Scientists strike invisible gold in the deep sea—locked inside fool's gold
Pyrite, an iron sulfide ore, is often known as fool's gold because its shiny metallic luster and pale brass-yellow color can easily fool the untrained eye into mistaking it for real gold. This time, however, 360 kilometers (220 miles) south of Tokyo, scientists have uncovered invisible gold within pyrite structures found deep beneath the ocean at the Higashi-Aogashima Knoll Caldera hydrothermal field.
With the help of robotic submarines that dived more than 700 meters (2,300 feet) below sea level, researchers collected rock samples from volcanic vents and underwater mounds scattered across the floor of a deep-sea caldera. Peering inside these rocks using secondary-ion mass spectrometry through tiny drill holes, they discovered that the minerals at this site contain record-breaking concentrations of gold, reaching as high as 1.9 wt% (19,231 ppm).
In search of hidden treasure
Instead of being present as gold granules or nodules, as found in conventional gold mines, the metal was locked as a solid solution within the crystal lattice of seafloor pyrite. This discovery, published in Scientific Reports, could give geologists a new way to identify promising mining sites around the world.
The Higashi-Aogashima Knoll Caldera is an underwater volcanic crater located east of Japan's Aogashima Island. Its floor is home to three active hydrothermal fields—the Central Cone, Southeast and East sites—where superheated, mineral-rich fluids continuously vent from beneath Earth's crust.
A caldera unusually rich in gold
The region is dotted with towering black smoker chimneys and massive sulfide mounds rich in minerals such as pyrite, chalcopyrite, sphalerite and galena.
When scientists began investigating these hydrothermal structures in 2015, they uncovered an astonishing amount of gold in the rocks—reaching 275 parts per million (ppm), with an average of 102 ppm. The concentration was exceptionally high compared with similar deep-sea gold deposits worldwide, which typically contain just 0.01 to 43 ppm.
Most of this was visible gold grains, but scientists were curious whether the same material had invisible gold hidden inside pyrite, commonly found in the region.
How the team traced hidden gold
In this study, researchers collected rock samples from all three active hydrothermal fields and sorted them into four types based on their morphology: berry-like clusters (framboidal), layered shells (colloform), and well-formed or partial crystals (euhedral and subhedral).
Some of the rocks were crushed into a fine powder and placed under a mass spectrometer to measure the rocks' total gold and arsenic content, and individual mineral grains were scanned with electron beams to map the distribution of metals such as lead, copper and arsenic.
Finally, using the ultra-sensitive secondary ion mass spectrometry (SIMS) technique, they detected invisible gold at the atomic scale by drilling microscopic holes into the rocks.
Gold woven into pyrite
What surprised the researchers most was how the gold existed. Instead of forming tiny nuggets trapped inside the mineral, the gold was woven directly into pyrite's crystal structure, atom by atom. They also found that this could only happen when elements such as arsenic, lead and copper were present. These elements cause structural distortions in the pyrite lattice, creating vacancies that allow gold atoms to fit within the crystal and become trapped.
This was reflected in the positive gold-arsenic correlation, in which gold concentrations increased alongside arsenic concentrations. This occurs because arsenic substitutes for sulfur in the pyrite structure, creating space for the larger gold ions to enter.
Not all pyrite, however, was equally rich in gold. The concentration depended on where it was found and under what conditions it formed. The Central Cone Site had the highest concentrations, followed by the Southeast Site and the East Site. Colloform pyrite, formed when superheated hydrothermal fluids rapidly collided with cold seawater, contained the most gold, followed by framboidal, subhedral and euhedral pyrite.
This work shows how advanced micro-analytical tools can uncover valuable materials that were once overlooked and reveal how gold and other metals move and concentrate within active vent systems at the seafloor. The findings could also help identify where hidden gold lies, with pyrite's texture and chemical fingerprints acting as clues pointing to the richest gold-bearing zones.
Written for you by our author Sanjukta Mondal, edited by Sadie Harley, and fact-checked and reviewed by Andrew Zinin—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Yuichi Morishita et al, SIMS discovers invisible gold in pyrite from the high-grade seafloor hydrothermal deposits in the Higashi-Aogashima knoll caldera, Izu-Ogasawara arc, Japan, Scientific Reports (2026). DOI: 10.1038/s41598-026-58760-z
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Citation: Scientists strike invisible gold in the deep sea—locked inside fool's gold (2026, July 13) retrieved 13 July 2026 from https://phys.org/news/2026-07-scientists-invisible-gold-deep-sea.html
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