The Mineralography Characteristics And Its Genetic Significance Of The Tianbaoshan Pb-Zn Deposit In Huili Sichuan

Tianbaoshan Pb-Zn ore deposit is located in the territory of Baiguowan village,Huili County, Sichuan Province, the southern of Hengduan Mountains, and it is one ofthe large Pb-Zn deposits in the famous Sichuan-Yunnan-Guizhou low-temperaturemineralization area, China. The geotectonic position of deposit is the western marginof the Yangtze block and in the middle of Kangdian axis. It is belongs to the PaleozoicDiandong carbonate platform, which is at the west side of the Yangtze craton, and theedge of Proterozoic Kangdian basement complex. The deposit is obviously controlledby Anning River fault zone.The regional geological and tectonic evolution of the Tianbaoshan deposit hasexperienced five major evolutionary stages:（1） Late Archean-early middle and lateProterozoic, the double basement formation stage. Archean Kangding group constitutethe crystalline basement of this area, the north-south intermittent distribution. In theearly middle and late Proterozoic, at eastern and western of the crystalline basementdeformed after Jinning movement, constitute the folded basement of this area.（2）Early Sinian, the continental rift stage, formed a discontinuous sedimentary cover.（3）Late Sinian-late Paleozoic, the passive continental margin stage, formed a relativelycontinuous sedimentary cover in this area. Provide a channel for later fluid migration.（4） Late Permian-late Triassic, the mantle plume activity and continental rift stage,Emeishan basalt erupted. This event might provide a partial material source for theformation of deposit.（5） Late Triassic-Paleogene, the Orogenic stage,Sichuan-Yunnan-Guizhou region was under strong east-west strss squeezed. Longmenmountain-Cuiping Mountain uplifted, and at the same time, formed a foreland basin atthe margin of the Yangtzs plate. These special geotectonic position, tectonic evolutionand magmatic activity, provide a very favorable geological and tectonic conditions forthe Sichuan-Yunnan-Guizhou low-temperature mineralization area to formed a seriesof Pb-Zn deposits, Carlin type gold deposits, and orogenic type gold deposits. Atpresent, the predecessors have already found over400Pb-Zn deposits and mineralizedpoints. The ore of Tianbaoshan Pb-Zn ore deposit was hosted in the middle of the UpperSinian Dengying Formation（Z2d2）.According to the difference of lithology it can bedivided into four levels, and the main ore-bearing layer is the third one （Z2d2-3）：Theupper part is gray to light gray thick-bedded dolomite, the lower part is gray-dark graymedium thick layer to thick bedded dolomite. Locally see siliceous dolomite,occasionally see sand lens, commonly see gray chert nodules and bands, calcite veinsand recrystallization phenomenon. The Dengying Formation dolomites generally havehigh porosity and permeability, and have the characteristic of hydrothermal dolomite.The main metallic minerals of Tianbaoshan Pb-Zn deposit including: sphalerite,galena, chalcopyrite, pyrite, chalcocite, freibergite, pyrargyrite, siderite, limonite,cerussite, malachite, etc. The types of ore structure are as follows:（1）Dense massivesphalerite-galena ore.（2） Dense massive sphalerite-chalcopyrite-galena ore.（3）Dense massive chalcopyrite ore.（4） Massive sphalerite-galena ore.（5） Veins andstockwork sphalerite-galena ore.（6） Disseminated and veinlet sphaleritesphalerite-galena-chalcopyrite ore.（7） Brecciated sphalerite-galena ore.The surrounding rock alteration of Tianbaoshan deposit is relatively simple.Mainly are silicification, dolomitization, pyritization and weak sericitization.The ore body is obviously controlled by faults, outputs mainly as stratiform,stratoid, and lenticular. The ore body exists in faults, interlayer gliding structures, theturning point of folds, and the Custer solution space, showed a significant feature ofepigenetic low-temperature hydrothermal deposit. The mining area can be dividedinto two parts, named Tianbaoshan ore block and Xinshan ore block. Ore body ofTianbaoshan ore block is mainly hosted between the south wing of nearly east-westShagou anticline, and the north wing of nearly east-west Shagou syncline. F2fault isthe main ore controlling structure of Tianbaoshan ore