The role of p-T conditions, host rock lithology, phase separation, and organic compounds on metal mobility and metal sulfide deposition in spatially resolved hydrothermal vent areas.
DFG Special Priority Programme “Dynamics of Ore Metals Enrichment“ – DOME (SPP 2238)
This is a joint project between our Marine Trace Metal Geochemistry group at Constructor University and the Isotope Geochemistry group of Prof. Simone Kasemann at the University of Bremen and other partners. Our goal is to disentangle the different influence parameters on mobilization, transport and deposition of metals in hydrothermal vent sites to understand the key processes driving metal enrichment in hydrothermal ore deposits. The chemical composition of hydrothermal fluids and related mineral precipitates depend on different parameters and processes, which include host rock composition, pressure and temperature conditions, fluid pathways in the subsurface, water-to-rock ratio, phase separation and phase segregation, and magmatic degassing (Fig. 1). In addition, dissolved organic molecules (either microbially produced or products of hydrothermally degraded organic material) are known to have partly strong metal complexing capacities that can significantly influence metal transport and solubility versus precipitation. Hence, distinctive hydrothermal compositional signatures are produced in relation to these parameters, and time. While end-member compositions have been determined for many vent fields discovered so far, it has often been difficult to clearly identify the role of individual processes on the overall chemical composition of the fluids and minerals precipitating from them.
We suggest carrying out both field investigations and to elucidate the role of individual parameters, including host rock type, temperature, phase separation, and organic matter experimentally. We will explore the possibility of using Sr, Li and B isotope signatures of vent fluids and precipitates as tracers of fluids controlled by specific parameters. This will help us to disentangle the respective roles of these factors in natural vent settings and predict metal enrichment in hydrothermal fluids and mineralization as a function of the environmental parameters.
For the field work, we will focus on slow-spreading ridge systems, which have been shown to host hydrothermal systems that are stable in activity and composition over longer periods (at least decades) of time. This enables us to exclude the factor time as an additional variable. We use the opportunity of our participation in cruises to the northern Mid-Atlantic Ridge, such as the recent cruise M190, and the collaboration with the BGR Hannover and their regular research cruises to the German license areas on the Central and Southeast Indian Ridge as part of the INDEX project (Fig. 2). For the experimental work, autoclaves with flexible gold bags containing the samples (liquid and solids) will be used at temperatures up to 400°C; here, the individual parameters will be tested for their efficiency in metal mobilization and precipitation and the related isotopic signatures. Finally, thermodynamic modeling using Geochemists Workbench GWB, for calculating solid-solution equilibria under specific conditions and reaction paths will be applied, using our field and experimental data as baselines and for verification.
We anticipate that the results of this project will enable us to better understand the control factors of hydrothermal ore formation and enrichment of special metals of interest for modern technologies and to guide exploration of such deposits.