The Research On Geological Characteristics And Metallogenesis Of The Jinchanghe Fe-cu-pb-zn Polymetallic Deposit, Yunnan Province

The Jinchanghe Fe-Cu-Pb-Znpolymetallic deposit is a concealed mineral depositlocated in the north part of the Baoshan massif in China. It is located in thecross-cutting zone of the Baoshan-Shidian Anticlinorium and the Lancang RiverFracture. The ore bodies occur in the interlaminar fracture of the Jinchanghe Anticlineof Cambrian Hetaoping Formation, and they are controlled by the NW fault and theNE fault. Four stages including skarn stage, retrograde altered stage, quartz sulphidestage and carbonate stage are recognized based on the field relationship and mineralassociations.The authors investigate the mineralogical characteristics with skarn minerals asthe study object and by using electron microprobe technology. The analysis ofelectron microprobe show that most of skarn minerals in Jinchanghe ore deposit arecalcium skarn minerals, the end member of garnets is dominated by andradite, withminor grossular. The clinopyroxene comprises hedenbergite and diopside. Theamphibole in Jinchanghe deposit include actinolite, ferroactinolite and grunerite.There is a high iron level of ilvaite, which are usually accompanied with magnetite. Asmall amount of skarn minerals are manganoan minerals, including spessartine,manganoan hedenbergite, manganoan actinolite and manganoan ilvaite.There are vertical alteration zonation from deep to shallow and horizontalalteration zonation from east to west: remote and buried plutonâ†'calcium skarn zonewith Feâ†'calcium skarn zone with Cuâ†'manganoan skarn zone with Pb andZnâ†'marbleized limestone. The alteration zone of the Jinchanghe ore depositindicates that there is a higher temperature and oxidation zone in the middle part ofthe vertical profile and in the east part of the horizontal profile. Compared withzoning models of skarn minerals in domestic and overseas polymetallic ore deposits,it is assumed that the remote magmatic hydrothermal fluid intrudes through thecross-cutting zone of two faults, and the transudation effect occurs in the surroundingrocks and the ore body forms at last.The Rb-Sr isotopic dating is carried out on sphalerite and its intergrowth mineralassemblage samples (pyrite, galena, chalcopyrite and quartz) from the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit. The results of Rb-Sr isotopic dating shows that themetallogenic epoch is about117～120Ma and the Jinchanghe Fe-Cu-Pb-Znpolymetallic deposit formed in Early Cretaceous. The(87Sr/86Sr)iof hydrothermalmineral assemblage is equal to0.713885and is closed to the (87Sr/86Sr)iofZhibenshan granite. Based on the above, the authors consider that the ore-formingmaterials of the ore bodies in the Jinchanghe Fe-Cu-Pb-Zn polymetallic deposit werederived from the crust and the mineralizationwas related tothe local silicic magmatismin Late-Yanshanian. It can be inferred that there are concealed intermediate-acidintrusive rocks based on the negative gravitational anomaly of the mining area. Studyof the geodynamical setting indicates that the formation of the deposit is the responseto the collision orogenesis of Tengchong block and Baoshan block during the closureof the Meso-Tethys period, and is related to the crustal anatexis in Baoshan blockaffected by the collision.The ore-forming process can be divided into early, middle and late stages, whichis characterized by garnet-fluorite veins, quartz-calcite-sulfides veins and non-orequartz-calcite veins, respectively. Based on petrographic observation, five types offluid inclusions are distinguished including pure vapor inclusions (PV-type),vapor-rich liquid inclusions (V-type), pure liquid inclusions(PL-type), liquid-richliquid inclusions (L-type) and daughter mineral-bearing inclusions (S-type). Gascomponents of fluid inclusions are mainly H2O,CO2,CH4and N2. Cations of liquidcomponents are mainly Ca2+and Na+, while anions are mainly SO2-4and Cl-.Homogenization temperatures of these ore-forming stages are from early to late(148.2℃～550℃),(135.3～423.5℃) and (116.5℃～250.3℃), respectively, whereassalinities are (0.2～5wt%NaCl.eqv,6～13wt%NaCl.eqv,14～17wt%NaCl.eqv),(0.2～16.0wt%NaCl.eqv),(0.2～5.7wt%NaCl.eqv), respectively. The density of theore-forming fluid ranges from0.53g/cm3to1.02g/cm3. The δ13C values obtainedfrom fluid inclusions in calcite range from-7.2‰to-3.7‰, δ34S in sulfide range from3.9‰～7.1‰, the Jinchanghe deposit yield δ18O values of-1.10‰to10.25‰andcorresponding δD values of-135.6‰to8.3‰, suggesting that the mineralizing fluidsoriginated mainly from magmatic water, react with the surrounding rocks and accompanied participation of meteoric water. It was concluded fromsyntheticalanalyses that phase separation of magmatic water and fluid mixing with meteoricwater as well as pressure reducing and boiling of the fluid in the fractures might havebeen thethe important mechanism for deposition and enrichment of sphalerite, galenaand other mineralizing elements.