The historical mines of Almadén, which were actively functioning for over two millennia, produced a third of the world’s mercury — a total of 7,500,000 flasks (Hernández, 1995). After mining and metallurgical production ceased in 2003, the mines were turned into a museum. Efforts are currently underway to have the mines declared a World Heritage Site.
Almadén is situated in the southwestern part of the province of Ciudad Real in Spain. A Roman roadway passed by the Alcudia Valley, to the south of Almadén, between the cities of Emérita Augusta (now Mérida) and Cástulo (now Linares). Another roadway, a bit further to the west, started in the Alcudia Valley and went via Cordova to the centre of the Iberian Peninsula, with a branch going to Almadén. This exceptionally well-networked geographical location contributed to the discovery, exploitation and commercialization of the extensive resources at Almadén. Although these historic Roman roadways are no longer in use and have been replaced by modern roads, along many stretches they remain quite well-preserved.
In geological terms, Almadén is situated in the central area of the Iberian Peninsula, a part of the Central Zone of the Hercynian mountain range. It is part of the Vertical Folders Domain. However, in northern Spain, this area abuts the Recumbent Folders Domain. The succession of compact quartzite and soft slate beds found in this setting, together with the vertical position of the layers, results in a characteristic and spectacular Appalachian landscape. Unique minerals such as massive cinnabars (extraordinary pieces of crystallized mercury sulphide) and barites with cinnabar inclusions are found in abundance in this region. The epigenetic mineralization of cinnabar and other minerals (barytes, dolomites, etc.) is associated with Hercynian orogeny. An exceptional universal geochemical anomaly has generated the deposit.
The first known use of the resource was in making the mineral pigments that were used in numerous prehistoric paintings. The name Almadén comes from the Arabic word for mine. The Almadén mine was described by the Arab geographer Al Idrisi of Ceuta in the 12th century. At that time, more than a thousand men worked at the mine, which had already been excavated to a depth of 420 metres. Centuries earlier, the Romans had begun extracting cinnabar in this area after vermillion had been successfully commercialized throughout the Mediterranean. Pliny the Elder (AD 23-79) had described the distillation of native mercury from cinnabar in marmites. Lead, silver and copper were also obtained at the mines of Quinto del Hierro and El Mesto, east of Almadén. Although there were many other mines in Spain, the one at Almadén was the largest and most extensively developed.
In the Middle Ages, alchemists were preoccupied with concocting the philosopher’s stone — a magical substance that could purportedly transmute base metals into gold. Mercury was thought to be one of the basic reagents of philosopher’s stone. Mercury was also an important ingredient in many medieval medicines. The Swiss chemist and doctor Theophrastus Bombastus von Hohenheim (1493-1541), who was better known as Paracelsus, rejected traditional medical orthodoxy and successfully identified the main symptoms of various illnesses such as goitre and syphilis. To treat them, he used sulphur and various mercury-based compounds.
The importance of Almadén is evident from its role in one of the defining events of Western civilization — Christopher Columbus’ voyage to the Indies. In The History of the Indies (Book 1, Chapter LXV and LXVI), Father Bartholomew de las Casas (1474-1566) reports that Columbus, before embarking on his journey to the New World, had asked the Catholic Monarchs Ferdinand and Isabella to furnish him with the services of gold panners and miners from Almadén (Prieto, 1968). Between 1525 and 1645, under the reign of Charles I, Almadén was controlled by the Fugger family. Later, from 1835 to 1911, control of the mines was vested with the Rothschild family.
With the discovery of mercury mines in Huancavelica in 1563, colonial South America’s needs of mercury were met by the Vice Royalty of Peru. However, New Spain (as Mexico was then called by the Spanish), continued to rely on the mercury supply from Almadén. Quicksilver would be transported from Almadén to Seville. Protected by warships, a flotilla bearing mercury and other goods would leave from Seville and sail to Veracruz, Mexico. The cargo would then head to Mexico City and the rest of the territory over the Royal Roadway. On the return trip, the ships would carry silver ingots bearing the royal stamp.
Even in those early days, there was great cultural exchange between South America and Europe. At the beginning of the 16th century, a special type of mercury furnace, called xabecas, was introduced to Almadén. In the xabecas furnaces, ceramics pots were filled with cinnabar, sealed with clay and heated from below. These furnaces found their way to the Huancavelica mine in 1598.
Another such example was the use of gunpowder in mining. First employed in 1626 in the town of Schemnitz (now known as Banská ?Stiavnica in present-day Slovakia), gunpowder reached Almadén in 1689; it was also used to build the drainage gallery of the Our Lady of Bethlehem adit at Huancavelica. Technology also flowed in the opposite direction. Kilns invented in 1633 by the prospector Lope Saavedra Barba in Peru were introduced at Almadén in 1646 by Juan Alfonso de Bustamente.
For a very long time, the Spanish economy subsisted on the mining of mercury and precious metals coming from the Indies. To ensure its sustenance, the best Spanish scientists were sent there to develop mining activity. Examples of Spanish scientists who played important roles as expatriates include Antonio Ulloa (1716-1795), who mentioned the existence of platinum in his work Historical Account of the Trip to Southern America (1748); the Elhuyar brothers, Juan José (1754-1796) and Fausto (1755-1833), who discovered tungsten in 1783; and Andrés Manuel del Río (1764-1849), who discovered vanadium in 1801.
Another important Spanish scientist who travelled to conduct research in America was Jerónimo Ayanz (1513-1613), who in 1606 invented a steam pump for the extraction of water in the Potosí mine. His invention was one step ahead of the pumps that Thomas Savery invented in 1698 and Thomas Newcomen invented in 1712. All of these pumps were the precursors of the steam engine that Watt famously invented in 1768 (García Tapia, 1992). The Watt pump itself was introduced in Almadén at the beginning of the 19th century.