The Oceans and Seafloor Massive Sulfide Deposits

Abstract

The ocean dominates the Earth's surface, but despite decades of exploration it remains poorly explored, with major geological, oceanographic and biological discoveries frequently being made. The majority of the ocean floor is underlain by relatively young, mafic oceanic crust, which is covered by modern sediments. A complex interplay between geological processes, related seafloor geomorphology, and a multitude of oceanographic processes controls the distribution of oceanic mineral deposit-forming environments in time and space. The most important deep ocean mineral deposits are ferromanganese crusts and nodules, and sulfide-rich deposits that are linked to submarine hydrothermal activity. Submarine hydrothermal systems are associated with magmatism and seafloor volcanism, which is principally concentrated along tectonic plate boundaries. In these environments circulation of seawater through the crust results in heating and chemical modification of the water to generate metal-rich hydrothermal fluids that may precipitate sulfide minerals at or below the seafloor. The resulting seafloor massive sulfide (SMS) deposits typically comprise a near-surface massive sulfide mound, underlain by sulfide-rich veins and disseminated mineralization. The chemical composition, morphology, rate of formation and size of SMS deposits varies as a function of geodynamic setting, the style of volcanism and tectonics, and water depth. Once an SMS deposit has accumulated on the seafloor it may be altered by a variety of hydrothermal, diagenetic and seafloor weathering and erosion processes. Geological understanding of the seafloor and the formation of SMS deposits is continuously evolving, and will help to focus ocean exploration in those areas likely to have the greatest mineral potential.