Nanling Range Of South China Research Articles

Reconstruction of the topographic evolution of the Nanling Range in South China and its implications for the East Asian Monsoon evolution

The East Asian monsoon is the largest periodic airflow on Earth and significantly affects the climate of East Asia. However, considerable controversy exists about the onset timing of the East Asian monsoon. As one of the southern barriers blocking the northward movement of the warm and humid airflow, the Nanling Range has likely recorded key topographic information related to the East Asian monsoon onset and development. We used apatite and zircon (UTh)/He data obtained from the Shaoguan–Guidong horizontal cross-section to reconstruct the two-dimensional (2-D) paleotopography of the Nanling Range on a long-term scale. Four vertical profiles in Shulouqiu, Erjian, Sanfenshi, and Leiwangdian were used to constrain the exhumation history of the Nanling Range. The result revealed the following: 1) The drainage divide began to move from south to north at 80 Ma. At 80 Ma, the south segment of the cross-section reached a peak elevation of ∼3.6 km. The asymmetric topography experienced a rapid elevation (and relief) decrease from 80 Ma to 40–30 Ma. The four vertical profiles also experienced increased cooling and high exhumation rates from 100 Ma to 40–30 Ma. 2) The south segment experienced more rapid exhumation than the north segment from 80 Ma to 40–30 Ma. The rapid exhumation of the south segment during the Late Cretaceous–Paleocene is probably related to the activity of the Nanxiong Fault, and the rapid exhumation of the south segment during the Eocene probably results from the onset of the East Asian Monsoon.

Ore-forming process of the W–Sn and Cu skarn mineralization in the Huangshaping deposit (Nanling Range): Constraints from scheelite geochemistry and cassiterite U–Pb geochronology

The Nanling Range in South China is endowed with abundant Jurassic W–Sn and Cu skarn deposits; however, the ore-forming age and process of these deposits lack adequate comparative studies. The Huangshaping deposit in the Nanling Range coincidently develops both W–Sn and Cu skarn mineralization systems, providing a good window to address these issues. Multiple generations of hydrothermal scheelite were identified at Huangshaping, including SchA-1, SchA-2, and SchA-3 in the W–Sn system, and SchB-1, SchB-2, and SchB-3 in the Cu system. Scheelite in the two systems has similar textural evolution, presenting as regular oscillatory zoning (SchA-1, SchB-1), chaotic oscillatory zoning (SchA-2, SchB-2) truncating the regular oscillatory zoning of SchA-1 and SchB-1, respectively, and homogeneous texture (SchA-3, SchB-3) replacing the early scheelite in the respective system. Rare earth elements (REEs) substitute into SchA-1 and SchB-1 mainly via mechanism of 3Ca2+ = 2(REEs, Y)3+ + □Ca, whereas those incorporate into SchA-2, SchA-3, SchB-2, and SchB-3 via mechanisms of Ca2+ + W6+ = (REEs, Y)3+ + Nb5+ and 3Ca2+ = 2(REEs, Y)3+ + □Ca. Continuously decreasing Mo concentrations and increasing Eu anomalies from SchA-1 to SchA-3 and from SchB-1 to SchB-3 reflect progressively decreasing oxygen fugacity (fO2) of hydrothermal fluids in the two systems. The higher Sr concentrations in scheelite from the W–Sn system than that from the Cu system indicate stronger fluid-rock interaction in the W–Sn system, consistent with its more development of skarn. Cassiterite U–Pb geochronology from the W–Sn and Cu systems at Huangshaping yielded lower intercept ages of 159.1 ± 0.6 Ma (MSWD = 1.8, N = 38) and 161.5 ± 0.8 Ma (MSWD = 1.6, N = 25), respectively. Combined with previously published age data from the regional W–Sn and Cu skarn deposits in the Nanling Range, it is inferred that Cu skarn mineralization may have formed earlier than W–Sn with age boundary of ∼ 159 Ma. And the age of ∼ 159 Ma might represent an important shifting time for the Cu mineralization to W–Sn mineralization in the Nanling Range. This study highlights that the textural and geochemical evolution of scheelite can provide important constraints on the ore-forming process in different skarn mineralization systems.

Calcite U-Pb, pyrite Re-Os geochronological and fluid inclusion and H-O isotope studies of the Dafang gold deposit, South China

