Carlin-style gold province linked to the extinct Emeishan plume

Abstract

Carlin-style gold deposits constitute one of the most important types of Au resources in the world. Previous studies on these deposits correlated the source of Au with metal-enriched sedimentary formations or metasomatized subcontinental lithospheric mantle (SCLM) associated with oceanic subduction. The role of mantle plumes in generating Carlin-style deposits has remained enigmatic due to lack of adequate evidence. Here we investigate the second largest Carlin-style Au province in the world, after Nevada in USA, within the Youjiang basin in the eastern part of the ∼260 Ma Emeishan large igneous province (LIP) of southwestern China. We present a novel model for the genesis of this ore province based on thermodynamic modeling, which envisages that cumulates formed by high degree (over ∼80 wt.%) of crystal fractionation from the Emeishan plume-derived magmas under low oxygen fugacity conditions generated an enriched juvenile lower crust. Our new results from integrated in situ zircon geochronology and oxygen isotopes of mineralized tuffs from the Au deposits hosted in the Emeishan volcanic rocks reveal zircon growth at ∼129–136 Ma and ∼239 Ma with δ18OVSMOW values of +5.9‰ to +6.9‰, suggesting that the gold mineralization events in the Youjiang basin followed the Emeishan plume activity and that the ore-forming fluids were of magmatic origin. In conjunction with evidence from the Emeishan LIP for native gold grains that precipitated in the early fractionation stage under low oxygen fugacity, we propose a model involving juvenile lower crust beneath the eastern Emeishan province as a potential Au reservoir, the reactivation of which by later magmatic-hydrothermal activity associated with oceanic subduction events generated the large auriferous province in the Youjiang basin. We therefore conclude that the crustal magmatic underplate generated by mantle plume has the potential to contribute to the formation of Carlin-style Au deposits, thus offering new insights into the possible link between mantle plumes and various types of Au deposits such as porphyry, sediment-hosted and orogenic Au deposits associated with LIPs.