Geologists in New Zealand have discovered a huge reserve of precious metals dissolved in super hot reservoirs and springs hidden away within a system of volcanoes. The findings were published online in Geothermics this month.

Taupo is a supervolcano located on North Island, and it began erupting about 300,000 years ago. The top of the volcano collapsed about 27,000 years ago, creating a crater (known as a caldera) that’s now partially filled by a lake. Taupo is the largest volcano in what’s called the Taupo Volcanic Zone. Water in the geothermal systems within this very active area is heated from below by magma, which produces scalding hot water that breaks down the surrounding rocks. As a result, the water becomes laden with gold and silver.

A team led by University of Utah’s Stuart Simmons identified several deepwater reservoirs that are packed with precious metals. Their concentrations of gold range between 0.1 to 20 parts per billion, while their silver concentrations vary between 2 and 2,000 parts per billion. One of these water reservoirs, called Rotokawa, might produce as much as 70 kilograms (154 pounds) of gold a year. When combined with another reservoir called Mokai, the two could produce up to 7,500 kilograms (16,534 pounds) of silver in a single year. 

Production wells drilled into these sorts of reservoirs could yield as much as $2.71 million in gold and $3.6 million in silver a year, Science News reports. However, to extract these metals, the authors write, new technologies will need to be developed so as not to interfere with the area’s geothermal energy production.