layer, and the hydrothermal quartz vein, respectively (abbreviated as Cst-I to Cst-IV) were measured by laser ablation inductively coupled plasma mass spectrometry and electron probe microanalysis to establish chemical criteria for the application of cassiterite as a useful geological tracer mineral. In situ U–Pb dating of Cst-I, Cst-III, and Cst-IV yielded Tera–Wasserburg intercept ages of 150.3±5.2, 145.8±4.6, and 146.9±3.5 Ma, respectively. These ages are consistent with the previously published monazite and columbite U–Pb ages of 150.2–141.0 Ma for the Shihuiyao ore-bearing granites, indicating a genetic relationship between granite magmatism and Ta–Nb–Sn mineralization. The composition of the studied cassiterites within the whole magmatic–hydrothermal evolution process yields some petrographic dissimilarities and geochemical trends from xenothermal to epithermal environments, which can be used to fingerprint the fluid evolution of the Shihuiyao deposit. For example, the magmatic cassiterites (Cst-I and Cst-II) are strongly enriched in Ta and yield low Nb/Ta ratios compared to the Cst-IV cassiterites from shallow hydrothermal veins. The occurrence of wodginite-group minerals and the highest W concentrations in cassiterite from the UST quartz layers suggests that the main enrichment in W is primarily controlled by magmatic fluid exsolution during the magmatic–hydrothermal transition stage. Additionally, hydrothermal cassiterite is generally lighter in color and characterized by complex internal oscillatory zoning with alternate dark (Cst-IVa) and light (Cst-IVb) bands. Cst-IVa cassiterites have similar W, Nb, and Ta contents but much higher Ti contents compared to Cst-IIIb cassiterites related to primary magmatic fluid, whereas Cst-IVb cassiterites exhibit sharply decreasing W but elevated Ti contents, suggesting pulsed exsolution of magmatic ore‑forming fluids and the involvement of external fluid in a distal open-fluid systems during the late mineralization stage. Therefore, the chemical variations of cassiterites are not only robust tracers pointing to magmatic–hydrothermal centers but also effective in discriminating the primary source of alluvial cassiterite and evaluating its metallogenic potential during a natural heavy mineral survey, supporting the use of cassiterite as an indicator mineral for exploration targeting.

Formation and evolution of multistage hydrothermal fluids in the Baishitouwa quartz–wolframite vein‐type deposit in the southern Great Xing'an Range tungsten belt, NE China: Constraints from individual fluid inclusion LA‐ICP‐MS analysis

Revealing hydrothermal evolution from the early oxide to late carbonate stages for quartz–wolframite vein‐type deposits is essential for understanding the ore‐forming process. In this study, we choose the Baishitouwa tungsten polymetallic deposit located in the southern Great Xing'an Range tungsten belt as a case study, and present detailed deposit geology and in situ fluid inclusion (FI) analyses including microthermometry, laser Raman spectra, and LA‐ICP‐MS microanalysis to address this issue. Four stages of hydrothermal activity were identified: (1) quartz–wolframite (I), (2) quartz–wolframite (II)–pyrite–chalcopyrite, (3) quartz–polymetallic sulphides, and (4) quartz–carbonate. Four types of FIs were recognized: CO2‐rich, CO2‐bearing, liquid‐rich, and brine inclusions. Microthermometric data showed that the homogenization temperatures and salinities from the early to late stages are 380–460°C, 7.4–17.3, and 29.3–43.2 wt% NaCl equiv., 300–390°C and 7.1–17.0 wt% NaCl equiv., 220–320°C and 2.7–8.1 wt% NaCl equiv., and 150–250°C and 0.5–4.8 wt% NaCl equiv., respectively, suggesting a decreasing trend. Geochemically, all stage fluids contained high Rb and Mn concentrations, high Rb/Na, Cs/Na, Li/Na, K/Na, Rb/Sr, low K/Rb, and consistent Cs/Rb and Cs/(Na + K) ratios, indicating that the mineralizing fluids originated from a common source—an underlying, geochemically uniform, and highly fractionated granitic magma. Fluid immiscibility and cooling are the main mechanisms for wolframite precipitation, whereas greisenization is subordinate; the incursion of meteoric water into the hydrothermal system initiated at the sulphide stage, and fluid mixing is the dominant mechanism for sulphide precipitation.