On the banks of the Río Huana Mayu, in the upper Potosí barrios of Cantumarca and San Antonio, are some fine ruined examples of the ingenios (smelters). These were formerly used to extract silver from the ore hauled out of Cerro Rico. There were originally 82 ingenios along 15km of the stream. Some remaining ones date back to the 1570s and were in use until the mid-1800s. Most tours of the Cerro Rico mines include a stop at a working ingenio as part of the trip.
Each ingenio consists of a floor penetrated by shallow wells (buitrones) where the ore was mixed with mercury and salt. The ore was then ground by millstones that were powered by water that was impounded in the 32 artificial Lagunas de Kari Kari.
