| Gejiu tin polymetallic deposit,located in the southeast of Yunnan Province,is an important part of the tin polymetallic metallogenic belt in Southeast Yunnan.This paper chooses cassiterites from 6 types of deposits have been found in the Gejiu ore district as the research object.The doctoral dessertation title of The Study of Geochemical Characteristics of Ore-forming Fluid and the Metallogenic Mechanism on Gejiu Tin-polymetallic is selected based on the National Natural Science Fund Project of the study of cassiterite mineralogy,mineral chemistry and cassiterite U-Pb chronology in Gejiu super tin-polymetallic deposit(serial number:41262004).The research on ore-forming fluids of six types deposits in Gejiu ore district is based on the micro-temperature measurement,the laser Raman,the chromatographic,the OES and C,H,O isotope.The results reveal the evolution of ore-forming fluids and metallogenic mechanism,and establish the spatial distribution model of deposit.The following main achievements from this study are obtain.1?The cassiterite fluid inclusions reveal that fluid inclusions from Gejiu ore district only are aqueous two-phase(type I).According to variation characteristics of the temperature measurement process,it is subdivided into C02-containing inclusion(type ?a)and non-C02 inclusion(type Ib).The fluid inclusions from the skarn Type deposit and tourmaline veinlet belt type deposit are type ?b inclusions.And the fluid inclusions from other 4 types deposit are type ?b and type ?a inclusions.2?Micotemperature measurement results show that from massive sulfide type deposit-greisen type deposit-skarn type deposit-tin containing dolomite type deposit-tourmaline veinlet belt type deposit-interlayer oxidation type deposit,the temperature gradually decreases(average temperature from 423.7?-400.3?-389.5?-350?-345?-313.9?).The salinity of fluid gradually decreases,but the salinity of fluid from interlayer oxidation type deposit is not positively correlated with the temperature(average salinity from 16.4wt%-11.7wt%-11.5wt%-7.3wt%-7.2wt%-14.3wt%).The density remained essentially unchanged(average density from 0.7g/cm3-0.68g/cm3-0.68g/cm3-0.72g/cm3-0.71g/cm3-0.79g/cm3).3?Laser Raman and Chromatography analysis show that the gas phase in fluid is mainly CO2,which contains a small amount of CH4?N2?O2?CO?C2H2+C2H4?C2H6.Cations are mainly Na+?K+,followed by Ca2+?Mg2+.Anions are predominantly Cl-?SO42-,containing a small amount of F-?NO3-.Combined with the result of the analysis,the ore-forming fluids of Gejiu tin polymatallic deposit belong to CO2-rich,Cl-rich,Na-rich fluid system.4?C?H?O isotope study results and combined with inclusions composition study indicate that the primary ore-forming fluid of Gejiu tin polymetallic deposit is the multi-source mixed magmatic hydrothermal.Mineralization process mix with atmospheric,resulting in reduced fluid temperature and cassiterite precipitation.5?Combined with above analysis,the Gejiu tin polymetallic deposit is closely related to the granite.With the granite as the center,the spatial distribution of various types deposits is regular,that is,from massive sulfide type deposit-greisen type deposit-skarn type deposit-tin containing dolomite type deposit-tourmaline veinlet belt type,the depth of mineralization is gradually shallow,and interlayer oxidation type deposit is distributed from shallow from deep.Accordingly,the prospecting should be carried out around the granite. |
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