Research On Mineralizing Fluid Geochemistry Characteristics And Genesis Of Yingzuishan Gold Deposit,Gansu Province

Yingzuishan Gold deposit, in the convergence place of Northern China Plate, TarimPlate and Qilian Orogen, is located on the west side of Caledonian Northern QilianOrogen，which is one of the most important Cu-Au ore-forming region of China. Onthe basis of Regional Metallogenic theories, the characteristics of YingzuishanDeposit mineralizing fluid, Au, metallogenetic type and mineralizing model areresearched by Fluid Inclusion, H-O and S isotope geochemistry study. Results are asfollows:(1) Yingzuishan Gold Deposit is occurred in Heicigou Formation and strictlycontrolled by NWW faults, with the mineralizing roof being slates and the lithologiccharacteristics of backplane being very complicate.(2) There are little fluid inclusions in quartz, whose diameters and gas/liquid ratios arevery small. The type of fluid inclusions can be subdivided into pure gas inclusions,pure liquid inclusions and gas-liquid inclusions.(3) The temperatures of the early mineralization phase vary from145.9to313.0℃,the major mineralization phase from133.8to259.2℃, and the later mineralizationphase from95.8to188.5℃. In light to the formula of salinity and density calculation,we can find that the salinity and density of mineralizing fluid are0.35to6.4%, and0.69to0.98g/cm3respectively. According to the salinity and temperature of fluidinclusions, the pressure and depth can be calculated, being6.9to24.1MPa and0.69to2.41km respectively. In general, Yingzuishan Gold Deposit Mineralizing fluids areone of middle-low temperature, low salinity, middle-low density and shallowenvironment.(4) Both the gas and liquid component of mineralizing fluid are mainly CO2and H2O,with little H2S、CH4、H2and N2.(5) H-O isotope study shows mineralizing fluid is a kind of mixed hydrothermal fluid.Mineralizing fluids in the early mineralization phase mainly originate from magmaticwaters, and there are some atmospheric waters them in their migrating process.Furthermore, there may be little metamorphic water. (6) S isotope indicates the intrusions of uitrabasic magma in the deep provide somemetallogenic material and mineralizing fluids extract some Au from host rocks in theirmigrating processes.(7)In Cambrian, Heicigou Formation may provide some Au for mineralization.Northern Qilian palaeoocean subducted down to Northern China Plate in Ordovician.During Silurian and Devonian, Middle Qilian collided with North China Plate andformed a series of NWW trending faults. Mineralizing fluids migrated upward alongthe faults, extracted some Au from host rocks and mixed with some atmosphericwaters and little metamorphic water after being resisted by the slates. In this process,Au precipitated and concentrated in the alteration zones. Yingzuishan Gold Depositbelongs to orogenic deposits.