Discussion On Geological Characteristics And Genesis Of Sandiao Gold Deposit In Dadu River Area

According to the scientific research item of “the research on metallogenic model and prospecting model of gold metallogenic belt in Dadu River area” from China Geological Survey Bureau, this thesis focuses on Sandiao gold deposit, studying the geologic structure of it on the basis of summarizing and further analyzing former huge research. By comparing with mineral inclosures such as quartz and pyrite which are closely related with mineralization, and the features of stable isotopic, it finds out the geologic feature of Sandiao gold deposit and discusses the origin of this deposit. It gets new discovery and understanding as the followings shows :Sandiao gold deposit is located in Dadu River gold metallogenic belt. The tectonic structure of this area belongs to Yangtze continental margin-Kang Dian basement fault block- Kangding rock in the north end. The regional structure is the north-south Dadu river ductile shear fault zone. It is produced before sinian system crystalline basement in Kangding complex.The ore bodies all hosted in mix granite outer contact zone of plagioclase amphibolite and migmatization plagioclase amphibolite. The Au elements in plagioclase amphibolite in ore-forming process is activated, migrated and enriched.Two ductile- brittle shear rupture zones in mining area of F1 and F2 controls deposit spatial orientation and the gold ore belts of Number?and Number ?. The internal structure of gold ore belt is composed of quartz vein and alteration phyllonite. The gold mineralization is most closely related with wall rock alteration like pyritization,sericitization, carbonatization and silicification.Gold ore body in mining area is from gold quartz vein of Number I. Ore minerals are mainly pyrite and chalcopyrite. The gangue minerals are mainly quartz, sericite,muscovite, etc. The ore texture is mainly based on crystallization, metasomatism,pressure structure. And its structure is mainly on massive and disseminated structures.Natural ore types are mainly based on metal sulphide quartz vein type. Some are less based on altered rock type gold ore. The industrial ore types belongs to low sulfur natural gold ore. The gold mineral is mainly on native gold, presenting the shapes of perfectly round, emulsion droplet and kernel which are embedded in the fissure and clearance of quartz, pyrite, chalcopyrite and other sulfide. Based on mineralization geological process and the order of priority, the gold deposit can be divided into two metallogenic epoches as hydrothermal one and supergene one. And the hydrothermalmetallogenic epoch can be divided into gold-pyrite-quartz mineralization stage and gold-polymetallic sulfide mineralizing stage.Mineralization is mainly due to hydrothermal filling and metasomatism.Suffering regional dynamic thermal metamorphism in multi-stages such as Jinning-Chengjiang stage or Indosinian-Yanshan stage, the presinian system basement rocks becomes heavier molten lava hot liquid in deep crust, extracting gold, copper and other ore-forming elements in basic magmatic rocks which are the main rock.Finally, the Himalayan ore fluid along the fault zone moves to ductile-brittle shearing phyllonite band to form the ore body. The ore-forming temperature is between 200?and 300?, and the depth is from 1.5 kilometers to 3 kilometers. The main liquid state element of ore-forming solution is water, secondly followed by cationic K+and Ca2+,and anionic CI-and SO42-. The gas phase composition is mainly CO2, secondly followed by N2, CO2 and a little CH4. Its salinity is medium and the degree of mineralization is high, presenting properties of alkaline hot brine with high concentration. The redox potential is positive, of lower reduction parameter and oxygen fugacity. Sulfur deposits are from Kangding group of base migmatization metamorphic rock. Sandiao gold deposit belongs to such type of gold deposit as epigenetic gold bearing sulfide quartz vein with hypabyssal medium-low temperature,due to remelting magma hydrothermal gold deposit.The above results and understanding play an important role in the ore prospecting and prediction in the future in Dadu area. Meanwhile, it also has a new big effect on the ore prospecting and exploration work in other areas in China.