Genesis of Copper Mineralization in the Lanping Foreland Basin, Southeastern Tibetan Plateau: Insights from Re–Os Geochronology and Sulfide Geochemistry at Baiyangping

Abstract

A series of sediment-host base metal deposits, related to the collision between the Indian and Asian plates, are distributed in the Lanping basin in the southeastern Tibetan Plateau. The genesis of these deposits remains controversial. Here, we report Re-Os isotopic data of chalcopyrite-tennantite and laser ablation mineral mapping from the Baiyangping deposit, a large sediment-hosted Cu-Pb-Zn deposit. The isochron age, which offers the first insight into the absolute age of the Cu mineralization, at 30.8 ± 1.4 Ma (MSWD = 2.7, n = 5, ±2σ). This demonstrates the application of the low-level Re-Os system in chalcopyrite-tennantite dating, with high 187Re/188Os (400–10,000 ppb) but low Re abundances (3–20 ppb). La-ICP-MS analysis show that sphalerite intergrown with chalcopyrite from Cu-rich mineralization exhibits a fibrous texture formed in a setting where vein cementation kept pace with dilation and is enriched in Ag, As, Cu and Sb. This is a common feature of basinal rocks influenced by compressional tectonics. In contrast, euhedral sphalerite in Pb-Zn orebody is enriched in Fe and Cd and displays concentric and sectoral zoning patterns. It was formed by precipitation into open space, probably assisted by structural dilation along jogs on extensional faults in transpressional or extensional zones. The Baiyangping deposit within thrust belts occurs as a result of synorogenic stress transition from compression to transpression/extension during the Cenozoic after Indo-Asian initial-collision. Regional metallogenesis also shows that Cu mineralization formed along thrust fault during the extrusion and Pb-Zn mineralization focus on extensional zones and extensional faults.

Keywords: Re-Os geochronology, LA-ICP-MS mapping, Copper metallogeny, Baiyangping, Regional metallogeny