Metallogenic Setting And Metallogenesis Of Nonferrous-precious Metals In Lesser Hinggan Mountain, Heilongjiang Province

Lesser Hinggan Mountain is located in the eastern section of giant Central Asia-Hing Meng orogenic belt, the intersection area of Siberia plate, North China plate and the Pacific plate. It is a composite orogenic belt undergoing interactions of the three plates, mainly influenced by Paleo-Asian Ocean tectonic domain before the Mesozoic, and reconstruction and superposition activities of the Pacific plate since the Mesozoic, therefore constitutes a unique tectonic evolution background in this area.Petrology, geochemistry, chronology researches on mineralization-related magmatic rocks are carried out within Lesser Hinngan Mountain. It is suggested that ages of these intrusive rocks center on 200-170Ma and 120-100Ma. Great amounts of granitoids formed during 200-170Ma, mainly distributed nearly north-south trending along the Yichun-Yanshou fold belt, belong to calc-alkaline-high-K calc-alkaline series, I type (including the highly fractionated I-type) granites, magnetite series,with a high degree of oxidation, forming by subduction of the Pacific plate; volcanic and shallow intrusive rocks are contributed to mineralization during 120-100Ma, and formed due to lithospheric thinning after subduction.Based on the field work and laboratory study, we are approaching a new understanding on the genesis types and characteristics of deposits in studying area:Xiaoxilin lead-zinc skarn deposit is sedimentary exhalative lead-zinc deposits (Silver mine type SMS); Laodaomiaogou lead-zinc deposit is of hydrothermal vein type, different from the type of main ore body within Xiaoxilin ore field; Cuihongshan Fe-Mo polymetallic skarn deposit is formed during early Yanshanian, due to the Pacific subduction, instead of originally concerned as the product of the Caledonian superimposed Indosinian and Yanshanin magmatic hydrothermal activities.According to Westra et al (1981) on the classification of porphyry molybdenum deposit, we consider Huojihe, Luming porphyry molybdenum deposit are belong to the calc-alkaline series, pluton type. There are two types of molybdenum mineralization:quartz-molybdenite veins (Granite is not altered) and film-like mineralization (granite is altered into phyllic), according to rock and molybdenum mineralization characteristics, we propose to redefine this type as stockwork molybdenum deposit, in order to expand the idea of for porphyry deposit prospecting.After revising diagenetic mineralization ages and reunderstanding of ore genesis, we again reclassify the metallogenic series in the study area, two series can be divided: magmatism-related Mo-W-Cu-Pb-Zn deposit series in Early Yanshanian and volcanic-subvolcanic rocks related Au-Ag mineralization series in the late Yanshan.Finally, the paper summarizes the regional mineralization laws in space and time:in space, it can be divided into Yichun-Yanshou Mo-Fe-Pb-Zn-W-Sn-Cu-Ag metallogenic subzone and Lesser Hinggan Mounain NW-trending Au-Ag ore subzone. Mineralization in former subzone is well controlled by Mesozoic magmatic activity, also by specific strata (such as Cambrian Qianshan group, Ordovician Xiaojingou group, etc.), and NE, NNE and NW structures; the latter is controlled by volcanic eruption zone along NW-trending Basin and Range boundary fault in the late Yanshanian, with smoe low-sulfidation epithermal deposits. Three metallogenic periods are determined:Early Cambrian, early Yanshanian and late Yanshanian metallogenic period.Based on mineralization analysis, A lot of fluid inclusions tests have been carried out in geological fluids Laboratory in Earth Sciences department, Jilin University, using Linkam THSM-600 hot and cold units to determine the ore-forming fluids homogenization temperature, salinity, density, pressure of each typical deposit, and calculate the depth of mineralization for the study area, provided large amount of data for further research in Lesser Hing'an area.Luming and Huojihe molybdenum porphyry deposits are comparable, ore types are mainly molybdenite quartz veins, homogenization temperatures of fluid inclusion are concentrated in 180-360℃, molybdenite precipitated between 280-360℃, salinity of L type is concentrated in 3.05-6.58 wt% NaCleqiv whereas S type concentrated in 39.23-47.60wt% NaCleqiv by the disappearance of daughter mineral. Inclusion characteristics of each stage showed the overall evolution of ore-forming fluid may:firstly isolated a high temperature, middle-low salinity single fluid phase from the magma chamber, then isolated a high salinity fluid and coexisting gas phase when pressure changing from lithostatic to hydrostatic due to pressure reducing and fluid boiling. Mo enriched and precipitated in the residual fluid during 300-360℃. Overall, with the evolution of ore-forming fluids, minerals precipitated, ore-forming system was gradually cool down as well as the salinity decreased.Majority S type fluid inclusions in early stage of Chuihongshan Mo polymetallic deposit homogeneous by final dissolution of daughter minerals, a few by disappearing bubbles, homogenization temperature is concerntrated in 291-330.5℃, corresponding fluid salinity (NaCleq) is 37.29%-40.17%, homogenization temperature of L type is concentrated in 240-315℃, salinity in 6.44%-9.60%; Inclusions types of quartz sulfide stage mainly are L and V type, a small amount of S type. Homogenization temperature can be divided into two concentration intervals 180-234℃and 252-288℃, corresponding to molybdenite stage and copper lead zinc mineralization stage.Sandaowanzi gold deposit mainly formed in the 230-270℃, roughly equal to sulfide-quartz veins and quartz-gold-telluride stage; Dongan gold deposit mainly formed in the 220-280℃, belonging to the low-temperature deposit; Wulaga gold deposit forming temperature mainly concentrated in the range 150-220℃, equal to the tempreture of gold-bearing chalcedony quartz-polymetallic sulfides stage. The three deposits are all low salinity low-density.