This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Projects involving the mining of seafloor massive sulfide (SMS) deposits around hydrothermal vents already face criticism over their destructive nature, and now these projects may face a new concern: spontaneous combustion. A new study, published in Scientific Reports, describes how certain samples of rock brought up from SMS deposits have unexpectedly caught fire.
The study indicates that conditions at the surface, combined with processing activities, may turn some of these rocks into a hazard. Hydrothermal vents on the ocean floor release heated water rich in minerals that result in metal-rich deposits over time. These deposits can become valuable sources of copper, zinc, gold and silver.
However, the deposits also contain sulfur-bearing minerals that can release heat when they react with oxygen in the air. If that heat builds up, the material can spontaneously combust. Spontaneous combustion has been occasionally documented in sulfide mines on land, referred to as volcanogenic massive sulfide deposits (VMS).
Some safety practices have been developed for land-based mines, but seafloor rocks are more porous and likely require different safety practices. The authors of the new study write, "The production of heat through exothermic reactions has not been investigated in SMS deposits but has the potential to cause rapid-onset fires on ships. There are several recent studies of oxidation reactions in SMS material, although SMS deposits are much less studied than VMS deposits.
"Specifically, textural and mineralogical differences between SMS and VMS rocks, and differences in oxidative environment such as the availability of oxidants and increased corrosivity of seawater compared to fresh water are still undergoing investigation and description, and potential mining procedures for SMS deposits are still being developed." In 2022, the team collected 57 rocks from the hydrothermally active Escanaba Trough, a part of the Gorda Ridge in the northeast Pacific Ocean. During a processing procedure in their lab, the rocks were freeze-dried and then crushed. This created additional heat, which caused two of the samples to spontaneously combust.
They generated heat and smoke even before the crushing began, reaching temperatures above 100 °C, likely due to oxygen exposure. The combusted rocks were rich in sulfides, along with 39 other rocks out of the 57. To sort out what caused these rocks to unexpectedly catch on fire without any external flame, the team decided to compare the combusting and noncombusting samples using mineral identification, microscopy, chemical analysis and laboratory heating tests.
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