Two seafloor sulfide rocks caught fire on their own after freeze-drying and crushing
Two of 57 rocks collected from the Escanaba Trough combusted without an outside flame in a lab, according to a Scientific Reports study. The authors write that no engineering controls exist yet for mining modern seafloor sulfides.
The Scientist · Science desk
Two part-of-whole bars. 2 of 41 marcasite-rich samples combusted. 2 of 57 rocks collected combusted.
- Of marcasite-rich samples, claim 5 2 of 41 samples 4.9% computed
Of marcasite-rich samples The rest of the 41
- Of rocks collected, claim 16 2 of 57 rocks 3.5% computed
Of rocks collected The rest of the 57
| Share | Part | Whole | Percent | Claim |
|---|---|---|---|---|
| Of marcasite-rich samples | 2 samples | 41 samples | 4.9% (computed) | 5 |
| Of rocks collected | 2 rocks | 57 rocks | 3.5% (computed) | 16 |
What happened
- Both rocks that combusted were dominated by marcasite, an iron sulfide made of extremely small crystals.
- The two samples gave off heat and smoke before crushing began, reaching more than 100 degrees C, probably from exposure to oxygen.
- Calculations showed marcasite oxidation with oxygen generally releases more heat than the dissolved-iron reactions that apply to pyrrhotite.
- On that basis the team thinks modern seafloor sulfides could be more prone to self-heating than the older deposits mined on land.
Why it matters
- constraint Fire practice from land sulfide mines cannot simply be carried over, because seafloor rock is more porous and likely needs different safety measures.
- exposure The hazard appears at the surface and during processing, so the risk sits with the vessels and plants that handle the ore.
- decision Sampling programs face a choice: the team says seafloor material, likely much of a future mine's output, is poorly sampled and needs wider study before the risk can be set.
As phys.org describes the study [1], the team collected 57 rocks in 2022 from the Escanaba Trough, part of the Gorda Ridge in the northeast Pacific [2]. In the lab they freeze-dried the rocks and then crushed them, and the extra heat from crushing set two off [3]. Two of 57 is 3.5% [16]. Among the 41 marcasite-rich samples it is 4.9% [5][15]. Both figures belong to one site and one lab protocol.
The design was a comparison. The team set combusting and non-combusting rocks side by side using mineral identification, microscopy, chemical analysis and laboratory heating tests [13]. The small marcasite crystals in the burners had replaced an earlier mineral and kept its blade-like shape. The replacement left cracks and empty spaces, and that raised the surface area available for reactions with oxygen [7]. The earlier mineral appears to have been pyrrhotite, which previous research often identified as a self-heating hazard [8].
A comparison like this shows what the two burners had in common. It cannot show that texture alone causes ignition, because 39 of the 41 marcasite-rich samples did not burn [17]. The team says pH and exposure to light, among other factors, are involved, so how often combustion might occur is unclear [19].
Sulfide mining around vents already draws criticism for its destructive nature [14]. This study concerns the ore after it is raised. The authors 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." [20]
The thing this doesn't tell you is how often a ship's hold would burn. Ignition here happened in a lab after freeze-drying and crushing. The authors also write that "there are currently no established engineering controls for mining sulfide deposits from the modern seafloor" [11]. In our view, that makes the next dataset worth more than this one: ignition tests on more seafloor samples would give an operator a rate, and two events in one trough do not.
What to watch
- Ignition tests on seafloor sulfides from other vent fields, to see whether the 2-in-41 rate in marcasite-rich rock holds outside the Escanaba Trough.
- Experiments that vary pH and light exposure on marcasite-rich samples, since the team names both as factors without yet pinning down their effect.
- Any published engineering controls or combustion risk assessment for seafloor massive sulfide mining.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence55
- Adoption
- Insufficient
- Hype gap+10
- Incentives
- Insufficient
- Confidence50
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
A study published in Scientific Reports describes how certain samples of rock brought up from seafloor massive sulfide (SMS) deposits have unexpectedly caught fire.
- [2]
In 2022 the team collected 57 rocks from the hydrothermally active Escanaba Trough, a part of the Gorda Ridge in the northeast Pacific Ocean.
- [3]
During lab processing the rocks were freeze-dried and then crushed, which created additional heat and caused two of the samples to spontaneously combust.
- [4]
The combusting samples generated heat and smoke even before crushing began, reaching temperatures above 100 degrees C, likely due to oxygen exposure.
- [5]
Only two out of 41 marcasite-rich samples combusted.
- [6]
Both combusting rocks were dominated by marcasite, an iron sulfide made of extremely small crystals.
- [7]
The small crystals had replaced an earlier mineral while retaining a blade-like shape; the replacement created cracks and empty spaces, producing a higher surface area and allowing more reactions with oxygen, which made the rocks less stable.
- [8]
Marcasite appears to have replaced the iron sulfide mineral pyrrhotite, which previous research often identified as a self-heating hazard.
- [9]
Calculations showed that marcasite oxidation, which involves oxygen, generally releases more heat than reactions involving dissolved iron as the oxidizing agent, as with pyrrhotite.
- [10]
Spontaneous combustion has occasionally been documented in land-based volcanogenic massive sulfide mines, and some safety practices have been developed for them, but seafloor rocks are more porous and likely require different safety practices.
- [11]
The study authors write that, given SMS mining has yet to occur, "there are currently no established engineering controls for mining sulfide deposits from the modern seafloor".
- [12]
The study indicates that conditions at the surface, combined with processing activities, may turn some of these rocks into a hazard.
- [13]
To find what caused the rocks to catch fire, the team compared combusting and noncombusting samples using mineral identification, microscopy, chemical analysis and laboratory heating tests.
- [14]
Projects mining seafloor massive sulfide deposits around hydrothermal vents already face criticism over their destructive nature.
- [15]
Two combusting samples out of 41 marcasite-rich samples is about 4.9%.
- [16]
Two combusting rocks out of 57 collected is about 3.5%.
- [17]
39 of the 41 marcasite-rich samples did not combust.
- [18]
Based on the results, the team thinks modern seafloor sulfides could be more prone to self-heating than the more ancient deposits mined on land.
- [19]
Many factors appear to be involved in marcasite combustion, such as pH and exposure to light, making it unclear how often combustion might occur.
- [20]
The study authors 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."
- [21]
The team notes that material from the seafloor, likely to make up much of a future mine's output, remains poorly sampled and should be studied more extensively to determine risks for mining operations.
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Topics
- Deep-sea miningFollow
- Mining safetyFollow
- Seafloor massive sulfidesFollow