Study On Metallogenic Mechanism And Resource Forecast Of Hydrothermal Cu Deposits In The Central And North Of The Great Xing’an Range, NE China

The Great Xing’an Range of NE China hosts many hydrothermal Cu and other base andprecious metal mineral deposits and mineralization, is an important part of the giant CentralAsian endogenous metallogenic belt, and has been the focus of many recent studies. Mineralexploration in this area has discovered numerous large-, middle-, and small-sized Pb–Zn, Cu,and Mo deposits, including the Errentaolegai and Jiawula Pb–Zn deposits, the Duobaoshan andWunugetushan Cu–Mo deposits, the Lianhuashan and Naoniushan Cu–Ag deposits, and theMaodeng and Aonaodaba Cu–Sn deposits. The genetic types, timing of mineralization, anddynamic setting of mineral deposits in the Great Xing’an Range remain largely unknown. Thisstudy focuses on the geological characteristics, mineral deposit classification, fluid inclusion,geochemistry, and geochronology of hydrothermal Copper deposits in the Great Xing’an Range,and discusses the fluid evolution, the timing of ore formation and the source of magmas thatformed mineralization-associated plutons in this area. In addition, we seek to identify importantmetallogenic events and processes that affected the Great Xing’an Range.Here, we classify the Cu deposits in the region into three types: porphyry Cu–Mo,high-sulfidation epithermal Cu–Ag, and skarn Cu–Fe. The porphyry Cu-Mo deposits isexemplified by the Wunugetushan, Duobaoshan and Tongshan, these orebodies are hosted byDuobaoshan Formation and granodiorite （porphyry） or biobite granite, controlled byNW–SE-trending compressive shear faults or volcanic ring fracture and are tubular, lenticularand irregular forms in shape. Mineralization-related alteration is dominated by quartz–potassic,quartz–sericite, argillic, carbonate alteration, and propylitization. Ore minerals within the depositare dominantly pyrite, chalcopyrite, molybdenite, and bornite, with minor galena, sphalerite,pyrrhotite, tetrahedrite, and arsenopyrite.The formation of this deposit involved the followingfive mineralization stages, as deduced from mineral paragenetic relationships:（I） pyrite–quartz,（II） pyrrhotite–pyrite-quartz,（III） quartz–molybdenite,（IV） quartz–chalcopyrite, and （V）quartz–carbonate. The high-sulfidation epithermal Cu–Ag deposits are hosted by volcanic ringfracture, and orebodies have vein and lenticular forms. Alteration in the deposit is associated with vuggy/residual quartz, kaolin, chlorite, epidote, carbonate, and minor tourmaline, and apartially developed potassic alteration zone. The main ore minerals are pyrite, chalcopyrite, andpyrrhotite, with minor galena, sphalerite, arsenopyrite, molybdenite, and magnetite. Five stagesof ore formation have been identified based on paragenetic relationships:（I） pyrite–quartz,（II）quartz–magnetite–pyrite–chalcopyrite,（III） sulfide veins,（IV） quartz–polymetallic sulfides, and（V） quartz–carbonate. The skarn Cu–Fe deposits is associated with skarns and an EarlyYanshanian granodiorite, and the locations of individual vertical lenticular orebody locations arecontrolled by the intersections between skarns and bedding planes. Alteration is dominated byskarnification, with minor silicification, and chlorite, epidote, and carbonate development. Oreminerals within the deposit consist of magnetite and chalcopyrite with minor pyrite andmolybdenite. Six mineralization stages during deposit formation have been identified based onparagenetic relationships:（I） a dry skarn stage,（II） a wet skarn stage,（III） an oxidized stage,（IV）an early sulfide stage,（V） a late sulfide stage, and （VI） a quartz–carbonate stage.Fluid inclusions studies of mineralization-associated quartz within these deposits revealsthat homogenization temperatures for porphyry Cu deposits are＞500-470℃,470-420℃,420-330℃,330-220℃, and220-110℃; and salinity are＞11.8-7.44%NaCleq,7.2-4.0%NaCleq,52.0-3.2%NaCleq,39.6-2.89%NaCleq, and3.4-12.4%NaCleq, respectively.Homogenization temperatures for high-sulfidation epithermal Cu–Ag deposits are＞420-310℃,310-270℃,270-200℃,200-160℃, and160-80℃; and salinity are48.9-1.39%NaCleq,6.14-1.39%NaCleq,8.81-1.22%NaCleq,8.54-2.23%NaCleq, and5.55-4.17%NaCleq,respectively. Homogenization temperatures of sulfide stage for skarn Cu–Fe deposits are470-230℃230-110℃; and salinity are50.1-8.8%NaCleq,5.59-1.22%NaCleq.Daughter minerals hosted by fluid inclusions and raman anysis results indicated that initialore-forming fluid for porphyry Cu-Mo deposits is derived from magma, characterized by rich inCO₂and high oxygen fugacity; then CO₂escaped, oxygen fugacity reduced in mineralizationstage, fluid tranfered to reduction performance with poor in CO₂, and weak acid (CO₃^2-) inadvanced stage. The initial ore-forming fluid for high-sulfidation epithermal Cu–Ag deposits isderived from magma, characterized by contain CO₂, high oxidative and acid; then fluid tranferedto reduction performance, and weak acid (CO₃^2-) in advanced stage. The initial ore-formingfluid for skarn Cu–Fe deposits is derived from magma with little of CO₂, and tranfered to weakacid and reduction performance.Porphyry Cu-Mo deposits have two mineralization, the one is located in the east of theregion, around the Nengjiang and Heihe area, as exemplified by the Duobaoshan