Geology, Geochemistry And Genesis Of The Simaoling Gold Deposit In The Fengtai Ore Concentration Area, Western Qinling

The Simaoling gold deposit, located in the Fengtai ore concentration area of the Western Qinling and 5Km to the west of the super-large Baguamiao orogenic gold deposit, is a new proved medium sized orogenic gold deposit. It's basic research work is relatively weak and no systematic research reports. Based on detailed field study of Simaoling gold deposit, using some feasible methods such as systematically fluid inclusion homotemperature measuring, the gas-liquid phase composition, the trace elements and REE analysis, H, O, S, and C isotope studies and contrasted with the Baguamiao gold deposit, this thesis recognizes its characteristics and source of ore-forming fluid, source of ore-forming materials, and then gives a reasonable explanation about its genesis. The main conclusions that we got are as follow:1) The gold mineralization could be divided into three stages: the early quartz-sericite-sulfide stage, the middle polymetallic sulfide stage, and the late carbonation stage. Studies on fluid inclusions of the early and the middle stages show that the ore-forming fluids belong to the low salinity CO2-H2O system with intermediate temperature.In the metallogenic stage,the ore-forming fluid temperatures were 260℃; the ore-forming pressures was concentrated in 26~300MPa;the peak value of salinities was 9.00wt%NaCleq; and the densities were mostly from 0.822 to 1.055 g/cm3;the gas phase compositions were H2O > CO2> N2 > CH4 > CO. And the diversity of fluid inclusion types is resulted from the fluid immiscibility.The main type of the ore-forming fluids was Ca+-C1- type. By contrast with the Baguamiao gold deposit,it relatively enriching with Ca+ - ion and its pressure relatively higher indicated its carbonate-alteration more developed and its mineral buried deeper.2) H, O, S, and C isotope studies showed that the ore-forming fluid was mixed with meteoric water and magmatic whose features are more obvious; the rich CO2 fluid which came from the lower shear zone mantledegassing has deep origin and contributed to the migration and precipitation for ore-forming; its gold mineralization is developed in more open environment by contrast with the Baguamiao gold deposit; sulfur has the strata source and the magma source;In the metallogenic stage, temperature, pressure and salinity of fluids are lower, and the sulfur fugacity is higher, which are in favor of gold precipitation.3) The trace elements and REE analysis indicateed that the studied area lied in the passive continental margin and the sedimentary environment of the original rock may be seaboard environment with dry climate;after the sedimentary rock interfered with fluid, the microelements'geochemistry of wall rock and vein all changed, and the useful composition in the ore enriched; fade phyllite between different lithology usually be the advantageous ore-forming position; wall rock, to a certain degree, interrelated with ore and supplied ore-forming materials; the vein supplied minuscule ore-forming materials but promoted the activation, migration and enrichment of gold.4) Based on this study, the Simaoling gold deposit was a orogenic gold deposit as same as Baguamiao gold deposit; compared with the Baguamiao gold deposit,they had the similarity mineralization environment and ore-forming fluids and ore-forming material characteristics,but the Baguamiao gold deposit had relatively closed mineralizing conditions and higher sulfur fugacity which can win more possibility for the formation of the gold deposit.