Metallogenic Characteristics And Genesis Of The Zhongxing Pb-Zn Deposit, Inner Mongolia

Located in the southern part of Da Hinggan Mountain metallogenic belt,Zhongxing Pb-Zn deposit is a typical hydrothermal vein type deposit which wasdiscovered in recent years. Through systematic study of the geological andgeochemical characteristics of the Zhongxing Pb-Zn deposit, conclusions concerningthe mineral composition, the occurance of andesitic porphyrite, the genesis and themineralization mechanism of this deposit have been drawn as follows:（1）On the basis of detailed field geological survey and systematic laboratorystudy including microscope observation, electron probe scanning, the mineralcomposition and the occurance of silver has been identified. The results show thatZhongxing deposit has a small variety of minerals with galena, sphalerite, pyrite,marcasite, chalcopyrite and arsenppyrite. Part of the silver occurs as independentminerals, such as pyrrhotite and freibergite, which are embedded in sulfides asinclusions, the other part occurs as isomorphism in the crystal lattice of the sulfides,mainly galena.（2）The LA-ICP-MS U-Pb age study on the zircon of the andesitic porphyrite inZhongxing Pb-Zn deposit shows164±3.3Ma. Its major element is high-Kcalc-alkaline of continental marginal arc, combined with the REE and the trace elemetcharacteristics and the previous research in this region，it infers that the andesiticporphyrite were formed by the subduction of the Pacific plate on the North ChinaPlate.（3）The hydrogen isotope and the oxygen isotope data imply that theore-forming fluids of the Zhongxing deposit were hot brine, and occurs intensewater-rock reaction with the surrounding rock(W/R were0.05~0.2). The carbonisotope of calcite define a narrow range and the oxygen isotope values have a widerange, indicating that the carbon in the ore fluids was mainly derived from magma,the intense oxygen isotope exchange occurred between ore-forming fluids andmeteoric water. The sulfur isotope date demonstrated that sulfur was mainly fromdeep magmatic. The lead isotope infer that the lead in ores were mainly originatedfrom deep-seated magma of the deep lower curst and the upper mantle, with somecontributions from the upper curst. （4）The study of fluid inclusions shows that the homogenization temperaturesof the inclusions(the rangs were280~320,240~280,140~190℃) gradually decreasedfrom the early to the late stage, with the obviously reduced salinities (the means were5.06,4.65,3.13%NaCl.eqv) and a increasing trend of the densities(the means were0.80,0.78,0.92g/cm3), the ore-forming fluid of the Zhongxing deposit wascharacterized by middle-lower temperature, middle-lower salinity and middle density.（5）The author established metallogenic model. The tectonic setting of theZhongxing Pb-Zn deposit were formed in the transion period from lithospherecompression to extention. The tectonic made the deep molten material upwell andform a huge scale acidic magma. the magma emplaced along the northeast regionalfaults，and evolved into ore-fluids in the suitable space.