In 1546, Spain made almost simultaneous discoveries of silver in Zacatecas, Mexico (then Nueva Espana) and Potosi, Bolivia (then Alto Peru). The discovery of significant silver ore quickly highlighted the impracticality of (then) contemporary extraction techniques, as neither the grasslands of central Mexico nor the high Andes were rich in wood for firing ore. In 1554, this resource problem was solved by the refinement of the patio process – a low temperature extraction technique for silver involving liquid mercury. Spain had no shortage of mercury, as the Almaden mine in southwest Spain was (and still is) the largest mercury deposit in the world.
With an abundance of mercury in the Old World, and the discoveries of silver in Zacatecas and Potosi in the New, Spain began a 150 year period (1556 – 1710) of significant extraction and transport: mercury from Spain to the Americas, and silver from the Americas to Spain. Mercury from the Almaden mine was allocated most significantly to Mexico, arriving by galleon to Veracruz, then transported overland to the mines in Zacatecas. Once mined, silver traced the reverse route back to Spain. The difficulties inherent in transporting mercury to Bolivia were relieved by the 1564 discovery of mercury in Huancavelica, Peru. Peruvian mercury was predominated carried to Potosi, with silver transported back to the Pacific Coast, then north by ship to Panama City, overland to Portobello and then by galleon back to Spain. This mission/endeavor became known as the Spanish Treasure Fleet. At its peak in the early 1600s, the Fleet included ~ 50 ships that undertook multiple round-trip voyages per year. At this scale and for this duration, The Spanish Treasure Fleet may represent the largest and most well organized maritime transport endeavor in history.
The patio amalgamation technique also represents the first significant large-scale “open” use of mercury in industrial history. While the majority of the silver mined during the Spanish silver era is still in circulation in one discrete form or another, the majority of the mercury applied to the extraction of silver volatilized to the atmosphere. That mercury is untraceable – it is anywhere and everywhere and passing through every food web – terrestrial and marine – on the planet. The environmental legacy of that style of mercury utilization continues into the present day, with mercury release into the atmosphere a concern associated with multiple processes, including coal combustion, industrial chlor-alkali production and small scale gold mining. In the years I’ve spent professionally focused on mercury contamination and remediation, I’ve grown very interested in the historical and global legacy aspects of its use.