Metallogenic Mechanism Of The Jiaodong-type Gold Deposit,Shandong Province, China

The Jiaodong gold province is located in the south-east margin of the North China Block. It is an endogenic hydrothermal gold concentration area consisting of Precambrian basement and ultra-high pressure(UHP) metamorphic rocks, with multiple tectono-magmatic events during the Mesozoic.Based on detailed ore geology research, by using scanning electron microscope, hot-cathode CL microscopy on quartz, in situLA-ICP-MS element analysis of pyrite, fluid-inclusion and stable isotopic analyses, this thesis focuses on the metallogenic mechanism, defines the source-transportation- deposition progress of themetallogenic system and gold enrichment mechanism, and builds a metallogenic model of the Jiaodong-type gold deposit, the mainachievements are summarized below:(1) The ore-forming fluids of Jiaodong gold deposit belong to metamorphic fluids, which characterized by medium-low temperatures, medium-low salinities, and CO2-rich with minor CH4. The δD andδ18O values of ore fluids, δ13C values of calcite, and δ34S values of gold-hosting pyrite are-68‰ ~-33‰,-6.7 ~-6.3‰, and 4.3‰ ~ 8.9‰, respectively. Combined with the regional metallogenic background, the conjectured source of ore fluids is the subducting paleo-Pacific plate and its overlying sediments. The estimated P-T conditions and depth of gold mineralization during the main stage event ranged from 200 to 40 MPa,328 to 230?C, and 7.4~4.0 km.(2) The internal structure of regional NE-NNE trending fault zones and different types of fluid flow patterns resulted in the different types of gold mineralization. The regional gentle-dipfault zones, consisting of cataclastic series and tension-shearfracture plane, have pervasive typefluid flow pattern and controlled the altered-rock typedisseminated- and stockwork-style mineralization. The subsidiary steep-dip faults,consisting of tension-shearfracture plane and concentrated joint band, have channelized type fluid flow pattern and controlled thequartz vein typemineralization.(3) The high grade gold is mainly invisible goldwhich normally occurs in fractures in pyrite or overgrows pyriteboundary. The tension-shearactivity and progressive brittle deformation,leading fluid-wallrock sulfidation reaction and fluid immiscibility, resulted in pre-ore pyrite deposition, broken and corrosion. The gold deposited in fractures in pyrite or overgrows pyriteboundary and formed large scale gold deposits. Fluid unmixing is more important in the quartz vein-type ores and leads to a higher gold grade.(4)The low arsenic content, low Au/Ag ratio, appearance of galena and tellurobismuthite, and mass brittle deformation indicate the Jiaodong gold deposit has a similar genesis to the epizonal orogenic deposit.However, the Jiaodong gold deposits are characterized byunique strong extensionbackground,tension-shear tectonic environment, large scale of wallrock alteration,and the ore-forming fluid rooted in dehydration of the subducting plate. Its metallogenic background and environment, and alteration and mineralization characteristics are unique among the global existing typical gold deposits metallogenic model, thus belong to “Jiaodong-type” gold deposit.