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

• Published in: Arabian journal of geosciences Vol. 12; no. 23; pp. 1 - 19
• Main Authors: Tang, Wen-Hao, Li, Jian, Wang, Ke-Yong, Li, Shun-Da, Cai, Wen-Yan, Liu, Han-Lun, Wang, Yi-Cun
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.12.2019; Springer Nature B.V
• Subjects: Aluminum oxide; Carbon dioxide; Chalcopyrite; Cratons; Earth; Earth and Environmental Science; Earth science; Earth Sciences; Fluid inclusions; Fluids; Geochemistry; Geochronology; Geochronometry; Geology; High temperature; Isotopes; Lead; Low temperature; Meteoric water; Mineralization; Molybdenite; Molybdenum; Original Paper; Orogeny; Oxygen isotopes; Pyrite; Quartz; Radiometric dating; Rare earth elements; Silica; Silicon dioxide; Sodium chloride; Sulfide; Sulphides; Tectonics; Triassic; Zircon; China; H–O isotopes; Tectonic setting; Laojiagou deposit; Zircon U–Pb geochronology; Fluid inclusions; Whole-rock geochemistry
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-019-4845-7

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 two-phase (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.) CO 2 -rich fluid evolved to a low-temperature (< 280 °C) and CO 2 -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 δ 18 O H2O  = 4.4–4.8‰ and δD H2O  = − 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 SiO 2 , K 2 O, and Al 2 O 3 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.