Geological Characteristics And Metallogenic Prognosis Of Jiawula Ag-Pb-Zn Deposits In Inner Mongolia

Jiawula Ag-Pb-Zn desopits is shallow location, middle-lower temperaturebelongs to sub-volcanic epithermal vein deposits ,which is found byHeilongjiang Geological Exploration Bureau for Nonferrous Metals. In recent,the deposit is being explored because of its shallow location, large scale andgreat economical significance.The mine area is located in the southeast rim of Xiboliya platform and thewest side of the Eerguna-Hulun deep fault, namely the transitional crusttectonic region between Xiboliya platform and China-Korea platform. In thearea there were Erathem and the Pre-cambrian old basements. Eerguna-Hulundeep fault has entered intensive structure-magma active period with itsintensive action since Mescozonic Era. So it played a main role to stratas,structures, magmas and mineralization of the ore field.The northeast Muhaer fault and Jiawula-Chaganbulagen fault controlledthe north and south margin of the ore area. The volcanic-subvolcanicinstruction and eruption central and its radial, ring fault system developed inthe interchange part of northwest and northeast structures. The systemprovided ideal space for instruction, eruption of Yanshanian taxite andtransportation and precipitation of ore liquid.At present, there are forties ore bodies found in Jiawula ore area that theyare all situated in structure-crushed zone as nervation. The main ore body isrelated to the radial fissure and northwest tension-shear fault belts. Thedistribution of ore bodies has a close relationship with that of feldsparporphyry, quarz porphyry, etc. and ore bodies all occurs in structure-crushedzone near metallogenic period rocks or in its edge.The largest ore body of the area is No.2, whose length is 1700m, averagelevel thickness is 5.18m, somewhere, its deepening is bigger than 600m. Theycrop out discontinuously on the earth's surface, become one in depth. Thethickness and grade of bodies vary obviously, the coefficient of variation ofgrade is 88¹27% and the coefficient of variation of thickness is 81%. Theaverage grade of silver ore bodies is Cu 0.59%, Pb 3.37%, Zn 6.39%, Ag1168.75×10^-6.The surrounding alternation of ore bodies is usually limited instructure-crushed belt and wall rock near ore bodies and they are developedgreatly in the structure-crushed zone including ore bodies of nervation, butgraduately weakened in the both sides of them. The type of alteration consistsof silification, chloritization, carbonation, hydromuscovite-illitization,sericitization, fluoritization, epidotization, etc..According to researching the mineral compositions of inclusions, rocksand ores for the Jiawula deposit, it was thought that the deposit is formed bythree stages of metallogeny. The fist stage consists of arsenopyrite, pyrite,sphalerite, quartz with higher temperature;The second one includes sphalerite,arsenopyrite, magnetic pyrite, pyrite, galenite, chalcopyrite, native silver,quartz, carbonate, chlorite with low temperature, while the third is magnetite,sphalerite, chalcopyrite, pyrite, carbonate, quartz, etc. with lower temperature.The pattern age of Lead in ores of the deposit is chiefly in102.39Ma¹33.05Ma and K-Ar age of the quartz-porphyry is about 121.02Ma,so we deduce the metallogenic era is about in the late stage of upperCretaceous Epoch. The deposit has the feauture of small ore-forming pressureand shallow ore-forming depth. The metallogenic fluid inclusionscharacterized as middle-low temperature, pressure, fluid salinity and density.The inclusions have not only a great deal of Pb, Zn, Ag, Cu elements but alsoblack organic compound such as CO2, NH4. It shows that the surfical waterjoin in the metallogenic fluid. Metallogenic elements migrate as alkali metalionic complex and precipitated rapidly in proper temperature, pressure,concentration conditions.Magmatism was strong and frequent in the mine area, whose ages fromlate Hercynian to late Yanshanian, especially, the subvolcanic rocks of the latestage of Yanshanian are related close to mineralization, which provided Ag, Pb,Zn, Cu metallogenic elements and metallogenic fluid for the forming of thedeposit, in the mean time, minor metallogenic material came from wall rocks.By analyzing the feauture of geological, geochemical, geophysicalconditions of the mineralization and the distribution of geochemical,geophysical anomaly of the ore area, the author delineats three sorts ofore-forming forecasting areas in the mineral district and its neighboring areabased on geological anomaly theory, ore-forming forecasting theory ofsynthetic information and analogy method of geology as following:The first level forecasting area: Jiawula AgPbZnCu polymetallogenic areaThe second level forecasting area: Caxi area.The third level forecasting area: Yizishan area and Gaojigaoer area.