• The WTF Files

Underwater Caves in Mexico preserve one of the world’s oldest ochre mines

Crouching as she wound her way through a pinched underground corridor, a young woman grasped a torch in one hand, soot blackening the craggy ceiling above her. Guided by stacks of stones deeper and deeper in the darkness of the cave, she finally spied her prize: a blood-red vein of rock in the fire-lit wall. It would be 10,000 years before another pair of eyes saw it again.

Now the blood-red rock—a treasured crimson mineral known as ochre—has been found again, this time by underwater divers who were the first people in tens of centuries to return to these now-submerged caves. Scientists have confirmed that the site, now part of a coastal cave system in Quintana Roo, Mexico, is one of the Western Hemisphere’s oldest known ochre mining sites. Ochre, which was used for rock art, body decoration, tanning animal hides, and possibly medicine, was a prize miners would go to great lengths to obtain, from the jungles of Mesoamerica to the grasslands of Africa.

“The love of shiny red things is a pretty universal human trait. … It’s why we buy red sportscars,” says Spencer Pelton, an archaeologist at the University of Wyoming who wasn’t involved in the new work, but is excavating another prehistoric ochre cache in Wyoming.

The newly found site consists of three caves that were drowned by rising seas some 7000 years ago. In 2017, divers exploring tunnels deep within one cave, Sagitario, noticed sections with broken stalactites and stalagmites, curiously piled rocks, pitted walls and floors, and sooty ceilings. These sections were hundreds of meters from the cave’s mouth, where no natural light could penetrate.

The next year, they returned with McMaster University geoarchaeologist Eduard Reinhardt. Together they identified dozens more pits and trenches, which they took as evidence of mining activity. They named the site La Mina, Spanish for “the mine.” Radiocarbon dating revealed that the earliest deposits were left about 12,000 years ago and the youngest about 10,000 years ago. By looking at tiny fragments of the charcoal under a scanning electron microscope, the researchers learned the soot came from local, highly resinous trees that would have been perfect as torchwood.

Further analysis revealed these ancient miners were excavating remarkably high-quality ochre, the researchers report today in Science Advances. The miners fashioned digging tools from cave materials rather than bringing them from outside, explains Brandi MacDonald from the University of Missouri, who led the analysis. “They’re actually breaking off stalactites from the ceiling and using them as hammerstones and pile drivers to smash through the limestone.”

In 2007, researchers found the remains of a 12,500-year-old Paleoamerican teenage girl nicknamed Naia in another cave not far from Sagitario. Because of her presence, archaeologists knew that people, including young women, entered these caves. Now, MacDonald says, scientists may know why.

There’s no evidence to explain how the mine’s riches were used: The hot, humid jungle environment has decayed most archaeological clues. In addition to decoration, the ochre’s unusually high arsenic content could have made it an effective bug repellant, MacDonald says. Whatever its use, the mine appears to have been abandoned after about 2000 years, before the rising seas inundated the caves. It’s not clear why the mining operation halted.

The study is a welcome addition to what we know about humans’ longstanding special relationship with ochre, says Christopher  Davis, a Chicago-based anthropologist who studies rock art in South America. The findings also suggest people were willing to go through a lot of trouble to get their hands on ochre, Pelton says. “We’re just really attracted to this substance.”