<p>Active continental margins are key settings for magmatic-hydrothermal ore deposits, yet the mechanisms of subduction-driven deep material mobilization and metal enrichment remain a major research focus. Mercury isotopes, with distinct mass-dependent and mass-independent fractionation signatures, provide a powerful tracer for studying Earth’s material cycles. Here we show that mercury isotope analysis of four porphyry copper systems in active continental margins indicate that deep magmatic fluids exhibit positive Δ¹⁹⁹Hg values. This signature, which is also observed in previously documented epithermal gold deposits, resembles that of oceanic sediments. This implies that oceanic slab-derived volatiles play a key role in activating deep-seated materials. Systems hosted in terrigenous clastic rocks exhibit negative δ²⁰²Hg and Δ¹⁹⁹Hg values, indicating the addition of upper crustal fluids. In contrast, hydrothermal systems without intrusions show positive δ²⁰²Hg and slightly negative Δ¹⁹⁹Hg values, suggesting that long-distance fluid migration and water-rock reactions caused mercury isotopic variations and contributed to ore metal re-enrichment.</p>