Study On Geochemistry And Metallogenic Mechanism Of The Getang Large-scale Gold Ore Deposit, Guizhou Province, China

The Getang gold deposit, which is a large-sized gold deposit in Southwestern Guizhou province, is located in the transition belt between the Yangtze Block and the South China Fold Belt. It is a typical Carlin-type Au deposit, and is clearly controlled by the sedimentation-structure-alteration body(SBT). Systematic and in-depth study on the regional metallogenic geological background, ore deposit geology, metallogenic age, geological and geochemisitry indicates that Carlin-type gold deposit in this region can be grouped into "Getang type" and "Lannigou type". The dynamic background, origins of ore-forming fluid and metals, main ore-controlling factors, geological and geochemical characteristics and metallogenic conditions of the Carlin-type gold deposits in the area have been discussed by comparative study. In addition, combined with the tracers of elemental geochemistry, fluid inclusion geochemistry, stable isotope and radioactive isotope geochemistry for quartz, pyrite and fluorite and Rb-Sr and Sm-Nd dating of fluorite and pyrite, the major achievements have been as follows:(1) The major ore-controlling factors of the Carlin-type Au deposit in the study area are structure, SBT and ore-containing strata. The deposit is typical structure-fluid coupling mineralization. Studied on the regional geological setting, mining geology, deposit geology, mineralization age, geological and geochemical aspects, Carlin-type gold deposit in the area are grouped into "Getang type" and "Lannigou type". By the comparison study, the dynamics background, main ore-controlling factors, mineralization conditions, sources of ore-forming metals and fluids, geology and geochemistry and mineral deposit characteristics have been discussed.(2) The in-depth resrarch of the structure, formation, evolution and ore-controlling laws of SBT has been discussed. The SBT is a regional-scale sedimentation-structure-alteration body, the bottom interface contacts with P2m as rugged the Dongwu unconformity, its top interface contacts with the Longtan Formation of the Upper Permian (P3l2-1) thin dark-gray carbonaceous shale is also a structure-controlling interface. The Dongwu unconformity structure is main conduit structure of ore-forming fluid migration and the SBT is the main ore-hosting structure. The prototype of SBT at the Dongwu movement and interlayer sliding tectonic zone was formed under the region stress field in the Indo-Yanshan period, also silicified breccias resulted from the along-layer migration of the high-pressure ore-foming fluid.the slip-sheet structure system in which the Dongwu unconformity controlled the distribution and location of silicified breccia gold ore-bodies (mineralization), and limited the formation and position of deposit. Due to differences between the kinetic energy of the high-pressure fluid and SBT internal fabric materials and mechanical structure bearing capacity of its top structural planes, high pressure fluid can upward breakthrough, resulting in the SBT to be some size, order times and the levels, that is a deposit can form the multiple SBTs of ore-controlling and ore-bearing structure, but the most important SBT distributs above P2m.(3)By field survey and research, it is suggested that the SBT without basalt distribution can analogy with "Dachang layer" in the Qinglong area. The sedimentary environment, mineral sources, textures and structures, rock mechanical conditions, the ore characteristics are similar, and all are produces of the Dongwu movement, are major ore-controlling and ore-bearing structures in region.(4) By the interpretation of regional geophysical data and seismic data, in this area,the mantle uplift existed,and led to the SN-trending concealed intrusion, and it is suggested that deposit are mainly distributed in the mantle uplift belt. In addition, isotopes and REE geochemical studies suggest ore-forming fluids and partial metals came from magmatic hydrothermal. The research of regional geology, deposit geology, particularly the trace elements, REE fluid and isotope geochemistry indicates that the ore-forming fluids are mixture of magmatic hydrothermal from the depth origin and meteoric water. The magma activity (the Permian Emeishan Mantle Plume) did not only bring into metallogenic material, but also created the favorable conditions for the occurrence of power mineralization.(5) By study on the measure and comparison of mineralization period, it is comsidered that the mineralization age of Au deposits is 82-140 Ma. Meanwhile, the period of Sm-Nd method (35.83±0.37Ma)represents the mineralization and alteration event in lateritic or gossan-type gold deposit in the Himalayan period after the formation of gold deposit.(6) The layered SBT is the main ore-controlling structure and ore-bearing structure in the "Getang type" gold deposits, and the high-angle faults are the main ore-controlling factors in the "Lannigou type" gold deposits.The SBT metallogenic model of Getang gold deposit is proposed. In addition, the regional metallogenic model, it is "ectopic-homologous -simultaneous-structure", is raised for the Carlin-type gold deposits in the study area. These conclusions have an important guiding role for study on metallogenic theory, prospecting prediction and exploration of Carlin-type gold deposits in this area.