Geology And Ore-forming Fluid Geochemistry Of The Changkeng-Fuwan Gold-sliver Deposit, Guangdong Province

The Changkeng-Fuwan gold and sliver deposits are located at the juncture among the northwestern margin of the Upper Paleozoic fault-basin, the southwestern segment of the Mesozoic-Cenozoic Sanshui rift-basin, and the three regional deep-faults of Guangzhou-Conghua, Gaoyao-Huilai, Xijiang, with the strikes of NNE, EW, and NW, respectively. The Changkeng-Fuwan gold and silver deposits are large scale fine disseminated deposits, which has been discovered in recent years. Gold and silver deposits occur in the same inter-bedded tectonic crush belt, which are independent ore-bodies characterized with gold in the upper part and silver in the lower part. Therefore, they have drawn attention from geologists both in China and abroad. The dissertation studied the characteristics of the geology, the fluid inclusions and isotopes in detail on the basis of the full and accurate field geological research and systemic laboratory analysis. Combined with the geochronologic studies, the dissertation discussed the mineralized mechanism and established metallogenic model of the Changkeng-Fuwan gold and silver deposits.Changkeng-Fuwan gold and silver deposits are controlled by the tectonic crush belt, and the layer-like or lenticular ore bodies occurred in Zimenqiao Formation, Lower Carboniferous and Xiaoping Formation, Upper Triassic. The gold precipitation can be divided into three main stages as follows: quartz-pyrite-phyllic, polymetallic sulphide stage, and quartz-carbonate stages. The sliver pricipitation can be divided into three main stages, which are quartz-pyrite-phyllic stage, polymetallic sulphide stage and quartz-carbonate stages.By studing the characteristics of fluid inclusions, we have found that there are two types of fluid inclusions: liquid inclusions and liquid-rich inclusions. The homogenization temperature of the gold ore-forming fluid ranges from 158~282℃, with the peak values within the range of 190~220℃. The ice-point temperatures of the gold deposit fluid inclusions range from-0.2 to-6.6℃. The salinity varies from 0.35~9.88% NaCleq. The homogenization temperature of the silver ore-forming fluid ranges from 146~289℃, with the peak values within the range of 190~220℃. The ice-point temperatures of the Sliver deposit fluid inclusions range from-0.1 to-8.0℃. The salinity varies from 0.18~11.70% NaCleq. From the early stage to the late stage of mineralization, the temperature and salinity of ore-forming fluid were gradually decreased.Through the studies of the sulfur and lead isotope indicate that metallogenic materials of the deposit mainly come from the magma, partly from the surrounding rock. The carbon and oxygen isotopic data are consistent with derivation of carbon mainly from a mixed magma of mantle with crust source and dissolve marine carbonates. H, O, He and Ar isotopic researches indicate that the metallogenic hydrothermal fluid mainly contained magmatic hydrothermal and mixed with the meteoric water and increasing gradually with mineralization process.The geological and geochemical analyses indicate occurrence of fluid mixing during evolution of ore-forming fluids, as the mineralization proceeds, the temperature and salinity of the ore-bearing hydrothermal fluids were gradually decreased, and the mixing of magmatic water with meteoric water resulted in the precipitation of ore-forming materials.