Potosí

Mercury amalgamation is adapted for Potosí's silver ores

The new silver boom depended on pairing two mountains roughly 1,500 kilometres apart: Potosí's silver and Huancavelica's mercury.

1571–1572: a technique retuned for Andean ore

During 1571 and 1572 the Spanish miner Pedro Fernández de Velasco adapted a relatively inexpensive mercury-amalgamation technique, known as beneficio de cajones, to Andean ores and conditions.

Viceroy Francisco de Toledo summoned him to demonstrate the process at Cusco, then employed him to teach it to refiners at Potosí. The method recovered silver from low-grade ore that could no longer be treated efficiently by the existing fuel-intensive smelting.

Mercury from one mountain, silver from another

By 1572 mercury shipments from Huancavelica were reaching Cerro Rico, supplying the material the new refining required. Records show 348 quintals arriving at Potosí in 1572 and 569 quintals in 1573.

Construction of Potosí's new ore-crushing and amalgamation mills began in 1572. By 1576 the district had 108 refining ingenios.

Not one year, and not the chemistry alone

The date usually given as 1571 is too precise. Scholarly accounts variously distinguish Fernández de Velasco's 1571–1572 adaptation, introduction in 1572, broader implementation through 1572–1576, and effective adoption around 1574, partly because they use introduction, adaptation, and mine-wide adoption to mean different stages.

There was no single-day production explosion. The marked surge is visible after about 1575, and it depended on mercury supply, hydraulic infrastructure, capital, and the mita labour draft as much as on the chemical technique.

Potosí's silver output grew almost sixfold between 1575 and 1590.

Sources

Researched 24 Aug 2026 7 sources not yet audited Date disputed

How this was checked

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Date disputed. Sources disagree; the research places it at ~1572.

What the sources leave uncertain

The listed date of 1571 is too precise. Scholarly accounts variously distinguish Fernández de Velasco’s 1571–1572 adaptation, introduction in 1572, broader implementation during 1572–1576, and effective adoption around 1574.
This entry combines several developments—experimentation, official sponsorship, mercury deliveries, mill construction, labor reorganization, and the later output boom—that did not occur on one day or even in one year.
Sources disagree partly because they use introduction, successful adaptation, and mine-wide adoption to mean different stages.