Key Metallogenic Control System Of The Beishou-chenjia Antimony-lead-zinc Polymetallic Deposit In Yizhang County, Hunan Province

Beishou-Chenjia antimony-lead-zinc polymetallic deposit is located in the W-Sn polymetallic concentration area in Southern Hunan, which has an excellent regional geological metallogenic background. Based on the theory of "metallogenic system", the author carried out a comprehensive study of the stratigraphies, tectonics, granite porphyries, mineralization characteristics, cryptoexplosive breccias and fluid inclusions in the region, basically verified the source of metallogenic material, ore-controlling factors and metallogenic mechanism, and its key metallogenic control system.The systematic analysis of the stratum geochemical characteristics show that the Qiziqiao Formation suffered the highest dolomitization, has obvious enrichment of S, Pb, Zn, Sb and other ore-forming elements. Compared to the stratum of fresh carbonate in this area, silicified rocks have the Pb, Zn, Sb synchronous enrichment phenomena. From the deep to the shallow, the correlation between Pb, Zn, Sb and other ore-forming elements of country rock and elementary assemblage associated with the granite porphyry gradually becomes lower. We identified numerous Pb, Zn, Sb geochemical anomalies in the northeast fault zonesThe granite porphyries which form in the extensional tectonic environment in this area belong to the crust remelting type. The granite porphyries with low alkali, relatively high aluminum and sodium potassium ratio which varies greatly are rich in the volatile and ore-forming elements, intensively interacted with fluid-melting and having obvious cryptoexplosive characteristics. The granite porphyries which are significantly rich in Pn, Zn, Sb are major source of metallogenic materials in this orefield. The cryptoexplosive breccias, including explosive breccias, shatter breccias and mixed breccias, are mainly restricted to the joint regions of the granite porphyry dykes and the NE-striking faults. In addition, the convergence of the main fracture, in the Northeast, connected with granite porphyry and its branch of fracture has the relatively small size of cryptoexplosive breccias. The cryptoexplosive breccia is an important ore bearing position and the mineralization mainly occurs in the matrix of the cryptoexplosive breccias.The ore-forming fluids with low-to-moderate temperature and low salinity, have the characteristic of mixed sources of magmatic water and meteoric water. Fracture crack and the breccias are the main channel of ore-fluid migration and the main part of the unloading and settling of the ore-forming substances. The main factors, which influence the Pb, Zn, Sb and other elements unloading and settling, are decompression boiling, fluid mixing and cooling.Beishou-Chenjia antimony-lead-zinc polymetallic deposit belongs to the low-to-moderate-temperature epithermal metallogenic system associated with the Yanshan period granitic magma. The metallogenetic factors which control the deposit formation and emplacement through coupling in the ore district, include the formation lithology and fabric, NE main trending faults, the crust remelting Yanshanian granitic magma and cryptoexplosion.