Mining in Andalucia

Geology of Andalucía: Mountains, Minerals & Motion

Understand the fascinating geology of Andalucía: from the ancient Sierra Morena to the dynamic Betica Cordillera and volcanic Cabo de Gata. Discover tectonic forces, mineral wealth, and the region's geological history.

By Nick Nutter on 2025-03-10 | Last Updated 2025-03-10 | Mining in Andalucia

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El Hornillo - Ore Loading pier at Aguillas

Unveiling Andalucía's Geological Wonders: Tectonics, Minerals, and Ancient Landscapes

Even a brief study of the geology of Andalucía reveals a breathtaking kaleidoscope of movement accompanied by unimaginable temperatures and pressures. The whole landscape is in constant motion although so slowly that it is barely perceptible in a normal lifetime.

The Sierra de los Filabres in Almeria for instance, is rising at an average rate of 2 millimetres per year, about 160 millimetres in an eighty-year human lifespan. Of those 16 centimetres, perhaps half will have eroded in the same length of time. Still, even 8 centimetres is measurable. The eroded material eventually finds its way into the sea where it contributes to the next generation of sedimentary rock.

For much of the time we humans, plodding around on the surface of Andalucía, have little appreciation of what is happening far beneath our feet. Faults, like the Carboneras Fault, realign themselves on an almost daily basis, creating fissures in the crust. Most realignments are so small that they barely register on the Richter Scale. Occasionally we feel a slight shudder and very occasionally we shake in our boots.

Volcanic activity, although dormant on the surface, still acts deep in the Earth’s crust, pushing magma and super-heated, mineral laden, water into crevices, nooks and crannies, where crystals form and metallic elements wait to be discovered in millennia far in the future.

The tectonic plates, some like the Eurasian plate, continental in size, others like the Alboran plate, a relative newcomer on the scene and barely larger than a province, move across the surface of the world in a wondrous ballet, sometimes coming together, as they do along the Andalucían coast, sometimes diverging, as is happening along the Catalonian coast.

Exploring Andalucía's Major Geological Regions

Physical map of Andalucia

Andalucía has three main geological areas.

Sierra Morena's Ancient Origins: The Iberian Massif and Hercynian Orogeny

The Iberian Massif or Hercynian Massif of the Meseta outcrops to the north of the Guadalquivir valley and forms the mountainous lineament of Sierra Morena.

The Sierra Morena is a prominent mountain range traversing the northern parts of Andalucía, from Huelva in the west, across the northern parts of Seville and Córdoba provinces to Jaén province in the east.

It consists mainly of strongly folded and deformed, metamorphic (schists, quartzites and limestone marbles) and igneous (granites and similar) rocks, formed between more than 550 and 250 million years ago. They form part of the old Iberian continent whose coasts were lapped by the sea that occupied the greater part of what is now Andalucía.

At the core of the Sierra Morena lies a foundation of ancient Palaeozoic bedrock, predominantly composed of granite and quartzite. These resilient rocks form the backbone of the range.

During the Palaeozoic, the convergence of the African and Eurasian tectonic plates subjected marine sediments and volcanic rocks to immense pressure. This colossal force, known as the Hercynian Orogeny, sculpted these ancient materials into the majestic mountain range we observe today.

The Iberian Pyrite Belt: A Global Hotspot for Massive Sulphide Deposits

Iberian Pyrite Belt

The Iberian Pyrite Belt is a distinctive area and forms part of the western Sierra Morena.

The Iberian Pyrite Belt, stretches 250 kilometres from Portugal to Seville.It contains the world’s most extensive repository of massive sulphide deposits.

350 million years ago, during the Devonian period, volcanic activity, deep within the earth’s crust, created superheated water under extreme pressure.

Forced up towards the surface, the minerals dissolved in the hydrothermal fluid, mixed with molten magma, solidified within the rock and expelled through hydrothermal vents.

This rare combination of volcanic and hydrothermal activity, expelling on the bottom of the ocean, produced eight giant volcanogenic massive sulphide deposits.

