Structural Deformation And Evolution Of The Lannigou Gold Deposit And Its Surroundings In Southwestern Guizhou,china

Lannigou gold deposit is also called“Jinfeng gold deposit”,where is located in the middle of Southwest Guizhou Province,and it is an important Carlin-type gold deposit in the Triassic flysch formation in Nanpanjiang basin of China.Lannigou gold ore has the characteristics of large resource reserves,has 109 ton gold reserves(average grade:3.83g/t),and has important research value and economic value.Due to its special geotectonic location where is in southwest Guizhou Province,the Lannigou gold ore cross Yangtze massif and Youjiang orogenic belt and located at the intersection of the Paleo-tethys Ocean and the marginal-Pacific tectonic system.Since the late Paleozoic,the present tectonic pattern has been formed after several periods of intense tectonic movements.Based on previous research results,this paper conducts field geological survey,its indoor structural data collation and analysis,and seismic data analysis in the Lannigou gold deposit and its periphery,in this paper,the tectonic deformation characteristics and evolution sequence of the study area are defined,what's more,the dynamic background of tectonic evolution and its influence on mineralization are discussed.At the same time,it is also of great significance to the exploration of the deep and peripheral concealed ore for the Lannigou gold deposit.As for the structural deformation characteristics and evolution of the Lannigou gold deposit and its adjacent areas,the main conclusions are as follows:(1)The study area has strong tectonism and complex tectonic deformation.The main structural lines of this study area were classified into two groups,trending northwest and northeast respectively.And fold-fault association is the main tectonic type.There are various types of folds here,such as:inclined fold?angular fold?overturned fold?recumbent fold and convolute fold,etc.And the main fault styles are thrust faults and some are normal faults.(2)Through detailed field observation and mechanical analysis of the main faults and the secondary tectonic phenomena(folds,faults and joints)developed in the hanging wall and heading side around the Lannigou gold deposit area,and then analyzed its geometry and kinematics,in this paper.Notably,faults with obvious thrust properties are LWF?BCF?XZF and XNF.However,the conjugate shear joint and angular tectonic breccia in fault fracture zone at the heading side of BF show that BF has the nature of normal fault.At the same time,the BF also shows the nature of reverse fault in many places,so it has complex structural deformation characteristics.We think that the structural deformation characteristics are divided into extension and compression.(3)The study area underwent two distinct development stages in late Paleozoic-Triassic.Among them,late Paleozoic-Middle Triassic early Anisian is extensional stage,while since the middle Anisian is compressive stage.As the tectonic background transforms into compression,some of fault properties are reversed.There is a clear reflection on the seismic profile:the faults show the nature of reverse fault in the shallow part,but it still retains the feature of normal fault in the deep formation.According to the volcanic zircon U-Pb and ³⁹Ar-⁴⁰Ar dating of the T₂xm²,it is inferred that the tectonic switch time should be shortly later than 248Ma or 246Ma.(4)The tectonic deformation of Lannigou gold deposit area is closely related to the evolution of Nanpanjiang basin.During the Hercynian-Indochina period,the Nanpanjiang basin experienced a transition from extensional basin to compressional basin.And during the Devonian-middle Triassic,for the Nanpanjiang basin,this is the formation stage of extensional basin,and then,in middle Triassic and latter,it turns into foreland basin.Therefore,the formation of Lannigdou gold deposit is a part of the Nanpanjiang basin's tectonic evolution.The development and evolution of Nanpanjiang basin what is closely related to the cracking,subduction and closure of the Paleo-tethys Ocean,is the main geodynamic source for deformation during the Devonian-Triassic.(5)Tectonic factors play a significant role in controlling the mineralizing process of Carlin-type gold deposit in this area.According to the seismic profile,LWF and QLF extend down to the metamorphic basement of Nanpanjiang basin,it can connect the source rocks of Devonian to the deposits,and they may provide a great number of organic matters and migration channels for ore-forming fluid.Moreover,there are geochemical anomalies and gold occurrences in the south of LWF,it's concluded that the deep and peripheral of the Lannigou gold deposit have good prospecting potential.