and Tongshan （480±13Ma or482～486Ma and）, and the mineralization is related to paleozoic granodiorite;another is generally located along the Deerbugan Fault in the northeastern Great Xing’an Range,represented by Wunugetushan, associated with Early Jurassic porphyritic monzogranite （188Maor178±10Ma）. High-sulfidation epithermal Cu–Ag deposits are located in the middle of theGreat Xing’an Range, as exemplified by the Lianhuashan and Naoniushan, and the oldest zirconU–Pb concordia ages from mineralization-related granodiorite and dacite in the study area are242.9±2.7Ma and222±5Ma, suggesting that significant Cu mineralization occurred duringthe Triassic. Skarn Cu–Fe deposits are located in the southeast of the region, as exemplified bythe Xiaoduobaoshan, and mineralization is largely related to Early Jurassic granodiorite（171.9±1.7Ma）.Mineralization-associated intrusions all are I type granites with high SiO₂, Al2O3, and totalalkali （K2O+Na2O） contents, and generally enriched in the light rare earth elements （LREE）,incompatible trace element （LILE: Rb, Ba, K, Th, and U）, depleted in the heavy rare earthelements （HREE）. They have weak or negligible Eu anomalies [Eu=2EuN/（SmN+GdN）] thatrange between0.77and1.05, and chondrite-normalized REE patterns that decrease from left toright. Most intrusions are characterized by low initial Sr values （（87Sr/86Sr）i=0.7011–0.7079）,positive Nd values （Nd（t）=0.3–6.7）, and old two-stage model ages （TDM2=486–945Ma）,together with their diagenetic age, suggest that magmas from Duobaoshan, Lianhuashan andNaoniushan that were generated during partial melting of the lower crust after subduction ofPaleo-Asian ocean and a region of Neoproterozoic depleted mantle, the magmas ofWunugetushan and Xiaoduobaoshan originated during partial melting of both juvenilePaleo-Asian oceanic crust and lower crustal material after collision between the NCC and theSiberian Craton.Based the studies of fluid inclusion and origin of magma, the fluid evolution andore-forming process are summarized as following. When the temperature and pressure dropdown to360℃and38.6MPa in Duobaoshan, initial ore-forming fluid boiled and break throughthe wall rocks, which directly resulted in metal-rich cryogenic fluid went into porphyry fliudsysterm, mixing with high-temperature magma hydrothermal, and sunsequently metal sulphidestarted to unloading and filled in rocks and fractures as disseminated or veinlet. Wheras, whentemperature and pressure drop down to420℃and38.8MPa in Lianhuashan, the initial fluid tookplace boiling, however the boiling did’t cause large-scale minerlization, as temperature andpressure continued to fell down at300℃and25.7MPa, and subquently mixing with meteoricwater, which caused solubility of metal complexes or halide drastically reduce, huge metal When temperature and pressure drop down to410℃and80MPa in Xiaoduobaoshan, mixingoccurred between initial ore-forming fluid and low-temperature and low-salinity formation fluid,at the same time balance of mixed fluid broke by intermittent activity of schistose, andsubquently took place strongly boiling, numerous metal unloading, and formed massive anddisseminated orebodies.Hydrothermal Cu deposits in this area are closely related to subduction of the Paleo-AsianOcean, subduction of the Paleo-Pacific Plate, and closure of the Mongolia–Okhotsk Ocean. TheJiamusi–Songnen and Erguna–Xing’an microplates began to amalgamate after the MiddleOrdovician, with final collision occurring between the Late Devonian and the EarlyCarboniferous along the Hegenshan–Heihe suture zone, forming the Heilongjiang Plate. SeveralEarly Paleozoic island arc assemblages have been identified in the Xing’an Terrane, includingthe paleozoic arc and caledonian granites, and is associated with the Duobaoshan and TongshanCu deposits. Subsequent suturing of the NCC and the Heilongjiang Plate took place along theSolonker–Xar Moron–Changchun Fault, with final closure of the Paleo-Asian Ocean betweenthe Late Permian and Early Triassic. Contemporaneous subduction-or collision-relatedmagmatism occurred in the southern Xing’an Terrane, associated with the formation ofnumerous mineral deposits, including the Lianhuashan and Naoniushan Cu–Ag deposits.Subduction of the Mongolia–Okhotsk Ocean started in the Late Permian, and the ocean wasclosed between the Late Jurassic and the Early Cretaceous associated with suturing of the NCCand the Siberian Craton. Many subduction-or orogenic-related granites were intruded during thisperiod, leading to the formation of many Cu deposits, including the Wunugetushan, Babayi, andBadaguan Cu–Mo deposits. Afterward, under influence of subduction of Paciffic plate, thickenedlower crust that caused by the early disappeared ocean basin occured partial melting, andupwelling along the faults, and finally formed a series of metal deposits, such as theXiaoduobaoshan and Sankunggou Cu-Fe deposits.As discussed above, the Great Xian’an Range can be divided into three metallogenicprovince: Nenjiang-Duobaoshan, Deerbugan and Wulanhaote. The first two province had beensuffered intense erosion, and generally erosion depth is grearer than2km, which causedhigh-sulfidation epithermal deposits almost destroyed; whereas, because of shallow erosion,three types of deposits are all preserved in the latter province.