The Dafang gold deposit is one of the representative gold mineralization in southern Hunan province, South China. The gold orebodies mainly occur in the contact zones between late Jurassic granodiorite porphyry and late Paleozoic limestone as well as the fractures in them. Three primary mineralizing stages have been identified: pyrite + arsenopyrite ± chalcopyrite + quartz (stage I), pyrite + gold + calaverite + polymetallic sulfides + quartz (stage II), and pyrite + arsenopyrite + quartz + calcite (stage III). Pyrite samples separated from stage II yielded a Re-Os isochron age of 149 ± 16 Ma. Calcite samples from stage III demonstrated a U-Pb age of 157.7 ± 6.5 Ma. The above ages are similar to the zircon U-Pb ages of the local granodiorite porphyry although field evidences did not support a genetic link between them. The newly obtained mineralizing ages for Dafang indicate that this deposit is most likely related to deep or nearly late Jurassic intrusions (e.g., the Baoshan porphyry intrusion) and that this gold mineralization is synchronous with the large-scale W-Sn mineralization (160–150 Ma) for the Nanling Range in South China. The measured δDH2O (−103.5 to −81.4 ‰) and calculated δ18OH2O (−4.1 to + 4.9 ‰) isotope compositions for different stage vein quartz suggest that the Dafang ore-forming fluids were initially dominated by magmatic water, and were diluted by meteoric water in the late stage. Fluid inclusion studies indicate that the ore fluids belong to the H2O-NaCl-CO2-CH4 system, which cooled during its evolution (e.g., 230–337 °C, 150–246 °C, and 91–178 °C for stages I to III, respectively) with varied fluid salinity (4.7–9.2, 4.7–23.3, and 2.1–9.9 wt% NaCl eqv. for stages I to III, respectively). Fluid inclusions assemblages with different vapor and liquid phase ratios in a single quartz growth, and their similar homogenization temperatures with varying fluid salinities supported the fact that fluid boiling occurred in ore stage II. Combined with geological occurrences and the results from this study, we propose that gold was mainly transported in a reducing condition, and fluid boiling and host-rock sulfidation are the key factors for gold deposition at Dafang.

Differentiated enrichment of magnetite in the Jurassic W–Sn and Cu skarn deposits in the Nanling Range (South China) and their ore-forming processes: An example from the Huangshaping deposit

Abundant Jurassic magnetite-rich W–Sn and magnetite-poor Cu skarn deposits were discovered in the Nanling Range of South China. However, their ore-forming processes and the mechanism of differentiated magnetite enrichment are still poorly constrained. The Huangshaping represents a typical skarn deposit in the Nanling Range, which developed both W–Mo–Sn and Cu mineralization systems, providing a good window to address this issue. In the Huangshaping W–Mo–Sn system, abundant magnetite was formed in three generations (Mag-1, Mag-2, and Mag-3). Mag-1 shows core (Mag-1c)-mantle (Mag-1 m)-rim (Mag-1r) texture, with abundant nano-inclusions trapped in the oscillatory-zoned Mag-1 m. Porous Mag-2 replaced Mag-1 along sharp and irregular boundaries, and both Mag-1 and Mag-2 were replaced by cassiterite. Mag-3 occurred along with quartz-bismuthinite veins and also replaced Mag-1. Magnetite-4 (Mag-4) has a homogeneous texture and occurs locally in the Huangshaping Cu system. The mineral assemblage, texture, and geochemistry suggest a hydrothermal origin for all these magnetite types and possible magmatic-hydrothermal pulses in the W-Mo-Sn system. The first magmatic-hydrothermal pulse was likely associated with granite porphyry and formed Mag-1 in a closed system with increasing oxygen fugacity (fO2) and decreasing concentrations of trace elements. The abundant nano-inclusions in Mag-1 m suggest probable local supersaturation of trace elements in the magnetite-fluid interface. The irregular contact, porosities, and lower trace element concentrations (e.g., Mg, Al, Si, Ca, and Mn) of Mag-2 reveal that it may have formed via the dissolution and reprecipitation process (DRP) of Mag-1. This process was possibly controlled by decreasing fO2. The second magmatic-hydrothermal pulse derived from the granite porphyry may have formed Mag-3, evidenced by the increasing temperature, decreasing fO2, and high trace element concentrations (e.g., Mg, Al, Si, Ca, and Mn). In the Cu system, the quartz porphyry-derived ore fluid may have formed Mag-4 under lower temperature and fO2 than in the W–Mo–Sn system. Besides, we suggested that the paucity of magnetite in these Jurassic Cu skarn deposits of the Nanling Range was likely caused by the low Fe concentration in the ore-related magma, genetically associated with the amphibole fractionation during the magma formation. This may respond to the extensional formation environment of Jurassic Cu and W–Sn skarn deposits in the Nanling Range, caused by the asthenosphere upwelling linked to the Paleo-Pacific subduction.

Mineral prospectivity mapping based on wavelet neural network and Monte Carlo simulations in the Nanling W-Sn metallogenic province

