Tectonic setting of the Youjiang giant tin belt, South China: New findings from the Pingna W-Sn deposit

[Display omitted] •Late Cretaceous regional transtension governed the world-class Youjiang tin belt, South China.•Polyphase deformation is favorable for Sn-W mineralization.•Releasing bend of the NW-striking Pingna fault controlled Sn mineralization localization.•Liujie and Liushigou anticlines regulated W mineralization localization.•New muscovitization-bordered W-Sn vein swarms found in the Youjiang giant tin belt. Growing evidence suggest that extensional/transtensional settings are favorable for the formation of tin deposits, yet the underlying geodynamic mechanism remains equivocal. The Pingna W-Sn deposit, found in the underexplored interior of the giant tin belt within the Youjiang Basin, South China, offers a unique opportunity to explore and better constrain the current geodynamic model for tin mineralization. This deposit, composed of NW- to NWN-striking vein swarms with W-Sn mineralization, is hosted in the Middle Triassic clastic rocks without igneous rocks near its mineralization. Structural analysis indicates that the Youjiang fold-and-fault belt and the ore-related structures in the Pingna deposit experienced five deformation phases (D1–D5). The pre-ore NE-striking compression (D1; σv = σ3) initiated fault-fracture meshes, followed by NE-striking extension (D2), while NW-striking compression (D3; σv = σ2) enhanced the vertical connectivity of the meshes. Syn-mineralization E-W extension (D4; σv = σ1) facilitated upward through-going flow and hydrothermal fluids infilled the meshes, forming a fault-vein system. The mineralized veins were cut across by post-ore WNW-striking oblique fault with sinistral and normal components (D5). The meshes dictated Sn-W orebodies localization. Hydrothermal veins formed in three stages: (I) muscovitization-bordered tin-dominated quartz vein swarms along the Pingna fault; (II) W-dominated lit-par-lit vein system; and (III) barren calcite veins crosscutting the former veins. The Pingna W-Sn mineralization formed during the Late Cretaceous as constrained by the cassiterite (Cst1) U-Pb age of 95.6 ± 2.4 Ma (2σ, MSWD = 1.2), muscovite (Ms1) 40Ar-39Ar plateau age of 93.9 ± 0.1 Ma (2σ, MSWD = 1.7), and molybdenite Re-Os age of 92.9 ± 1.2 Ma (2σ, MSWD = 0.3). Outward lateral zoning of the Sn-W mineralization, as well as associated muscovitization and silicification implies the epicenter of hydrothermal fluid is near the No. II vein swarm. Contemporaneous felsic dykes coupling with the inferred intrusions demonstrate t