The Ore Forming Environment And Mineralization Of The Barite Deposits In Xinhuang And Tianzhu Of The West Hunan And East Guizhou Province

Barite is an important Ba-rich minerals. It has been widely used in many aspects such as the petroleum engineering、chemistry and papermaking industries and so on.It’s an important and indispensable nonmetallic resources in human society. Now the barite is mainly used as oil and gas drilling mud weighting agent. The barite deposit, which located in Xinhuang and Tianzhu countries at the southeast of the Yangtze platform, is formed in the early Cambrian and become the largest barite deposit in the world. Therefore, the study of it has an important scientific significance.This paper carried out analysis of the mineralogy of barite by Electron microprobe, the comparative study of trace and rare earth elements about the barite ore and surrounding rocks, the sulfer isotope analyses and the organic geochemistry analysis. The forming environment and mineralization process has been discussed.The major achievements are as follows:(1)The mineral analysis by Electron Microprobe and the discovery of zoned hyalophane imply that the seafloor hydrothermal fluid which rich in Ba element have a significant contribute to the barite deposit.And it’s a process of episodic and progressive.(2)The trace elements ratios of V/Cr and U/Th and other indicators suggest that the deposits formed in an anaerobic environment.The rare earth elements reflected that the ore samples have obviously Ce element negative anomaly, higher Y/Ho value and Eu positive anomaly, implying that the ore-forming process was strong effect by the seafloor hydrothermal fluid.These indicators also reflected that the barium mainly come from the seafloor hydrothermal jet substance. (3)The value of the major elements, such as n(SiO2)/n(Al2O3)、n(Al2O3)/n(Al2O3+Fe2O3) n(Al)/n(Al+Fe+Mn)、n(Si)/n(Si+Al+Fe) indicate that the barite established in the continetal margin and was affected by the hydrothermal material. (4) The sulfur isotope composition of barite range from+40%o to +45%o,enriched in 34S,and the sulfer isotope of BaSO4 was characterized by tower style distribution, which indicating that the source of sulfur is of single-source and from the seawater sulfate. The δ34S of pyrite is lower than the δ34S of the sea water contemporary,indicating that biological bacteria action palyed an important role in the sulfate reduction in the seawater and imply that the barite deposit formed in an environment where a limited seawater exchange.(5) Most of the samples of the Xinhuang-Tianzhu barite deposit’s rocks have Ro values larger than 2%.The content of chloroform bitumen "A", the conversion rate of organic matter, Ts/(Ts+Tm)、C29Ts/(C29H+C29Ts), sterane isomerized index all reflect the organic matter is in the over mature stage, indicating that the ore-forming hydrothermal fluids accelerated the maturity of organic matter. The carbon number distribution of normal-alkanes and isoprenoids,the values of Pr/Ph、C30*/C29Ts and gammacerane index all suggest that the organic matter in the deposit are mainly sourced from the bacteria and algae of marine,and deposited in a reductive environment.The organic matter provides a certain energy for the form of barite and some algas and bacterias have the capability to precipitate barite to providing nucleation sites and enhancing crystal growth.Based on the above analysis, the barite deposit formed in a semiclosed-colsed lagoon and anaerobic environment where there is frequently seafloor hydrothermal activities, Biological and organic matter played an important role in the formation of barite deposit...