Mineral Chemistry And Genesis Of Sphalerite In Mengnuo,longling Lead-zinc Deposit,Western Yunnan

The bismuth-lead-zinc mine is one of the larger lead-zinc deposits in the Sanjiang metallogenic belt of western Yunnan,and is located in the town of Longling County,Yunnan Province.It is located at the intersection of the east branch of the Nujiang Fault and the Great Fault of the Boluo River.It is also at the east wing of the Yaoguan-salt-shifted southward slope.The ore body is present in the stratigraphic limestone,bioclastic limestone and bioreef limestone of the Lishuiba Formation in the Early Paleozoic Silurian.This paper mainly focuses on sphalerite in the bismuth-lead-zinc deposit.Firstly,through the field exploration in the mining area and surrounding strata,the spatial morphology of the underground ore body and the exploration of ore and surrounding rock characteristics,the corresponding rock and ore samples are collected;then the collected samples are processed,observed and compared indoorally to understand and master the mining area.The geological characteristics of the deposit and the morphology and output characteristics of the sphalerite in the deposits at different locations,the ore-forming period of the deposit and the stage division of the sphalerite in the deposit;and subsequent analysis by electron probes from different laboratories inside and outside the school Laboratory instruments such as instrument,plasma mass spectrometer and X-ray diffractometer are used to study the mineral chemical characteristics such as chemical characteristics and crystal characteristics of sphalerite in different stages of the deposit.Finally,combined with previous research results,the deposit is inferred.The genesis of the deposit and the type of deposit.Combined with the geological characteristics of the deposit and the morphology and output characteristics of sphalerite in different ore bodies in the deposit,the ore-forming period of the antimony lead-zinc deposit can be divided into sedimentary,hydrothermal and epigenetic periods.The sphalerite in the deposit can also be divided into the first stage of sphalerite in the depositional stage,the second stage of sphalerite in the early stage of hydrothermal fluid,and the third stage sphalerite in the late stage of hydrothermal fluid according to the order of mineralization: 1 The first stage of sphalerite in the sedimentary period is a brown-red sphaleritein the form of a mineral combination of sphalerite-galena-pyrite-(chalcopyrite);2.The second stage of early hydrothermal fluid is a brown-brown yellow sphalerite in the form of a combination of sphalerite-galena-pyrite-chalcopyrite-(magnesia);3.the third stage of sphalerite in the late stage of hydrothermal fluid is A tin-light yellow sphalerite in the form of a mineral combination of sphalerite-pyrite-galena-quartz vein and sphalerite-pyrite-calcite vein.The mineral chemistry characteristics of the three-stage sphalerite are different.The test results of various chemical elements in the first stage of sphalerite are relatively normal and stable;the crystal constant values ??are relatively close,ranging from 5.4095 to 5.411 ?,which is close to the theoretical value of 5.41 ?,which is related to its depositional environment.The variation range of the test results of various chemical elements in the second stage of sphalerite is relatively large,and the overall performance is relatively enriched in elements such as Fe,Mn,Te,In;the crystal constant value of sphalerite varies widely.It is 5.4115-5.4159 ?,which is obviously higher than the theoretical value of 5.41 ?,which reflects that the sphalerite is located in the early stage of hydrothermal mineralization and the ore-forming temperature is higher.The test results of various chemical elements in the third stage of sphalerite are slightly different,and the overall performance is relatively enriched in Cd,Ga,Ge and other elements;the crystal constant of sphalerite varies slightly,5.4067-5.409 ?,slightly lower than the theoretical value of 5.41 ? reflects that the sphalerite is located in the late stage of hydrothermal mineralization,and the ore-forming temperature is significantly lower than the second stage.According to the geological characteristics of the strontium-lead-zinc deposit and the mineral chemistry of the sphalerite in the deposit,combined with the research results of the predecessor on the deposit,it is speculated that the deposit of the deposit is due to: the shallow sea phase of the Early Paleozoic Silurian Sedimentary ore-forming environment;medium-low temperature hydrothermal ore-forming temperature of approximately 175°C-230°C;two hydrothermal fluids combined with shallow-layer bicarbonate-type hot brine and shallow-layer bicarbonate-type hot brine and atmospheric precipitation The ore-forming fluids are mainly land-based and sedimentary surrounding rocks,followed by multi-type mineralization materials consisting of biofractionation and tectonic hydrothermal fluids.According to the mineral chemistry characteristics of the three stages of sphalerite studiedin this paper and the spatial distribution and output morphology of the ore body,it is concluded that the ore-forming hydrothermal flow direction of the deposit during the hydrothermal period is from the deep to the shallow part of the mining area.Influenced by the structure of the mining area,the ore channel is not simply straight up or down from one side to the other side,but follows the structure to form a large range,multiple channels,and a complicated ascending process.It was also found that the deposit has many similarities with the MVT lead-zinc deposit.Based on the above research results,it is concluded that the strontium-lead-zinc deposit may be a MVT-type lead-zinc deposit.