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Characteristics Of Ore-forming Fluids And Metallogenesis In The Leimengou Porphyry Molybdenum Deposit, Western Henan Province

Posted on:2013-02-04Degree:MasterType:Thesis
Country:ChinaCandidate:X D ChenFull Text:PDF
GTID:2230330371482276Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
The Leimengou Mo deposit is located in East Qinling, a large metallogenic belt ofMo-W-Pb-Zn-Ag-Au along the south margin of the North China Craton. It is a typicalporphyry Mo deposits in the East Qinling polymetallic ore belt. According to the detailedstudy of geological characteristics of the deposit, electronic probe, X ray powder diffraction,transmission electron microscope were used to study the composition, crystal structure andmicrostructure of altered K-feldspar, fluid inclusion petrography, microscopic thermodynamics,group fluid inclusion composition evolution and stable isotope study were used to identifyore-forming fluid composition, salinity, temperature, pressure and other physical and chemicalconditions. From the perspective of migration and precipitation of Molybdenum, we discussedthe hydrothermal mineralization of the Leimengou Mo deposit.The ore are characterized by disseminated multistage stockworks. The metallization atLeimengou contain four hydrothermal stages:(Ⅰ) K-feldspar stage;(Ⅱ) Quartz-K-feldsparstage;(Ⅲ) Quartz-sulfide stage;(Ⅳ) Quartz-carbonate stage. The hydrothermal alterationtypes of wall rocks in the Leimengou Mo deposit include K-felspar alteration, biotitizaion,sericitization, phyllic alteration, silicification, epidotization, chloritization and kaolinitization,etc. K-feldspar alteration and silicification-sericitization are most closely associated with Momineralization, Massive K-feldspar alteration is the pre-mineraliztion, silicification–sericitization accompanying with the molybdenite.The K-feldspar have sharp interface with relic minerals (as quartz and plagioclase) andcontain numerous pores up to several hundred nanometers, and that most of them containirregular or needles of crystalline hematite and barite. These features all agree with theK-feldspar as the product of fluid-rock interaction. And the coexistence of hematite and bariteindicate that the ore-forming fluids in the early K-feldspar alteration stage are highly oxidizedand alkaline-rich.Petrography, microthermometries and composition of fluid inclusions demonstrate thatthe transportation stage of molybdenum are characteristics of medium-high temperature (>270410℃), medium to low pressures(83139MPa), medium to low salinities(214wt%)of H2O-CO2-NaCl system. the fluids of deposition stage accompanied with the escape of CO2,little decrease of temperature(230370℃) and pressure(75124MPa) with detached salinity of1.02to17.61wt percent NaClequivand31.39to40.61wt percent NaClequiv.Hydrogen-oxygen isotopic compositions indicate that magma fluid mixing with meteoricwater in various degrees as the main ore forming fluid. Carbon-oxygen and sulfide isotopes reveal the ore-forming fluid main from the deep region.Given that Mo is an element with high electrovalence and minorionic radius, itsconcentration and transportation increase in alkaline fluids and Mo tends to precipitate oncethe fluids became acid. We suppose that the early K-feldspar alteration stage can represent thetransportation stage of the molybdenum. The depletion of K decreased pH values of the fluids.The crystallization of hematite and barite help to reduce the fO2and SO42-to H2S andconsequently promote Mo deposition. Sericitization Mo combined with the S2-. The depositionof molybdenum occurred during the water-rock interaction process, The depletion of K,oxidizing condition to reducing environment decrease of pH and some extent fluidimmiscibility are actors that controlling the precipitation of Mo and the formation of the oredeposit.
Keywords/Search Tags:Hydrothermal mineralization, K-feldspar alteration, fluid inclusion, Leimngou porphyry Mo deposit, Western Henan
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