Zanna Anderson
Managing Editor
Despite the hardship of navigating the depths of the ocean, American and Chinese entities are racing to harvest critical minerals from the seafloor. According to the National Ocean Service, lithium, manganese, nickel, cobalt, copper and rare earth elements are among the critical minerals being mined on the seafloor. According to the Bureau of Ocean Energy Management, there are several types of deep-sea deposits, including polymetallic nodules, cobalt-rich ferromanganese crusts, polymetallic sulfide deposits, heavy mineral sands and phosphorites.
Polymetallic nodules can form through either the hydrogenetic or diagenetic process. The hydrogenetic process is the more common one: it occurs when metals are oxidized from the surrounding seawater into nodules that build up layer by layer over millions of years. To begin the process, the nodule must first have a nucleus, like a fallen shark tooth. When oxygen reacts with dissolved manganese and iron, the dissolved minerals precipitate and form a thin layer on the outside of the nucleus. Other important minerals that follow oxidized manganese and iron, such as cobalt, nickel, lithium, and zinc, also settle on the nucleus. The diagenetic process is very similar, but instead of reacting with elements in the water, precipitation forms from minerals in the seafloor sediment, making the formation process much faster than the hydrogenetic process.
Cobalt-rich ferromanganese crusts form in shallower areas of high volcanic activity. They contain minerals such as cobalt and platinum. The formation uses a precipitation process similar to that of hydrogenetically formed polymetallic nodules, but the minerals form specifically on volcanic rocks.
Polymetallic sulfides are formed near hydrothermal vents. This is because when hot, mineral-rich water escapes from these vents, it mixes with the sulfur to form metal sulfides, which then accumulate on the nearby ocean floor. These deposits hold metals such as copper, zinc, gold and silver.
Heavy mineral sands contain important minerals such as magnetite, ilmenite, leucoxene, rutile, zircon, garnet, monazite, titanium, zirconium and alumina. The sands are specifically composed of eroded fragments of metamorphic and igneous rocks in inland regions. According to the Virginia Department of Energy, the high concentration of heavy minerals is due to coastal, alluvial and eolian processes that carry away lighter sediments.
Phosphorites are another important deposit type, as they are a major source of phosphate for chemical and fertilizer production. There are many ways phosphorites can form, including through oceanic upwelling. Essentially, mineral-dense water upwells to the ocean surface and warms, causing phosphate to precipitate and fall to the seafloor.
These resources are important to the production of batteries, military technologies, phones, medical devices and so much more, which explains why two economic giants are after them. Deep-sea mining, however, has yet to be undertaken commercially, so there is limited information on how efficient the process is on a large scale. There is also a lack of information about the harm caused by deep-sea mining practices to fragile marine environments. Mining itself is not the only environmental concern. Some are worried about the effects of the construction and presence of infrastructure, and of the processing and transport of deep-sea minerals, on coastal communities.