The Iberian Pyrite Belt – Geology and Metallogeny

A contribution by Michelle Grantcharova (Grant Geoscience) and John C Menzies.  Michelle has been working on minerals exploration in the Iberian Pyrite Belt on advanced projects and is developing a considerable depth of knowledge of this important VHMS province.  Incidentally, Michelle is my daughter-geologist. This is a work in progress and we are working on new geological and metallogenic maps which will be added over time.  This will also form the basis for ongoing discussion of individual IPB deposits, discoveries and research.

Contribution to European Development Since Ancient Times

The Iberian Pyrite Belt (IPB) has been a cornerstone of European metallurgical activities since ancient times. Mining in the region dates back to the Phoenicians, Greeks and Tartessians around 3000 BCE, who exploited the rich ore deposits for the production of bronze and copper tools and artifacts. The Romans later developed extensive mining operations in the IPB, using the extracted metals to support their expanding empire. The region’s wealth of resources continued to be a crucial asset through the Middle Ages and into the Industrial Revolution, fueling advancements in metallurgy and manufacturing.

Over the centuries the mining region has gone through periods of great production, as well as during times of little or no activity. At certain times it has come to represent one of the districts with the highest production of pyrite, copper, silver, gold and manganese in Europe. More than 90 deposits have been discovered in the IPB, 9 of which are considered as giant (>100 Mt) volcanogenic massive sulfides (VMS). Among these deposits is the famous Riotinto, the largest VMS deposit in the world, with a total of 500 Mt of initial resources and has been exploited for 5000 years.

In the modern era, the IPB remains an important source of base metals for Europe. The continued exploitation of its ore deposits supports various industries, from electronics to construction. Furthermore, the extensive mining history of the IPB has fostered significant developments in mining technology and geosciences, contributing to the broader field of economic geology.

The Iberian Pyrite Belt’s rich geological history and its immense metallogenic wealth have left an indelible mark on the course of European development. From ancient civilizations to modern technological advancements, the IPB continues to be a linchpin in the region’s economic and industrial landscape.

Regional Geological and Tectonic Setting of the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB) spans southwestern Spain and southern Portugal and is 240 km long and 35 km wide located between Seville (Spain) and Grándola (Portugal). It is one of the most significant mineralized regions in Europe, renowned for its massive sulfide deposits rich in copper, lead, zinc, and associated metals. Its geological and tectonic evolution reflects complex interactions tied to the convergence and accretion processes within the Variscan Orogeny, which dominated the region during the late Paleozoic (Devonian to Carboniferous).

Tectonic Framework

The IPB is situated within the South Portuguese Zone (SPZ), the southernmost tectonic unit of the Iberian Massif, which forms part of the Western European Variscan belt.

Given its peripheral position in the Iberian portion of the Variscan Orogen and its sedimentary and faunal similarity to the Rheno-Hercynian Zone (Rhenish Massif, southern British Isles, Bohemian Massif), the SPZ is considered to be an external zone of the Variscan Belt. Its dimensions reflect the narrow Rheno-Hercynian Ocean, which opened at the southern margin of Laurrussia while the Rheic Ocean closed. The outcropping rocks range in age from the Lower-Middle Devonian (Pulo do Lobo) to the Upper Carboniferous and Permian.

In summary, the SPZ represents an accreted terrane that developed on the periphery of the Gondwana supercontinent and subsequently collided with Laurussia during the Variscan Orogeny. This collision resulted in extensive crustal deformation, metamorphism, and magmatism, forming the broader tectonic architecture of mainland Europe.

The South Portuguese Zone is subdivided from North to South into three units or domains: Pulo do Lobo, the Iberian Pyrite Belt and the South Portuguese Domain, which is located only in Portugal.

Geodynamic Setting

The IPB originated in a back-arc basin setting during the late Devonian to early Carboniferous. This environment was characterized by:

• Extensional tectonics that facilitated the thinning of the continental crust and the formation of a volcano-sedimentary sequence.
• Volcanic and hydrothermal activity is associated with rifting, producing a bimodal volcanic suite (felsic and mafic rocks).
• Deposition of massive sulfides within anoxic basins, creating one of the world’s largest repositories of volcanogenic massive sulfide (VMS) deposits.

Post-Variscan Evolution

Following the Variscan Orogeny, the IPB underwent a phase of tectonic quiescence and exhumation during the Mesozoic. Subsequent Alpine tectonics during the Cenozoic influenced the region by reactivating faults and contributing to the current geomorphological configuration of the Iberian Peninsula.

Geology of the Iberian Pyrite Belt

The IPB is primarily composed of volcanic and sedimentary rocks from the Carboniferous period, circa 350MA. The belt is 250 kilometers in length and 30 to 50 kilometers wide, containing some of the largest and most economically valuable concentrations of sulfide mineralization on Earth. The region’s geology is characterized by a series of volcanic events that resulted in the formation of extensive sulfide deposits. These deposits are primarily made up of pyrite, but also host significant quantities of copper, zinc, lead, and silver.

