| The Hehuashan lead-zinc deposit is located in the center of the Tongling ore district in the Middle-Lower River Metallogenic belt?MLYRMB?with large size.The ore bodies of the deposit are hosted by the limestone and dolostone of the Nanlinghu Formation from Lower Triassic.The ore area has two intrusions,namely the Hehuashan?HHS?intrusion to the west and the Dachengshan?DCS?intrusion to the east.The alteration is weak,including the potassic alteration,chloritization,carbonation and brecciation of sediments,and kaolinization,sericitization,and carbonation of the intrusions.The zircon LA-ICP-MS U-Pb dating results of the diorite and quartz diorite show that their weighted 206Pb/238 U ages are 133.0±2.1Ma and 130.1±1.7Ma,respectively,indicating that the intrusions of the Hehuashan deposit intruded in the early Cretaceous.The whole-rock geochemical analysis results show that the geochemical characteristics of the diorite of the Hehuashan deposit are similar to those of typical adakites,namely,the diorite have SiO2>56%?56.17%?65.90%?,Al2O3?15?15.10%?17.22%?,Mg O<3%?0.84%?2.22%?,Yb<1.9×10-6(1.35×10-6?1.64×10-6),Y < 18×10-6(11.60×10-6?15.70×10-6)with weak negative Eu anomaly.It suggests that the Hehuashan diorites maybe the joint product of partial melting of lower crust and partial melting mantle wedge.The tectonic discriminant diagram shows that the Hehuashan diorites were formed in a setting of compression or transition from compression to extension,maybe related to the subduction of ancient Pacific plate.The occurring of the Hehuashan diorites maybe give implications for new mineralization in the Tongling district.The main ore minerals of the Hehuashan deposit are sphalerite,galena,and trace amounts of pyrite,with the main gangue minerals of calcite and dolomite.The main ore rock types of the Hehuashan deposit are breccia and vein type composed by several types of sphalerite,including fine-grained crystalline sphalerite?FCS?,coarse-grained sphalerite I?CS I?,colloform sphalerite?CS?,spherical sphalerite?SS?,and coarse-grained sphalerite II?CS II?.The former four types of sphalerite are hosted by limestone or dolostone,whereas the CS II is hosted by marble close to DCS intrusion.The sphalerite from the Hehuashan deposit generally has higher Cd,Ge,and Tl and lower Fe and In contents,showing a similar elements concentrations to the sphalerite from MVT lead-zinc deposits.However,there are still some sphalerite show higher concentrations of In,Mn,and Hg,implying it's formation is related to the Yanshannian magmatic fluids activities.The main gangue mineral of calcite has low concentrations of rare earth elements?REE???REE less than 50 ppm?,indicating the fluid formed the calcite may not come from the magma.The REE chondrite-standardized diagram show features of LREE-rich and HREE-poor with light negative anomalies caused by the precipitation of sulfides.Yb/La ratios can be the indicator to the fractionation of REE,while the Yb/Ca ratios can indicate precipitation environment,namely,the decrease of Yb/Ca ratios means the dissolving of the carbonate,and the increase of the Yb/La ratios means that the fractionation is increasing.The diagram of Yb/Ca vs.Yb/La show that the fractionation was increasing during the mineralizing process.Furthermore,the wide ranges of Y/Ho rations of the calcite from the Hehuashan deposit implying a mixing of ore-forming fluids from different sources.The research of the fluid inclusions of calcite from the Hehuashan deposit showed that the formation of the Hehuashan deposit range from 75.2??198.8? with the corresponding salinity range from 0.02 ?17.26 wt.% NaCl equiv.,which the ore-forming stage temperature is between 87? ?148.5? with corresponding salinity range from 0.53?17.26 wt.% NaCl equiv.,and the late ore-formation temperature is between 75.2??198.8? with corresponding salinity range from 0.02 ?10.86 wt.% NaCl equiv.,implying that the Hehuashan deposit was formed from low temperature fluid that was a mixing of two different fluids such as basinal brine and meteoric water.The reduced sulfur?H2S?composed the sulfides was from the reduction of the sulfate hosted in carbonate such as barite and anhydrite or the preexist sulfide like pyrite.The reduce agent is the organic matters such as bitumen.The calcite from ore-forming stage and late have a range from 2.9‰ to +3.7‰ and +2.5‰ to +4.2‰,respectively.The value of ?18O range from +11.8‰ to +13.9‰?mean=12.9‰?and +12.5‰ to 14.8‰?mean=+13.3?,respectively.The values of ?DSMOW range from-100‰ to-89‰?mean=-93‰?and-98‰ to-74‰?mean=-88‰?.The ?13C and ?18O values of dolostone from the Nanlinghu Formation range from +0.2‰ to +3.7‰?mean=+1.6‰?and +17.7‰ to +22.4‰?mean=+21‰?.The distributions of the C-O isotopes imply that the calcite from the Hehuashan deposit were formed from the dissolution of the carbonate.The distributions of the ?DSMOW and calculated ?18OH2O values are far from the region of magmatic water,but the mixing region of meteoric water and organic water,implying the ore-forming fluid is a mixing of meteoric water and organic water.The ?34S compositions of sulfides from the Hehuashan deposit has a wide range from-7.8‰ to +9.7‰.The ?34S values of sphalerite,galena and pyrite range from-7.8‰?+9.7‰,-4.9‰?+8.2‰ and-0.9‰?+6.0‰,respectively.While the ?34S values the sulfate within the Triassic sediments range from +14.8‰?+23.9‰.The sulfur isotopic compositions are wider than the region of the magmatic sulfur,implying that the reduced sulfur came from the reduction of the sulfate by the agent of organic matters.The ore bodies of the Hehuashan deposit cut-across the Nanlinghu Formation sediments,but the magmatic intrusions cut-across the ore bodies,indicating that the formation age of the Hehuashan deposit is between Middle-Triassic and Early-Cretaceous.We have observed two stages mineralization based on the geology characteristics,sphalerite geochemistry,including early stage mineralization without relationship with the Yanshannian magmatic activities and the late stage mineralization related with the Yanshannian magmatic activities. |
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