The Nanling Range in South China is endowed with abundant W-Sn and other important rare metal resources associated with granitic intrusions, but the rate of new major mineral discoveries has been drastically diminished over the last decades. Data-driven mineral prospectivity mapping (MPM) using machine learning is emerging as a powerful tool in support of mineral exploration targeting at regional or camp scale. However, MPM based on supervised learning faces some general problems, notably including subtle information obscured in exploration data and imbalanced training samples. In this paper, we proposed a novel ensemble scheme for MPM using wavelet neural network (WNN) and Monte Carlo simulation (MCs) to address the forementioned issues. Specifically, the purpose of using WNN based on multiscale wavelet analysis is to capture weak or hidden (geophysical and geochemical) information caused by concealed ore deposits, while an undersampling MCs (UMCs) algorithm is employed to assess uncertainties caused by data imbalance and lessen its impact on MPM. Subtle (weak and mixing) information related to concealed mineralization, including geophysical and geochemical anomalies, were extracted using wavelet analysis at first, and then a dozen of predictive evidences was integrated based on WNN using UMCs for producing a W-Sn perspectivity map. The results suggest that WNN has a higher prediction accuracy (∼90%) in comparison to the artificial neural network (ANN) (∼85%). Moreover, the improved AUC value (∼0.9) of WNN based on UMCs compared to the classic ANN (∼0.82) and WNN (∼0.85) suggests that the proposed ensemble algorithm improves the geological generalization of machine learning. Revisiting WNN predictions by uncertainties produced more sharply focused exploration targets of W-Sn deposits (covering ∼5% of the study area). The resulting predictive map provides important clues of W-Sn deposit occurrences which could guide and stimulate future mineral exploration in the Nanling Range.

Cretaceous granitic magmatism and mineralization in the Shanhu W-Sn ore deposit in the Nanling Range in South China

Abundant Jurassic-Cretaceous W-Sn ore deposits are distributed in the Nanling Range in South China. However, the exact mineralization ages, relationships between mineralization and granitic rocks, and tectonic settings of these deposits remain controversial. As a giant quartz vein-type W-Sn deposit hosted in Devonian sedimentary strata, the Shanhu orebodies are featured by located about 4 km far away from the Yantianling muscovite granite. Zircon U-Pb dating of the Yantianling granite yielded ages of 101.0 ± 1.5 Ma and 100.4 ± 1.1 Ma, consistent with cassiterite U-Pb ages of quartz vein ores (100.2 ± 1.0 Ma and 100.5 ± 1.1 Ma), indicating a close genetic relationship between the granitic magmatism and quartz vein-type W-Sn mineralization. The Yantianling muscovite granite is characterized by highly silicious (72.01–74.62 wt%), high alkali (Na2O + K2O = 5.32–7.89 wt%) and strongly peraluminous (A/CNK = 1.11–1.81). The granite is enriched in Rb, Ta, Nd and U, and depleted in Sr, Ti and P. It displays right-declining chondrite-normalized REE patterns with strongly negative Eu anomalies, and has low Nb/Ta and Zr/Hf ratios, indicating that the granite experienced strong magmatic differentiation. The Yantianling granite has low whole-rock εNd(t) values (−9.5 to −9.3), zircon εHf(t) values (−12.7 to −7.8) and Paleoproterozoic model ages. The granite belongs to S-type and was derived from partial melting of meta-sedimentary crust. The low Ce4+/Ce3+ ratios (averaging 47) of zircon from the Yantianling granite indicated low oxygen fugacity, similar to other W-bearing granites in South China. This study indicated that Cretaceous granitic magmatism in the Nanling Range also has strong W-Sn mineralization potential. Combined with previous studies on coeval magmatic rocks and tectonic activities, we propose that the Yantianling S-type granite and associated W-Sn mineralization in the Nanling Range were formed during the regional lithospheric extensional environment.

Petrogenesis of Late Jurassic Pb–Zn mineralized high δ18O granodiorites in the western Nanling Range, South China

Amphibole-bearing granites are commonly considered to be I-type granites, derived by partial melting of igneous rocks. However, the contribution of sedimentary rocks to the source of such rocks is difficult to identify and remains debated. Here, we present a study of amphibole-bearing Pb-Zn mineralized granodiorites in the western Nanling Range of South China. LA–ICP–MS zircon U–Pb ages show that these granodiorites were generated during the Late Jurassic (ca. 161 Ma). They have variable SiO2 contents of 61.8–70.7 wt% and have high-K or shoshonitic characteristics, with varied Mg# (0.28–0.54). These granodiorites are enriched in Th and U, and depleted in Nb, Ta and Ti. They display enriched light rare earth element (LREE) and flat heavy rare earth element (HREE) patterns, with slightly negative to negligible Eu anomalies (δEu = 0.74–0.95). Given their high zircon δ18O values (8.8‰–11.9‰), as well as negative εNd(t) (−7.5 to −5.1) and zircon εHf(t) (−13.9 to −7.5) values, we suggest that these Pb-Zn mineralized granodiorites in the western Nanling Range were derived mainly by partial melting of Middle Neoproterozoic mafic volcaniclastic rocks from the Nanhua rift basin, South China, in the lower crust. This study provides an important insight into the genesis of amphibole-bearing granites. We suggest that the partial melting of crustal metasedimentary and metaigneous rocks is an important mechanism for the Mesozoic crustal reworking of South China, and granodiorites generated by such a mechanism should also favor Pb–Zn mineralization.

