The Baiyangping vein-type polymetallic mineralization as a response to shear zone development and block rotation in SE Tibetan Plateau

Abstract

The Baiyangping district is located in the northern Lanping Basin, SE Tibetan plateau. This area has undergone 80°–90° clockwise rotation around the Eastern Himalayan Syntaxis during the Oligocene–Early Miocene. Three major shear zones (Gaoligong, Biluoxueshan–Chongshan, and Ailao Shan–Red River) define the regional scale architecture that hosts the Baiyangping district. Several N-S structures parallel to the Biluoxueshan-Chongshan shear zone in the Baiyangping district underwent simple shear during ore formation. The Baiyangping district orebodies consist of two conjugate sets of veins (WNW-and NE-striking) and bedding-parallel veins. Block rotation occurred along the main shear zones, and conjugate veins occupied Riedel shear fractures (R and R′). Dilation occurred under progressive simple shear as the veins rotated. Ore-forming fluids migrated upwards into the dilating zones, and interacted with host rocks which buffered the fluids, increasing δ¹³C_PDB values in higher carbon content host rocks, and then sealing the space. Repeated cycles of dilation and cementation formed the orebodies of the Baiyangping district. This study highlights how block rotation can be linked to structures that control ore vein formation at the outcrop scale within obliquely convergent orogenic belts.