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The Shimensi deposit (South China) is a newly discovered W-Cu-Mo polymetallic deposit with a reserve of 0.76 million tones WO3, one of the largest tungsten deposits in the world. We report elemental and Sr-Nd isotopic data for scheelites from the giant deposit, to determine the source region and genesis of the deposit. Scheelite is the most important ore mineral in the Shimensi deposit. Trace elements (including REEs) and Nd-Sr isotopic compositions of scheelites were used to constrain the origin of the mineralizing fluids and metals. Our data reveal that the REEs of scheelite are mainly controlled by the substitution mechanism 3Ca2+ = 2REE3++ ∎Ca, where ∎Ca is a Ca-site vacancy. Scheelites from the Shimensi deposit show negative Eu anomalies in some samples, but positive Eu anomalies in others in the chondrite-normalized REE patterns. The variation of Eu anomalies recorded the ore-forming processes. Considering the close spatial and temporal relationship between the mineralization and porphyritic granite, we think the negative Eu anomalies were inherited from the porphyritic granite and the positive ones from destruction of plagioclase of country rock during fluid-rock interaction. The variation of cathodeluminescence (CL) color of a single scheelite from red to blue and to yellow was likely associated with the increase of REE contents. The scheelites hosted in the Mesozoic porphyritic granite with negative Eu anomalies formed in a primitive ore-forming fluid, whereas the scheelites hosted in Neoproterozoic granite with positive Eu anomalies precipitated in an evolved ore-forming fluid. The high Nb, Ta, LREE contents, and LREE-enriched REE patterns of scheelites from the Shimensi deposit reveal a close relationship with magmatic hydrothermal fluids. The scheelites from the Shimensi deposit are characterized by low εNd(t) values (-6.1 ∼ -8.1) and unusually high and varied initial 87Sr/86Sr ratios (0.7230∼0.7657). The εNd(t) values of scheelites are consistent with those of the Mesozoic porphyritic granite, but the Sr isotopic ratios are significantly higher than those of the granites, and importantly, beyond the Sr isotopic range of normal granites. This suggests that the ore-forming fluids and metals cannot be attributed to the Mesozoic porphyritic granites alone, the local Neoproterozoic Shuangqiaoshan Group schists/gneisses with high Rb/Sr ratios and thus radiogenic Sr isotopic compositions should have contributed to the ore-forming fluids and metals, particularly, in a later stage of ore-forming process, by intense fluid-rock interaction. This is different from a commonly accepted model that the ore-forming fluids and metals were exsolved exclusively from the granite plutons.

The Shimensi super-large tungsten polymetallic deposit is located in the Late Jurassic–Early Cretaceous Porphyry–Skarn tungsten ore belt in the south Yangtze metallogenic belt. There are three types of mineralization: veinlet-disseminated type, thick quartz vein type and hydrothermal cryptoexplosive breccia type. Based on geological studies, this paper presents new petrographic, microthermometric, laser Raman spectroscopic and hydrogen and oxygen isotope research on the fluid inclusions from the deposit. The results show that there are five different types of fluid inclusions: liquid-rich inclusions, vapor-rich inclusions, pure liquid inclusions, pure vapor inclusions, and fluid inclusions containing a solid crystal. The homogenization temperatures of the fluid inclusion range from 140 °C to 270 °C, the salinities are 3 wt.%–5 wt.% NaCleq and the densities of ore-forming fluid range from 0.64 g/cm3 to 0.99 g/cm3. For the analyses of laser Raman spectroscopy, the ore-forming fluids can be approximated by a Ca2+-Na+-SO42−-Cl− fluid system with small amounts of CO2, CH4 and N2. Otherwise, the data of the pressure, pH and Eh show a fluid metallogenic environment of low pressure, weak acid and weak reduction. The values of the homogenization temperature in the three types of orebodies suggest that the mineralization is characterized by a decrease in temperature under the conditions of fluid immiscibility. The H-O isotope values are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water, and meteoric water is added with the process of magma rising.

The world-class Shimensi tungsten (W)-polymetallic deposit is located in Jiangnan Orogen, with an estimated reserve of 742.5 kt WO3 @ 0.195% W, 403.6 kt Cu and 28 kt Mo. In this paper, the trace elements and Pb-O isotopes of scheelite (the main ore mineral) are presented to study the ore-forming material source and ore-forming fluid evolution. The results show that the REE distribution in scheelite is mainly controlled by the substitution mechanism of 3Ca2+ = 2REE3+ + □Ca (where □Ca is the Ca-site vacancy). Oxygen isotope data indicate that the scheelite mineralization occurred under high-temperature oxygen isotope equilibrium conditions, and that the ore-forming fluid has a magmatic–hydrothermal origin. The variation in scheelite Eu anomalies and the wide range of scheelite Y/Ho ratio indicate that the ore-forming fluid evolves from reducing to oxidizing, and the early-stage and late-stage ore-forming fluid may have been relatively rich in F− and HCO3−, respectively. The significant Mo decrease in scheelite from the early to late stage that are opposite to the influence of fO2 variation may have resulted from the crystallization of molybdenite and Mo-rich scheelite. Lead isotopes of the ore minerals of scheelite, wolframite, molybdenite and chalcopyrite can be divided into three groups, similar to these of feldspars in different granites. Both the Mesozoic porphyritic and fine-grained biotite granites have Pb isotope ratios similar to the ores, which suggests that the former two are the main ore material source.

The newly discovered Shimensi deposit is a super-large tungsten-copper (W–Cu) deposit with a metal reserve of 742.55 thousand tonnes (kt) W and 403.6 kt Cu. The orebodies are hosted in Mesozoic granites, which intruded the poorly documented Shimensi granodiorite belonging to the Jiuling batholith, the largest intrusion (outcrop > 2500 km2) in South China. Our new SHRIMP (Sensitive High Resolution Ion MicroProbe) zircon dating revealed that the granodiorite at Shimensi (ca. 830–827 Ma) was formed coeval (within analytical uncertainty) or slightly earlier than those in many other places (ca. 819–807 Ma) of the Jiuling batholith. The Neoproterozoic Shimensi granodiorite is peraluminous and high-K calc-alkaline, and contains low P content with no S-type trend (positive P2O5 vs. SiO2 correlation) displayed, thus best classified as peraluminous I-type. The I-type classification is also supported by the zircon REE patterns, largely (93%) positive εHf(t) (−0.87 to 6.60) and relatively low δ18O (5.8–7.7‰). The Neoproterozoic Shimensi granodiorite was formed after the continental arc magmatism (ca. 845–835 Ma), but before the post-collisional S-type granite emplacement (ca. 825–815 Ma) in the Jiangnan Orogen. Therefore, we propose that the Shimensi granodiorite was formed in a collisional/early post-collisional setting. The δ18O increase from the Shimensi granodiorite to many younger (ca. 819–807 Ma) granodiorites (6.0–8.5‰) in the Jiuling batholith probably reflects an increase of supracrustal rock-derived melts with the progress of collision. The Shimensi granodiorite contains low zircon Ce4+/Ce3+ and Eu/Eu*, suggesting a relatively reducing magma that does not favor porphyry Cu–Au mineralization. This left a high background Cu concentration (avg. 196 ppm) in the Neoproterozoic granodiorite, which may have contributed to the Mesozoic W–Cu mineralization, when the granodiorite is intruded and assimilated by the Mesozoic granites.