Study on fluid characteristics and discussion on its metallogenic model of Yangchongli gold deposit in the Tongling, Anhui Province

The Yangchongli gold deposit is a new type of gold deposit ( fracture zone altered rock type) discovered in Shujiadian metallogenic district of Tongling ore-cluster region in the Middle and Lower Yangtze River Metallogenic Belt. Ore bodies mainly occurred in the Silurian cataclastic rocks which were contacted with monzodiorites. The homogeneous temperature obtained from fluid inclusions range in 220. 1 similar to 445. 3 degrees C with an average of 328. 3 degrees C , mainly in 275 similar to 375 degrees C, the calculated salinity is from 0. 18% to 8. 00% NaCleqv, with a mean of 2. 52% NaCleqv, indicating these fluids belong to high temperature, low salinity and low density oreforming fluid. Laser-Raman gas-liquid phase composition analysis shows that the gas phase compositions of the inclusion are mainly composed of CO2 and H2O, while the liquid phase compositions are mainly composed of H2O, which may contain little CO2. The H and O isotopic compositions of fluids show that the delta D and delta O-18(H2O) values are ranging from - 85 parts per thousand to - 50 parts per thousand, and from 0. 76 parts per thousand to 3. 76 parts per thousand, respectively, indicating that the fluids are mainly from the magmatic hydrothermal fluid and meteoric precipitation, and are significantly affected by the action of meteoric precipitation. The chronology of the two intrusions and their interpenetration show that the emplacement time of pyroxene diorite was earlier than that of monzodiorite. The fluid inclusions of the two deposits in this area show that the fluid inclusions of the Yangchongli Au deposit have similar temperatures with the Shujiadian Cu deposit, but relatively low salinity. According to the inmiscivable fluid ore-forming mechanism, the variation of the temperature and pressure of the ore-forming fluid in the Yangchongli Au deposit is the main forming factor of the ore-forming material deposition. Combined with previous studies on S, Pb and other isotopes in the mining area, we believe that the Yangchongli Au deposit and the Shujiadian Cu deposit are two metallogenic events in the same area, and the Yangchongli Au deposit is the end of the metallogenic system.