Metallogenesis Of The Dongyang Gold Deposit In Fujian Province And Its Origin

Fujian Dongyang gold deposit is located in the middle of Zhouning-Huaan Tectonic Belt,south of Middle-Fujian Au-Ag metallogenic province.The widespread tectonic and magmatic events provided favorable condition for large scale mineralization.We use methods of genetic mineralogy,element-isotope geochemistry,isotope chronology and fluid inclusion,etc,to research the magmatic rocks,hydrothermolites and ore body related to the metallogenic system,and finally get the diagenetic-metallogenic age,characteristics of minerogenetic structures,construction of the metallogenic system,ore-forming fluids and source materials,based on which to set up the metallogenic model.Dongyang gold deposit is characterized by minuteness disseminated-veined rhyolite porphyry type ore body.The altered minerals are dominantly sericite and quartz,secondly of kaolinite and calcite,etc.Pyrite is the main metallic gold-bearing mineral,with some mineral inclusions of copper pyrites,sphalerite and gelenite.The Rickman index,ratio of Al2O3/(K2O+Na2O+Ca O)and 104×Ga/Al of the ore bearing subrhyolite porphyry is 0.16-1.74,1.76-3.69,2.5-10.6,respectively,together with related diagrams indicating peraluminous-calcalkaline A-type granite.The ratio of Nd/Th and Sm/Nd is 2.24-2.92 and 0.17-0.23,respectively,together with the other elements character,showing the dyke was derived from a mixture of partially melted Al-rich crustal material,with an input of mantle components.The source for the deposit was also derived from a mixture of crustal material,with an input of mantle components.The ore-forming fluids were dominantly composed of magmatic water,with some input of meteoric water.The temperature,salinity,density,pressure and mineralization depth is 150-170?,4.33%-5.96%,0.90-0.99g/cm3,33.5-49.1MPa and 2.3-4.2km,respectively,indicating the deposit belongs to epithermal type.The gold is mainly hosted in the pyrite as nanocrystalline and solid solution.The zircon U-Pb diagenetic age of dykes is 160 Ma,in accord with the Rb-Sr age of pyrite hosting in the ore body is 164 Ma,indicating the dykes is ore-forming geological body of the deposit.Dongyang gold deposit and the dykes are production after subvolcanic rock intruded into the main volcanic edifice and volcanic fractures,with the ore-bearing hydrothermal fluids upwelling through the pathways opened up by the subvolcanic rocks,extracting ore-forming elements from the basement metamorphic rocks and subvolcanic rocks.