Geological And Geochemical Features And Genesis Of The Dongping Gold Deposit In Chongli County,hebei Province

Dongping Gold Deposit is located in the western part of the Yanshan, which tectonic position is the middle part of north edge of North China Craton. It is a new-type gold deposit first found in alkaline rock of China. The ore-bearing stratum is amphibolite-granulite facies metamorphic rocks system composed by a set of hornblende plagioclase gneiss, amphibolite, biotite schist and leptite of the Archean Jiangouhe Formation, Sanggan Group. The Shuiquangou syenite alkaline complex is the mineralized geological body.Based on the study of the geological features, systematic analysis of major elements, trace elements, rare earth elements and stable isotope composition characteristics of the deposit rock(ore), the following main results and understanding are obtained in this paper.(1) The studies suggest that Shuiquangou syenite alkaline igneous complex is the mineralization geological body of Dongping gold district. The Shuiquangou alkaline complex is dominated by monzonite and syenite. There is no clear boundary between them,and they are gradual transition. At present, more than 10 gold deposits(occrrences) have been found in the rock mass, like Dongping, Hougou and so on. The characteristics of these deposits are controlled by faults, sulphide content is low(less than 5%), and development of gold-bearing quartz veins or K-feldspar veins. Both inside and outside the contact zone of the complex suffered strong potassic and silicification alteration. The rock mass shows close relationship with Dongping gold deposit in space.(2) By observing different types of ores and the polished section, the polished thin section by laboratory microscope, the mineralization stages of the deposit metallogeic epoch were divided. The Dongping gold deposit formed in hydrothermal stage, can be divided into four mineralization stages: K-feldspar-quartz stage(weak gold mineralization);quartz-pyrite stage(an important mineralization stage); quartz-polymetallic sulphides stage(the main mineralization stage); pyrite-carbonate phase(the final stage, less relationship with mineralization).(3) The major elements, trace elements and REE characteristics shows that ore-forming fluids should be relatively rich in Si4+, K+, Na+ and other ions. The Shuiquangou alkaline syenite complex and the Sangganqun gneiss both provide ore-forming materials. The stable isotope indicate that the ore-forming fluids evolved from the mixed fluid of deep magmatic solution and meteoric water; carbon probably originated from deep; sulfur source is from mantle; lead comes mainly from the mantle and the crust and mantle mixing subduction zone.(4) Combining previous studies with the research in this paper, the genetic type of the Dongping gold deposit is discussed. The author prefers that Dongping gold deposit is a mesothermal gold deposit associated with Shuiquangou alkaline syenite complex.