Characteristics Of Ore Forming Fluids And Geochemistry Of Saidu Gold Deposit, Altay

Altay polymetal metallogeny belt is belong to Central Asia Tectonic metallogenic zone. Saidu gold deposit,located in Habahe country, is out of the typical gold depositis in south-Altay. It is orogenic gold deposit,strictively controlled by ductile-shear zone,occur in altered mylonite zone of Mall-Kakkuri belt. In recent years, geological workers have done some research on the metallogenic characteristics, but nothing on the the nature of the ore-forming fluids and sources of the fluids. The research was done inroom combined with field works. The inroom work cotained microphysiography, microscopic measuring temperature, LRM(laser raman microprobe) and stable isotope analysis of the fluid inclusions from the deposit. I identified the ore-forming fluids and evolution of fluid, and revealed the source of ore-forming fluids and material sources.The homogenization temperatures of fluid inclusions in vein quartz are from 101 to 296℃, mainly concentrated in 160～200℃. The salinities of fluids are 0.35 to 9.86wt%Nacl, with an average of 4.23 wt%Nacl, and densities of 0.76 to 0.98 g/cm3. The results of these researches show that the ore-forming fluids had a low to moderate temperatures, with low salinities and low densities. LRM analysis shows that the fluids are in rich in volatile such as CO2, N2, in early mineralization stage, and evoluted to be rich in water in late mineralization stage, which is identical with the characteristics of the fluids of orogenic gold deposit.Theδ18OH2O of fluids for the Saidu gold deposit change from -5.60~8.09‰, with an average of -0.49‰. TheδD values are -60.10~-66.15‰, with an average of -62.54‰. Ore-forming fluids were originally magmatic water, and mixed by meteoric water in late mineralization stage. Theδ34S values of sulfides in gold deposit range from 3.53‰to 5.88‰, with an average of 4.86‰. The lead isotopic compositions are not variable, that is, 206Pb/204Pb=18.10~18.359, 207Pb/204Pb=15.488~15.579, 208Pb/204Pb=38.112~38.355. The sulfur and lead isotope studies indicate that ore-forming materials originated from the depth portion, and have close relations with magmatic activity. The ore materials were obtained from rocks in low crust during orogenic period.