Characteristics And Genesis Of Copper-Molybdenum Mineralization In Huaduoshan Area, Nenjiang County, Heilongjiang Province

The Huaduoshan area is situated in the northwest of the Sankuanggou-Duobaoshan metallogenic belt in Nenjiang County,Heilongjiang Province.The Cu?Mo mineralization is associated with granodiorite and mainly occurs as quartz veins in granodiorite.Hydrothermal alteration consists of silicic-,potassic-,sericite-,and propylitic-altered distributed outward from the center wall-rocks.The alteration/mineralization processes comprise four stages:?I?magnetite+pyrite+quartz,?II?molybdenite+chalcopyrite+pyrite+quartz,?III?chalcopyrite+pyrite+quartz,?IV?pyrite+quartz.There are a lot of fluid inclusions?FIs?in the quartz vein,NaCl sub-minerals?S-type?,liquid-rich two phase?VL-type?,and rare vapor-rich two phases?V-type?FIs were identified in stage I.Microthermometric results indicate that the FIs yield completely homogenized to a liquid H₂O phase(T_h-total)at 374⁴47°C,and salinities of 3.5⁵0.7 wt.%NaCl eqv.S-type and VL-type FIs were identified in stage II.These FIs yield T_h-total at 327³95°C,and salinities of 7.4⁴7.5 wt.%NaCl eqv.Only VL-type FIs were identified in stage III and stage IV.These FIs yield T_h-total at 220³40°C and salinities of 1.2¹1.5 wt.%NaCl eqv.Microthermometric results indicate that hydrothermal fluids evolved from NaCl-H₂O system hydrothermal solution of high-temperature,high salinity to NaCl-H₂O system of medium-to high-temperature,low salinity.Hydrogen and oxygen isotopes confirm that the ore-forming fluids of stage I,II were derived from magmatic water,and hydrothermal fluids had gradually shifted to meteoric water(Stage I:?D=-102.4‰^-94.6‰,?¹⁸O_H2O=7.2‰⁹.1‰;Stage IV:?D=-117.1‰^-115.6‰,?¹⁸O_H2O=-4.3‰^-3.1‰).The analysis results of sulfur isotope(?³⁴S=-2.7-0.8‰)and lead isotope(²⁰⁶Pb/²⁰⁴Pb=18.236¹8.599,²⁰⁷Pb/²⁰⁴Pb=15.504¹5.557,²⁰⁸Pb/²⁰⁴Pb=37.816³8.629)show that it involved in the mantle and crustal materials.The zircon U-Pb geochronology results show that the ages of the granodiorite are172±1 Ma.It is consistent with the Re-Os age of molybdenite?172.4±2.7 Ma?,indicating that mineralization is associated with the granodiorite.The granodiorite samples have high SiO₂,K₂O and Al₂O₃,and low MgO and CaO contents,belongs to the weakly peraluminous?A/CNK=0.96⁰.99?,with the characteristics of high-K calc-alkaline and I-type granite.The rocks are all enriched in light rare earth elements?LREEs?and large ion lithophile elements?LILE,Rb?Ba?U?K?,but depleted in high field strength elements?HFSE,Nb?Ta?Ti?P?.The above characteristics indicate that the granodiorite in ore district was formed in the active continental margin.Considering the regional tectonic background,the Cu-Mo mineralization in ore district associated with the active continental margin tectonic environment formed by the subduction of the Paleo-Pacific plate to the Eurasian plate in the Middle Jurassic.