Mercury isotopes as a tracer for material cycling at active continental margins

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. Oceanic slab-derived volatiles play a key role in activating deep-seated materials and driving metal enrichment, according to measurements of fractionation signatures in mercury isotopes from four porphyry Cu systems in active continental margins.