block. Ore body of Xinshan oreblock is hosted between the Xinshangou anticline and Xinshangou syncline.Tianbaoshan Pb-Zn ore deposit is one of the most representative deposits in theSichuan-Yunnan-Guizhou low-temperature mineralization area. Our predecessorshave done a lot of intensive study about ore deposit geology, ore field structure,geochemistry, fluid inclusions, surrounding rock alteration etc. And obtained a lot ofresearch results, generally considered this deposit is a typical strata-bound ore deposit,some scholars called it as Dadu River type Pb-Zn ore deposit. However, for the mostbasic ore mineralogical characteristics research of Tianbaoshan Pb-Zn ore deposit isrelatively weak. Therefore, in this thesis, I chose mineragraphy characteristicsresearch of Tianbaoshan Pb-Zn ore deposit as the topic. I was tried to figure out the mineralogical characteristics of the deposit, and the relationship of ore minerals, andmineral produce order. Based on these, divided the deposit metallogenic stages andmetallogenic periods. These works can provide basic mineralography data forunderstanding metallogenic model. Then summarize the main controlling factors fordeposit, provides basic theoretical support for establishment of regional prospectingmodel, guide mine deep and periphery prospecting.Based on the field geological survey of the Tianbaoshan Pb-Zn ore deposit, Ifigured out the scale and occurrence of ore bodies, the surrounding rock alteration ofore bodies, and the main controlling factors of ore bodies. I paid special attention toobserve the interspersed relationship of ore bearing veins, and determined thesequence of their formation. During the research process of this thesis, in order to geta better understanding of the structural characteristics of deposit, I carefully observed2014midway,2036midway,2064midway,2074midway and2084midway ofTianbaoshan ore block. I totally collected32pieces of rock and ore samples, grindeda certain number of slices and polished sections. After that, I identified these slicesand polisher sections under the microscope and totally took244photographs. Besides,I did some electron microscopy scanning and electron microprobe studies.Based on the study of these slices and polished sections, I determined the kindsof metal minerals, the macro and micro interaction of minerals（ore structure, oretectonic）, the sequence of mineral formation. And then I divided Tianbaoshan Pb-Znore deposit in to three main mineralization periods and five mineralization stages.Through these studies, I divided the mineral generated order of TianbaoshanPb-Zn deposit as follows: Strawberry pyriteâ†'pyrite+sphaleriteâ†'pyrite+sphalerite+galenaâ†'sphalerite+galenaâ†'cerussite+smithsonite+hemimorphite+mackinawite+limonite. The ore formation process had experiencedthree matallogenic periods, named deposition-diagenesis period, hydrothermalmineralization period and supergene oxidation period. Hydrothermal mineralizationhas three stages: sulfide-silicaton stage（generated pyrite+sphalerite+quartz）,sulfide-dolomitization stage（generated sphalerite+galena+dolomite）, calcitizationstage（no mineralization, generated calcite）.In this thesis, I also did some surveys and study about the cause of formation ofcopper mine in Tianbaoshan Pb-Zn deposit. The main copper mineral within themining area are as follows: chalcopyrite, freibergite, azurite, malachite etc. Throughmacro survey of mining area, preliminary think that the formation of copper ore hadno direct relationship with the formation of Pb-Zn ore. The copper body should be products of another mineralization, might closely related to the extensive grewdiabase veins.According to the structural characteristics, the ore bearing surrounding rockproperties, the ore body occurrence characteristics, the surrounding rock alterationtypes, the ore structural control, and previous research results of Tianbaoshan Pb-Znore deposit. The author of this thesis identified Tianbaoshan Pb-Zn ore deposit is atypical Mississippi Valley-type（MVT）Pb-Zn deposit. Tianbaoshan Pb-Zn ore depositcan be compared with Daliangzi Pb-Zn ore deposit of Huidong, Huiz（eQilinchang oredeposit, Kuangshanchang ore deposit）ore deposit of Yunnan, and also can becompared with Pb-Zn ore deposit in the Mississippi Valley of America.