Stratigraphy

• The IPB consists of three main lithostratigraphic units:
  • The Phyllite Quartzite Group (PQG),
  • the Volcanic Sedimentary Complex (VSC), and
  • the Culm Group, and the,
  • the Baixo Alentejo Flysch Group (BAFG).
• The PQG is the lowermost unit, composed of grey shales with intercalations of quartz-sandstones, quartzwacke, siltstones, minor conglomerate, and limestones, with an age range from the early Givetian to late Famennian-Strunian (Middle Devonian to Carboniferous lower boundary, 388-359 Ma). Its minimum thickness is estimated at 2000 m but remains unknown since the footwall does not outcrop. The depositional environment was a shallow low-energy marine platform (Sáez and Moreno, 1997).
• The VSC overlies the PQG and is of late Famennian to mid-late Visean age (Upper Devonian to Middle Carboniferous, around 350-340 Ma) and is the most economically important group in the IPB as it is host to the polymetallic sulfide deposits and manganese deposits. In lower mafic volcanic rocks, rhyolites, dacites and dark shales, hosting Volcanogenic Massive Sulfide (VMS) deposits, overlain by dark to purple shales and volcanogenic and volcaniclastic rocks, hosting Mn oxide deposits. The VSC includes a bimodal submarine volcanic succession with VMS deposits spatially associated with dacites and rhyolites, corresponding to effusive/explosive lava-cryptodome-pumice cone volcanoes.
• The Culm Group is the uppermost unit of the IPB and consists of thousands of meters of flysch from the late Visean to Moscovian age (Middle to Upper Carboniferous, around 330-315 Ma). It is commonly associated with the Baixo Alentejo Flysch Group (BAFG) and is considered to be its basal unit. The Culm Group is composed of three subunits: the basal shaly formation, a main turbiditic sequence and a limited sandstone formation (Moreno, 1993). It represents the infill of a foreland basin.

Structural Geology and Relationship to Mineralization

The Iberian Pyrite Belt (IPB) is characterized by a complex structural history that has influenced the location and geometry of volcanogenic massive sulfide (VMS) deposits. The structural controls on mineralization in the IPB can be summarized as follows:

• Regional Tectonic Setting: The IPB is situated within the South Portuguese Zone (SPZ) of the Iberian Massif, a region affected by significant Variscan deformation. This tectonic activity has resulted in isoclinal folding, thrusts, and faults that have profoundly influenced the distribution of ore deposits. The IPB is bounded by the Pulo do Lobo Domain to the north and overlain by the Baixo Alentejo Flysch Group.
• Variscan Orogeny: The Variscan Orogeny played a crucial role in the structural evolution of the IPB. This event resulted in:
  • NW-SE/W-E trending folds and SW- or S-verging thrusts. These folds and thrusts are particularly evident in the west-central and eastern IPB, respectively, and are associated with NE- or N-dipping planar cleavage.
  • Transpressional tectonics: This process led to lower crust decoupling and the intrusion of deep mafic sills, which are thought to have contributed to the metallogenesis of the IPB.
  • Late to post-Variscan strike-slip faults: These faults trend either N-S to NNW-SSE or NE-SW to ENE-WSW, and exhibit dextral or sinistral (both extensional) movement, respectively. The first set of faults hosts late Variscan Cu-Pb-Ba veins and Mesozoic dolerite dykes.
  • Remobilization of Metals: The Variscan deformation resulted in the remobilization of metals, leading to the formation of high-grade ore shoots in some deposits. For example, Cu enrichment is associated with shear zones in the Aguas Teñidas and Magdalena deposits.
  • Fault Systems: Fault systems are critical structural features that control the ascent of hydrothermal fluids and the location of mineralization. These include:
  • Oblique faults: Late Variscan strike-slip oblique faults, oriented N-S to NNW-SSE or NE-SW to ENE-WSW, which can be dextral or sinistral (both extensional). These faults often host late Variscan Cu-Pb-Ba veins and Mesozoic dolerite dykes.
  • Fracture systems: The deposits are often associated with fracture systems that acted as conduits for hydrothermal fluids, leading to the formation of stockwork zones and massive sulfide bodies.
• Lithological Controls: Deposit location is also influenced by the lithostratigraphy of the IPB:
  • Volcanic Sedimentary Complex (VSC): The VSC hosts most of the IPB’s massive sulfide deposits. There is a strong spatial association of VMS deposits and dacites and rhyolites, often in effusive/explosive volcanic settings.
  • Felsic Volcanic Centres: The ore deposits are often located in the marginal areas of domes within pumice-rich volcanoclastic units. Lava domes consisting of coherent lithofacies, surrounded by hyaloclastite breccia and autobreccia, are often associated with massive VMS ore while stockworks are more common in brecciated units which likely had greater incipient permeability.
  • Black Shales: In the southern IPB, many VMS deposits are hosted within black shales, which provided a reducing environment for the precipitation of sulfides.
• Lithological contacts: Contacts between different rock types can provide zones of structural weakness that allow for the focusing of mineralizing fluids and sulfide deposition.
• Stratabound nature: The deposits are often stratabound, meaning that they are located within specific layers or strata of the VSC. This is particularly true of the massive sulfide orebodies.
• Orebody Morphology: The IPB orebodies typically exhibit a classic VMS-type morphology, including:
  • Stratabound tabular to lenticular massive upper lens: This is often found at the top of the volcanic sequence.
  • Underlying pervasive veining and sulfide dissemination: These stockwork zones are the feeder zones for the massive sulfides and often associated with multiple concordant faults and fractures.
  • Multiple orebodies: Major mining districts can consist of several interconnected massive orebodies, like Neves Corvo, Riotinto, and Tharsis.
• Deformation Textures: Microscopic and macroscopic deformation textures, such as mylonitization, stretching, and pressure shadows, are common in the IPB. These textures provide evidence of the tectonic activity that affected the ore deposits after their formation.
• Hydrothermal Fluid Pathways: The stockwork zones, characterized by networks of sulfide-rich veins, represent the pathways through which hydrothermal fluids ascended to the seafloor. These zones are critical for the formation of massive sulfide deposits.
• Influence of Magmatism: Magmatic activity, from approximately 375 to 330 Ma, also played a crucial role in the formation of the IPB. This magmatism produced mafic, intermediate, and felsic volcanic and subvolcanic rocks. The heat from these magmatic intrusions drove the hydrothermal systems and influenced the structural evolution of the region. The emplacement of large volumes of mafic magmas created an anomalous geothermal environment.
• Supergene Alteration: Weathering processes can result in supergene enrichment, which is structurally controlled by the underlying mineralization. This enrichment is often exploited for gold, silver, and copper.

