Research On Metallogenic Character And Nonlinear Metallogenic Dynamics At The Zhaishang Gold Deposit, Western Qinling Mountains, China

Located in the western part of the Min-Li ore belt in the western Qinling mountains, the Zhaishang deposit is a large Carlin-like type disseminated gold deposit and has reserves of Au of approximately 120 t. Gold mineralization is strictly controlled by faults. With the method of field geological investigations, fluid inclusions, nonlinear theories and geochemical, we studied the geology, mineralizing fluid, faults characters, elements distrbution and metallogenetic geodynamical in the Zhaishang gold deposit, author concluded that:1 Ore mineral are quite complex and consist of sulfides, oxides, sulfosalt, sulfate, carbonate and tungstate. Besides the most common minerals there are pyrite, chalcopyrite, tetrahedrite, galena, sphalerite, scheelite, siderite and barite, author identifed domingite for the first time in the deposit.2 In microthermometry and micro laser raman spectroscopy analyses, the range of mineralizing fluid temperature is 92 to 293℃, the fluid salinity is range from 0.18 to 23.01% and the mineralizing fluid density is range from 0.75 to 1.03g/ cm3, which is mid-low temperature, low salinity and density fluid; the main gas composition is CO2 and CH4.3 The sphalerite, scheelite and ankerite displayed the compositional zoning patterns. The nonuniform elements distribution in minerals was proved by EPMA and SEM results. It implied that the mineralizing fluid was in a non-equilibrium system duiring the mineralizing process. It also suggest the mineralizing temperature has a quick cooling and slow recoverr process, which lead the precipitation and enrichment of Au.4 Using the method of nonlinear theories to study the elements distribution, showed that Au, Sb, Hg, W and Zn have the differents mineralizing menchanism and maybe exist the probability of multi period enrichment. Sb, Hg, W and Zn can be considered as the path finder elements of Au.5 Synthesizing the studies above, author concluded the mechanism of the Zhaishang gold deposit as follows: the stable isotope characters in the Zhaishang gold deposit showed that the mineralizing fluid has the characters of precipitate water and deep-sourced fluid. The main power of fluid activation and transportation are tectonic and geothermal gradient. The sedimentary strata of the Devonian and the Permian lay the foundations for gold pre-enrichment and material exchange of fluid and wall rock. Tectonics not only plays a positive role for fluid transportation, but also provides the channel for the mineralizing fluid. Fluid flowing and reacting in the porous rock cause the change of porosity and permeability. The parameters such as temperature, pressure and p H, emerged instability at the same time, the system evolve to a new stable time-space structure and lead the precipitation of mineral elements. The geology-geochemical field in the Zhaishang deposit presents the time-space structure of fractal in different scales, that reflect the dynamical mechanism of fractal growth and self-organization in the deposit.