Magmatic‐Hydrothermal Mineralization Sequence in Xinlu Ore Field, Guangxi, South China: Constraints from Zircon U‐Pb, Molybdenite Re‐Os, and Muscovite Ar‐Ar Dating

AbstractThe Xinlu Sn‐polymetallic ore field is located in the western Nanling Polymetallic Belt in northeastern Guangxi, South China, where a number of typical skarn‐, hydrothermal vein‐type tin deposits have developed. There are two types of Sn deposits: skarn‐type and sulfide‐quartz vein‐type. The tin mineralizations mainly occur on the south side of the Guposhan granitic complex pluton and within its outer contact zone. To constrain the Sn mineralization age and further understand its genetic links to the Guposhan granitic complex, a series of geochronological works has been conducted at the Liuheao deposit of the ore field using high‐precision zircon SHRIMP U‐Pb, molybdenite Re‐Os, and muscovite Ar‐Ar dating methods. The results show that the biotite‐monzogranite, which is part of the Xinlu intrusive unit of the Guposhan complex pluton, has a SHRIMP U‐Pb zircon age of 161.0 ± 1.5 Ma. The skarn‐type ore has a 40Ar‐39Ar muscovite plateau age of 160 ± 2 Ma (same as its isochron age), and the sulfide‐quartz vein‐type ore yields an Re‐Os molybdenite isochron age of 154.4 ± 3.5 Ma. The magmatic‐hydrothermal geochronological sequence demonstrated that the hydrothermal mineralization took place immediately following the emplacement of the monzogranite, with the skarn metasomatic mineralization stage predating the sulfide mineralization stage. Geochronologically, we have compared this ore field with 26 typical Sn deposits distributed along the Nanling Polymetallic Belt, leading to the suggestion of the magmatic‐metallogenic processes in the Xinlu ore field (ca. 161–154 Ma) as a component of the Early Yanshanian large‐scale Sn‐polymetallic mineralization event (peaked at 160–150 Ma) in the Nanling Range of South China. Petrogenesis of Sn‐producing granite and Sn‐polymetallic mineralization were probably caused by crust–mantle interaction as a result of significant lithospheric extension and thinning in South China in the Late Jurassic.

Metal source and wolframite precipitation process at the Xihuashan tungsten deposit, South China: Insights from mineralogy, fluid inclusion and stable isotope

The Xihuashan tungsten deposit, hosted in the late Jurassic granitic pluton in the Nanling Range of South China, has a total resource of about 81,300 tonnes of WO3 with an average ore grade of 1.08% WO3. Wolframite is the dominant ore mineral and intergrown with quartz in the main mineralization stage. Ore-forming fluids trapped in wolframite have δD and δ18O values from −82‰ to −64‰ and 7.4‰ to 8.8‰, respectively. Those in quartz have similar δD (−72‰ to −58‰) and δ18O (6.8‰ to 8.0‰) values, indicative of a magmatic fluids simultaneously trapped by quartz and wolframite. LA-ICP-MS analyses for individual fluid inclusion show that this mineralizing fluid contains measurable Li, Rb, Cs, K, Na, Ti, Cu, Zn, As and W (1–125 ppm with average of 19 ppm) while depleted in Fe and Mn. The wolframite from the Xihuashan tungsten deposit contains high FeO (10.9–17.7 wt%) and MnO (5.9–12.7 wt%) contents with Fe/(Fe + Mn) atomic ratio of 0.46 to 0.75, thus requires the availability of external Fe and Mn. We detect that the Fe and Mn contents in mica from the greisen are remarkably lower than primary mica from granite. Some magmatic micas were observed in greisen and were subjected to hydrothermal alteration. Compared to the core, the rim of these micas depleted in Fe, Mn, F, and Na. The siderite and pyrophanite are formed along cleavage planes of altered magmatic mica that are evidence to be due to Fe and Mn release during granite alteration. Thus, we demonstrate quantitatively that magmatic fluids at Xihuashan provide W in solution, whereas the hosted granite alteration contributes Fe and Mn to precipitate wolframite. It is also supported by wolframites have trace and rare earth elements characteristics similar to those of granite and some characteristics similar to the greisen. Therefore, the ore-forming fluids has components derived from the last highly evolved residual granitic melt and components acquired by releasing through the hosted granite alteration. Fluid-rock interaction exert a principle control on wolframite precipitation. Based on mineralogy, fluid inclusion and stable isotope, we proposed three-stage process to illustrate the genetic link between tungsten mineralization and granite.

