Potosí Silver Extraction by Amalgamation

Timeline

1. c. 1554–1560Pachuca · PachucaSpanish metallurgist Bartolomé de Medina successfully developed the patio amalgamation process at Pachuca, New Spain: crushed ore, salt, copper-iron catalysts, and mercury were trodden together on open plaster patios to form silver amalgam, which was then distilled to separate the mercury, breaking the bottleneck of low-grade silver mining.
2. 1571–1580Potosí (Cerro Rico) · PotosíFrancisco de Medrano and others introduced the patio amalgamation process to Potosí, then the world's largest silver mine; in the 1570s numerous patios were built at the foot of Cerro Rico, where Indian laborers trod low-grade ores, causing silver output to rise sharply.
3. c. 1580–1650Potosí and the Acapulco–Manila route · PotosíAmalgamation brought Potosí silver production to its historic peak from the late 16th to mid-17th century; vast quantities of silver reached Europe and East Asia via Spanish treasure fleets and the Manila galleons, reshaping global trade and monetary systems, while mercury poisoning and labor losses exacted a heavy social cost.
4. c. 1700–1900Andean mining districts · AndesAfter the 18th century Potosí's output declined; the amalgamation process continued in Peru, Mexico, and elsewhere with local improvements; in the 19th–20th centuries flotation and cyanidation gradually replaced patio amalgamation, though the process's historical impact on the colonial silver economy continues to be studied.