In summary, the structural controls on mineralization in the IPB are a complex interplay of regional tectonics, fault systems, lithological variations, and magmatic activity. These factors have collectively influenced the formation, distribution, and morphology of the VMS deposits, making the IPB a unique and highly mineralized region. The structural features such as folds, thrusts, and faults, along with the lithological controls exerted by the VSC and its specific volcanic and sedimentary units, have influenced the localization of the ore deposits and the pathways of hydrothermal fluids. Understanding these structural controls is vital for effective mineral exploration and resource assessment in the IPB.

Geochemistry of the Iberian Pyrite Belt Host Stratigraphy

The Iberian Pyrite Belt (IPB) is characterized by a complex geological history and a diverse range of rock types with distinct chemical compositions. The volcanism of the Volcanic Sedimentary Complex (VSC) is mainly bimodal, with a predominance of felsic rocks over basic rocks.

Volcanic Rock Chemistry

• Felsic rocks, ranging from dacite to high-silica rhyolites, belong to a calc-alkaline series.
  • Rhyolites display moderate Light Rare Earth Element (LREE) enrichment, pronounced negative Europium (Eu) anomalies, and relatively flat to slightly Heavy Rare Earth Element (HREE) enrichment. They also show Nd and Sr enrichment, which is typical of a crustal signature. Their geochemistry suggests they were generated by fractionation and partial melting of amphibolites at low pressure.
  • Dacites are enriched in A_l2O₃, TiO₂, and P₂O₅ and display smaller negative Eu-anomalies compared to most rhyolites.
• Basic rocks include basalts and dolerites.
  • Tholeiitic lavas show a wide range of geochemical characteristics and medium La/Nb (1–2) and Y/Nb (2–7) ratios, similar to recent continental tholeiites. Higher ratios of La/Nb (>2) and Y/Nb (>6) have some affinities to arc-related basalts.
  • Alkaline-affinity basalts display higher TiO₂, P₂O₅, and LREE and lower Y/Nb ratio. They are similar to recent within-plate basalts and are mostly restricted to the western and southern parts of the IPB.
  • Trace element modeling of the basic rocks indicates mixing between E- and N-MORB (mid-ocean ridge basalt) and assimilation of crustal material.
• Andesitic lavas also occur, although they are subordinate on a regional scale. They are spatially and temporally associated with tholeiitic basic lavas and fall into the field of normal calc-alkaline series rocks (K₂O < 2.5 wt %).
• Several periods of volcanism, from 384 to 359 Ma are recognized.

In summary, the IPB is characterized by a bimodal volcanic suite with felsic rocks displaying crustal signatures and basic rocks showing evidence of mantle and crustal mixing. The ore deposits are enriched in sulfide minerals and associated with hydrothermal alteration.

Metallogeny of the Iberian Pyrite Belt

The metallogeny of the IPB is a direct consequence of its unique geological formation. The belt is home to more than 90 known deposits, with some of the most notable being Riotinto, Neves-Corvo, and Aljustrel.

