Project (1): Shallow to Intermediate-Depth Hydrothermal Systems and Enrichment of Volatile Elements

During the Bridge Hell Expedition M192/2 (2023) in the Cycladic Arc aboard the research vessel FS Meteor, we investigated the hydrothermal smoker field surrounding the volcanic island of Milos in Greece. The collected samples differed fundamentally from their deep-sea counterparts and displayed compositions dominated by minerals such as barite, orpiment, realgar, and stibnite, composed of Ba, As, Sb, and S, as well as Ag–Pb–Cu–Zn–rich Sb sulfosalts. These minerals precipitated from hot, acidic fluids that leached metal(loid)s from the crust and from volcaniclastic sediments beneath the seafloor during their ascent, before reacting with the cold seawater of the Aegean Sea. Boiling of the fluids led to elemental fractionation, causing some elements to remain within the sub-seafloor sediments while others vented at the seafloor and formed chimney-like structures.

In this project, we aim to investigate these processes in order to better understand the mineralization observed on the seafloor. This is particularly important as scientific interest in these systems is increasing alongside industrial demand. The key elemental composition of Sb, As, Ba, and Ag was classified as critical by the U.S. Geological Survey and other institutions in 2025, highlighting their economic importance. These elements play key roles in the production of semiconductors, electronic circuits, and batteries that are essential for AI systems and electric vehicles, as well as for renewable energy technologies, the oil and gas industry, medicine, and military applications. Hydrothermal geochemistry is therefore directly linked to current industrial priorities. To achieve our research objectives, we apply a wide range of analytical methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the geochemistry of stable sulfur and radiogenic strontium isotopes.

Project (2): Coupled Se and S Isotope Systematics of Sulfides – A Novel Tool for Tracing Magmatic Volatile Inputs into Submarine Hydrothermal Systems

The second project focuses on the influence of magmatic volatiles in hydrothermal systems. These are chemical compounds and elements that originate directly from the magmatic body located beneath the hydrothermal circulation cell below the seafloor. Such volatiles significantly contribute to the elemental budget of hydrothermal fluids, drive fluid circulation, modify fluid chemistry, influence the leaching and transport mechanisms of metal(loid)s, and control the dynamics of mineral precipitation. The crustal sources of metal(loid)s, as well as the processes occurring during their transport from their origin to the seafloor, are not yet fully understood.

We address this question by combining trace element measurements with traditional (δ³⁴S, Δ³³S) and non-traditional (δ⁸²Se) stable isotope systems to better understand how elements become enriched in hydrothermal environments. However, the signatures of fluids and their precipitates at the seafloor change significantly during fluid ascent. This requires isotope systems that are less sensitive to fractionation and overprinting by seawater signatures. Selenium (δ⁸²Se) fulfills these requirements because it has a strong affinity for enrichment in magmatic volatiles, is strongly depleted in seawater relative to hydrothermal fluids, and exhibits chemical properties similar to sulfur, which it substitutes in many sulfide minerals. In addition, the mixing of hydrothermal fluids with seawater has only a minor effect on the δ⁸²/⁷⁶Se signal of resulting hydrothermal sulfides, making it more suitable than sulfur isotopes for tracing metal sources.

In this study, we investigate hydrothermal systems around the globe that represent a continuum from host-rock-dominated to magmatic-volatile-influenced fluid conditions: (1) the smoker field of the Nifonea Volcano in the Coriolis Troughs, (2) the Pacmanus hydrothermal field in the eastern Manus Basin, and (3) volcanogenic massive sulfide mineralization in Cyprus. These sites, characterized by different host-rock lithologies and variable inputs of magmatic volatiles, are ideally suited for our novel Se isotope approach. We aim to determine the δ⁸²/⁷⁶Se composition of submarine hydrothermal precipitates, characterize the Se and S isotope signatures of associated lavas, investigate δ⁸²/⁷⁶Se fractionation during mineralization, identify chemical fingerprints for tracing sub-seafloor fluid processes, and quantify Se and S inputs in these systems. This project therefore establishes a novel, integrated Se–S isotope and trace element approach to unravel the complex interactions between magmatic and hydrothermal processes that control the mobilization, transport, fractionation, and enrichment of metal(loid)s.