The work and main results of SEA METAL FLUX can be summarised into its four main objectives
1. What contributes to different metal signatures of VMS deposits?: The type, amount and distribution of metals within a VMS deposits is affected by different factors such as composition of the lavas, how fluids rise through the crust and are vented on the seafloor or even by the oxidation of the ores by seawater after their formation. We studied ores, lavas and oxidised ores using various mineralogical and geochemical isotopic techniques, (osmium-Os and lead-Pb, strontium-Sr and sulfur-S) to understand the relative influence of those factors. We studied two VMS deposits with different features and concluded that growth mainly above seafloor as large in large hydrothermal fields is facilitated by faulting (Mandoos). Deposits sealed by impermeable rock (jaspers) grow by hydraulic fracturing beneath the seafloor. Metals are mobilised from the volcanic footwall, and reflect their composition, which defies the paradigm of metal leaching from deep reaction zones. We also provided important constraints to the effects of secondary processes on metal redistribution and upgrading.
2. What is the primary metal budget of the oceanic crust? We quantified how much metal exists in the oceanic crust that can be mobilized during hydrothermal alteration. For this, we studied a crustal profile from the upper crust down to the mantle transition drilled by the Oman Drilling Project. We concluded that the upper crust mostly comprises secondary (hydrothermal) sulfides, the hydrothermal/magmatic sulfides ratio decreasing with depth and increasing towards areas of higher fluid flow.
3. What are the fluid pathways of metal cycling? We strived to understand how hydrothermal fluids travel through the crust from very hot, near magmatic conditions (~900C) down to “cooler” temperatures (<350), and how metals and sulfur are scavenged to ultimately form a VMS deposit. We assessed hydrothermal alteration in different rocks based on S and Sr isotopes and how much metal (Copper, Zinc) was scavenged or deposite. We concluded that Sulfur and Sr isotopic signatures are often decoupled during hydrothermal processes and have characteristic patterns along the oceanic crust. Sulfur and metal remobilization in the upper oceanic crust far exceeds that in the lower crust although seawater is sometimes introduced at depth along faults. The crust-mantle transition is the most complex domain and a sequence of gabbros, dunites and rodingites (metasomatized gabbro sills) were thoroughly investigated
4. A model for metal fluxes in the oceanic crust Our ultimate objective is to bring all information together to produce a numerical model for metal sulfur and cycling in the oceanic crust using appropriate modelling software. Preliminary data show that sulfur and metal remobilization in the upper oceanic crust is much more significant than what is recorded in in-situ modern crust, supporting the view that metal and sulfur fluxes are much more significant in ophiolites.
Exploitation
SEA METAL FLUX scientific outcomes are exploitable for scientists and mining and exploration stakeholders (companies and governments) working with modern day or ancient Volcanogenic Massive Sulfides. Also, to scientists working with subseafloor hydrothermal processes or with the biogeochemical sulfur cycles and their relation with deep-life processes. All data pertaining VMS of Oman are of special interest to local stakeholders from Public Authority for Mining and Mining companies in Oman. All results will be made available in published conference and manuscripts, with datasets being made available in the ZENODO open database as per FAIR principles.
