Zixuan Wang , Yuanchuan Zheng, Bo Xu, Hongda Hao, Zengqian Hou

The prevailing view suggests that the formation of porphyry Cu deposits involves differentiation of water-rich, metal-bearing juvenile magmas, with subduction of oceanic slabs supplying the necessary volatiles. However, the occurrence of significant porphyry Cu deposits in continental collision zones, where such volatile sources are absent, challenges this paradigm. We analyze a global dataset of whole-rock platinum-group elements and apatite compositions of ore-forming magmas in both subduction and collision zones, combined with Monte Carlo simulations. The results reveal that ore-forming magmas in collision zones exhibit significantly higher degassing efficiencies compared to those in subduction zones. To explain this, we integrate whole-rock geochemistry, mineral thermobarometry, and thermodynamic modeling, proposing that lower water contents of collision zone ore-forming magmas lead to shallower magma storage depths, significantly enhancing degassing efficiency. In contrast, higher water contents of subduction zone ore-forming magmas result in greater emplacements, limiting degassing efficiency. Despite this limitation, higher magma fluxes in subduction zones compensate for lower degassing efficiencies. These findings highlight distinct frameworks of water content, storage depth, and magma flux between subduction and collision zone porphyry Cu deposits. The synergistic interplay of these factors, rather than simply water-rich magmas, is fundamental to porphyry Cu formation.