Vein In Sandaowanzi Area Of Heilongjiang Province Chronology And Geochemistry Research

Daxing'anling is an important low-temperature hydrothermal deposit metallogenic area inNortheast China.The unique Sandaowanzi gold deposit has been discovered in the area in recent years.The previous studies were mostly focusing on the deposit itself,but lacking relevant research on various types of dike(vein)rocks that cut through the veins and ore-bearing surrounding rocks.In this thesis,the petrology,chronology and geochemistry of basic to acidic vein rocks in Sandaowanzi area were studied.Based on the LA-ICP-MS zircon U-Pb dating results,all types of vein rocks in the study area were formed in the late Early Cretaceous(133-106 Ma),and the age of medium-basic vein rocks is 116.40-109.6 Ma,acidic vein rocks Of age is 114.9-112.6 Ma.Therefore,the metallogenic age of the Sandaowanzi gold deposit can be limited to 125.3 ~ 116.4 Ma,which is basically consistent with the previous research results.7 diabase porphyry rocks and 3 diorite porphyry rocks belong to high-K calcium-alkaline metaaluminous series rocks,and 3 rhyolite porphyries belong to high-K calcium-alkaline strong over-aluminum series rocks.The two have different magmatic source areas: the mesobasic vein rock is derived from the mantle and has a low initial value of 87 Sr / 86Sr(i)(0.705178 ~ 0.705347),which is smaller than the average value of the present continental crust(0.7211),during the uplift The middle-crusted crust is not very contaminated,and may undergo separation and crystallization mainly based on monoclinic pyroxene;the acidic vein rock is formed by partial melting of the lower crust,and the mantle-based basic magma under the intrusion provides heat for it.Based on the study of tectonic environment-magmatism,this paper believes that the strong volcanic activity in the northeastern region of the late Early Cretaceous(133-106 Ma)is mainly related to the subduction-withdrawal of the Izanai Plate,and was influenced by the previous Late Jurassic-Early Cretaceous The Mongolian-Okhotsk Ocean subducted southwards to the blocking effect of the Ergun block,and the asthenosphere material activity space was restricted.Under the tectonic background of large-scale extension and thinning of the lithosphere,the thickening of the lower crust in the northeast region was dismantled,and the massive upwelling of the asthenospheric material caused partial melting of the lithospheric mantle,and the basic magma invaded the upper crust along the magma channel.Due to the faster emplacement speed,the heat carried by the basic magma caused local thermal anomalies in the upper crust,and the upper crust rocks were partially melted to form acid magma.During the Early Cretaceous period,the entire northeastern region was in a plate-drawing extensional tectonic setting.Therefore,volcanism and mineralization were strong during this period,and a series of early Cretaceous copper,lead,zinc,gold and other metal deposits were formed.