Studies On Geological And Geochemical Features Of Pb-Zn Ore Deposit In Yaolaojian-longmenjian, Dongzhi, Anhui Province

Anhui is one of the important nonferrous metals metallogenetic areas in China.But inMesozoic,especially in Yanshanian nonferrous metals mineralization was extensive.Yaolaojian-Longmenjian Pb-Zn ore deposit was recently discovered in Dongzhi, SouthwestAnhui. Establishing a new prospecting situation.Explaining the genesis ofYaolaojian-Longmenjian ore deposit is of great significance to understand themineralization and the geological evolution correctly and expand the scale of mineraldeposit.In this paper, based on systematic analysis to geologieal data of the study area, andsynthetic studies on Pb-Zn ore-deposit by applying multiple disciplines and methods suchas microscopic identification, rock trace element analysis, fluidinclusion and isotopegeology, analysising the fluid inclusion’s charcters,the physicochemical conditions andthe ore-forming materials source.Through the above studies, ore-forming materials sourceand mineralization mechanism has been discussed, metallogenic model has been establishedpreliminarily.Pb-Zn deposits are mainly produced in the north-east to the fault zone and nearthe north-south zone to the secondary structure, Pb-Zn orebody distributes in the fault zonenear to construct the composite parts,controlled by structures obviously. The wallrock alteration, including silicification,carbonate,pyrite,and so on.Ore minerals are mainlygalena, sphalerite and pyrite;Gangue minerals are mainly quartz, small amounts of chloriteand calcite. The electron microprobe study found that Pb-Zn occurrence mainly in theform of galena and sphalerite containing pyrite and chalcopyrite,occasionally pyrolusiteand ilmenite.According to petrochemical characteristics of Daicun porphyry pluton,we draw theconclusion that pluton belongs to the calc-alkaline basalt series. It displays that pluton hasthe character of rich Kalium and natfium，as well as the character of rich calcium isobvious,consistent with that rock is rich in calcic mineral.The reason may be that when themagma rises，it suffers from the crust calcic matter’s strong contamination，which is calledthe crust’s assimilative hybridism.Evidence illuminates that the intrusive granitic magmaand remelting of the crystalline basement provided an important source of ore formingmaterials.Deep source of magma which are rich in Pb, Zn, Cu, Au and other elementsprovide a basis for ore-forming elements. Fluid inclusion in mineralization phase are primary inclusions,no seeondary andpseudoseeondar inclusions.They have variety shapes,including grain of rice-like,oval,irregular round and various irregular shapes:their most sizes range from2to10um:Thetype of inclusions are simple,including liquid-rich phase,vapor-riehPhase and single liquidphase.Thermodynamic parameters of fluid inclusions indieate that: the temperature of themain stage of mineralization is170～220℃,the salinity0.53～23.05wt%,the density0.60～1.10g/cm3. which indicate that ore-forming fluid of the study area has alow-medium temperature,low salinity,low density charaeteristics,so the genetic type of thedeposit is a epithermal deposits with low temperature. Theoretical mineralization depth is60～1450m, average296.1m, it is shallow moderate ore-forming depth. The ore-formingfluid salinity decreases with decreasing temperature,Implying meteoric water can dilute theore-forming fluids.δ18OH2Oof ore fluid average7.27‰, showing that magmatic waterfeature. The fluid is from magmatic water mixed with meteoric water,and heating of orebodies comes from magma.Theδ34S of study shows that S mainly from typical mantle. Hydrothermal calcitesfeature implies that ore-forming fluid and material for hydrothermal deposits are derivedfrom mantle.Granite porphyry granitoids and wall rock are rich in chalcophile elements ofCu, Pb, Zn, Ag.Geochemical characteristics of granite-porphyry granitoids indicate thattheoriginal magma was upper mantle alkli basalt, which was contaminated by crustmaterials during the intrusion. Eu Positive anomaly of Ore may be speculated that the rareearth elements in hydrothermal fluids can be provided by the deep magma.Theore-forming minerals are provided by the deep magma and the surrounding.Based on the above studies, the most significant fruits of this study can be concludedas follows.1) The ore-body be filled in the form of single pulse or stockwork veins,and inthe filling process there were obvious cryptoexplosion.2) Magmatic origin of Daicunporphyry pluton shows crust-mantle mixing source region.3) The fluid is from magmaticwater mixed with meteoric water,and heating of ore bodies comes from magma.Daicungranite porphyry pluton and clastic rocks(Pt2h) may provide ore-forming materials.4) Theore-forming elements may have multiple sources and a crust-mantle mixing feature. Theore-forming minerals are provided by the deep magma and the surrounding strata(surrounding rock).5) the deposit is a shallow tectonic, magmatic, and stratigraphic jointcontrol in low temperature hydrothermal deposits.6) The metallogenic model of Pb-Zndeposit has been established.