Characteristics And Genesis Of The Luowei Silver-lead-zinc Deposit In Guangxi Province

The Xidamingshan area is one of the main Ag-Pb-Zn mining and important metallogenic prospecting regions in Guangxi province. Most of the Ag-Pb-Zn deposits in this area are of hydrothermal vein-type. The Fenghuangshan Ag-Pb-Zn and Lujing Pb-Zn deposits are two representative deposits of this type in the Xidamingshan area. Geological investigation and microscopic observation combined with analyses of fluid inclusion, major and trace elements, and stable isotopes have been carried out on the Fenghuangshan Ag-Pb-Zn and Lujing Pb-Zn deposits, with a focus on the analysis of their origin.The following are major achievements obtained in this thesis.1. Mineral cross-cutting relation and assemblage support division of the formation process of the Fenghuangshan Ag-Pb-Zn and Lujing Pb-Zn deposits into hydrothermal and supergene metallogenic epochs. The hydrothermal metallogenic epoch can be further divided into three stages, including quartz-pyrite stage, quartz-polymetallic sulfide-silver mineral stage, and carbonate-polymetallic sulfide-silver mineral stage (the main stage) in the Fenghuangshan Ag-Pb-Zn deposit, and quartz-pyrite stage, quartz-polymetallic sulfide stage (the main stage) and carbonate stage in the Lujing Pb-Zn deposit.2. The analyses of fluid inclusions are consistent with defining the ore-forming fluids of the two deposits as middle to low temperature, low salinity, and low density fluids, and occurring of the mineralization at near-surface. The temperature, salinity, density and pressure of the ore-forming fluid at the main stage are defined as about 245℃, 7.34wt.% NaCl equiv, 0.87 g/cm3 and 36.0×105Pa in the Lujing Pb-Zn deposit, respectively; and about 170℃, 2.1wt.% NaCl equiv, 0.92g/cm3 and 9.14×105Pa in the Fenghuangshan Ag-Pb-Zn deposit, respectively. The hydrogen and oxygen isotopic analyses support the formation of the two deposits by the same epoch of hydrothermal activity, and derivation of the ore-forming fluids from magmatic water mixed with a little meteoric water.3. Trace elements and stable isotopic analyses indicate derivation of sulfur and lead-zinc of the two deposits from magma and Cambrian and Lower Devonian clastic rocks, respectively, but derivation of silver in the Fenghuangshan deposit from clastic rocks of the Cambrian, especially the Huangdongkou Formation in it. 4. Element geochemical analyses indicate an origin of the Cambrian and Lower Devonian clastic rocks of the Xidamingshan area from normal terrigenous clastic sediments in passive continental margin. Contents of silver, lead and zinc in these clastic rocks are higher than background values of these elements in upper continent crust. These features, together with little record of synsedimentary igneous and hydrothermal activity in these sediments, indicate occurrence of metal enrichment mainly by post-sedimentary hydrothermal activity. The higher tungsten, bismuth and molybdenum contents of the quartz porphyry dikes imply that the vicinity and depth of the quartz porphyry could be the potential prospects for these metals.