Two-stage mineralization of the Qiushulin molybdenum deposit in the North China Craton: Constraints from fluid, isotopic, and geochronologic data

Résumé fourni par la source

The Qiushulin molybdenum deposit, located in the central Taihang Mountains of the North China Craton (NCC), is hosted at the contact zone between the quartz monzonite porphyry and the Neoarchean Fangli gneiss. LA-ICP-MS zircon U-Pb dating of the quartz monzonite porphyry yielded a weighted mean 206 Pb/ 238 U age of 132 Ma. Combined with whole-rock geochemical characteristics, indicated that it was formed by the partial melting of mantle-derived amphibolite/basalt in the Early Cretaceous, which was caused by the subduction of the Paleo-Pacific plate (PPP) beneath the NCC and subsequent plate rollback. Re-Os dating was performed on molybdenite, obtaining two stages of metallogenic ages. The former metallogenic age is 130 Ma, which is broadly consistent with the age of the quartz monzonite porphyry and comprises the first two mineralization stages: (Ⅰ) quartz pyrite, (Ⅱ) quartz polymetallic sulfides. The latter metallogenic age is 113 Ma, which comprises the last mineralization stage: (Ⅲ) quartz carbonate. The petrography, microscopic thermometry, and laser Raman results of fluid inclusions indicate that the main component of the inclusions is CO 2 , dominated by three-phase primary inclusions, with liquid-rich secondary inclusions also observed. The primary inclusion for stages I and II mineralization temperatures are 357–427 ℃ and 257–381 ℃, with salinities of 6.54–9.44 wt% and 2.96–11.61 wt%, respectively. The calculated capture pressures for stages I and II mineralization are 200–276 MPa and 203–248 MPa, and the ore-forming depth is about 8.34 km. H-O isotope analysis reveals that for stage I, the ranges of δD V-SMOW and δ 18 O H2O are − 58.1 to − 59.0 ‰ and 5.37 to 6.07 ‰, respectively, plotting near the primary magmatic water field. For stage II, the ranges of δD V-SMOW and δ 18 O H2O are − 59.4 to − 60.8 ‰ and 4.40 to 4.48 ‰, respectively, shifting towards the meteoric water line. This indicates that the ore-forming fluid was mainly primary magmatic water, and as the mineralization proceeded, meteoric water was added. Combined S-Pb isotope composition indicates that the metallic minerals are mainly derived from the mantle-lower crust. Based on the research of the Qiushulin molybdenum deposit and host rock quartz monzonite porphyry, together with previously regional tectonic-magmatic events, ore geology, and the geochronologic and isotopic data, we suggest that the Qiushulin molybdenum deposit is a typical porphyry-type deposit. Its formation is attributed to the crust-mantle magma interaction triggered by lithosphere extension and asthenosphere upwelling during the rollback of the subducted PPP beneath the NCC, accompanied by multi-stage tectonic magmatic activities and mineralization superposition.

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