The emerging industry of deep-sea mining could end up in flames after researchers discovered that some rocks collected from the bottom of the ocean can heat up and even spontaneously combust once they’re brought to the surface and exposed to air.
In a recent paper published in Scientific Reports, researchers from the United States Geological Survey (USGS) warn that some rocks containing deep-sea minerals may catch fire once at the surface. The findings highlight a potential hazard that needs to be better understood before mining massive sulfide deposits from the seafloor.
Fire hazard
Using a remotely operated vehicle, the researchers collected 57 samples of metal sulfide-rich rocks from four different regions in the Escanaba Trough. The hydrothermal area along the southern Gorda Ridge off the U.S. West Coast created deep-sea deposits rich in metals like zinc, copper, and iron.
The rocks were crushed and freeze-dried in the lab, with two of the samples experiencing spontaneous combustion when exposed to air. To figure out how and why the rocks performed this pyrotechnic trick, the researchers tested how the samples responded to increasing temperatures. They then compared the chemical composition and mineralogy between the combustable rocks and other samples.
The combusting rocks were composed primarily of nanocrystalline marcasite, a form of iron sulfide that appears to be unstable when exposed to oxygen. The use of heat and other forces, like crushing, breaking, and grinding the rocks, can supply enough energy to initiate oxidation. That can then lead to the rock samples self-heating.
Cautionary tale
The discovery offers a dangerous precaution to the industry of deep-sea mining. Although the industry has not yet gone into full-scale commercial operations, it is currently undergoing technology trials.
The International Seabed Authority (ISA) recently issued 31 exploration contracts for extracting sulfide minerals on two deep-sea ridges, the Northern Mid-Atlantic Ridge and Southwest Indian Ridge.
While it’s not certain that every rock from the deep seabed is prone to combustion, the researchers highlight that there is potential danger that could impose new safety regulations on the industry.
“If [seafloor massive sulfide] mining occurs, rocks brought to the surface would experience conditions dramatically different from those on the seafloor, including exposure to oxygen and changes in temperature, pressure and moisture,” according to a statement by USGS. “Such changes could affect how sulfide minerals react and how much heat they generate.”