Metallogenic controls on the granite-related W–Sn deposits in the Hunan–Jiangxi region, China: evidence from zircon trace element geochemistry

The Nanling Range in South China is well known for its rich granite-related W–Sn deposits. To elucidate the controls of different granite-related W–Sn metallogenesis in the region, we chose five representative ore-related granites (Yanbei, Mikengshan, Tieshanlong, Qianlishan, and Yaogangxian intrusions) in the Hunan–Jiangxi region, and studied their magmatic zircon ages and trace element geochemistry. Our new zircon data showed the differences in ages, temperatures and oxygen fugacity of the ore-forming magmas. Zircon U–Pb ages of the Yanbei and Mikengshan intrusions are characterized by 142.4 ± 2.4 and 143.0 ± 2.3 Ma, respectively, whereas the Tieshanlong and Qianlishan intrusions are 159.5 ± 2.3 and 153.2 ± 3.3 Ma, respectively. The Sn-related intrusions were younger than the W-related intrusions. The Ti-in-zircon thermometry showed that there was no systematic difference between the Sn-related Yanbei (680–744 °C) and Mikengshan (697–763 °C) intrusions and the W-related Tieshanlong (730–800 °C), Qianlishan (690–755 °C) and Yaogangxian (686–751 °C) intrusions. However, the zircon Ce4+/Ce3+ ratios of the Yanbei (averaged at 18.3) and Mikengshan (averaged at 18.8) intrusions are lower than those of the Tieshanlong (averaged at 36.9), Qianlishan (averaged at 38.4) and Yaogangxian (averaged at 37) intrusions, indicating that the Sn-related granitic magmas might have lower oxygen fugacities than those of the W-related. This can be explained by that, in more reduced magmas, Sn is more soluble than W and thus is more enriched in the residual melt to form Sn mineralization. The difference in source materials between the Sn-related and the W-related granites seems to have contributed to the different redox conditions of the melts.

Genesis and hydrothermal evolution of the Tiantangshan tin‐polymetallic deposit, south‐eastern Nanling Range, South China

The Tiantangshan tin‐polymetallic deposit, located in the Nanling Range of South China, is a medium‐sized polymetallic deposit found in the region in recent years. The deposit is hosted within volcanic rocks, and the orebodies occur in the cupola and outer contact zone of the concealed quartz porphyry, as well as the altered fracture zone of the volcanic rocks close to the intrusive contact. In light of field evidence and petrographic observations, the mineralization can be divided into four stages: greisenization stage (stage I), quartz–cassiterite–wolframite stage (stage II), quartz–fluorite–cassiterite–sulfides stage (stage III), and post‐ore stage (stage IV). Three types of fluid inclusions are present in the hydrothermal topaz, quartz, and fluorite, including H2O‐rich (W‐type, WL‐ and WV‐ subtypes), CO2‐bearing (C‐type), and solid‐bearing (S‐type). Four stages of fluid evolution are observed by detailed fluid inclusion studies: (a) Stage I fluids are trapped under two‐phase immiscible condition, as evidenced by the coexistence of primary aqueous (W‐type) and aqueous‐carbonic (C‐type) fluid inclusions preserved in topaz and quartz; the fluid inclusions display homogenization temperatures of 378–448°C and salinities of 6.0–17.5 wt.% NaCl equiv. (b) Similarly, fluid inclusions in stage II quartz also record immiscible condition, as identified by the coexistence of W‐type and C‐type fluid inclusions with lower homogenization temperatures (308–400°C) and salinities (1.8–14.5 wt.% NaCl equiv.). (c) Stage III fluids are characterized by the coexistence of widespread WL‐subtype, minor S‐type, and rare WV‐subtype fluid inclusions, with similar homogenization temperatures (230–369°C) but contrasting salinities (0.5–39.5 wt.% NaCl equiv.), which indicates an episode of fluid boiling occurred in this stage. (d) Stage IV marks the end of the hydrothermal system characterized by the lower temperatures (175–298°C) and salinities (0.2–3.9 wt.% NaCl equiv.) W‐type fluid inclusions trapped. Microthermometry and H–O isotopes indicate that the early ore‐forming fluids (in stage I) exsolved from the granitic magma and underwent progressive mixing with meteoric water during subsequent ore‐forming process (in stages III and IV). The water–CO2 fluid immiscibility is the main mechanism of cassiterite and wolframite precipitation, while fluid boiling and mixing are probably thought to be the dominant mechanisms for the deposition of sulfide at Tiantangshan. 40Ar/39Ar dating of hydrothermal biotite intergrown with cassiterite shows that tin‐polymetallic mineralization occurred at ~133 Ma which is coeval with the hidden intrusions. Taken together, these lines of evidence confirm that the Tiantangshan deposit is a magmatic hydrothermal greisen–quartz–vein type tin‐polymetallic deposit that formed in the lithospheric extension and thinning setting associated with the postsubduction Paleo‐Pacific Plate tectonic regime that influenced South China.

