Geology, Geochemistry And Genesis Of Luming Molybdenum Deposit In Tieli, Heilongjiang Province

The Luming molybdenum deposit is located in the south-central part of theYichun-yanshou metallogenic belt, which lies in the east of the Songnen Massif, on thecollision zone of Songnen Massif and Jiamusi Massif. As anexception allylarge porphyrymolybdenum deposoit, the Luming molybdenum deposit is highly concerned recently. Inthis thesis, by studying the geology, geochemistry, mineralization age, andphysicochemical minerogenetic conditions, we discuss the mineralization material sourceand metallogenic dynamics, and then reveal the genesis of the deposit.The major orebodies are hosted in the monzonitic granite and granite porphyry withmetallic minerals inside, and wall rock alterations are characterized by zoning of typicalporphyry deposoit. Geochemicalchara cteristics show thatmonzonitic graniteandgraniteporphyry belong to high-K calc-alkaline I-type granites, and the crust-mantleactionoccurredin the Magma source. The granites show the characteristics of C adakiticrock, showingthat the magma derived from partial melting of the thickened lowercontinental crust. Initial Sr isotope ratio of the ore-bearing rock (87Sr/86Sr) ranges from0.708946to0.711256, that isbetween mantle derived magma and crust derived magma,indicatingthe characteristics of crust-mantle contaminationin the magma source region.δ34S value of S isotope in metallic minerals molybdeniteranged between5.37‰to6.71‰, close to that of the mantle magma, indicating metal ores may come fromthemantle-derived magma.Most fluid inclusions in the quartz veins,which is related to mineralization,aregas-liquid two-phase inclusions.The primary homogenization temperature of them focus between280℃and320℃. Based on thehomogenization temperature, we cancaculatethat the fluid salinity is between2.06wt%NaCl and22.45wt%NaCl, the value ofmineralized pressure is between123.34×105Pa and418.52×105Pa, and the mineralizeddepth is about from0.41km to1.4km. It shows that the Luming molybdenum depositformed in medium-high temperature hydrothermal type molybdenum deposit in shallowenvironments. Two groups of the zircon206Pb/238U ages ofmonzonitic granite measured byLA-ICP-MS zircon U-Pb dates are194.8±0.7Ma and176.2±2.1Ma, suggesting that thegranite were formed in the Early Jurassic. Combined with the regional geologicbackground, it is considered that Jiamusi Massif matched with Songnen Massifin the earlyYanshanian, which could be related to bidirectional subduction of the Mongol-Okhotsktectonic system and Circum-Pacific tectonic system. Under plating occurred in deepmantle-derived basaltic magma, formingthe new lower crust in the region. Partial meltingof the new lower crust formed adakitic magma, and completed the initial enrichment ofore-forming elements molybdenum. Due to the continuous subduction of the Pacific plate,adakitic magma intruded upwards along the fissures, and the late hydrothermal activitiesfinally formed the Luming porphyry molybdenum deposit.