Spanish miners discovered rich silver deposits at Cerro Rico, and a settlement at Potosí quickly grew into a major mining center. Early output relied heavily on smelting and Andean wind-driven furnaces (guayras), which worked best with high-grade, near-surface ores. This discovery created a long-term demand for a more reliable way to refine lower-grade silver ore.
A new silver-refining method—the patio process—used mercury to bind with silver in crushed ore, allowing silver to be recovered from lower-grade material. This reduced reliance on fuel-intensive smelting and made mining profitable where wood and high-grade ore were limited. The method’s spread sharply increased mercury demand across the Spanish Empire.
Large cinnabar (mercury ore) deposits at Huancavelica became known to Spanish authorities and miners in the 1560s. The mercury from this region soon became essential for refining silver by amalgamation, especially for Andean silver centers such as Potosí. This discovery helped tie one mining district (mercury) to another (silver) in a single colonial supply chain.
By the mid-1560s, many of the richest, easiest-to-smelt ores at Potosí were depleted, and silver output dropped. This made technologies like mercury amalgamation more important because they could process deeper, sulfide-rich ores that were harder to smelt. The change increased dependence on steady mercury supplies from places like Huancavelica.
The Spanish Crown moved to control Huancavelica’s mercury because mercury was strategically important for silver refining and royal tax income. State oversight helped direct mercury toward major silver districts and supported a tighter colonial extractive economy. This step also set the stage for labor drafts and regulated sales that prioritized imperial revenue.
Viceroy Francisco de Toledo formally established the city of Huancavelica to support the mercury district and strengthen royal control. The city helped organize production, storage, and shipment of mercury for silver refining elsewhere. Urban institutions (officials, warehouses, accounting offices) made mercury extraction a more centralized colonial enterprise.
Colonial authorities expropriated key Huancavelica mine holdings and expanded a system of private operating leases (often described as asientos) under state supervision. Under this approach, private miners produced mercury but were required to sell output under fixed terms, while the Crown managed taxes and redistribution to silver mines. The arrangement aimed to keep mercury flowing to Potosí and other silver centers while protecting royal revenue.
To maintain mercury output, Toledo extended a colonial mita (rotational labor draft) to Huancavelica, drawing Indigenous workers from surrounding communities. The mita supplied labor for dangerous underground mining and refining ovens, linking coercive labor directly to the mercury needed for silver extraction. This policy tightened the relationship between colonial administration, forced labor, and mineral production.
A mint was established at Potosí to convert silver into coin, making the region’s output easier to tax, standardize, and trade. Coined silver helped connect Andean extraction to long-distance commerce across the Atlantic and beyond. This institutional change reinforced why mercury supply from Huancavelica mattered: more refined silver meant more coinage and more state revenue.
Colonial officials increased the number of drafted workers to sustain mercury production as demand rose. Research on long-term exposure notes that the mita began with hundreds of laborers and was expanded dramatically, reflecting the scale of mercury needed for Andean silver refinement. The expansion also intensified health risks and social disruption in the recruiting regions.
Huancavelica’s mercury output reached high levels from the late 1500s into the mid-1600s, supporting large-scale silver amalgamation in the Andes. Over time, depletion of rich veins, dangerous working conditions, and administrative limits contributed to falling output. As mercury became harder to obtain, silver refining costs and constraints increased across dependent mining districts.
A major collapse in the Santa Bárbara mining complex in 1786 reportedly killed hundreds and damaged critical underground workings. The disaster reduced productive capacity and added to existing problems from depletion and unsafe conditions. This shock weakened the mercury supply chain that had supported Andean silver extraction for more than two centuries.
By the end of the 1700s, Huancavelica mercury production fell sharply compared with earlier centuries. Reduced mercury supply made amalgamation-based silver extraction harder to sustain at previous levels, especially as silver output at places like Potosí also declined. The system that linked forced labor, mercury production, and silver refining entered a more fragile phase.
Peruvian mercury production at Huancavelica and its role in silver extraction (1570–1800)