Reworked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intrusion, Nanling Range, South China

Microgranular enclaves, which can provide important petrogenetic indications for the host granitoids, are commonly observed in the Middle-Late Jurassic Cu-Pb-Zn-bearing granodiorites in the Nanling Range of South China. The origin of these Cu-Pb-Zn-bearing granodiorites is still controversial, with two different hypotheses: crust-mantle mixing and partial melting of the mafic lower crust, primarily based on geochemistry and geochronology. Detailed petrographic and mineralogical studies have been carried out on the Tongshanling granodiorite and its microgranular enclaves to provide new textural and compositional constraints on the petrogenesis. The microgranular enclaves have dioritic compositions with a mineralogy dominated by plagioclase, amphibole, and biotite. Abundant residual materials, such as mafic mineral clots, inherited and metamorphic zircon, and Ca-rich core plagioclase, occur in the enclaves and are in favor of a restite origin. The amphibole-rich clots are considered as vestiges of residual pyroxene-rich precursors from the source. Three different types of amphibole, i.e., magmatic, metamorphic, and magma reworked metamorphic amphibole, have been recognized in the granodiorite and its enclaves. The magmatic amphibole occurs as enclosed and idiomorphic isolated crystals in the granodiorite with Al and Si contents of 1.34–2.12 apfu (atoms per formula unit) and 6.25–6.88 apfu, respectively, and a ΣREE content of 307–764 ppm. The metamorphic amphibole, with a granoblastic triple-junction texture, occurs as aggregated crystals dominantly in the enclaves and a few in the granodiorite. It has actinolitic compositions (Al: 0.31–0.81 apfu, Si: 7.33–7.72 apfu) and distinctly lower contents of incompatible elements (ΣREE: 99–146 ppm). The magma reworked amphibole has intermediate compositions (Al: 0.81–1.59 apfu, Si: 6.71–7.35 apfu, ΣREE: 317–549 ppm) between the magmatic and metamorphic amphibole. The zonal amphibole-rich clots exhibit increasing Al and decreasing Si contents from interior amphibole to exterior amphibole and also from core to rim in amphibole grains, and the outer parts of enclave magmatic zircon have higher ThO2 + UO2 contents and lower Zr/Hf ratios than the inner parts, showing the process of magma reworking of the restite enclaves. Based on the textural and compositional evidence, these microgranular enclaves are thought to be reworked restite enclaves. This is also supported by thermobarometric calculation. A model illustrating the formation process of reworked restite enclave has been proposed. Combined with previous experimental studies of partial melting, the Tongshanling granodiorite is deduced to be derived from dehydration melting of amphibolite in the mafic lower crust. The fertile amphibolitic source is beneficial to the formation of Cu-Pb-Zn-bearing granodiorites in the Nanling Range.

Zircon geochronology and geochemistry of the Xianghualing A-type granitic rocks: Insights into multi-stage Sn-polymetallic mineralization in South China

Highly evolved Sn-polymetallic mineralization-related granites are intensively developed in the Nanling Range of South China. In this study, two types of granitic rocks (albite granite and greisenized granite) from the Laiziling pluton in the Xianghualing area were studied to elucidate magma evolution and the genesis of mineralization. The A-type Xianghualing granitic rocks are characterized by high SiO2 (69.16–85.04%), Rb (759–2110 ppm), Ta (17.2–50.8 ppm), Nd (2.8–82.4 ppm) and 87Sr/86Sr (0.907275–4.181262) and low MgO (0.01–0.98%), TiO2 (0.01–0.03%), Sr (1.4–70.2 ppm), Ba (1.4–132.5 ppm), Eu (0.03–0.21 ppm) and 143Nd/144Nd (0.512283–0.512326). The whole-rock εNd(t) values range from −6.3 to −6.0, with T2DM ages of 1426–1454 Ma. The zircon εHf(t) values mostly range from −10 to −5, with dominant TDMC values of 1400–1800 Ma. This suggests that the Xianghualing granitic rocks were derived from partial melting of Mesoproterozoic basement rocks in the Cathaysian Block, in a lithospheric extension setting. Zircon U–Pb dating yielded five age clusters: Proterozoic (>900 Ma, n = 9), Silurian (~430 Ma, n = 4), Triassic (~220 Ma, n = 16), Jurassic (~150 Ma, n = 62) and Cretaceous (~80 Ma, n = 28). Zircon internal textures, trace element contents and Hf isotopic compositions indicate that they formed from a range of sources including residual zircons from the magma source region, detrital zircons from local sediments, zircons captured from pre-existing magmatic rocks with obvious mantle signatures, magmatic and fluid-altered zircons, and late stage hydrothermal zircons. This suggests significant fractional crystallization, weak wall-rock assimilation/contamination and intense fluid differentiation/metasomatism during the genesis of the Xianghualing granitic rocks. M-type REE tetrad effects are seen not only in bulk rock compositions, but also in individual zircon grains, indicating that highly fractionated and reduced F-rich fluids played an important role in the formation of Sn-polymetallic mineralization. Guided by the major Mesozoic W–Sn ore-forming events occurring in the Cathaysian Block of South China, a multi-stage genetic model is proposed for the Xianghualing granitic-minerogenic system: initial enrichment of W–Sn in the Triassic (~220 Ma), dominant Sn-polymetallic metal precipitation in the Jurassic (~150 Ma), and superimposed mineralization in the Cretaceous (~80 Ma).