Mineralization

• Deposit Characteristics: The IPB contains approximately 90 VMS deposits, estimated to have contained over 1700 Mt of ore before erosion. About 20% of the total resource has been mined, and 10-15% has been lost to erosion.
• Metal Content: These deposits are rich in base metals, with estimated resources of 14.6 Mt Cu, 34.9 Mt Zn, and 13.0 Mt Pb, plus significant amounts of Ag, Au, and Sn.
• Host Rocks: The deposits are primarily hosted within the Volcanic Sedimentary Complex (VSC), although there are some deposits hosted in black shales, for example, Aznalcóllar and Tharsis.
• Types of Deposits: The deposits are classified as felsic-siliclastic types, with most being of the Zn-Pb-Cu or Zn-Cu-Pb rich types. The deposits can be stratiform polymetallic massive sulfide bodies, semi-massive to disseminated polymetallic pyrite bodies, and stockwork ores. There are also gossan type deposits which can contain elevated gold and silver (for example, part of Riotinto, Cobre Las Cruces and Cobre Las Cruces).
• Ore Minerals: The major minerals in massive ore include pyrite, sphalerite, chalcopyrite, and galena, with cassiterite present at Neves Corvo and the recent discovery of La Romana. These minerals are also found in stockwork ore along with a quartz-chlorite-sericite-carbonate assemblage.
• Zonation: A typical metal zonation pattern includes a Cu-rich stockwork at the base and lower portion of the massive ore, with Zn-Pb massive ore above and extending laterally.
• Age: The deposits are either Strunian (Late Devonian) in the southern IPB or mostly Tournaisian (Early Carboniferous) in the northern IPB.
• Giant Deposits: The IPB includes 9 giant VMS deposits (>100 Mt), including Riotinto, Tharsis, Aznalcóllar and Los Frailes, Masa Valverde, Sotiel-Migollas, and La Zarza in Spain, and Neves Corvo and Aljustrel in Portugal. Three are supergiant deposits (>200 Mt): Río Tinto, Neves Corvo, and Aljustrel.

Alteration

• Hydrothermal Alteration: Hydrothermal alteration is pervasive throughout the IPB, affecting various rock types in both the hanging wall and footwall of the ore deposits.
• Hanging Wall Alteration:
  • Volcanic rocks are altered to sericitic or chloritic-dominated pyrite-bearing rocks.
  • Jaspers are altered to cherts due to hematite reduction to magnetite, and the formation of chlorite, carbonate, pyrite, and Mn silicates.
  • Pelitic sedimentary rocks are commonly veined with chlorite (Mn-rich), sericite, carbonate, barite, and sulfide.
• Footwall Alteration: The footwall often contains stockwork zones characterized by networks of sulfide-rich veins with a quartz-chlorite-sericite-carbonate assemblage.
• Mineralogical Changes: The alteration is marked by mineralogical changes, including:
  • Sericitization, particularly in felsic volcanic rocks.
  • Chloritization, often Mn-rich, in pelitic sediments and altered volcanics.
  • Pyritization, which is widespread.
  • Carbonatization with carbonate minerals present in stockwork and hanging wall alteration.
• Geochemical Trends: Hydrothermal alteration leads to geochemical changes including:
  • Enrichment in metals like Cu, Zn, Pb, Ag, Au and Sn
  • Addition of S, Fe, Mn, and CO2
• Depletion of more mobile elements in altered rocks like Na, K.
• Ore-Forming Fluids: S-, O-, H-, and C-isotope data suggest that ore-forming fluids were primarily modified seawater, with a potential magmatic fluid contribution in some deposits.

Relationship between Mineralization and Alteration

• The alteration is a critical process for the formation of VMS deposits.
• The spatial distribution of alteration zones and ore deposits is closely linked, with massive ore found at the top of felsic effusive units and stockworks in autoclastic and pyroclastic breccias.
• Alteration patterns serve as important guides in the exploration for new ore deposits.

In summary, the IPB’s base metal deposits exhibit a complex interplay between mineralization and hydrothermal alteration. The alteration is characterized by the transformation of volcanic rocks into sericitic or chloritic assemblages, the alteration of jaspers to cherts, and the veining of pelitic sediments, all of which are closely associated with the deposition of sulfide minerals. The distribution of these alteration zones, along with the geochemical changes, are key to understanding the economic potential of the region.

Major Base Metal Deposits of the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB) is known for its numerous volcanogenic massive sulfide (VMS) deposits, including several giant and supergiant deposits. These deposits vary in size, metal content, and grades. It is typical for the VMS deposits in the IPB to occur in clusters.

