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[Display omitted] • Both the granite porphyry and the Baiyinchagan deposit formed approximately 140 Ma ago. • The ore-forming fluid is characterized by medium–high temperature and low salinity. • The ore-forming fluid was dominantly derived from magmatic fluid mixed with meteoric water. • The ore-forming material was mainly derived from granitic magma. The superlarge Baiyinchagan Sn–Ag–polymetallic deposit of Inner Mongolia is located in the west slope of the southern Great Xing'an Range, NE China. The vein orebodies of the deposit occur in the NEE-trending fault zones. The mineralization process at the deposit can be divided into four stages: quartz–fluorite–cassiterite–sphalerite stage (stage I), quartz–fluorite–cassiterite–sulfide stage (stage II), quartz–calcite–sulfide stage (stage III), and quartz–stibnite stage (stage IV). Cassiterite U–Pb dating indicates that the Baiyinchagan deposit formed approximately 140 Ma ago, and zircon U–Pb dating for granite porphyry in the Baiyinchagan deposit yielded an age of 140.8 Ma. Two types of fluid inclusions (FIs), including liquid-rich and gas-rich inclusions, have been distinguished in quartz and fluorite veins. The homogenization temperature of the FIs in the stage I ranges from 318 °C to 351 °C with salinities of 1.2–3.8 wt% NaCl eqv. The homogenization temperature of the FIs in the stage II is 262–276 °C with salinities of 1.8–3.4 wt% NaCl eqv. The homogenization temperature of the FIs in the stage III ranges from 174 °C to 233 °C with salinities of 1.8–3.0 wt% NaCl eqv. The homogenization temperature of the FIs in the stage IV is in the range of 136–168 °C, and the salinity is 0.8 wt% to 2.4 wt% NaCl eqv. The ore-forming fluid of the Baiyinchagan deposit is characterized by medium–high temperature and low salinity. The δ18O water and δD values of ore-forming fluid range from −13.5 ‰ to 9.5 ‰ and −119 ‰ to −84 ‰, respectively, indicating that the ore-forming fluid was dominantly derived from magmatic fluid mixed with meteoric water. The calculated δ34S H2S values range from −12.3 ‰ to −6.2 ‰, implying that the sulfur mainly came from granitic magma, but magmatic degassing occurred during mineralization. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the sulfides are in the ranges of 18.180–18.339, 15.525–15.643, and 38.005–38.477, respectively. The Pb isotopic compositions of sulfides indicate that the Pb mainly derived from granitic magma that may be formed by partial melting of orogenic materials. Fluid immiscibility and mixing were the two primary mechanisms for mineral precipitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mineralization of the Quanzigou Mo deposit is closely related to the quartz porphyry. • The Hongniangshan complex mainly originated from partial melting of a Paleoproterozoic lower crust. • Both the medium–coarse-grained granite and the porphyritic granite experienced magmatic mixing. • Magma of the complex experienced fractional crystallization in different extent. • The Hongniangshan complex emplaced in a post-collisional tectonic setting. The Quanzigou porphyry molybdenum deposit is located in Fengzhen County, Inner Mongolia, China, belonging to the northern margin of the North China Craton. A Yanshanian granitic complex, namely the Hongniangshan complex, is exposed in the deposit, mainly composed of medium–coarse-grained granite, porphyritic granite, and quartz porphyry. The Mo orebodies occur mainly in the porphyritic granite as ore-bearing quartz veins or veinlets. Previous study on molybdenite Re–Os and zircon U–Pb dating suggests that the Hongniangshan complex emplaced during 173–160 Ma and that the Quanzigou Mo deposit formed at ca. 160 Ma. Geochemical analyses in this study show that all these Middle–Late Jurassic granites are peraluminous, high-K calc-alkaline granite, featured by enrichment in Rb, Th, U, Hf, and Zr and depletion of Ba, P, and Ti, with high K 2 O/Na 2 O ratios. Nearly all the samples from the medium–coarse-grained granite and the porphyritic granite show weakly negative Eu anomalies, whereas the negative Eu anomalies of the quartz porphyry are moderate or strong. The Hongniangshan complex has low zircon ε Hf (t) values (−14.4 to − 6.7), old single-stage and two-stage model ages (1099–1471 Ma and 1637–2124 Ma, respectively), and low K-feldspar Pb isotopic compositions (206Pb/204Pb = 17.019–17.590, 207Pb/204Pb = 15.365–15.489, 208Pb/204Pb = 37.002–37.670), with K-feldspar δ18O values of 8.0–10.4‰, suggesting that the granitic complex was predominantly originated from a Paleoproterozoic lower crust source. Geochemical characteristics, combined with results from previous studies, show that the Quanzigou Mo mineralization was closely related to the quartz porphyry. The Middle Jurassic medium–coarse-grained granite was likely formed in the back-arc extension environment triggered by the subduction of the Mongol–Okhotsk Ocean and the Paleo-Pacific plate, and the formation of the Late Jurassic porphyritic granite and the quartz porphyry was controlled by both the post-collisional process of the Mongol–Okhotsk orogenic belt and the coeval subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]