Jurassic magmatism related Pb-Zn-W-Mo polymetallic mineralization in the central Nanling Range, South China: Geochronologic, geochemical, and isotopic evidence from the Huangshaping deposit

The Nanling Range in South China is characterized by extensive Mesozoic magmatism and coeval nonferrous and rare metal mineralization. Huangshaping is a world-class Pb-Zn-W-Mo polymetallic skarn deposit in the central Nanling Range. Magmatic rocks occurring in this ore district include quartz porphyry, granite porphyry, granophyre, dacite porphyry, and aplite, with only the first three granitoids genetically associated with polymetallic mineralization. Most of the orebodies are constrained within the contact zones as skarn and veins between these granitic stocks and the carbonate wall rocks.Since the age of the quartz porphyry is still controversial, and studies of the dacite porphyry and aplite are absent, we focus on these magmatic rocks first. LA-ICP-MS zircon U-Pb dating suggests that the crystallization ages of the quartz porphyry, dacite porphyry, and aplite are 154.3±1.9Ma, 158.1±0.8Ma, and 148.4±3.4Ma, respectively. Combined with previously published age data, we infer the evolutionary sequence of magmatic rocks should be dacite porphyry→quartz porphyry→granite porphyry (granophyre)→aplite. The quartz porphyry, dacite porphyry, and aplite yield high contents of high field strength elements (Zr+Nb+Ce+Y=255–440ppm), high ratios of 10,000×Ga/Al (2.6–3.2), and prominent depletions in Ba, Sr, Eu, P, and Ti, indicating their crustal affinities to A-type granites. They have negative εNd(t) values (−9.4 to −7.0) and high initial Pb isotopic ratios (206Pb/204Pbi=18.307–18.644, 207Pb/204Pbi=15.689–15.742, 208Pb/204Pbi=38.589–38.986), suggesting that they were probably derived by partial melting of ancient granulitic crustal materials.The sulfide minerals exhibit a wide range of δ34SV-CDT values from −22.6 to 24.2‰, with 206Pb/204Pb of 17.669–19.708, 207Pb/204Pb of 15.492–15.714, and 208Pb/204Pb of 37.880–39.789, indicating that sulfur, lead, and other associated metals were derived from a mixture of magmatic components and the Carboniferous wall rocks. Fluid inclusions in pyrrhotite, sphalerite, and marmatite samples have 3He/4He ratios of 0.12 to 1.53 Ra, with calculated mantle helium proportions of 1.3 to 18.9%, indicating a predominantly crustal origin for the ore fluids, with minor inputs from the mantle. The Huangshaping deposit is a typical example of the genetic relationship both spatially and temporally between Jurassic magmatism and polymetallic metallogeny in the Nanling Range.

Tracking magmatic and hydrothermal Nb–Ta–W–Sn fractionation using mineral textures and composition: A case study from the late Cretaceous Jiepailing ore district in the Nanling Range in South China

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~91–89±1Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~30μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~10μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.

Petrogenesis of Triassic granites from the Nanling Range in South China: Implications for geochemical diversity in granites

Abstract A combined study of whole-rock major-trace elements and Sr–Nd isotopes, zircon U–Pb ages, Hf and O isotopes as well as biotite geochemistry was carried out for Triassic granite intrusions from the Nanling Range in South China. The results provide insights into the effects of source composition and melting conditions on the geochemical diversity of granites. The granites of interest are peraluminous, and contain primary muscovite and tourmaline. They are characterized by high zircon δ18O values of > 9.0‰, high initial 87Sr/86Sr values of ~ 0.7200, and homogeneous eNd(t) values of − 11.3 to − 9.8, as well as variable zircon eHf(t) values of − 12.2 to − 5.8. Biotite geochemistry is similar to that of common peraluminous granites. An integrated interpretation of these petrological, mineralogical and geochemical data indicates that these granites were derived from partial melting of metasedimentary rocks under variable physicochemical conditions. The differences in whole-rock and biotite geochemistry between the intrusions are ascribed to the variable effects of source heterogeneity and melting temperature. The Luxi intrusion exhibits higher contents of MgO, FeOT, TiO2 and CaO than common melts derived from metasedimentary rocks, tight variations in major-trace elements and homogeneous Sr–Nd isotopic compositions, and homogeneous biotite composition with high Mg# [= Mg / (Mg + Fe) in molar] and lower whole-rock A/CNK values [= Al2O3 / (CaO + Na2O + K2O) in molar]. These can be explained by originating from a relatively mafic metasedimentary source. On the other hand, the geochemical diversity of granites can be caused by the difference in melting temperature in addition to the source heterogeneity. This is suggested by the Xiazhuang and Fucheng intrusions which exhibit similar range of SiO2. Nevertheless, the Fucheng intrusion is ferroan, and high in TiO2, (Na2O + K2O)/CaO, TiO2/MgO, Ga/Al and Zr + Nb + Ce + Y, but low in CaO, MgO and Mg#. Most of its major elements and their ratios are similar to those of A-type granites that were generated from F-rich rocks at high temperatures, consistent with the enrichment of Fe and F in its biotite. Thus, partial melting of a metasedimentary restite at reduced conditions after previous melt extraction is suggested to produce the geochemical feature of A-type granites in the Fucheng intrusion. In contrast, partial melting of fertile metasedimentary rocks would produce normal S-type granites like the Xiazhuang intrusion, with its geochemical variations ascrible to source heterogeneity and differential melting. Therefore, the geochemical composition of granites is primarily dictated by the composition of source rocks in addition to the physicochemical conditions of partial melting.

