During the Miocene Period (between 24 to 20 million years ago), several volcanic centres in the Macusani District in Puno, southern Peru, were active. Uranium was carried to the surface by acidic magma, forming rhyolite lava flows. These uranium-rich magma flows extended out from the volcanic centre in all directions and covered over 21,000 km2.

Subsequently, hot hydrothermal fluids liberated by the same deep magmatic chamber and/or trapped in the viscous lava flows, welled up and flowed down the slopes of the eruption centres (volcanoes).

Repeated processes of solubility and precipitation have increased the uranium content from a low dissemination in the acidic lavas into layers of uranium-rich rocks.