Study On The Characteristics And Genesis Of Lead-Zinc Polymetallic Mineralization In Luohe Area, Nenjiang County,Heilongjiang Province

The Luohe area is located in Nenjiang County,Heilongjiang Province,and the geotectonic position is located in the northwest end of the northwest copper polymetallic metallogenic belt from sankuanggou to Duobaoshan in the north of Daxinganling.The lead-zinc polymetallic mineralization in the area is mainly vein like,controlled by NE trending fault structure,and the associated wall rock alteration is successively developed from deep to shallow potash,silicification,sericitization,chloritization,epidotization,etc.according to the mineral combination and vein cutting relationship,the hydrothermal mineralization can be divided into the following three stages:I.chalcopyrite-pyrite-quartz stage;II galena-sphalerite-quartz stage;III calcite-quartz stage.The study of fluid inclusions shows that there are a large number of inclusions in the ore-bearing quartz vein.In stage I,there are two types of inclusions:gas-liquid two-phase?L-type?and a small amount of rich gas phase?V-type?.The homogenization temperature of inclusions is 321.2³72.1?,the salinity is 1.56⁸.15wt%NaCleqv;in stage II,there are two types of inclusions:L-type and V-type,the homogenization temperature is 235.3²83.1 In the third stage,only L-type inclusions are developed.The homogenization temperature of inclusions is 160.0¹78.1°C,and the salinity is1.56⁴.17wt.%NaCl eqv.The results of micro temperature measurement showed that the fluid evolved from H₂O^NaCl system with high temperature and medium salinity to H₂O^NaCl system with low temperature and low salinity.The results of hydrogen and oxygen isotope analysis of fluid inclusions show that the range of fluid hydrogen isotope??D?in phase I is-100.3‰^-86.7‰,and that of oxygen isotope(?¹⁸O_H2O)is 3.6‰⁵.3‰,suggesting that the ore-forming fluid is mainly from magmatic water;the range of hydfluid rogen isotope??D?in phase II is-112.5‰^-105.7‰,and that of oxygen isotope(?¹⁸O_H2O)is-0.7‰^-0.2‰,indicating that the ore-forming fluid is mainly from magmatic water The fluid source has gradually changed into precipitation;the sulfur isotope(?³⁴S)value of ore is-7.2‰^-4.5‰,indicating that the ore-forming material source is mainly intermediate acid magma;the lead isotope(²⁰⁶Pb/²⁰⁴Pb=17.79¹8.21,²⁰⁷pb/²⁰⁴Pb=15.425¹5.519,²⁰⁸pb/²⁰⁴pb=37.592³7.762)the analysis results show that the ore-forming materials may come from mantle or orogenic belt and be closer to the characteristics of mantle lead,so it is inferred that the main ore-forming materials may come from crust mantle mixed source.Therefore,the lead-zinc polymetallic mineralization in the area is due to high temperature magmatic hydrothermal vein type mineralization.The zircon ages and geochemistry of the middle and fine grained biotite granites and granodiorites,which are closely related to mineralization,are studied by means of LA-ICP-MS zircon U-Pb dating,major trace and rare earth element ICP-MS analysis.The results show that the ages of the middle and fine grained biotite granites and granodiorites are?254.3±1.6?Ma and?254.5±1.5?MA respectively.It shows that the age of speech activity is the Indosinian period of Early Triassic.The results of rock geochemical analysis show that it is generally characterized by calc alkaline per-aluminous,low content of radioactive elements,enrichment of light rare earth elements,large ion lithophile elements such as Ba,K,Sr,depletion of heavy rare earth elements and high field strength elements such as th,Nb,Ta,Ti,which are consistent with the geochemical characteristics of subduction zone magma.It has a weak negative euro-pium anomaly,which is consistent with the characteristics of igneous geochemistry formed in island arc environment and active continental margin arc environment.Therefore,we can speculate that the mineralization in the Luohe area is the product of the two-way subduction of the Mongolia Okhotsk Ocean plate in the Triassic.