Study On Ore Genesis Of The Malian Gold Deposit, Jiayin, Heilongjiang Province

The Malian gold area was located in the north of Jiamusi upwarping,consists of Malian gold deposit,Fengfanggou and Xiaomaliangou mineral occurrence. The major strata outcropping in the area include Proterozoic Heilongjiang terrain, lower Cretaceous Ningyuancun Group (K1n),Taiqihe Group(K1t), Upper Cretaceous Fuminhe Group (K2f),Taipinlinchang Group (K2tp),Yuliangzi Group(K2yl),Cenozoic Neogene Pliocene-Oligocene Sunwu Group and Pleistocene-Holocene fluvial Facies sedimentation.The intrusive igneous rock mainly Proterozoic Era arkosic gneiss, ophite and Mesozoic Era ganite, ganite-porphyry and quartz vein ,tandileofite-porphyrite et al.The area structure are Neanticlinorium and NNE,EW,NS fault ,which development in Heilongjiang terrain.In the mining area, exposed strata is mainly upper-petrofabric of Heilongjiang terrain whereas the intrusive igneous rock mainly diorite,dacite-porphyrite,quartz vein,the structures are mainly multiple fold which is attitude is NE in the Heilongjiang terrain,and the fault attitude are NNE ,NNW ,NE ,SN et al. among them the SN and NW fault are formed before premetallogenic and metallizing phase,whereas the NE fault is the compressional faulting of the postmineralization,The mineralization type of the Malian gold deposit is sulfid altered mylonite type,while a small quantity of the orebody is sulfide quartz vein type,the most ore minerals are native gold, the syngenesispyrite ore minerals are pyrite, mispickel, which total content are less than 5%.the gangue mineral were quartz, plagioclase, carbonate, micagrou chlorite ,while there are also have some epidote,actinolite, illuderite, garnet, tourmaline , graphite et al. Accordance with formation orders, combination features and relationships of these minerals, mineralization can be divided into three phases: quartz—metal stoxida steage, quartz—gold—sulphide stage, quartz—calcite stage.The wall-rock alteration are mainly muscovitization, silication, epidotization, and pilitation,carbonatation and so on, in the deposit. The vicinity between gold- mineralization and the wall-rock alteration is the silication.The host rock of Fengfanggou and Xiaomaliangou mineral occurrence is Heilongjiang terrane, mineral occurrence is composed mainly of auriferous quartz veins, the ore minerals is mainly composed of pyrite and limonite, the gangue minerals is composed of quartz chlorite, sericite, epidote, the main texture of the ore bodies are semi-self-shaped, the main structure of ore bodies dissemination structure,There are many type of host rock alteration,such as ferritization sericitization and propylitization. Mineralization of Fengfangou mineral occurrence can be divided into three phases: Sericite—Pyrite steage, quartz—Pyrite stage, quartz—Kaolin stage.In Malian gold deposit , the fluid inclusions were devided into two types, the one is the gas-liquid two-phase ,which is the most fluid inclusion type of Malian gold deposit holding about 95%.According to the gas-liquid ratio ,this one also cloud be devided into 5%～30% and 30%～40% two types,the shape of the gas-liquid two-phase rotundatus,areellipse and irregular, the size were between 2-10μm, the hepredomination was 6μm,the other were pure gas or liquid inclusions,the shape of inclusions were elliptic,regular or irregular. homogenization temperature of NaCl-H2O fluid inclusions of two-phase is 140℃~310℃, and different temperatures correspond to different stages of mineralization; salinity is 0.5%～4.5% and density is 0.72-01.2g/cm3, so ore-forming fluids is the low-salinity, low-density fluid; calculated mineralized pressure is 7.65～24.07MPa, and forming depth is 0.97-1.79km; components by laser Raman studies have shown that gas compositions of inclusion are mainly CO2,H2O and CH4.The main ore-forming fluid which is CO2-CH4-H2O system shows the characteristics of metamorphic fluids.By studying the result of the previous data,combine with the features of the fluid inclusions obtained ,we can see that Malian gold deposit mineralization fluid hydrothermal are from the deep metamorphic mixed with the atmospheric precipitation. As the Heilongjiang terrane is one of the major source of minerals. As Fengfangou and Xiaomaliangou mineral occurrence has similainties with Malian gold deposit on geological features and fluid inclusions, suggests that they are the same type of gold deposit .Conclusion from the CL image analysis and LA-ICP-MS U-Pb age of testing of zircon in Muscovite albite schist shows that zircon in Muscovite albite schist include three groups:Ⅰ. Neopaleozoic early Permain (266.3±5.5 Ma),Ⅱ. Early Neopaleozoic ordovician (467～486Ma),Ⅲ. Mesozoic Era early Triassic (235～245Ma).The first group zircon is formation of zircon in crystallization processes for initial rock or limited the deposition age of the Heilongjiang terrane,within the previous data and our examination, we can limited that gold deposits of the ore-forming age is 180Ma.Combine with regional geologic characteristic,we can speculate that mineralized thermal power source of Malian gold deposits come from the orogenics between Jiamisi and Songnen massifs, to be influenced by Paleozoic Centeal Asian.Mineralized fluids reaulted in transformation between extrusion and extension during high pressure metamorphism,which occurred when subducting, turn back to superficial part.Mineral substance concentrated and deposited as surrounding rock eluvialed when fluid migration .From resarch result of the ore-forming age, mineralized material sources , mineralized thermal power source and ore-forming fluids shows that: As the Paleo-Asian Ocean closed,Jiamusi and Songnen massifs occoured collision,in deepness mineral-bearing fluids generated, As the rising progress along the fracture, Fluid is mixed by atmoshpere precipitation and leachied Heilongjiang Group resulting in obtaining part of ore-forming materials, ultimately is precipitate in the form of sulfur quartz vine ore body in the NE fault,which fromed Malian gold deposit and Fengfanggou and Xiaomaliangou mineral occurrence .Compared Malian gold deposit with some type domestic and overseas'orogenic gold deposit ,we found they have some common depaetments .So we concluded that Malian gold deposit which development in tectonic zones is orogentic gold deposit.