Ore Genesis And Geodynamic Settings Of Tungsten Deposits In Eastern Jilin And Heilongjiang Provinces

Eastern Jilin and Heilongjiang Provinces is located in the east part of Central AsiaOrogenic Belt, situated between the Siberian Plate and North China Plate. This area is acomplex tectonic region that experienced superposition activities of Paleo Asian Oceanand Pacific Ocean tectonic domain, which resulted in advantageous metallogenicgeological conditions and abundant mineral resources. Geological prospecting of tungstendeposits in recent years has made obvious breakthroughs in the area, but the theory level isrelatively low. This thesis focuses on the geological and geochemical characteristics,ore-forming fluid, geochronology and tectonic settings of typical deposits, such asYangjingou, Wudaogou, Baishilazi, Cuihongshan, Yangbishan, and discusses their theore-forming materials source and geodynamic settings. Such major conclusions are drawnas followings.1. The Yangjingou scheelite deposit recently discovered in Hunchun area, firstlarge-scale tungsten deposits in Northeast China, has been systematically studied. Thedeposit is identified as scheelite-quartz vein type which is rare type in both at home andabroad. It’s proved that Yangjingou deposit is closely related to Late Permian I-S transitiontype and formed in Triassic (40Ar/39Ar age of hydrothermal muscovite is（230.79±1.19）Ma). The diagenetic and metallogenetic material of this deposit was derived from the deepsource. Moreover, the diagenesis and mineralization of Yangjingou deposit are associatedwith the subduction of Paleo Asian Ocean to Xing’an-Mongolia Orogenic Belt in latePaleozoic.2. According to their ore genesis, tungsten deposits in the area can be divided into hydrothermal vein type and skarn type. The major orebodies of hydrothermal vein typedeposits are usually hosted by stratum or Late Paleozoic granitic intrusions, and aregenerally scheelite-quartz veins. The mineral composition of the ore is relatively simple.Wall-rock alterations include silicification, greisenization, kaolinization, muscovitizationand chloritization. The orebodies of skarn deposits are usually lenticular and are controlledby contact zone between granites and the stratum. Wall-rock alteration types includeskarnization, silicification, chloritization, epidotization, kaolinization, carbonatization andfluoritization. The skarn type can be further divided into independent skarn type andaccompanying skarn type thanks to ore mineral assemblages in these deposits.3. Granite intrusions associated with hydrothermal vein type tungsten mineralizationare mainly granodiorite. These rocks have high-Si, Al and alkali-rich, and display thefeatures of bequasi-peraluminous/weakly peraluminous calc-alkaline series, which areusually I type granites or I-S transition type granites. Granite associated withmineralization of skarn mineralization can be divided into two groups, the first is I-type,represented by quartz diorite or quartz monzonite, and the second is S-type, represented bymigmatized gneissic granite. Quartz diorite or quartz monzonite belongs to bequasi-aluminous calc-alkaline series, have enrichment of LREE and depletion of HREE and thehigh field-strength element (Nb, Ta etc). Migmatized gneissic granite belongs toperaluminous calc-alkaline series, have enrichment of LREE, Rb and depletion of HREE,Ba, Sr, Nb, Ta, Ti etc.4. Studies on fluid inclusions and H-O isotope from the main mineralization stage ofdifferent deposits show that gas components of fluid inclusions from hydrothermal veintype deposits are mainly H2O, CO2and N2, and occasionally small amounts of CH4. Theore-forming fluid of hydrothermal vein-type deposits are the NaCl-H2O-CO2system andmainly from magmatic water. Gas components of fluid inclusions from skarn deposits aremainly H2O, CO2and occasionally a small amount of CH4, which indicates that theore-forming fluid of skarn deposits belongs to the NaCl-H2O system and the mixture ofmagmatic water and meteoric waters.Rare earth element and trace element analysis of the scheelite show that scheelitesfrom hydrothermal vein-type tungsten deposits have no fractionation of LREE and HREEand a strong positive Eu anomaly, show the characterization of Ⅱ-type which originated from deep source. Scheelites from skarn deposits have obviously fractionation of LREEand HREE and a weak Eu anomaly (positive or negative), and ore-forming material isclosely related with the ore-bearing stratum and metallogenetic rock.5. Diagenetic and metallogenetic ages of different tungsten deposits show thathydrothermal vein type deposits (represented by Yangjingou deposit) were formed in thelate Permian to early Triassic, and the metallogenic age was determined to230.79±1.19Ma. Skarn tungsten deposits are clearly divided into two phases, the earlier isrepresented by Yangbishan tungsten deposit in Jiamusi region, zircon U-Pb ages ofmetallogenetic intrusion in Yangbishan deposit is determined to (507.6±1.0) Ma. Thelater is represented by Cuihongshan W-Mo polymetallic deposit and Baishilazi tungstendeposit. The emplacement age of metallogenetic granitic intrusion from Baishilazi depositwas (198.27±0.80) Ma, and molybdenite Re-Os isochron age of Cuihongshan deposit is(198.9±3.7) Ma.6. By comprehensive studies of diagenetic and metallogenetic age, geochemicalcharacteristics of representative deposits and tectonic evolution, it can be concluded thathydrothermal vein-type tungsten deposits in Eastern Jilin and Heilongjiang Provincesformed at island-arc active continental margin in Late Permian-Triassic period, when thesubduction of Paleo Asian Ocean to the northeast block groups played an important role intectonic evolution of this area. Early Jurassic skarn deposits, represented by Cuihongshanand Baishilazi, occurred at island-arc active continental margin, with diagenetic andmetallogenetic material from crust-mantle mixed source, formed under the subduction ofthe Pacific plate to the Eurasian Plate including the study area in early Jurassic. EarlyPaleozoic skarn deposit represented by Yangbishan formed under the tectonic setting ofsyn-collisional, with diagenetic and metallogenetic material from crust, and is closelyrelated to the continental collision between the Jiamusi Massif and Songnen Massif inEarly Ordovician.