On The Geochemical Process Of Mineralization Of Telliurium Deposit In Dashuigou Of Shimian County In Sichuan Province

Dashuigou tellurium deposit of Shimian, Sichuan province is located in the connecting part of Geosyncline and Western Yangtze platform, eastern Songpan-Garze orogenic belt and middle part of nappe structure of Mt. LongMen-Mt. DaXue-Mt. JingPing. Regional tectonic activities are very strong here. There are two nappe decollement ductile shear zones namely XiYoufang and Binduo and other slice belts such as crab and snail slice belt, Dashuigou slice belt and Hongba slice belt are formed. The magmatism is intensive. The igneous rock is grown. The exposed rocks include Jinningian granite and quartz diorite, Indosinian, Yanshanian-Xishanian granite, monzogranite, diorite, quartz diorite and small scaled Hercynian basic rock and ultrabasic rock dike. Tellurium deposits have occurred mainly in nubby coarse grained dolomitic marbles of the Middle and lower Triassic, belted carbon bearing muddy dolomitic marbles that contained calcareous metamorphic basic volcanic rocks. There are strong hydrothermal fluid activities in mining area. Wall rock alteration is developed. Dolmitization is the main trend followed by albitization, amphibole rock-biotite-chloritized alteration, sericitization or muscovitizatio, siliconization and pyritization. The most important mineral assemblages are dolomite-calcite-pyrrhotite-pyrite-quartz-sericite-daphyllite, Tsumoite, bismuthinite, tellurobismuthite, sylvan and so on.Based on the study of background of regional tectonics and geochemical characteristics of deposit, this paper systemically studies the geochemical process of origin, movement and assembles of ore forming of tellurium deposit. The study includes the origin of ore-forming material resources, The main research contents include:the source of deposit, physical; chemical and thermodynamic conditions of ore-forming fluid; migrating form of tellurium element and geochemical mechanism of precipitation preconcentration of tellurium element. And it discusses the metallogenic model of tellurium deposit. Through the above study, reached the following understanding:Firstly, the regional geologic tectonics of Dashuigou tellurium deposit is very complicated. There are not only successive activities of regional discordogenic fault but also activities of hypomagma in many times. There are still effects of very important and strong tectonic-thermal events. The formation of this deposit is closely tied with activities of regional discordogenic fault, activities of hypomagma in many times and strong tectonic-thermal events.Secondly, the lanthanon proportion model is right deviation. Tellurium deposit has obvious characteristics of positive Eu anomaly, negative Ce nomaly, light rare earth elements loss and heavy rare earth elements enrichment. It is contrary to the characteristics of host rock, namely light rare earth elements enrichment, heavy rare earth elements loss and slightly losses of Eu and Ce. Also Dashuigou Te deposit on granite REE, trace elements and other parts of granite mine production of rare earth elements, trace elements were compared. The results show that the loss of a large ditch with deep granite REE Eu (Eu), depleted trace elements U, Th, low Ba, Nb, Sr characteristics. It predicts that the forming of tellurium deposit is related with the deep geological process. It predicts that the forming of tellurium deposit is related with the deep geological process.Thirdly, the lead isotope evidences prove that ore-forming materials of tellurium deposit came obviously from the crust and mantle materials. Deposit minerals, rocks and ores of lead△β-βγ causes, map projection range also showed that the deposit formation is closely related with the magmatic activity. Sulfur isotopic composition of deposits δ34S value comes almost to a smaller and smaller range. Tellurium deposit forming material with obvious from the characteristics of crust and mantle. The carbon isotopic composition of CO2is also evident in the characteristics of the magma source of carbon. The isotopic evidence proves consistent, tellurium and sulfur mineralization agent, carbon is likely homologous, both from the deep.Fourthly, the features of hydrogen and oxygen isotopes composition of ore-forming fluids in different stages show that the fluid in the initial or early ore-forming stage has the characteristics of hydrogen and oxygen isotopes composition of magmatic water. The fluid in the stage of ore-forming is mainly composed of magmatic water. But there was wet precipitation mixed into it. It indicates that ore- forming fluid is mainly not wet precipitation but deep fluid.Fifthly, chemical and thermodynamic conditions of ore-forming fluid of Geochemistry and Thermodynamics show that ore-forming thermal fluid is middle-low salinity and density fluid. The results of temperature test of inclusions show that tellurium deposit is mesothermal or hyperthermal deposit. In the early hyperthermal stage, ore-forming thermal fluid was alkaline fluid. In the mesothermal stage of ore forming, it was alkalescence fluid. In the late stage of ore-forming, it was subacidity fluid. It shows that the ore forming of tellurium is a process of decreasing of alkalescence but increasing of acidity. Oxidation-reduction potential is gradually increasing with the lowering temperature of ore-bearing thermal fluid. In the early hyperthermal stage, oxidation-reduction potential is relatively low. It increases relatively in the middle and late hyperthermal stage. It indicates that the process of ore-bearing thermal fluid is a process that oxidation-reduction potential increasing. It also shows that the ability of deoxidization of ore-forming fluid is high in the early hyperthermal stage. Ansd its oxidation capacity is low. The increasing of oxidation-reduction potential in the middle and late hyperthermal stage shows that the capacity of deoxidization of thermal fluid is weak relatively. But its oxidation capacity is strong. Next, the changes of oxygen fugacity and sulfur fugacity are as follows:with the lowering of temperature and pressure of thermal fluid, the oxygen fugacity and sulfur fugacity are coming down. It can be deducted that the tellurium element in the deposit are likely to transport in the relative reduction environment and be reduced in relative oxidation environment.Sixthly, in the ore-forming thermal fluid, tellurium element transports in three forms includes tellurium-chlorine complex, tellurium-sulfur complex and tellurium-hydrogen complex. With the changing of chemical and thermodynamic conditions of ore-forming fluid, tellurium-chlorine complex, tellurium-sulfur complex and tellurium-hydrogen complex go through a chemical resolving process. Tellurium is deduced and concentrated into ores.