A Study On The Magmatic Rocks And Faults Of The Zhaojikou Pb-Zn Deposits, Dongzhi, Anhui Province

The Zhaojikou Pb-Zn deposit is a lead-zinc polymetallic deposit discovered currently in southern Anhui Province. The total resources of lead and zinc from the deposit have reached more than 50 million and are expected to further expand. Based on the regional geological survey and drill-core samples observation, the magmatic rocks and fault structures in the ore district are studied in this paper. First, according to the studies of petrography, petrological chemistry and geochemistry and geochronology, the rock types, diagenetic material resources, diagenetic tectonic environment and the relations between magmatism to mineralization are discussed. Second, according to the analysis of K-Ar ages of the gouge sample, the time limits of tectonic movement of the Dongzhi fault are determined. Combined with the regional geological evolution and structural stress field analysis, the effects of the Dongzhi fault to mineralization are dicussed. The main results of this paper are as follows:Granodiorite porphyry, granitic porphyry and diorite porphyrite are three main intrusive rocks in the Zhaojikou ore district. Granodiorite porphyry occurs as stock, while granitic porphyry and diorite porphyrite occur as veins. They all are calc-alkaline series chemically. The magma of the granodiorite porphyry and granitic porphyry likely dominated from the crustal and contaminated the mantle magma, and the diorite porphyrite maybe formed by the crust-mantle-derived magma. The geodynamic background of the magmatism of the intrusive rocks are intra-continent orogeny extrusion to tension transition.The zircon U-Pb isotopic ages of granodiorite porphyry and granitic porphyry are around 145Ma, while the age of diorite porphyrite is about 129.0 Ma, and the latter is cut by ore bearing quartz veins. The diorite porphyrite is closely relate to mineralization of lead-zinc deposits in the region.Intrusive rocks contain a large number of inherited zircon, reflects diagenetic material have a large amount crust rocks. The isotopic ages of inherited zircon focused on 740Ma～ 890Ma, the ages are unanimous with Neoproterozoic granite and andesitic basalt and andesite of Neoproterozoic Qingbaikouan Puling Group in south Anhui Province. The ages of the inherited zircons reflect the tectonic- magmatic event took place between the Cathaysia plate and the Yangtze plate in the Jinning period. Otherwise, the ages of small amount of inherited zircons in the intrusive rocks are more than 1000 Ma, which indicates the continental crust in the region has early Proterozoic or Archean basement.Veins and stockwork of ore body in the Zhaojikou lead-zinc deposits distributed in the Dongzhi Fault and NNW secondary tensile fracture. Ore body by east fault zone in pelitic filling control, the eastern side of the Dongzhi Fault have not seen mineralization.The age of fault gouge arel26.6 and 138.3Ma, indicate activities during the early - late Yanshan period of in the tectonic rushed zones of Dongzhi Fault formation in the late Yanshan.