Ore genesis and tectonic setting of the Laojiagou porphyry molybdenum deposit, Inner Mongolia, China: evidence from geol
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ORIGINAL PAPER
Ore genesis and tectonic setting of the Laojiagou porphyry molybdenum deposit, Inner Mongolia, China: evidence from geology, fluid inclusions, H–O isotopes, zircon U–Pb geochronology, and geochemistry Wen-Hao Tang 1 & Jian Li 1 & Ke-Yong Wang 1,2 & Shun-Da Li 1 & Wen-Yan Cai 1 & Han-Lun Liu 1 & Yi-Cun Wang 1 Received: 15 March 2019 / Accepted: 9 September 2019 # Saudi Society for Geosciences 2019
Abstract The Middle Triassic Laojiagou porphyry Mo deposit is located in the Xilamulun metallogenic belt, along the northern margin of the North China Craton (NCC). Molybdenum mineralization is associated with a monzogranite porphyry and occurs primarily in quartz veins and veinlets hosted in wall rocks affected by potassic, silicic, sericitic, and propylitic alteration. The ore-forming process is divided into three stages, characterized by veinlets comprising molybdenite + pyrite + quartz (stage I), pyrite + chalcopyrite + molybdenite + quartz (stage II), and pyrite + quartz (sulfide-poor) (stage III). We identify three fluid inclusion types in quartz grains: carbonic (C-type), liquid-rich twophase (L-type), and rare vapor-rich two-phase (V-type) inclusions. Microthermometric results indicate that an initial high-temperature (> 350 °C) and low-salinity (< 10 wt% NaCl equiv.) CO2-rich fluid evolved to a low-temperature (< 280 °C) and CO2-poor fluid, comprising dominantly of meteoric water. Hydrogen and oxygen isotopes indicate that initial ore-forming fluids were magmatic and became progressively mixed with meteoric water (stage I δ18OH2O = 4.4–4.8‰ and δDH2O = − 105.8 to − 101.5‰). Zircon U–Pb dating indicates that the monzogranite porphyry formed at 232.2 ± 3.6 Ma (MSWD = 0.88). The porphyry has high SiO2, K2O, and Al2O3 and low MgO and CaO concentrations and is classified as high-K calc-alkaline and weakly peraluminous. All samples are enriched in light rare earth and large-ion lithophile elements and depleted in high-field-strength elements. Our results indicate that the Laojiagou porphyry Mo deposit formed in the Middle Triassic, associated with post-orogenic extension following closure of the Palaeo-Asian Ocean. Keywords Laojiagou deposit . Fluid inclusions . H–O isotopes . Zircon U–Pb geochronology . Whole-rock geochemistry . Tectonic setting
Responsible Editor: Domenico M. Doronzo * Ke-Yong Wang [email protected]
Han-Lun Liu [email protected]
Wen-Hao Tang [email protected] Jian Li [email protected]
Yi-Cun Wang [email protected]
1
College of Earth Sciences, Jilin University, 2199 Jianshe Street, Changchun 130061, China
2
Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources of China, Changchun, China
Shun-Da Li [email protected] Wen-Yan Cai [email protected]
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Introduction The eastern segment of the Central Asian Orogenic Belt (CAOB) in northeast (NE) China records multiple tectonic and magmatic events including the subduction–accretion of the Palaeo-Asian Ocean, the evolution of the Mongol– Okhotsk Ocean, and subduction of the Palaeo-
