The deposit is in the lower part of the Pucara formation, a limestone series with thin tuff beds, of Liassic age, near its contact with the Carboniferous Catalina volcanics. It lies on the southwest flank of the Yauli anticline, formed by Tertiary folding. Manto ore, formed before the climax of the Andean orogeny, consists mainly of ferroan sphalerite and pyrite, with negligible chalcopyrite. These were later brecciated tectonically to form two zones of 'breccia ore'. The last phase of mineralization involved formation of epithermal cross veins with sphalerite, pyrite, galena, tetrahedrite, and jamesonite, and irregular cementation of fragments in the breccia ore by sphalerite-galena and pyrite-marcasite. Supergene alteration, particularly pronounced in the breccia zone, has formed ore much enriched in silver (native silver, argentite, pyrargyrite).