Fluid Evolution And Ore-forming Process During Mesozoic Tectonic Transition In Zhaoping Fault Zone

The northwestern Jiaodong peninsula is one of the most important gold provinces in China. The annunal gold output in this region is one fourth of aggregate yields of China. There are about 50 percent of gold deposits situated in the Zhaoping fault belt(ZPFB). Therefore, studying ZPFB is of theoretical and practical significance in the ore-forming and ore-prospecting process. In order to investigate fluid evolution and ore-forming process of gold deposits during Mesozoic tectonic regime transition in the ZPFB, the paper takes the theories of regional metallogeny as a guide, carries out the test analysis of temperatures and Laser Raman Microspectrometry in Study of fluid inclusion, and the H-O isotopic studies, by using fluid geology and geochemistry, presents an analysis on source and evolution of ore-forming fluids during tectonic regime transition, discusses the gold mineralization and its fluid dynamics background of ZPFB. The main conclusion and cognition in the paper are:(1) The fluid inclusions in the ZPFB can be mainly divided into three types: aqueous inclusions, H2O-CO2 fluid inclusions and CO2-H2O-CH4 inclusions.(2) Fluid inclusion studies show that ore-forming fluids of gold deposits are consistent in the ZPFB with similar mineralizing temperature and pressure conditions, and characterized by intermediate-low salinity (0.35-11.69wt% NaCl), low density (0.65-0.98 g/cm-3), near-surface(0.7-1.9km), and weak reducing(the value of reduction parameter is 0.06-2.88). The best mineralizing temperature and prssure are 180-330℃and 30-45Mpa。(3) Oxygen and hydrogen isotope data show that ore fluids are of magmatic origin and metamorphic water contribution is minimal, however, there would be mixture water of the magmatic water, metamorphic water and little atmospheric water at the shallow crust; The ore types of Zhaoping fault gold deposit-zone are different because of the difference of ore-forming environment, ore-forming fluid filled in the fissures and mainly formed quartz vein type deposits in brittle fracture area; the gold-rich fluid alternated with host rocks and mainly formed altered rock type deposits in the depth facies of the fault because the less open of ore-forming environment.(4) The main mineralization stage of gold deposits in ZPFB can be divided into two stages: At the early stage,represented by Dayin’gezhuang and Xiadian gold deposits, the mineralization is related closely to hydrothermal activity of Guojialing batholiths, and the ore type is mainly altered rock type; At the late stage, represented by Linglong and Taishang gold deposits, the mineralization is related closely to hydrothermal activity of Guojialing batholiths, and the ore types are mainly altered rock type and quartz vein type. (5) The tectonic regime transition is the basic motive force during ore-forming process in the ZPFB, and gold deposits are formal in the same mineralization-geodynamic circumstance, at the same time, gold metallogeny is one of expression form of Mesozoic tectonic regime transition.(6) The gold mineralization keeps on extending southwestward at ZPFB, and large magma chamber oriented east-west is evident in east Jiaodong, distrubuting major extensional faults, which are important indications for ore-prospecting process in gold deposit accumulation region of eastern Shandong.