Here’s a summary of major deposits in the IPB, with details on their tonnages and grades:

Giant and Supergiant Deposits

• Riotinto (Spain): This is a supergiant deposit, with original tonnages around 2500 million tons of mineralized rock. About a fifth of this was massive sulfides with an average content of 45% S, 40% Fe, 0.9% Cu, 2.1% Zn, 0.8% Pb, 0.5 g/t Au and 26 g/t Ag.
• Neves Corvo (Portugal): Another supergiant deposit, with estimated massive sulfide resources of >300 Mt, including about 150 Mt of polymetallic massive sulphides. The deposit also contains significant tin mineralization, largely cassiterite. In 2020, the copper ore, which is the principal exploited ore type, comprised 31 Mt at 8% Cu, 0.2% Pb, 1.4% Zn, while the polymetallic complex sulphide mineralisation (Zinc ore) contained a further 33 Mt at 0.46% Cu, 1.13% Pb, 6.72% Zn, 40 g/t Ag. The tin ore-bodies zone contained 2.9 Mt at 2.4% Sn, 13.4% Cu, 1.3% Zn, 1 g/t Ag.
  • Ore Reserves – copper ore (1.6% Cu cut-off): Proven + Probable – 25.09 Mt at 2.1% Cu, 0.2% Zn, 0.2% Pb, 31 g/t Ag.
  • Mineral Resources – copper ore: Measured – 6.985 Mt at 3.4% Cu, 0.8% Zn, 0.3% Pb, 44 g/t Ag. Indicated – 51.023 Mt at 2.1% Cu, 0.8% Zn, 0.3% Pb, 34 g/t Ag. Inferred – 12.923 Mt at 1.6% Cu, 0.8% Zn, 0.3% Pb, 34 g/t Ag.
  • Ore Reserves – Zinc ore Proven + Probable – 24.774 Mt at 0.3% Cu, 7.5% Zn, 1.8% Pb, 80 g/t Ag.
  • Mineral Resources – Zinc ore: Measured – 10.660 Mt at 0.3% Cu, 7.8% Zn, 1.8% Pb, 66 g/t Ag. Indicated – 57.742 Mt at 0.3% Cu, 6.7% Zn, 1.4% Pb, 61 g/t Ag. Inferred – 4.071 Mt at 0.4% Cu, 5.7% Zn, 1.6% Pb, 64 g/t Ag.
• Aljustrel (Portugal): Another supergiant deposit, with massive sulfide resources of >200 Mt. It consists of 6 deposits: Feitais, Moinho, São João, Estação, Algares and Gavião, with the Feitais being the biggest of all with 55 Mt of ore. The average grades of these deposits comprising the Aljustrel complex are approximately 3.4% zinc, 1.2% lead, 0.8% copper, 36 grams per ton (g/t) silver, and 1 g/t gold.
• Tharsis (Spain): The Tharsis mining district comprises 16 massive sulfide lenses with original reserves around 133 million tons. The biggest deposit includes the Filón Norte, San Guillermo and Sierra Bullones ore bodies, with a minimum original tonnage of 88 million tons with 46.5% sulphur, 2.7% zinc and lead, and 0.7% copper.

The estimated resources and grades in the seventies at Tharsis cluster deposits are 115Mt at 0.5%Cu, 0.6%Pb, 2.7%Zn. The deposits are hosted in back shales.

Among the resources exploited were copper, silver, gold and pyrite, which was sold for the production of sulphuric acid. The most important and recent mines are those of Filón Sur (Ag and Au) and Filón Norte (pyrite), both of which are open-pit mines, which ceased activity towards the end of the 20th century.

Recent exploration has identified the extension of mineralization at depth, revealing substantial mineral resources totaling 120.6 Mt in the JORC category, with 79% classified as Measured and Indicated Resources. Additionally, 8.5 Mt of Stockwork-type ore, containing notable amounts of gold and cobalt, has been identified, though it has not yet been factored into the economic model.

• Aznalcóllar-Los Frailes (Spain): These are two stratabound lenses of massive sulfides with total reserves of 161Mt at 0.4%Cu, 1.4%Pb, 2.7%Zn. The Aznalcóllar deposit is hosted in black shales and largely exhausted, whereas Los Frailes deposit is hosted in volcanic rocks (massive dacite) and still has more than 70 Mt to be mined at 0.3%Cu, 2%Pb, 4%Zn grades. Strong ore zonation is present with copper in the footwall and zinc and lead in the hanging wall.
• Masa Valverde (Spain): This VMS deposit was discovered in 1990 and has total resources of >90 Mt at 0.62% Cu, 1.3% Zn, 0.62% Pb, 0.61g/t Au and 29 g/t Ag. It is hosted in volcanic rocks.
• Sotiel-Migollas (Spain): This is another example of a giant VMS deposit with >130 Mt consisting of two bodies – Sotiel and Migollas, primary hosted in black shales. Migollas had original resources of >57 Mt at 0.88% Cu, 1.12% Pb, 2.23% Zn, whereas Sotiel had >75Mt at 0.56% Cu, 1.34% Pb, 3.16% Zn, 24 g/t Ag and 0.21 g/t Au.
• La Zarza (Spain): This is another of the 9 giant VMS deposits within the IPB. It is a stratiform orebody with the upper and middle parts of the pyritic orebody are zinc- and lead-rich, whereas the lower part is copper-rich. The deposit had an initial resource of 161 Mt at 1.24% Cu, 1.9% Pb, 2.9% Zn, 47 g/t Ag, and 1.79 g/t Au in 1981.

