Search

The Xihuashan tungsten ore deposit in the central Nanling region, South China is a vein-type hydrothermal deposit associated with the Late Jurassic granitoids that were previously thought to be the products of crustal anatexis alone. In this study, we use helium (He) and argon (Ar) isotopes of fluid inclusions entrapped in pyrite and arsenopyrite to determine the origin of the ore-forming fluids. The 3He/4He ratios of the crushed fluid inclusions vary from 0.15 to 1.16 Ra, with a mean of 0.72 Ra (Ra, the atmospheric 3He/4He ratio of 1.4 × 10−6), indicating the presence of mantle-derived noble gasses in the fluids. The amounts of the mantle-derived noble gasses are estimated to be between ∼2 and 17%. The 40Ar/36Ar ratios of the fluid inclusions vary from 306 to 1023, with an average of 440. These ratios are significantly higher than the average crustal value, indicating the presence of air-saturated water in the volatiles released from the mineral separates. The results from this study indicate that the associated, coeval granitoids, which is believed to provide the ore-forming fluids during magma evolution, are not the products of pure crustal melts. Mantle-derived volatiles and heat was also involved in the genesis of the host granite pluton.

The Shimensi deposit is a newly discovered, super-large tungsten (W) polymetallic deposit in northwestern Jiangxi Province, South China. In this paper, we reported new zircon U–Pb ages for the ore-bearing porphyritic biotite granite (151.3 ± 2.8 Ma) and fine-grained granite (150.1 ± 1.2 Ma and 150.7 ± 2.4 Ma), which represent the oldest Mesozoic granitic magmatism reported at Shimensi. Our ore-bearing granite porphyry ages (142.7 ± 2.3 Ma and 143.3 ± 1.5 Ma) have better constrained the timing of the Jurassic-Early Cretaceous ore-forming magmatism. Geochemically, the Shimensi granitoids are strongly peraluminous, with high contents of SiO2 (70.7–78.7 wt%) and K2O (>4.0 wt%), P2O5, Rb, Ta and U, and low contents of Ti, Sr, Ba and HREEs. The rocks also show positive P2O5 vs. SiO2 correlation, suggesting a highly-fractionated S-type affinity. Different from most W-bearing granites in the Jiangxi region, the calculated zircon eHf(t) (−10.0 to −2.4; two-stage model ages: 1350–1824 Ma) and δ18Ozircon values (+6.40 to +8.87‰) of the Shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks, probably with combined contributions from the Neoproterozoic Shuangqiaoshan Group metamorphic rocks and Jiuling granodiorite. The calculated zircon Eu/Eu∗ (0.05–0.58; mean = 0.20) and Ce4+/Ce3+ (3.83–96.49; mean = 20.99) ratios of the granites indicate very low oxygen fugacity (fO2) for the ore-forming magmas, a highly favorable factor for W mineralization. Potentially W and Cu-rich source rocks, and highly-fractionated and reducing granitic magmas, were important factors that triggered super-large W mineralization at Shimensi.

The Nanling Range, South China, was world-famous for hosting abundant granitoid-related copper-lead-zinc (Cu-Pb-Zn) polymetallic ore deposits and quartz vein-type wolframite (W) ore deposits, both of which have roughly similar formation ages predominately between 150 and 160 Ma with a peak of ca. 156 Ma. In this study, accessory minerals from typical Cu-Pb-Zn-bearing and W-bearing granitic rocks are compared in terms of elemental and isotopic compositions. Apatite from W-bearing granites in the Xihuashan pluton has lower eNd(t) value (−11.9 to −8.6) than that from Cu-Pb-Zn-bearing granitic rocks in Shuikoushan with eNd(t) value of −8.7 to −4.2 and initial 87Sr/86Sr ratio of 0.7097–0.7109. Zircon grains in Xihuashan, yielded eHf(t) value from −14.9 to −11.4, δ18O value from 8.6‰ to 10.4‰, and highly variable and negative δ7Li value (−45.8‰ to −3.8‰), whereas those in Shuikoushan have relatively higher eHf(t) value (−10.6 to −8.1), lower δ18O value (8.4‰–9.7‰), and highly variable δ7Li values from −12.7‰ to +17.6‰. In situ Hf-O-Li isotopic compositions of zircon and Sr-Nd isotopes of apatite, suggesting that the Shuikoushan granitic pluton was likely generated from dehydration melting of amphibolite from a metal-fertile mafic source in the middle-to-lower crust, whereas the Xihuashan granitic pluton could be derived from partial melting of metapelite with minor amphibolite in the middle to upper crust. The geochemical records in accessory minerals fingerprint that the Shuikoushan granitic magma was characterized by high Cl content (0.11–1.44 wt%) and logfo2 value (>ΔFMQ+1), whereas the Xihuashan granitic magma have elevated F (3.51–4.80 wt%) and Li (3.49–42.4 ppm) contents with low logfo2 value (

The Shuikoushan ore district, located in southern Hunan Province, South China, contains Pb–Zn–Au mineralization hosted in the Devonian to Triassic strata and Mesozoic granodiorite intrusions. Ore minerals are mainly pyrite, sphalerite, galena and minor molybdenite. Molybdenite, usually intergrown with pyrite, formed during Pb–Zn hydrothermal mineralization. In order to determine the precise age of Pb–Zn mineralization and further understand the relationship between magma emplacement and hydrothermal mineralization in the ore district, molybdenite Re–Os dating and zircon SIMS U–Pb dating were undertaken. The zircon U–Pb dating reveals that the granodiorite intrusion was emplaced at 158.8 ± 1.8 Ma (MSWD = 0.40). Re–Os isotopic age of seven molybdenite samples yields model ages ranging from 157.5 ± 2.5 Ma to 161.0 ± 2.4 Ma, and gives a well-defined 187Re–187Os isochron age of 157.8 ± 1.4 Ma (2σ, MSWD = 1.3), indicating the timing of Pb–Zn mineralization in the Shuikoushan ore district at about 158 Ma. This date coincides well with the zircon SIMS U–Pb age of the granodiorite, revealing a genetic association between the Pb–Zn mineralization and the granitic magmatism. Combined with geochronological data published for other Pb–Zn–(Cu) deposits in southern Hunan, it can be concluded that the granodiorite-related Pb–Zn mineralization throughout southern Hunan mainly occurred at 160–156 Ma, rather than 180–170 Ma or 170–160 Ma as considered previously. The Pb–Zn mineralization and major W–Sn mineralization in southern Hunan are coeval and may be related to the same geological event.

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.