In 1545, rich silver ore was discovered at Cerro Rico (the “Rich Mountain”) near present-day Potosí in the Andes. This find quickly drew Spanish settlers, Indigenous labor, and capital into a remote high-altitude region. It set the starting point for one of the Spanish Empire’s largest resource-extraction systems.
Soon after the discovery, the settlement of Potosí was established to support mining at Cerro Rico. The town grew around extraction and processing needs, including housing, supply markets, and transport services. Its rapid growth made it a key administrative and commercial hub for Upper Peru (today Bolivia).
In the first decades, miners focused on especially rich near-surface ores that could be smelted with relatively simple furnaces. This helped silver output rise quickly, feeding royal taxes and private profits. The early boom also encouraged migration and tighter Spanish control over the region.
A major mercury (quicksilver) source began operating at Huancavelica in Peru in 1564. Mercury was essential for extracting silver from lower-grade ores using amalgamation, a chemical method that binds silver to mercury. This mercury supply became a strategic link in the Potosí production chain.
In 1570, the Spanish Crown appropriated the mercury deposits at Huancavelica. This strengthened state influence over a critical input for silver refining. Control over mercury supply and pricing gave imperial authorities leverage over colonial silver output and tax revenue.
With mercury available from Huancavelica, amalgamation methods were adopted in Potosí in the early 1570s to treat lower-grade ores. This shift mattered because it allowed production to continue even after easily smelted ores became harder to find. It also sharply increased mercury use and environmental and health harms around refining centers.
Under Viceroy Francisco de Toledo, the Spanish state expanded and reorganized forced Indigenous labor for the mines through the mita system. The first mita recruits are widely documented as arriving in Potosí in 1573. This policy helped stabilize labor supply for large-scale mining and refining, while intensifying coercion and social disruption in many Andean communities.
To standardize silver for taxation and trade, Spanish authorities created minting capacity tied to the Potosí mining center. By the mid-1570s, mint operations were underway in Potosí, supporting large-scale coin production. Coinage made silver easier to move, count, and use in long-distance commerce across the empire and beyond.
By the early 1600s, Potosí had grown into one of the most populous cities in the Americas, supported by mining income and a large service economy. The city’s size required organized governance, public works, and supply systems to keep mining and refining running. Its municipal records reflect how tightly urban life was linked to the silver industry.
In 1609, Álvaro Alonso Barba developed a faster heated-pan method of silver amalgamation in Potosí, often called the cazo (pan) process. Compared with patio-style processing, this approach reduced treatment time by using heat in shallow vessels. It illustrates how technical changes were pursued to sustain output as mining conditions became more difficult.
In 1640, Barba published Arte de los metales in Madrid, a major early technical text describing mining and refining methods used in the Andes. The book helped spread practical knowledge about silver-ore treatment beyond Potosí. It also shows how imperial extraction depended on both coercive labor systems and specialized technical expertise.
After very high production in the late 1500s, Potosí’s silver yields declined over the 1600s. By the 1660s, output was reported as less than half of what it had been in the first decade of the 1600s, reflecting ore depletion, higher costs, and operational strains. The decline reduced the mine’s ability to drive imperial revenue at earlier levels, even though extraction continued.
By 1700, Potosí remained an important mining center, but the system that fueled its earlier surge had weakened. Lower yields meant tighter pressures on labor, mercury supply, and local provisioning, and the city’s growth slowed compared with its peak era. This point marks a clear transition: Potosí continued producing silver, but its role as the dominant driver of Spanish imperial silver exports had diminished from the 1500s high point.
Silver mining and export from Potosí in the Spanish Empire (1545–1700)