Geological and geochemical characteristics and genesis of the Biliyagu lead-zinc-silver deposit, Inner Mongolia

Abstract: Located in the northwest of Hailar-Genhe Mesozoic volcanic basin, the Biliyagu lead-zinc-silver deposit occurs in the Upper Jurassic Manketouebo Formation acidic volcanic rocks and is controlled by the NW-trending faults, with the orebodies being mainly of vein type. LA-ICP-MS zircon U-Pb dating of rhyolitic volcanic breccia lava indicates that its age is (159.2±1.8) Ma. Based on the relationship between the rock and the mineralization, the authors hold that the deposit was formed in late Jurassic. Major element geochemistry of rhyolitic volcanic breccia lava and rhyolite is characterized by high SiO2 (68.31%-77.18%), potassium (3.39%-4.28%), and aluminum (11.74%-14.93%) and low sodium (0.14%-0.18%), suggesting high potassium calc-alkaline series. The REE content of rocks is low (93.65×10?6-98.94×10?6), and has characteristics of high LREE and LREE/HREE ratios as well as weak Ce negative anomaly and Eu negative anomaly. Combined with the features of the rocks such as the loss of the Sr and the obvious enrichment of LREE, it is inferred that the volcanic rocks originated from the plate. The magma of rocks might have been derived from the upper mantle and mixed with crustal materials. Combining this study with regional tectonic evolution characteristics, the authors hold that the deposit was formed during the closure period of Okhotsk plate in a tensile extension environment.