Study On Mineralization Of Qixiashan Pb-Zn Deposit, Nanjing,China

Qixiashan lead-zinc polymetallic deposit is located at the west of Ningzhen ore-concentrated area, in the Middle Lower Yangtze River Valley metallogenic belt. The orebody mainly consist of sphalerite and galena, which is distributed in the carboniferous Gaolishan group(C1g) and Huanglong group (C2h), are generally spreading along the strata and the main fault (F2),and extend for hundreds of meters in vertically direction.The deposit can be divided into three metallogenic epochs: syn-sedimentary epoch, hydrothermal epoch and supergene epoch, moreover, hydrothermal activity can be subdivided into four metallogenic stages composed of magnetite-rhodochrosite-quartz stage (Ⅰ), chalcopyrite-arsenopyrite-pyrite stage (Ⅱ), sphalerite-galena-pyrite stage (Ⅲ)and calcite-barite-quartz stage(IV).Analyzing fluid inclusions of the sphalerite and gangue minerals indicate that the mineralization temperature of hydrothermal activity ranges from 109℃-361 ℃, belonging to medium-low temperature. The mineralization temperature gradually decreases with precipition of sphalerite and galena; The salinity variation shows relatively wide with the range of 0-18 wt%, indicating it is within medium-low salinity; The density is 0.56-1.10 g/cm3, with an average of 0.94 g/cm3, which belongs to medium density; The vapors are H2O±CO2±CH4, and the liquids are H2O±CO32-.Based on the LA-ICP-MS trace elements analysis of sphalerite, and the results demonstrate that sphalerite is enriched in Mn, In, Sn and depleted Co, T1, As. The trace element characteristic of sphalerite show that the Qixiashan lead-zinc polymetallic deposit is a skarn deposit. The ore-forming fluid is derived dominantly from the magmas, and later contained the meteoric water. The genesis of Qixiashan deposit can be summarized as follows:with deeper magmatic hydrothermal fluid moving upward, and leaching the primary sedimentary strata, thus forming the orebody. In a word, it is a compound deposit revealing that it is a skarn-type lead-zinc deposit.