Scientists have discovered record concentrations of hidden gold locked inside pyrite, the mineral commonly known as fool’s gold, beneath the Pacific Ocean near Japan. The finding could help geologists identify new gold-rich deposits by looking for chemical signatures hidden within the mineral rather than visible gold particles.
The discovery came from the Higashi-Aogashima Knoll Caldera hydrothermal field, about 360 kilometers south of Tokyo and more than 700 meters below sea level. The underwater volcanic crater contains three active hydrothermal fields where superheated, mineral-rich fluids rise through Earth’s crust and escape from vents on the seafloor.
Over time, these fluids build towering black smoker chimneys and sulfide mounds rich in minerals such as pyrite, chalcopyrite, sphalerite, and galena.
Researchers analyzed rocks from active hydrothermal vents
Researchers used robotic submarines to collect rock samples from the Central Cone, Southeast, and East hydrothermal fields. They analyzed the rocks using several laboratory techniques, including secondary ion mass spectrometry (SIMS), which detects elements at the atomic scale by drilling microscopic pits into mineral grains.
The analysis revealed gold concentrations of up to 1.9% by weight, or 19,231 parts per million, inside pyrite. Researchers said these are the highest concentrations of invisible gold reported from this type of deep-sea hydrothermal deposit.
Gold was locked inside the pyrite crystal structure
Unlike gold found in conventional mines, the metal did not occur as visible grains or tiny nuggets. Instead, gold atoms were built directly into the crystal structure of pyrite, forming what scientists describe as a solid solution. This means the gold became part of the mineral itself rather than existing as separate particles.
Scientists have discovered record levels of hidden gold locked inside deep-sea pyrite beneath the Pacific Ocean near Japan. Instead of forming visible nuggets, the gold was built atom by atom into the mineral's crystal structure. pic.twitter.com/MneaxJmWUy
— Tom Marvolo Riddle (@tom_riddle2025) July 13, 2026
The team found that this process depended on the presence of arsenic, lead, and copper. These elements slightly altered the pyrite crystal structure, creating tiny defects that allowed gold atoms to become trapped. Samples with higher arsenic levels also contained more gold, suggesting arsenic plays an important role in concentrating the precious metal.
Gold concentrations varied across sites and pyrite types
Not all pyrite contained the same amount of hidden gold. Samples collected from the Central Cone site showed the highest concentrations, followed by the Southeast and East sites. The richest gold was found in layered colloform pyrite, which forms when extremely hot hydrothermal fluids cool rapidly after mixing with cold seawater. Framboidal pyrite contained the next highest levels, followed by subhedral and euhedral crystals.
The researchers built on earlier work from 2015, when exploration of the same hydrothermal field uncovered visible gold concentrations of up to 275 parts per million, far exceeding the 0.01 to 43 parts per million typically reported from similar deep-sea deposits worldwide. The new study set out to determine whether pyrite from those deposits also contained hidden gold.
Findings could guide future gold exploration
Published in Scientific Reports, the findings show that microscopic textures and chemical fingerprints within pyrite can reveal valuable gold deposits that would otherwise remain undetected. Researchers said the approach could improve future mineral exploration by helping identify the most promising gold-bearing zones beneath the seafloor.
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