Other Notable Deposits

• Aguas Teñidas (Spain): This is a large VMS deposit with >65 Mt of Cu and Pb-Zn ore and is considered to have good exploration potenital.
• Magdalena (Spain): This VMS with >43 Mt Cu and Pb-Zn ore was only discovered in 2013. It reports some high-grade Cu grades.
• Las Cruces (Spain): This is a world-class VHMS deposit (>30 Mt) with initial reserves of > 17 Mt grading 5.8% Cu in the secondary enrichment zone and 36.6Mt grading 1.13% Cu, 0.97% Pb, 2.14% Zn and 25.4 g/t Ag in the primary sulfide orebody. This deposit has two types of gossans – a red gossan which is the typical gossan for the region with hematite, goethite and low gold content, and black gossan which has siderite, galena and higher gold content.
• Lousal (Portugal): VHMS deposit (>30 Mt).
• S. Domingos (Portugal): VHMS deposit (>30 Mt).
• Concepción (Spain): VHMS deposit (>30 Mt).
• La Romanera (Spain): VHMS deposit (>30 Mt).
• San Miguel (Spain): This deposit is in the northern zone of the IPB.
• Soloviejo (Spain): This is a significant manganese deposit VMS deposit. It is the largest of a cluster of smaller Mn deposits.

General Ore Grades

• The average grade of all VMS deposits in the IPB is 45% S, 40% Fe, 1.3% Cu, 2.0% Zn, 0.7% Pb, 26 g/t Ag and 0.5 g/t Au.

Commercial Mining Operations – Status Update

Major Mines and Operating Companies in the Iberian Pyrite Belt (IPB)

Minas de Riotinto (Spain)

• Operator: Atalaya Mining
• Resources: Copper, with minor gold and silver by-products
• Overview: One of the oldest and most iconic mining sites in the IPB, Minas de Riotinto has been in operation since ancient times. The current operations focus on open-pit mining and processing of copper ores, with significant investment in modernizing facilities and increasing production capacity.

Neves-Corvo (Portugal)

• Operator: Lundin Mining
• Resources: Copper, tin, zinc, and lead, with minor silver
• Overview: A key underground mine in the IPB, Neves-Corvo is a world-class producer of copper and zinc. Lundin Mining continues to expand operations, including the development of the Zinc Expansion Project to boost output and extend the mine’s life.

Aguas Teñidas (Spain)

• Operator: Sandfire Resources (acquired from MATSA)
• Resources: Copper, zinc, and lead
• Overview: Part of the MATSA mining complex, Aguas Teñidas is an underground mine employing modern mining and processing technologies.

Magdalena Mine (Spain)

• Operator: Sandfire Resources (part of MATSA)
• Resources: Copper, zinc, and lead
• Overview: Another critical part of the MATSA complex, Magdalena Mine is a modern underground operation with advanced ore processing capabilities.

Sotiel (Spain):

• Operator: Sandfire Resources (acquired from MATSA)
• Resources: Copper, zinc, and lead
• Overview: Part of the MATSA mining complex, Sotiel is an underground mine employing modern mining and processing technologies.

Aljustrel (Portugal):

• Operator: Almina – Minas do Alentejo
• Resources: Zinc, lead, and copper
• Overview: The Aljustrel mine, an underground operation, has experienced several cycles of activity and closure over the years.

Las Cruces (Spain)

• Operator: First Quantum Minerals
• Resources: Copper
• Overview: This open pit mine is exploiting a high-grade supergene copper orebody, Las Cruces employs hydrometallurgical processes for copper cathode production. The mine has a significant environmental management program due to its location near sensitive ecosystems. It also comprises a primary sulfide orebody to be explored in the near future.

São Domingos (Portugal):

• Operator: Currently inactive
• Resources: Historical producer of copper and sulfur
• Overview: One of the oldest mines in the region, São Domingos played a pivotal role in the 19th-century mining boom. Although currently inactive, it remains of historical and geological significance.

Tharsis (Spain):

• Operator: Tharsis Mining
• Resources: Copper, zinc, and sulfur
• Overview: Tharsis has a rich mining heritage dating back to Roman times. Recent efforts focus on exploring opportunities for reactivating mining operations.

