A Seafloor Volcano in the Desert
The semi-arid landscape of Cabo de Gata-Níjar Natural Park is one of Europe's geological sites. It is the continent's driest region, a landscape of sharp volcanic peaks and jagged cliffs that meet the Mediterranean. This terrain is the exposed remnant of a massive volcanic complex that was active during the Miocene epoch, between 7.5 and 15 million years ago. The volcanic activity resulted from the complex collision between the African and Eurasian tectonic plates.
The gold deposits in the park's Rodalquilar area formed within an 8-kilometer-wide volcanic caldera that collapsed around 11 million years ago. After the collapse, magma deep below the surface continued to heat the surrounding rock to between 400 and 500 degrees Celsius. This heat created a hydrothermal system, where seawater and groundwater percolated through fractures, became superheated, and dissolved metals from the volcanic rocks. These hot, acidic, metal-rich fluids then rose toward the seafloor. When they mixed with the cold seawater, the abrupt change in temperature and chemistry caused the dissolved minerals, including gold, to rapidly precipitate out of the solution, forming veins of ore. This type of mineral deposit is a low-sulfidation epithermal deposit.
The Gold Rush of Rodalquilar
While mining for other minerals like alum has occurred in the region since Roman times, the gold rush began in 1864 when prospectors made the first discoveries. This gold is not large nuggets but exists as microscopic particles embedded within quartz veins, often alongside lead and silver. Extracting it required crushing the ore and using chemical processes like amalgamation with mercury or, later, cyanide leaching.
The main period of industrial mining took place in the late 19th and 20th centuries. A British company, Minas de Rodalquilar S.A., introduced compressed air drills and explosives in 1929. The operations were nationalized after the Spanish Civil War. In 1956, a new processing plant, the "Denver" plant, was opened, becoming the largest of its type in Western Europe. At the industry's peak, the town of Rodalquilar had a population of 1,400, with about 1,000 people working at the mine. Between 1943 and 1966, the state-run operation extracted approximately 1.6 million metric tons of ore. The gold eventually ran out, and the mines officially ceased production in 1966. Today, the concrete ruins of the processing plants and abandoned miners' cottages are across the landscape.