"Mining has been continuous in the Cerro Rico de Potosi since 1545. The outstanding mineralization is confined to definite vein systems, the Mendietta being the trunk system. A detailed consideration of structure emphasizes the en echelon arrangement as characteristic of all systems. Mineralization has been dependent on structure and on zoning, and not on favorable or unfavorable rock types. In the Pailaviri section three periods of mineralization are indicated, and a consideration of these periods and their relationship to structure is a Possible indication of what to expect in depth."