Reflections on Exploration Implications

The Iberian Pyrite Belt (IPB) presents significant opportunities for mineral exploration and understanding the geological and structural controls is crucial for effective targeting. The following points summarize exploration considerations:

Volcanic Setting and Lithological Controls

• Volcanic-Sedimentary Complex (VSC): The VSC is the primary host for massive sulfide deposits.
• Felsic Volcanic Rocks: Massive sulfide deposits are often associated with felsic volcanic rocks, particularly dacites and rhyolites. The spatial relationship of VHMS deposits with these rocks, especially in effusive/explosive volcanic settings, is an important exploration guide.
• Rhyolitic Domes: Exploration should target the marginal areas of rhyolitic domes, where massive sulfides are commonly found in pumice-rich volcanoclastic rocks. Lava domes with surrounding hyaloclastite and autobreccia should also be targeted, as massive ore is often found at the top and stockwork zones in the brecciated units.
• Black Shales: In the southern IPB, black shales host many VMS deposits. These provide a reducing environment for sulfide precipitation.
• Lithological Contacts: Lithological contacts can be zones of structural weakness. These contacts are key for exploration as they often focus mineralizing fluids and sulfide deposition.
• Stratabound Nature: Deposits are frequently stratabound, which means they occur within specific layers of the VSC. This can help focus exploration efforts on favorable stratigraphic horizons.

Structural Controls

• Folds and Thrusts: The IPB is characterized by NW-SE trending folds and SW-verging thrusts. These structures influence the location of ore deposits, so understanding the structural framework is important for exploration.
• Fault Systems: Faults, especially late Variscan strike-slip faults trending N-S to NNW-SSE or NE-SW to ENE-WSW, can be pathways for hydrothermal fluids and should be targeted during exploration.
• Fracture Systems: Fracture systems that serve as conduits for hydrothermal fluids are critical for forming stockwork zones and massive sulfide bodies.
• Transpressional Tectonics: The transpressional regime led to lower crustal decoupling and intrusion of deep mafic sills that played a role in metallogenesis and should be considered in exploration.
• Remobilization Zones: Exploration should consider areas where Variscan deformation may have been more intense resulting in remobilization of metals, potentially leading to high-grade ore shoots. This may include shear zones in deposits like Aguas Teñidas and Magdalena.

Hydrothermal Alteration

• Alteration Halos: Intense hydrothermal alteration halos in the footwall of massive sulfide orebodies are important exploration indicators. Chloritization and sericitization are common features.
• Zoning: The alteration zoning, progressing from sericite in the outer zones to chlorite in the core of the hydrothermal systems, can be used to vector towards ore deposits.
• Silicification and Carbonatization: These alteration types are associated with hydrothermal activity and can indicate proximity to ore zones.
• Geochemical Vectors: The Fe/(Fe+Mg) ratio in chlorite and the (Ba+K)/Na ratio in muscovite (sericite) can serve as criteria for evaluating the intensity of alteration and can be used as vectors to mineralization.

Mineralization Style

• Stockwork Zones: Exploration should focus on areas with stockwork zones, characterized by sulfide-rich vein networks that channel hydrothermal fluids.
• Massive Sulfide Bodies: The search should include areas with stratiform massive sulfide bodies, often found at the top of volcanic sequences, as well as underlying zones of veining and sulfide dissemination.
• Multiple Orebodies: Major mining districts can consist of several interconnected massive orebodies (e.g., Neves Corvo, Riotinto, Tharsis). Exploration should consider the potential for multiple, interconnected deposits – clusters.

Magmatic Activity

• Bimodal Magmatism: The IPB is characterized by bimodal magmatism (felsic and mafic rocks), however, intermediate (andesitic) rocks are also present. Their role in ore genesis needs to be further studied.
• Deep-Seated Magmas: The rise of deep-seated magmas, associated with crustal thinning, were likely instrumental in the evolution of the hydrothermal systems. Areas with evidence, including regional geophysical evidence) of such magmatic activity should be considered in exploration.

Fluid Sources

• Modified Seawater: Hydrothermal fluids are often derived from seawater that has been modified by interaction with volcanic and sedimentary rocks.
• Magmatic Fluids: In some cases, magmatic fluids may contribute to mineralization (e.g., the Sn-Cu mineralization at Neves Corvo). Understanding the nature of the hydrothermal fluids can help with exploration.

Supergene Enrichment

• Gossans: Exploration should consider areas with gossans (weathered ore deposits) and supergene enrichment. These are typically enriched in Au-Ag and Cu.
• Redox Zones: The redox transition zone, where Cu is concentrated, is another exploration target, although not as extensively represented in all IPB deposits.

Regional Heterogeneity

• Spanish vs. Portuguese IPB: The Spanish part of the IPB has a higher density of deposits due to greater VSC outcrops. Exploration in the Portuguese sector may benefit from improved techniques and new exploration models.

In conclusion, mineral exploration in the IPB should integrate a comprehensive understanding of the lithological, structural, hydrothermal, and magmatic controls on mineralization. Geochemical mapping, combined with geological and geophysical data, is crucial for identifying new exploration targets and for understanding the complex ore-forming processes in this world-class metallogenic province.

