Geologic And Fluid Inclusion Characteristics Of The Xiyi Zn-Pb Deposit In Baoshan,Yunnan Province

Xiyi Zn-Pb deposit is located in the Baoshan- Zhenkang lead, zinc, copper, iron and other metal ore mineralization belt, which is located in the central and northern of Baoshan Block. Baoshan Block located between the Nu Jiang fracture and Lancang Jiang fracture. The main research about Xiyi Zn-Pb deposit is basic geology. But the study about the characteristics and evolution of ore-forming fluid is less. There are some disputes about the origin of the deposit. This study through the field geological exploration, the microscopic identification, fluid inclusion testing, find out the deposit geologic characteristics and fluid properties, discussed the genetic type of ore deposits.Orebody presents like-layered, vein and lenticular output. It mainly hosted in the carboniferous xiangshan group(C1x), devonian system heyuanzhai group(Dh), devonian system xiangyangsi group(D1x). Ore body is mainly controlled by f-17 fracture that move towards north east. Sphalerite, galena, pyrite, marcasite, arsenopyrite, are the main primary metal minerals. The gangue minerals are calcite, quartz and barite. Metasomatic texture, metasomatic relict texture, cementation texture, staggered structure crush texture are the main ore structure. Disseminated, net vein, breccia, block and so on are the main ore structure. Carbonate lithification, pyritization, baratization are the main alteration types. According to contain vein cut through relationship, containing mineral calcite vein is divided into three periods respectively, sphalerite-galena-calcite phase(I), galena-calcite phase(II), and quartz-pyrite-calcite phase(III).Research on fluid inclusions show that calcite vein of three periods in Xiyi Zn-Pb deposit mainly contain liquid-vapor two-phase aqueous inclusions and a small amount of pure liquid inclusions.In the second stage, third stage we found pure methane gas phase inclusions. The ore-forming fluid temperature in the range of 100 ~ 200 ℃, the peak temperature in the range of 110 ~ 110 ℃; the change of salinity in the range 11~21% NaCleq range, most of data is more than 14% NaCleq, peak salinity range in 16~18%NaCleq.Fluid density changes in the range of 0.99 ~ 1.1 g/cm3, much greater than 1 g/cm3. Ore-forming fluid has the high salinity, medium density, low temperature characteristics. Ore-forming pressure range between 312~ 312 bar, metallogenic depth is about 1.0 ~ 1.8km, with a mean of 1.2 km.In conclusion, characteristics of Xiyi Zn-Pb deposit exhibited in regional geological background, ore deposit geological and fluid inclusion studies are all consistent with those of MVT Zn-Pb deposit indicated that Xiyi Zn-Pb deposit is Mississippi Valley Type.