Importance: Mining Metals

Ophiolites are slivers of seafloor that have been thrust up on land by movements of Earth’s tectonic plates. They provided one of the early clues to the existence of seafloor hydrothermal vents. These pieces of ancient oceanic crust contain large metal-rich ore deposits that scientists thought must have formed in the deep seafloor at the Mid-Ocean Ridge crest.

With the discovery of seafloor hydrothermal vents, scientists no longer have to study the formation of these mineral deposits by looking at ancient, weathered materials on land. They can now watch as metal-rich deposits actively form at seafloor vents. When scientists compared the structure of a seafloor mineral deposit to that of an ore deposit in Cyprus, they found striking similarities. They learned new lessons about where to look for ore deposits and why those rocks are often breccias – small pieces of volcanic rock cemented together by hydrothermal minerals.

They also learned that seafloor hydrothermal deposits can be more than a thousand times richer in some metals than mineral deposits on land. However, mining metals from deep in the ocean has generally been considered very costly and not very practical. Some scientists also have concerns about the impact of mining operations on the seafloor environment and the animal communities around vents.

Now, however, the idea of mining seafloor hydrothermal deposits is gaining ground. A Canadian company, Nautilus Minerals, has leased the rights to mine some hydrothermal fields in about 1600 meters of water on the north side of Papua, New Guinea. They plan to use tethered, remotely operated vehicles to break the material into chunks that can be carried in suction pipes back to the ship, and then taken by barge to shore for processing.

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