Metallogenic Regularities Of Gold Deposits In Upper Heilongjiang Metallogenic Belt And Its Prospecting

Upper Heilongjiang metallogenic belt, located in the extreme northern part of heilongjiangprovince, is a level Ⅲ metallogenic belt in the Daxing’anling mineralization province, and it’stectonic unit corresponding to the Upper Heilongjiang basin or Mohe basin. The geotectonicposition of study area is situated in the collision belt between China northeastern microplate andSiberia plate at the western of Mongolian-Okhotsk fold belt and northeastern part of Ergunmicroplate, its neboring to Bulieya microplate in Russia in the east, to Daxing’anling Derbuermetallogenic belt in the south, and to Siberia plate in the west and north. The study area hasexperienced history of its basement forming、paleoasian ocean forming and developing as wellas evolution of the close of Mongolian-Okhotsk ocean and the northwestward subduction of thewestern Pacific plate successively. Magmatic activity is frequently presented by Jinian periodand Yanshanian. The structures are characteristics by folds, ductile deformation and faults. Themetallogenetic condition is advantageous rich in gold resources presented by the medium tolarge-scale gold deposits, such as, Shabaosi, Hulalin, Baoxinggou,Shiwuliqiao gold deposit andso on, aswellas nuberoeus placer gold deposits in this belt, showing better prospecting potentialfor gold deposit.The genetic types of gold deposits in this belt are typical of hydrothermal deposit, related tothe magmatic activity closely in the early Cretaceous extensional environment. According to themetallogenic temperature and the host rock, this gold deposits are further divided into threecategories:1）meso-hypothermal cryptoexplosive breccia type, hosted in cryptoexplosive brecciapipe，the typical representative by Hulalin gold deposit;2) medium-temperature hydrothermaltype, ore-hosting in sedimentary rocks, widely developed in the belt, occurring in or controlledby secondary faults of over-thrust nappe with metamorphism. Of which are typical representativeby Shabaolin and Baoxinggou gold deposit;3) medium-low temperature hydrothermal type,occurred in volcanic rocks, controlled by fault structures related to hypabyssal intrusiverocks-subvolcanic rocks, typical representative byShiwuliqiao gold deposit.Fluid inclusions study of this gold deposits shows that the fluid inclusions type of meso-hypothermal cryptoexplosive breccia type includes daughter crystal-bearing three phaseinclusions. Ore-related fluid inclusion is typical of NaCl-H2O with containing CO2,CH4andhigher N2，associated with magmatic hydrothermal. The peak of homogenization temperaturerange in320~380℃, maximum temperature exceeding590℃. This features interpreted as themetallogenic mechanism of magmatic fluid "boiling" and different fluids mixed. The fluidinclusion in the second deposit type is typical of two-phase inclusions, either riching in pure CO2,gas or gas-liquid phase. The peak of homogeneous temperature ranges from220to320℃. of ofcontaining The composition of CO2-N2-CH4-H2O in ore-forming fluid is reperisentive of themagmatic-metamorphic fluid system, with the domination of magmatic hydrothermal at the earlymetallogenic stage and the mixture of atmospheric precipitation and formation water at the latemetallogenic stage，suggesting metallogenic mechanism by the separation of fluid phase. Thefluid inclusions in the third ore type are well developed vapour-rich inclusions with minor simpleNaCl-H2O fluid phase. The peak of homogeneous temperature is range in320~400℃at the earlymetallogenic gas explosion stage and in240~280℃at late stage. The metallogenic mechanismof ore-forming fluid is resulted from the magma intrusive causing gas explosion at early stage,with the domination of atmospheric precipitation at metallogenic epoch, metallogenicmechanism is the mixture of fluid phase. According to the U-Pb dating studies of hypabyssalintrusive rock in this area, tages of gold mineralization ranges domainly from (141.1±0.9) Ma to(115.80±0.45) Ma, concentrating in early Cretaceous.The gold mineralization associated closely with, the evolution of Upper Heilongjiang basin.the Xinghuadukuo group-complex etc belong to the pre-Mesozoic strata is primative source ofgold, and the Mesozoic terrigenous clastic rock is the main source and host rock for gold deposit.The Mohe nappe and its secondary structure provide host space for gold mineralization. Theintermediate-acid magmatic activity in late Jurassic-early Cretaceous supply heat source andprovide part of ore-forming material. The analysis on formation, structure and metallogeneticspecialization suggests that Au is the main mineral resources in the Upper Heilongjiangmetallogenic belt. Both Jurassic clastic rocks of the Ershierzhan formation and lowerCretaceous volcanic rocks of the Ganhe formation are important role of ore formation.NS andNE structures are the important mineralization and ore-controlling structures, the goldmineralization has a close relationship with the early Cretaceous in the hypabyssal intrusive(spots). The diagenetic age for the hypabyssal intrusive body in Upper Heilongjiangmetallogenic belt tend gradually, from141Ma in west to112Ma in east, to be young, thedifference about30Ma. Meanwhile, the gold mineralization in tempral and spatial is associatedclosely with the felisic dyke or porphyry in the area. The age also have the same change trendagainst intrusive body. Gold deposits is mostly presented at north east and north west fault intersection in UpperHeilongjiang metallogenic belt. Its distribution trend to be northeast, occurring as " east-westlines of and north-east rows ". Furtherly, Upper Heilongjiang metallogenic belt (III) can bedivided into5sub-belts:1) Hulalin-Dongmazhaer Au;2)Laogou-Yixiken Au-Cu-Mo,3)Chang-Ying Au,4) Ershiyizhan-Baoxinggou Cu–Au,5) Fulahan Au metallogenic belts (Ⅳ).Analysis on denudation degree shows that the denudation in both sides is much intessive than itsin the central area, according to the lithology exposure extent from metamorphics throughsedimentary，to clastic rocks，and from intrusive rocks to volcanic rocks.Studies on relationship between gold mineralization and geophysics aswellas geochemistryshows that gold and polymetallic ore deposits in upper heilongjiang metallogenic belt is mostlyin transition area from gravity plus to minus field or in abrupt change gradient belt. Magneticanomaly is characterized by the background with a low magnetic field. The gradient beltbetween positive and negative magnetic field is a good position to looking for precious metal andnonferrous metal mineral deposit. Au anomalies can be used as a gold ore prospecting marksdirectly in the study area, As, Sb, Ag and other anomalies can be used As indirectore-prospecting criteria.Through the multiple metallogenic information analysis of GIS, output of deposits iscontrolled by structure, mainly controled by the northeast and northwest faults. Meanwhile,intersection area between northeast and northwest faults often have a good ore potentiality;higher formation entropy is conducive to mineralization. Annular structure recognized byRemote sensing is closely related to mineralization. Comparing with other strata formation,,Xinghuadukuo Complex Group is the most favorable metallogenic formation, likely to be themain source of raw material.5metallogenic prospect areas of A grade,8metallogenic prospectareas of B grade,4metallogenic prediction areas of C grade are eventually confirmded by thisevidences from weight method of MRAS evaluation system of mineral resources.