Overview

Increasing demand for base and precious metal resources, coupled with declining discovery rates, is now encouraging the search for alternatives, including mining on the seafloor. Metal-rich deep-sea hydrothermal vents have been discovered in more than 300 locations, with pilot mining already initiated in the Okinawa Trough (Japan), and advanced exploration completed on several deposits, including the Solwara 1 deposit (Papua New Guinea). These deposits are modern analogs of ancient volcanic-hosted massive sulfide (VMS) deposits, which have been a mainstay of the Canadian mining industry, and are shedding new light on the relationships between tectonics, volcanism, and hydrothermal activity that are fundamental to successful land-based exploration.

 
 

Model of the formation of seafloor massive sulfide deposits from Humphries (1998).

What are Seafloor massive sulfide (SMS) deposits?

Seafloor massive sulfide (SMS) deposits, also known as hydrothermal ore deposits or black smoker vents, form when a magmatic heat source drives the circulation of seawater through the ocean crust, where it leaches metals from the rocks. Metals may also be contributed by magmatic fluids that are degassing from the underlying magma chamber. These metals are then precipitated at or near the seafloor when the hot fluids mix with cold seawater. These deposits are a significant source of copper, zinc, lead, and gold, with minor amounts of other trace-metals, including cobalt, cadmium, indium, gallium, and germanium.

Where in the world?

SMS deposits are currently forming today on the seafloor in areas associated with increased magmatism; namely, along tectonic plate boundaries (mid-ocean ridges, volcanic-arcs, and back-arc basins). Many subduction-related deposits form within the Exclusive Economic Zones (EEZs) of countries around the Pacific Rim, while mid-ocean ridge-related deposits are found within international waters.

Distribution of vent sites around the world. (Image courtesy GEOMAR / S. Petersen)

Ship-based collection of water-column data using a CTD. (Image courtesy Schmidt Ocean Institute / RV Falkor)

What tools do we use to study deep-sea ore deposits?

The deep sea is a technically-challenging place to explore. We use a number of tools during sea-going research expeditions for a number of purposes:

  • To map the seafloor topography and structures, we use: ship-based multibeam bathymetry, acoustic backscatter, side-scan sonar, and high-resolution bathymetry from Autonomous Underwater Vehicles (AUVs).

  • To locate hydrothermal vent sites through water-column surveys, we use: Conductivity-Temperature-Depth (CTD) devices and Mini-Autonomous-Plume-Recorder (MAPR) devices.

  • To observe the seafloor and take samples, we use: Remotely Operated Vehicles (ROVs), TV-grabs, dredges, sediment corers, wax corers, and fluid samplers.

  • To measure geophysical characteristics of the seafloor, we use a wide range of geophysical equipment, including: magnetometers, seismic reflection/refraction systems, and Ocean Bottom Seismometers (OBSs).