Forced Labor and the Colonial Economy: Silver, the Mita, and the Encomienda

Colonial wealth rested heavily on silver mining. The deposit at Cerro Rico de Potosí, in present-day Bolivia, was discovered in 1545 and quickly became the most productive silver mine in the world, with the city growing to an estimated 120,000 to 160,000 inhabitants by around 1650, comparable to the largest cities in Europe at the time. The mines of Zacatecas (discovered 1546) and Guanajuato, in New Spain, complemented Potosí as the second great American mining center. The introduction of mercury amalgamation, the so-called "patio process" developed by Bartolomé de Medina in 1554-1555, made it possible to exploit lower-grade ores, using mercury drawn mainly from the Huancavelica mine in Peru (discovered 1563) and, to a lesser extent, from Almadén in Spain. An estimated 16,000 tons of American silver reached Spain between 1500 and 1650, financing much of the military and political expenditure of the Spanish Habsburg empire, with the royal fifth — a 20 percent tax on precious-metal output — among the Crown's principal sources of revenue.