Wang, ShiweiZhou, TaofaAnenburg, MichaelHollings, PeteZhang, LejunFan, YuCooke, David R.Fu, Bin2026-01-122026-01-122662-4435https://hdl.handle.net/1885/733804032Porphyry copper (-gold) deposits in both arc and non-arc settings are hosted by oxidized magmatic rocks, but the exact mechanism by which the source magmas of these non-arc deposits become oxidized remains obscure. Through whole-rock geochemistry, mineral chemistry, and zircon isotopic analyses, here we show that the Neoproterozoic root of the Cretaceous Shaxi porphyry copper-gold deposit in the Jiangnan orogen is reduced and copper-sulfide rich, whereas the Cretaceous ore-forming magmas are oxidized. An oxidized mafic melt flushed the Neoproterozoic root zone, extracted copper and gold, and transported them to the upper crust where the Cretaceous Shaxi deposit formed. Evidence is recorded in growth zones of clinopyroxene, zircon, spinel, and plagioclase. Our results indicate that the relatively reduced, sulfide-enriched sub-continental lithospheric mantle or lower crust is essential but not sufficient for the formation of fertile non-arc porphyry magmas. Addition of a newer oxidized magma is crucial for the formation of this mineralization style.This work was financially supported by the National Natural Science Foundation of China (42172078, 91962218, 41702071), and the National Key R&D Program of China (2016YFC0600206). M.A. was supported by Australian Research Council Linkage grant LP190100785. No specific permissions were required for the collection of samples. We sincerely thank the Editor, Santiago Tassara, and the two anonymous reviewers for their valuable comments, which greatly improved the manuscript. Special thanks to Professor Noel White and Professor José Piquer for their guidance during the revision process.10en© The Author(s) 2025.2025-11-0710.1038/s43247-025-02830-z105021131116