A decade after the Spanish Conquistadores toppled the Inca Empire (1532-34), an indigenous Andean prospector, Diego Gualpa, in 1545, stumbled onto the richest silver deposit in the world on a high mountain of 4,800 meters (15,750 feet) in the eastern cordillera of the Bolivian Andes.

Here in the shadow of what the Spaniards called the “Cerro Rico” (“Rich Mountain”) at 4,000 meters (13,200 feet) a mining boom town quickly developed. By the end of the sixteenth century, it had become one of the largest and the highest cities in the world, and in 1561, Philip ll of Spain, decreed that it should be known as the “Villa Imperial de Potosí.”

Peru already had a reputation as the source of unfathomable treasures thanks to the ransom in gold and silver gathered for the Inca emperor Atahualpa seized by the conquistador Francisco Pizarro in an ambush at Cajamarca which had amounted to a million pesos of fine gold and silver when melted down. A similar amount was seized from the Inca treasury of Cuzco. Pizzaro ordered Atahualpa executed by garrote in July 1533. When the Inca treasure arrived in Seville in 1534 it was enough precious metal to upset the money markets in Europe and the Mediterranean.

16^th Century Potosi and Global Trade

During the sixteenth century the population of Potosi grew to over 200,000 and its silver mine became the source of 60% of the world’s silver. Between 1545 and 1810 Potosi’s silver contributed nearly 20% of all known silver produced in the world across 265 years. It was at the core of the Spanish Empire’s great wealth. The Habsburg Holy Roman Emperor, Charles V, called Potosi “the Treasury of the World.”

He was right. Potosi became the engine of an international network which ended Eurasia’s bullion famine after 1550 and provided the silver flows that reached westwards across the Atlantic Ocean from South America via the isthmus of Panama to Spain and Europe, and to the east from Seville in Spain and Lisbon in Portugal to the Ottoman and Safavid Empires and to Mughal India and to China under the Ming and Qing dynasties.

After 1565 silver from the Americas also crossed the Pacific Ocean to the Spanish entrepôt at Manila in the Philippines (named after King Philip ll of Spain) and on from Manila by Chinese junks to the Fujian in China where the port of Quanzhou was one of the world’s busiest shipbuilding and commercial centers of overseas and coastal trade with more than 100,000 Arab traders living in the area.

From the 1550’s Potosi was at the center of the first explosive development of global intercontinental exchange creating the first true globalized economic and trading network. In effect it created the first global currency of exchange, the “pieces of eight” each with the mark “P” for the Potosi Mint established by the Viceroy of Peru (1569-1581), Francisco Alvares de Toledo, in 1574. The most famous image of the “Cerro Rico” came from the much-copied 1553 woodcut illustration published in the “Crônica del Peru” by Pedro de Cieza de Leon. By 1580 an Ottoman version of the “Cerro Rico” of Potosi was depicted in the Tarih-l Hind-l Garbi. In 1602 the Italian Jesuit missionary Matteo Ricci and his assistant Li Zhizou marked the “Potosi Mountain” (Bei Du Xi Shan) on their world map for Wanli, China’s Emperor.

Producing Silver

The great silver (and tin veins) of Bolivia’s Eastern Cordillera are the richest of both metals on the world. The “red mountain” is still producing silver, tin, zinc, lead, and other metals. The silver rich veins of the “Cerro Rico” are about a meter wide on average and the vines dive steeply into the mountain from the surface. Within decades the miners reached the water table at 400 to 500 meters depth.

The rich surface silver ores at Potosí were processed initially by smelting. Using stamp mills, powered by mules or water wheels, the silver ore was crushed to gravel then smelted in blast furnaces with lead and lead oxide. 6000 such furnaces (guayra), set on pedestals to capture the wind, covered the hills around Potosi during the early years burning wood, charcoals, and llama dung. The air blast was provided by sheep or goat skin bellows.

The water came from the warm mineral springs on the road to Oruro, where the “Ojo del Inca” (the Inca’s Baths) at Tarapaya provided the reagents to the dozens of early refineries. The massive salt beds of the Salar de Uyuni, the World’s largest salt flat, was several days walk away.

The silver-gold alloy produced in the early sixteenth century was first shifted to cupulation furnaces where the porous bone-ash-lined interior absorbed the oxidized lead. The pure silver and gold alloy remaining at the bottom of the couple where it was separated by a nitric acid method which had been introduced from Germany, then also part of the vast Habsburg domains.

The rapid introduction of the most modern technology was a characteristic of these early years of European colonial activity in the Americas. The dramatic rise in Spanish American silver production in the 1570’s was the result of the adoption at Potosi of the “patio” process of amalgamation of silver ores with mercury which produced a quadrupling of silver export from Peru in the ten years between 1576-1585.

The introduction of the “patio” method in Mexico about 1554 and is attributed to a merchant from Sevilla, Bartolome de Medina, who developed mercury amalgamation. The great advantage of the amalgamation over smelting was that it made the exploitation of lower grade silver ores profitable and greatly extended the range that could be worked, and salt mixed with mercury was used to extract fine grains from silver from what had before been worthless host rock.

The Silver Production Process

The ore for amalgamation was crushed to a fine powder and mixed with water and mercury, salt, and impure copper sulfate. The muddy composite was spread out over a stone paved courtyard (the “patio” hence the name “patio” process). Here it was agitated by a team of mules, and then heaped into piles where it stood for some weeks while the silver ore was separated chemically and amalgamated with mercury.

The mud was then washed away into troughs or vats (tingas) and the silver amalgam put into canvas bags, any free mercury filtering out. Pressed into bars the residual amalgam was then placed into small conical furnaces where the mercury was vaporized and recovered, though one quarter of the mercury was lost in the processing of silver ore. The silver was then taken to the office assay office for recasting and stamping with weight, fineness, and the royal coat of arms.

The repossessing plants were called “haciendas de minas” and were substantial establishments containing the stamp mill and incorporating the residence of the mine owner, his houses of workers and their families, as well as a chapel, stables for mules and horses, machinery sheds, and store houses. The buildings were constructed near streams whenever possible because water was essential to operate the machinery of the mill.