On the genetic classification and tectonic implications of the Early Yanshanian granitoids in the Nanling Range, South China

Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range of South China, and are associated with numerous non-ferrous and rare metal mineral deposits. These granitoids consist mainly of slightly peraluminous biotite monzogranites and K-feldspar granites that are closely associated in time and space with subordinate amphibole-bearing granites and muscovite-and garnet-bearing granites. In most previous studies, the biotite-bearing granites were classified as crustal transformation-type (corresponding to the S-type) granites which were interpreted to be derived from the regional Paleoproterozoic meta-sedimentary rocks. In this paper, we re-analyze the geochemical characteristics of a number of representative Early Yanshanian Nanling granitoids. There exists a clear negative correlation between SiO2 and P2O5 for the studied granitoids. The Early Yanshanian Nanling granitoid suites (including amphibole-bearing granodiorites→biotite monzogranites→K-feldspar granites→two-mica (muscovite) granites) are metaluminous to slightly peraluminous I-type or fractionated I-type granites. They were derived predominantly from Proterozoic igneous protoliths. The juvenile crust and/or newly mantle-derived materials might also have been involved in some of these granites. In addition, the I-and fractionated I-type granites are closely associated in time and space with minor amount of A-type felsic and mafic volcanic and intrusive rocks as well as alkaline rocks. All these rocks constitute a typical assemblage of anorogenic, intraplate magmatism, suggesting a dominant lithospheric extensional regime for the Nanling Range and neighboring region during the Early Yanshanian period.

New patent

The Jiepailing mining district in the Nanling range in South China is well-known for its granite-related Sn–Be–F-mineralization. Recently, drill holes have exposed an Nb–Ta–W–Sn mineralized granitic porphyry and topaz-bearing granite–greisen at depth, which we have studied here, using mineral (columbite, rutile, wolframite, cassiterite, zircon, and mica) major- and trace-element compositional data, mineral textures, and zircon and columbite U–Pb geochronology. Our age data shows that the porphyry and the granite and their mineralization formed at ~ 91–89 ± 1 Ma in the late-Cretaceous, and thus subsequent to the main ore-forming events of the region. Continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation. We propose that: (1) subhedral–euhedral, low-Ta columbite crystallized from melt; (2) euhedral–subhedral rutile and wolframite and subhedral and subhedral cassiterite up to ~ 30 μm in size formed at the magmatic–hydrothermal transition of the system; and (3) high-Ta columbite and subhedral cassiterite up to ~ 10 μm in size formed from subsolidus hydrothermal fluids. In combination with the Nb, Ta, W, and Sn compositions of zircon and mica, their textures and compositional variation allow us to track the magmatic to hydrothermal rare-metal fractionation (concentration, mobilization, and deposition) of the system in detail, despite our limited access to it through only two exploration drill cores. Using the Nb, Ta, W, and Sn concentrations in zircon (refractory, early-crystallized) and in micas (late equilibrated), respectively, was particularly useful for tracing the partial loss of Sn and W ore components from the intrusion, and to constrain the information which is crucial for any rigorous ore exploration.

The Ordovician Palaeogeography of Eastern Asia

Following introductory notes (1), the Ordovician formations in the Hwangho basin and Okcheon trough (2-3), the Ordovician trilobite, cephalopod and graptolite facies of the Yangtze basin and the Tsinling axis (4), the Lungshan group in Kwantung and Kwansi and the Ordovician formations in Indochina and the Yunnan-Malayan geosyncline (4-6) are successively described. The distribution of Ordovician cephalopod faunas and the areal variation of average thickness of the Ordovician system in Eastern Asia are shown in Figures 1-3. As in the Cambrian period, the Tienshan and Himalayan geosynclines were the main routes of migration through Eurasia (7).Finally, it is concluded that the Tomkolian and Wanwanian series designate the base of the Ordovician system in Eastern Asia. Like the Ozarkian system the Cambrovian pulsation cannot be maintained in the Palaeozoic stratigraphy of Eastern Asia. Judging from the variation of facies and thickness, the differential movements among tectonic elements in Eastern Asia became reduced in strength from Sinian to Korean (Chosen) and from Cambrian to Ordovician (8).In view of the fact that the Chosen group with the Toufangian series at the top is generally overlain by the Heian (Pyeongan) group para-unconformably in the grand Hwangho basin, the epi-Toufangian Middle Palaeozoic interval was the most stable land period for the part of Asia where little influence was recognizable either of the Caledonian or Variscan orogeny. The Kwansi disturbance or the late Silurian orogeny has, however, occurred in the Tsinling range in Central China and in the Nanling range in South China, although the Triassic Akiyoshi orogeny was stronger in many places of China, Korea and Southeast Asia.