Geochemistry, geochronology and petrogenesis of the ore-forming intrusive body in the Baoyintu molybdenum deposit, Inner Mongolia

Abstract: The Baoyintu molybdenum deposit in Inner Mongolia is a large porphyry quartz vein type molybdenum deposit discovered in the northern part of the Langshan Mountain, and the ore-forming intrusive body consists of plagiogranite, monzogranite, moyite and acidic fine-grained porphyry stock. The LA-ICP-MS U-Pb upper intercepting age is 2400 Ma, suggesting that the granite was derived from late Archean to early Proterozoic crustal rocks. Zircon LA-ICP-MS U-Pb dating shows that the ore-forming intrusive body was formed at four stages in the Indosinia period, i.e., (225.9±4.4) Ma-(237.5±5.9) Ma, (236.8±4.5) Ma-(244.3±4.2) Ma, (247.5±4.4) Ma and (252.1±3.4) Ma-(258.8±3.3) Ma; the isotopic ages imply that each stage of magma intrusion lasted for a long time, and the intervals between various stages of invasion were short. Elements at different stages of magmatic intrusion underwent some differentiation, the chemical composition of various stages of rocks shows oversaturated aluminum, potassium-rich features, with late aplite K2O/Na2O being the highest, and K2O and CaO being inversely correlated with each other. A comparison with Sr/Ba-Zr/Y ratios of major magmatic belts in the world shows that it is different from the oceanic crust melt, granite, consistent with the Yanshan belt, Qinling belt magmatic rocks, and close to Proterozoic metamorphic country rocks in geochemical characteristics. These features indicate that mineralized granites are genetically continental crust melt S-type granites.