In addition to the sulphides of iron, lead and copper, there are significant deposits of silver and gold.

The Betica Cordillera: Tectonic Plate Collisions and Mountain Uplift

The Betica Cordillera constitutes the second largescale unit. This much younger, large alpine mountain chain started uplifting approximately 25 million years ago and continues uplifting today.

It runs from Cádiz in the west to Almería in the east, extending through to Murcia, Valencia and the Balearics. Internally, a complex structure is present as a consequence of the piling up of rocks through thrusting during the slow collision of the Alboran Plate up and onto the Iberian Plate, and later uplifting.

To the north, the system is limited by the valley of the River Guadalquivir and to the south by the western Mediterranean Sea, an area often known by the name of the tectonic plate beneath that creates the depression between north Africa and the Iberian Peninsula, the Alboran Sea.

Powerful tectonic forces within the Earth’s crust relentlessly uplifted the range, subjecting it to erosion. Wind, rain, and rivers carved valleys and canyons, gradually exposing the underlying geological formations. This interplay between uplift and erosion has shaped the diverse topography of the Sierra Morena, from rugged, mountainous peaks to rolling hills.

The intense heat and pressure of the Hercynian Orogeny created a portfolio of minerals, including iron, lead, copper, and silver.

Andalucía's Neogene Basins: Sedimentary Records of Recent Geological Change

The Neogene Basins or depressions overall comprise the third largescale unit in Andalucía. During the emergence of the Betica Cordillera there were times in which the sea extensively covered depressed regions that are above sea level today, such as the Guadalquivir Basin and other intermontane basins like Guadix-Baza, Tabernas, Sorbas or Almería-Níjar.

They are young sediments, less than 25 million years old, characterised by having a limited degree of deformation, such that they hold an immense value for studying the recent geological history in this western sector of the Mediterranean.

Cabo de Gata's Volcanic Landscape: Magma, Minerals, and Coastal Evolution

Gold Mine at Rodalquilar

The Cabo de Gata is the youngest large scale geological formation to form in Andalucía. About 15 million years ago, the relentless advance of the North African tectonic plate into the European plates allowed the Earth’s crust to fracture and molten magma, from chambers deep within the crust, emerged on the surface.

Initially these eruptions were beneath the surface of the sea. As the land rose, further eruptions occurred, magma chambers collapsed and the volcanic mountains eroded, leaving the landscape we see today.

What is important here is that the volcanic activity introduced a different suite of minerals into the Cabo de Gata.

Whilst hydrothermal activity was responsible for most of the mineral deposition in the Sierra Morena and in the Sierras of the Betica Cordillera, the minerals found in the Cabo de Gata are primarily as a result of minerals being trapped in magma.

The garnets and cordierite near Nijar and the gold at Rodalquilar have to be extracted from igneous rocks of varying hardness and resilience.

Mining Andalucía's Mineral Riches: A Historical Perspective

Gold in quartz matrix

Over the course of millennia, a succession of civilizations capitalized on Andalucía’s mineral wealth. The Los Millarians, the Argars, Tartessians, Phoenicians, Greeks, Carthaginians, and Iberians all left their mark on the region’s mining history.

It was the Romans who truly transformed mining into a large-scale commercial enterprise, exploiting the vast lead mines of Linares and La Carolina, the silver lodes of Centenillo and the rich deposits of gold, silver, and copper at Rio Tinto and Tharsis.

The seven hundred year period of Muslim occupation and the three hundred years following the reconquest saw a reduction in mining activity in southern Spain.

It was not until the 19th century that the mining industry in southern Spain began to enter its boom years. The rejuvenation was fuelled by foreign companies, not least the British.

Great Britain capitalized on the opportunity, becoming a leading force in Andalucían mining investment. By the end of the 19th century, over six hundred British mining companies were registered across Spain, with a remarkable 201 of them focusing their efforts on the riches of Andalucía.

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