The Geochemistry Researches On Ore-forming Fluid And A Discussion For Ore Origin At Yinshan Polymetallic Deposit, Jiangxi Province

The fluid-inclusion geochemistry is one of the most important branch and also one of the most important methods of the ore-forming fluid geochemistry. Fluid-inclusion is only mark of fossil ore-forming fluid and is the key that can understand the mechanism of ore-forming processes. By means of fluid-inclusions methods, we can acquire some important information of physics and chemistry in ore-forming processes, retrace the locus of ore-forming processes and clarify the mechanism of ore-forming processes.Yinshan deposit is a large scale Cu-Pb-Zn-Au-Ag polymetallic deposit, is located at the Northeastern Jiangxi Province. Mineralazation is directly related to the activity of volcano-subvolcano eruption and intrusion. Using fluid inclusion petrography and microthermometry, the thesis embarks further studies on questions such as the physical and chemical conditions of the ore-forming processes, the evolving characteristics of ore-forming fluid at time and space, the origin of ore-forming fluid. On the basis of this, the paper specially discusses the ore precipitating mechanism and the ore origin. Fluid-inclusion observations and microthermometric data suggest that the ore-forming fluid is middle-low temperature hydrothermal solution, it also reports the presence of high-salinity inclusions containing hilite in porphyry rock and ore-hosted quartz vein. Homogenization temperature and salinity of ore-forming fluid show some regularity at space, this indicates that ore-forming fluid flow has directivity. The characteristics of homogenization temperature and salinity data also reports that this high-salinity inclusions were not generated by aqueous fluid immiscibility or boiling in ore-forming processes, but generated directly from a water-saturated crystallizing magmatic melt and that the main mechanism of ore deposition is the mixing of magmatic fluid and underwater not boiling of hydrothermal solution. The evidence of H, O isotope indicates that ore-forming fluid at early stage of ore-forming processes originated from magmatic water but later there was the mixing with groundwater or meteoric water.Beishan deposit which located on the most north part of Yinshan deposit has an independent change trend high to low in ore-forming temperature with from east to west in pace. This indicates that quartz porphyry 5# may be the mineralization center of Beishan deposit. The H and O isotope of water in fluid-inclusion at the Beishan deposit indicates that the ore-forming fluid originated from magmatic water and partly from volcanic vapor.Finally, the fluid inclusion characteristics of Yinshan deposit is compared with the typical fluid-inclusion characteristics in ore formation model of porphyry copper deposit. The ore-forming fluid of Yinshan deposit share certain similarities in the evolution of ore-forming fluids with porphyry copper deposits, which indicates a genetic link between the Yinshan polymetallic ore deposit and porphyry copper deposit in the depth of the deposit. It is concluded that Yinshan deposit is refereed to "transitional deposit" between the porphyry copper deposits and epithermal deposits.It seems possible that there is concealed porphyry copper deposit in the depth of Yinshan deposit.