Study On Metallogenic Cystem Of Wandashan Massif,Eastern Heilongjiang Province

The Wandashan massif is located in the eastern northeast China, eastern of Jiamusiterrane, southern of Xingkai terrain, western of Xihuote-Alin terrane. The Wandashanmassif is the important part of Wanda-Xihuote-Alin super-terrane, its other names areWandashan orogenic belt or Nadanhada terrain, and Mesozoic ophiolites outcropextensively in this area. According to ancient fossils and paleomagnetism, theWandashan Terrane formed from ocean basin near the equator during the MiddleTriassic, but in the Early–Mid-Jurassic it migrated to mid-and high-latitudes and waseventually amalgamated with the eastern reaches of the Jiamusi Massif (during theMid–Late Jurassic). Ultimately, it was thrust upwards within the Jiamusi Massif at thebeginning of the Early Cretaceous.According to metallogenic background, metallogenic mechanism of mineralizationof metallic ores in the study area, I have divided the Wandashan metallogenic cysteminto two categories: Late Paleozoic basic-ultrabasic rocks Cu-Ni metallogenic cystem,Early Mesozoic basic-ultrabasic rocks Cu-Ni-Co metallogenic cystem, Late Mesozoicacidic magmatic rocks Au-Ag metallogenic cystem. Late Paleozoic basic-ultrabasicrocks Cu-Ni metallogenic cystem was closely related to the subduction of thePaleoasian plate, and it was formed in the island-arc environment. Early Mesozoicbasic-ultrabasic rocks Cu-Ni-Co metallogenic cystem was closely related to thesea-floor spreading of the paleo-Pacific plate, and it was formed in the mid-ocean ridgeenvironment. Late Mesozoic acidic magmatic rocks Au-Ag metallogenic cystem was closely related to the thickened lithosphere delamination, and it was formed in thepost-collisional tensional environment.Late Paleozoic basic-ultrabasic rocks Cu-Ni metallogenic cystem was mainlyrelated to the basic-ultrabasic rocks in the Yuejinshan ophiolite belt, its mineralizationwas weak. And the Shuguangcun Cu mineralized point only has been found in thismetallogenic cystem. The basic-ultrabasic rocks of the Yuejinshan ophiolite belt arelocated in the southwest part of the Wandashan area, their diagenetic epoch was about311Ma, and they have with the same petrogeochemistry characteristic as island-arcbasalt. The subduction of the Paleoasian plate induced mantle material to flow up, inlate Paleozoic. During flowing up, mantle-derived magmas have undergone immiscibleseparation of metal sulfide, and being evolved into three parts: barren magmas, orebearing magmas, and ore pulp. Driven by metallogenic energy, the ore bearing magmasand ore pulp entered into the ore-contained space to form the Cu-Ni deposits. Duringthe Wanda-Xihuote-Alin super-terrane thrusting upward the Jiamusi Massif, the Cu-Nideposits were scraped from the the Paleoasian plate with basic-ultrabasic rocks, andformed the Yuejinshan ophiolite belt.Early Mesozoic basic-ultrabasic rocks Cu-Ni-Co metallogenic cystem was mainlyrelated to the basic-ultrabasic rocks in the Raohe ophiolite belt, its mineralization wasweak. The Yongxin Cu-Ni mineralized point and Xiangyang Cu-Ni-Co mineralizedpoint have been found in this metallogenic cystem. The basic-ultrabasic rocks of theRaohe ophiolite belt are located in the eastern part of the Wandashan area, theirdiagenetic epoch was about228Ma, and they have with the same petrogeochemistrycharacteristic as normal mid-ocean ridge basalts. The paleo-Pacific platetectono-magmatic actions were stong in early Mesozoic. The mass mantle magmaspoured from the mid-ocean ridge, and formed ore-forming basic-ultrabasic rocks.During flowing up, mantle-derived magmas have undergone immiscible separation ofmetal sulfide, and being evolved into three parts: barren magmas, ore bearing magmas,and ore pulp. Driven by metallogenic energy, the ore bearing magmas and ore pulpentered into the ore-contained space to form the Cu-Ni-Co