Seafloor massive sulfides form in various marine hydrothermal settings, particularly within volcanic arcs, where magmatic fluids may contribute to the metal budget of the hydrothermal system. In this study, we focus on the Kolumbo volcano, a submarine volcanic edifice in the central Hellenic Volcanic Arc hosting an active hydrothermal system. Diffuse sulfate-sulfide chimneys form a Zn-Pb massive sulfide mineralization with elevated As, Ag, Au, Hg, Sb, and Tl contents. These elements have similar behavior during magmatic degassing and are common in arc-related hydrothermal systems. Trace-element data of igneous magnetite, combined with whole rock geochemistry and numerical modelling, highlights the behavior of chalcophile and siderophile elements during magmatic differentiation. We report that, despite early magmatic sulfide saturation, chalcophile element contents in the magma do not decrease until water saturation and degassing has occurred. The conservation of chalcophile elements in the magma during magmatic differentiation suggests that most of the magmatic sulfides do not fractionate. By contrast, upon degassing, As, Ag, Au, Cu, Hg, Sb, Sn, Pb, and Zn become depleted in the magma, likely partitioning into the volatile phase, either from the melt or during sulfide oxidation by volatiles. After degassing, the residual chalcophile elements in the melt are incorporated into magnetite. Trace-element data of magnetite enables identifying sulfide saturation during magmatic differentiation and discrimination between pre- and post-degassing magnetite. Our study highlights how magmatic degassing contributes to the metal budget in magmatic-hydrothermal systems that form seafloor massive sulfides and shows that igneous magnetite geochemistry is a powerful tool for tracking metal-mobilizing processes during magmatic differentiation.

海底块状硫化物在各种海洋热液环境中形成，特别是在火山弧内，其中岩浆流体可能有助于热液系统的金属预算。在这项研究中，我们重点关注科伦坡火山，这是一座位于希腊中部火山弧的海底火山大厦，拥有活跃的热液系统。弥漫的硫酸盐-硫化物烟囱形成了砷、银、金、汞、锑和铊含量升高的锌铅块状硫化物矿化体。这些元素在岩浆脱气过程中具有相似的行为，并且在与电弧相关的热液系统中很常见。火成磁铁矿的微量元素数据与全岩石地球化学和数值模拟相结合，突出了岩浆分异过程中亲铜元素和亲铁元素的行为。我们报告说，尽管早期岩浆硫化物饱和，但在发生水饱和和脱气之前，岩浆中的亲铜元素含量不会减少。岩浆分异过程中岩浆中亲铜元素的守恒表明大多数岩浆硫化物不会分馏。相比之下，脱气后，岩浆中的 As、Ag、Au、Cu、Hg、Sb、Sn、Pb 和 Zn 被耗尽，很可能从熔体中或在挥发物的硫化物氧化过程中分配到挥发相中。脱气后，熔体中残留的亲铜元素并入磁铁矿中。磁铁矿的微量元素数据能够识别岩浆分异期间的硫化物饱和度以及区分脱气前和脱气后磁铁矿。我们的研究强调了岩浆脱气如何影响形成海底块状硫化物的岩浆热液系统中的金属预算，并表明火成磁铁矿地球化学是跟踪岩浆分异过程中金属流动过程的有力工具。