Northern Uruguay is home to one of the world’s largest amethyst deposits, but its formation has long been shrouded in mystery. Researchers are using cutting-edge technology to unravel their origin story and have discovered that these stunning gemstones crystallized at surprisingly low temperatures.
Amethyst is a type of quartz that can be identified by its striking purple hue. Gems are an important economic resource in Uruguay, home to the Los Catalanes mining district. This deposit is so important that it has been recognized by the International Commission on Geological Heritage (IUGS) as one of the “first 1000 IUGS geological heritage sites”. According to IUGS, the deposit is “unique” due to its large number of megageodes, vast reserves, and the quality and variety of gemstones.
Amethyst geodes (some over 16 feet tall!) are located in cooled lava flows. These ancient lava flows can be traced back to the breakup of the Gondwana supercontinent about 134 million years ago. Mining began in northern Uruguay more than 150 years ago and remains an important industry today. However, finding new geodes is difficult as not much is known about their origins and currently relies heavily on the experience of miners.
To learn more, researchers conducted a series of geological surveys in more than 30 mines to analyze geode minerals, groundwater, and water contained in geodes. The research includes high-tech techniques such as nucleation-assisted microthermometry (to examine tiny liquid-filled pockets in rocks) and triple oxygen isotope geochemistry (to analyze oxygen atoms in minerals). It was.
“The precision and accuracy of these new techniques allowed us to estimate with confidence the temperature and composition of mineralizing fluids,” said first author and postdoctoral researcher Fiorella Alduin Rode from the Center for Geosciences at the University of Göttingen. he said in a statement.
“Our findings support the idea that these amethysts crystallized at low temperatures from liquids such as groundwater.”
The results show that amethyst geodes formed at temperatures between 15 and 60°C (59°F and 140°F), which the researchers say is a surprisingly low temperature. . This suggests that amethyst was formed after the lava cooled.
Furthermore, the results revealed that the salt concentration of the mineralized fluid was low. The isotopic content also suggests that the water came from natural weather cycles. Researchers believe it probably came from groundwater contained in nearby rocks.
Knowing this could help us find more of these impressive crystals in the future.
“Understanding the conditions for amethyst formation, including the temperature and composition of the mineralizing fluid, the source of silica, the timing of mineralization, and its relationship to the host rock, is critical to understanding the process,” Lord said. Ta. .
“This could significantly improve exploration techniques and lead to sustainable mining strategies in the future.”
The study is published in the journal Mineralium Deposita.
