The Geological Characteristics And Genesis Of Yujiali Gold Deposit In Western Jiangxi Province

Since late 1970s, micro-fine disseminated gold deposits have been discovered with distribution areas mainly focusing on two Golden Triangles of Yunnan , Guizhou and Guangxi provinces (also known as the Dian-Qian-Gui area) and Sichuan, Gansu and Shaanxi Provinces(also known as the Chuan-Gan -shaan area). Academician Tu Guangchi, and Liu Dongsheng have proved that the gold deposits exist mainly in pyrites of calcarenaceous sedimentary rocks in micro-granular forms after past 20 years research. However, due to the complicated geological conditions(magmatic rocks, stratum and structure) and origin(the source for ore-forming materials, thermal and fluid) of the deposits, uncertain metallogenic process and model, there are still many arguments such as the mineralized origin and its sources. Geological explorations in recent years have discovered many micro-grained disseminated gold deposits for example, Wucun, Dashihu and Fengdingshan in Pingxiang-Gaoan sag belt, western Jiangxi Province, which makes west part of Jiangxi Province an important prospect area of gold mineralization. This sag is located at the junction of Yangtze Plate and South China Plate, which is a sinking belt during Late Paleozoic Era-Mesozoic Era between Jiuling Terrain and Wugong Terrain. Along the southern margin of Jiuling Terrain and northern part of Wugong Terrain, there are two large nappe belts developing along a fault in the sag, forming structural weak area. So the fault is one of major regional ore-controlling structures in western Jiangxi province. Although there have been previous studies on some of the gold deposits of this area, only few research is conducted on micro-fine disseminated gold deposits in western part of Jiangxi Province. Detail work is still needed for many deposits to make clear understand even the geological characteristics of the ore bodies and its origin. Therefore, the thesis chose Yujiali deposit in western Jiangxi province, and conducted site investigation of stratum, structure and rock features. Through analyzing and summarizing, Triassic Qinglong Formation has been defined as main host rocks with rock type of sedimentary breccia, impure carbonate rock and siliceous rocks. After recognizing under microscope, measurning by the scanning electronic microscope, electron probe on rock, ore, and their fluid inclusions, this paper has found that there are mainly four kinds of alterations as silicification, de-carbonation, clayization carbonization and pyritization; and the gold existed as micro-fine grain(about 0.0005mm) in pyrite, sililiceous minerals and carbonate minerals with forming temperature about 120℃~220℃. Finally, it was concluded Yujiali gold deposit was Carlin type with micro-fine grained disseminated texture. Thus comparative study has been conducted with other gold deposits in the metallogenic belt.