deposits. During theWanda-Xihuote-Alin super-terrane thrusting upward the Jiamusi Massif, the Cu-Ni-Co deposits were scraped from the the paleo-Pacific plate with basic-ultrabasic rocks, andformed the Raohe ophiolite belt.Late Mesozoic acidic magmatic rocks Au-Ag metallogenic cystem is closelyrelated to acidic magmatic rocks of the Wandashan massif, its mineralization was strong,and it is the main metallogenic epoch of the Wandashan massif. So far, we have foundone medium-sized deposit, four small-sized deposits and a quantity of mineralizedpoints in this metallogenic cystem. Acidic magmatic rocks are composed of acidicintrusive rocks and acidic volcanic rocks. The acidic intrusive rocks are located in theHamahe-Taipingcun, Hamatong reservoir, and northwest Dongfanghong town. And theacidic volcanic rocks are outcropped in the Datashanlinchang Formations and PikeshanFormations. The acidic intrusive rocks have with the same diagenetic epoch andpetrogeochemistry characteristic as the acidic volcanic rocks, they were formed inpost-collisional tensional environment.Lithosphere extension and thinning led to the conclusion that mantle materialmagmas rose to the crust in the Late Mesozoic. And new ore-bearing acidic magmasformed in the crust by partial melting. The metallogenic energy of the acidic magmaticrocks Au-Ag metallogenic cystem included thermal gradient, pressure gradient,concentration gradient, velocity gradient and chemical reaction. Driven by themetallogenic energy, the ore-bearing acidic magmas flowed upward, and evolved intomagmatic hydrothermal fluids and mineralization fluids. Because of the cooling andcrystal fractionation functions, the magmatic hydrothermal fluids crystallized turnedinto the acidic magmatic rocks near the earth surface. The mineralization fluids enteredinto different ore-contained space, and formed different genetic types of deposits. Forexample, the volcanic hydrothermal type deposit was formed by the mineralizationfluids filling in volcanic breccias. The skarn type deposit was formed by thehydrothermal metasomatic function of the mineralization fluids and carbonate rocks.The hot spring type deposit was formed by the mineralization fluids pouring into bottomof sea along some cracks. The quartz vein type deposit was formed by themineralization fluids turning into ore-bearing quartz veins. The epithermal deposit t wasformed by the cooling and crystal functions of the mineralization fluids near the earth surface.The Au-Ag deposits and acidic magmatic rocks are highly consistent in theirtemporal-spatial distribution. The Au-Ag deposits are mainly hosted in the acidicmagmatic rocks or the contact zones. According to zircon U-Pb isotope analysis results,we divide diagenetic epochs of acidic magmatic rocks into three groups:128.0Ma-135.2Ma,122.1Ma-124.0Ma,110.0Ma-117.1Ma. And age of Au mineralization of theSipingshan gold deposit is slightly younger than122Ma, Au metallogenetic epochs ofthe Xianfengbeishan gold deposit is113Ma-117Ma, age of Au mineralization of theYuejinshan gold deposit is109Ma-116Ma, Au metallogenetic epochs of the258highland and358highland gold deposit are110Ma-115Ma. Therefore, late Mesozoicacidic magmatic rocks Au-Ag metallogenic cystem is closely related to the late acidicmagmatic activity in the Wandashan massif.According to metallogenic geological conditions, geochemical anomalies andaeromagnetic anomaly, gravity anomaly, and distributive pattern of deposits, we showfour metallogenic prospect areas in the Wandashan massif. They are258highlandAu-Ag metallogenic prospect area, Dadingzishan Cu-Ni-Wi-Sn metallogenic prospectarea, Sipingshan-358highland Au-Ag metallogenic prospect area, and Yuejinshan-Xianfengbeishan Au-Ag-Cu metallogenic prospect area. These metallogenic prospectareas point out the specifical direction for the geological exploration work, having veryimportant significance.