The structural deformation characteristics and the control of gold mineralization of the upper Triassic flysch (Langjiexue Group) in Tibetan Plateau

Abstract

Located in the eastern section of the Indus‐Yarlung Tsangbo Suture Zone, the Triassic Langjiexue Group is also very important for the distribution of the orogenic gold deposits, such as Bangbu and Zhemulang. Two regional profiles (Jiacha profile and Lang County profile) in the Langjiexue Group have been chosen for systematic mapping. Combing with the method of Ar–Ar dating for mica, this paper provides a detailed analysis of the structural movements and stress periods of the Langjiexue Group, and the relationship between them with the orogenic gold deposits distributed within it, and finally, establish the structural control model for orogenic gold deposits in the Langjiexue Group. The structural deformation of the Langjiexue Group can be divided into 4 stages. In the D1 stage, shallow ductile shear played a dominant role with the principal stress of the reaction in a nearly E–W direction. The main stress of D2 stage was in an obviously S–N direction whose foliation of the axial surface was a ubiquitous phyllitic foliation and foliation. The structures of the D3 stage were superimposed on those of the D2 stage with the main stress of S–N direction. In the D4 stage, the principal stress of the structural movements was in a nearly E–W direction. According to the morphology and spatial positions of the profile folds, the main body of the Songre Formation in the southern parts of the tectonic profiles can be restored into a large reverse antiform, whereas the main body of the Tectonic mélange zone in the northern parts can be restored into a continuous large antiform and synform. Judging by the Ar–Ar plateau ages (56.04 ± 0.72 Ma, 47.98 ± 0.46 Ma) of the sericite in the two quartz veins that were arranged along the axial plane cleavage of the folders in D3 stage, the widely distributed quartz veins in the Langjiexue Group were mainly the outcome of fluid action accompanied by the structural deformation that occurred in the main Indo‐Asian collision orogenesis period, which were in consistent with the mineralogenetic epoch of the orogenic gold deposits in this region.