Progressive spatial and temporal evolution of tectonic triggers and metasomatized mantle lithosphere sources for orogenic gold mineralization in a Triassic convergent margin: Kunlun-Qinling Orogen, central China

Abstract

Abstract Whether orogenic gold deposits formed from crustal or subcrustal sources is debated, and their link to orogenic processes is ambiguous. Gold mineralization in the Triassic East Kunlun–West Qinling Orogen, China, displays a spatial zonation in terms of its ages and stable isotope compositions. In the West Qinling segment, most gold deposits formed in a back-arc setting at 220∼210 Ma during a collisional episode within late slab rollback. These deposits have dominant δ34S of 5∼15‰ and δ18Ofluid of 10∼14‰, whereas those formed in the suture zone at 210∼170 Ma, during a post-collisional episode after slab break-off, have lower δ34S of −5∼+5‰ and δ18Ofluid of 6∼10‰. In the East Kunlun segment, those deposits that formed in a continental-arc setting and its related suture zone at 240∼200 Ma, in collisional to post-collisional episodes associated with slab break-off, have δ34S and δ18Ofluid values that are essentially similar to those in the West Qinling suture. δ34S values of ore sulfide separates and rims of zoned pyrites that have mantle-like signatures, in contrast with crustal signatures of host rocks, are indicative of subcrustal ore-fluid sources. The combined chronological and stable isotope shifts are consistent with a model in which ore fluids for gold mineralization in a back-arc setting were sourced from mantle lithosphere that was metasomatized by subducted oceanic sediment; whereas those in a continental-arc setting—including its suture zone—were sourced from fluid derived from altered oceanic crust. This study thus provides new insights into the complexity of orogenic gold systems in evolving orogens.