The Mineralography Characteristics And Its Genetic Significance Of The Daliangzi Pb-Zn Deposit In Huidong, Sichuan

The Daliangzi Pb-Zn deposit is located in Huidong County, Sichuan Provience, and it is one of the famous large Pb-Zn ore deposits in the Sichuan-Yunnan-Guizhou polymetallic metallogenic belt. Its tectonic attribution belongs to the Kangdian basement complex belt second-order tectonic unit under the Yangtze continental block first-order tectonic unit. In this region, the basement faults are very developed, the basal complexs have intense deformation and often appear mylonite, and develop a series of anticline and syncline structure, mainly lies three periods of tectonic structure.The Sinian is the first stable epeiric sea sedimentary strata in the Yangtze block,its lithology mainly consist of carbonatite(dolomite, algal dolomite)and interbeds of clasolite, characterized by rich algae and stromatolite. Paleozoic erathem also has a certain distribution in the Daliangzi Pb-Zn mining area,the Yuhucun Formation or Maidiping Formation in the Lower Cambrian(∈1)is characterized by dolomitic phosphate, siliceous phosphate, shale and silicalite deposition. The Middle-Lower Cambrian(∈1-2)has the upper hand in fine sandstone-siltstone, the Upper Cambrian(∈1-3)is dominant in dolomite. The regional geology and tectonic evolution characteristics all above laid a favorable foundation on regional metallogenic geology and tectonic conditions for forming the Daliangzi Pb-Zn deposit.Exposed strata in Daliangzi mining area include Dengying Formation in the Sinian, the Qiongzhusi Formation in the Cambrian. The Dengying Formation is the main ore bearing strata of ore body. The structure of the mine is mainly the fracture and the joint that the main development is the fracture structure of the four groups which is respectively NWW trending, NW trending, EW trending and NE trending. The ore body is mainly located in the fracture structure and the black fracture zone. Most of the ore bodies are concentrated in the fracture zone of the boundary between F5 and F15. Furthermore, the so-called black fracture zone is actually part of the main ore body in which a large number of black carbonaceous matter and organic matter(asphalt) enriched. Daliangzi lead- zinc deposit include No. 1 ore body and No. 2 ore body. No. 2 ore body has been mined. The ore body shape is irregular, lenticular, saccate, veined and net veined. Wall rock alteration in this deposit is relatively simple that mainly include the silicide(flint and quartz), carbonation(dolomite, calcite), sulfide of(sphalerite, galena, pyrite), brown iron mineralization and peacock petrochemical. The low temperature surrounding rock alteration closely associated with mineralization which can be used as the important ore prospecting basis.Integrated field, geologic features of ore deposit, mine opening geological record compiling, polished sections and thin sections reveal the ore composition of the deposit that include sphalerite, galena, pyrite, marcasite, digenite, tetrahedrite, pyrargyrite, anglesite, cerussite, covellite, limonite and malachite. The gangue mineral consist of dolomite, calcite, quartz, kaolinite and barite. Ore structure type include mesh-vein structure, vein structure, disseminated structure, brecciated structure, massive structure and hypergene structure. Ore texture include crystalline texture, replacement texture, separation of solid solution texture and pressure texture, especially the replacement texture is most common. The major useful compositions of ore is zinc, followed by lead, mainly associated beneficial elements are Ag, Cd, S, followed by Ge, Ga, and harmful elements are P, As, Fe. According to studies of intergrowth relationships and assemblage characteristics of the ore mineral, the mineral arisen sequence of Daliangzi Pb-Zn deposit as follow: sedimentary dolomite + pyrite + pitch â†'crystallized dolomite + quartz + christophite + marcasite + arsenopyrite â†'brownness and yellow sphalerite + galena + tetrahedrite + pyrargyrite + pyrite + calcite + quartzâ†'pyrite + beige sphalerite + galena + chalcopyrite + calcite + quartz + pitchâ†' smithsonite + cerussite + greenockite + limonite + malachite + digenite. The deposit had experienced three different metallogenic periods, including sedimentary diagenetic period, hydrothermal period and supergenetic period.Based on the test data of S, Pb isotope geochemistry and fluid inclusion from predecessors, this paper suggest by further study that:Sulfur in the ore is mainly derived from the Dengying Formation in the Sinian, and lead is from moderate-deep metamorphic rock series in the crystalline basement volcanic-sedimentary formation of west Yangtze block;The ore-forming fluid is derived from residual water after evaporating and concentrating in the basin with feature of low temperature and low salinity, and organic matter may participate in the mineralization. Daliang deposit formation was closely related to fault structure, the black fracture zone and the dolomite in Dengying Formation, and among these dolomite and fracture structure system is the most important ore-controlling factors of the Pb-Zn deposit. During the Process of West Sichuan Plateau orogenic uplift in the Indo-China epoch, basin fluid happen long-distance migration and dissolved massive lead and zinc material of basement volcanic-sedimentary formation by the combination of the nappe, pressure torsional forces(geological tectonism) and gravity, and evolved into metallogenic hydrothermal. Then migrate to the high porosity- permeability dolomite in Dengying Formation, and immediately happen crypto-explosive function of the ore-forming hydrothermal, which led the wall rock to burst broken. Formed the fracture zone further provides a good space for transfer mineral deposition, ore blending and ore-containing of the ore-forming hydrothermal. The ore-forming hydrothermal happen TSR in fracture zone, prompting metal sulfide precipitate, subside and mineralize in the black fracture zone.According to the structural characteristics, the wall rock properties, the ore body occurrence characteristics, the wall rock alteration types, the ore structural control, and previous research results of Daliangzi Pb-Zn ore deposit. The author of this thesis identified Daliangzi Pb-Zn ore deposit is a typical Mississippi Valley-type(MVT)Pb-Zn deposit. Daliangzi Pb-Zn deposit can be compared with Tianbaoshan Pb-Zn deposit of Huidong, Huize(Qilinchang ore deposit, Kuangshanchang ore deposit)ore deposit of Yunnan, and also can be compared with Pb-Zn ore deposit in the Mississippi Valley of America.