Summary of Recent Discoveries in the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB), spanning southwestern Spain and southern Portugal, continues to be a focal point for mineral exploration, yielding significant new discoveries and advancements. Recent developments include:

Emerita Resources’ Nuevo Tintillo Project (Spain)

• Discovery: Emerita Resources identified new gold and silver-rich gossan zones approximately 1.5 km northwest of the historic Santa Flora copper mine. These zones feature outcropping gossan and siliceous breccias over a 400-meter strike length. Initial sampling revealed anomalous gold and silver values, indicating potential for substantial mineralization.

Pan Global Resources’ La Romana and Cañada Honda Discoveries (Spain)

• Discovery: Pan Global Resources reported significant copper mineralization at the La Romana and Cañada Honda targets. These discoveries are characterized by near-surface copper mineralization, with ongoing exploration efforts to delineate the extent and grade of the deposits.

Ascendant Resources’ Lagoa Salgada Project (Portugal)

• Advancement: Ascendant Resources initiated pre-feasibility stage metallurgical testwork at the Lagoa Salgada Project to confirm the potential for achieving standard recoveries comparable to other producers in the IPB. The project aims to combine resources from the North and South Zones, potentially leading to a larger resource base and extended mine life.

Emerita Resources’ Iberian Belt West Project (Spain)

• Advancement: Emerita Resources conducted Phase 2 metallurgical testing at the Iberian Belt West Project, focusing on the La Romanera and La Infanta deposits. The results indicated that copper, lead, and zinc concentrates could be produced at commercial grades, with base metal recoveries exceeding those of active mines in the IPB. This advancement enhances the project’s viability and economic potential.

References and Further Reading

This compilation of references should provide a solid foundation for further research and understanding of the Iberian Pyrite Belt.

Iberian Pyrite Belt (IPB) Overviews and General Studies

• Almodóvar, G.R., Castro, J.A., Sobol, F. and Toscano, M. (1997). Geology of the Riotinto Ore Deposits, Geology and VMS deposits of the Iberian Pyrite Belt. SEG Fieldbook Series, Society Economic Geologists, Volume 27, p. 165-172.
• Barriga, F.J.A.S. (1990). Metallogenesis in the Iberian Pyrite Belt. In: Dallmeyer, R.D., Martínez García, E., (eds.). Pre-Mesozoic Geology of Iberia. Berlin, Springer-Verlag, p. 369-379.
• IGME (1982). Síntesis Geológica de la Faja Pirítica del SO de España. IGME, Madrid. 106 pp.
• Leistel, J.M., Marcoux, E., Thieblemont, D., Quesada, C., Sanchez, A., Almodovar, G.R., Pascual, E., and Saez, R. (1998). The volcanic-hosted massive sulphide deposits of the Iberian Pyrite Belt. Review and preface to the special issue. Mineralium Deposita, v. 33, p. 2-30.
• Sáez, R.; Almodóvar, G.R.; Pascual, E. (1996). Geological constraints on massive sulphide genesis in the Iberian Pyrite Belt. Ore Geology Reviews, 11, 429-451.
• Tornos, F., Barriga, F., Marcoux, E., Pascual, E., Pons, J.M., Relvas, J., Velasco, F. (2000). The Iberian Pyrite Belt. In Large, R., Blundell, D. (eds.). Database on global VMS districts: CODES-GEODE, p. 19-52.
• Strauss, G. K., & Madel, J. (1974). Geology of massive sulphide deposits in the Spanish-Portuguese Pyrite Belt. Geol Rundsch, 63, 191–211.
• Sáez, R.; González, F.; Donaire, T.; Toscano, M.; Yesares, L.; de Almodóvar, G.R.; Moreno, C. (2024). Updating Geological Information about the Metallogenesis of the Iberian Pyrite Belt. Minerals 2024, 14, 860

Geology, Stratigraphy, and Tectonics

• Carvalho, D., Barriga, F.J.A.S., and Munha, J. (1999). Bimodal siliciclastic systems – the case of the Iberian Pyrite Belt. In: Barrie, C.T. and Hannington, M. D. (Eds.), Volcanic-associated Massive Sulfide Deposits: Processes and Examples in Modern and Ancient Settings, Reviews in Economic Geology, vol. 8 , SEG, p. 375-408.
• Moreno, C. (1993). Post volcanic Paleozoic of the Iberian Pyrite Belt: An example of basin morphologic control on sediment distribution in a turbidite basin. Journal of Sedimentary Research, 63, 1118–1128.
• Quesada, C. (1991). Geological constraints on the Paleozoic tectonic evolution of tectonostratigraphic terranes in the Iberian Massif. Tectonophysics, 185, 145–225.
• Silva, J. B., Oliveira, J. T., Ribeiro, A. (1990). Structural Outline, South Portuguese Zone. In R. D. Dallmeyer, E. Martínez García (Eds.) Pre-Mesozoic Geology of Iberia, Springer-Verlag, pp. 348–362.
• Yesares, L., Saéz, R., Nieto, J. M., Ruiz de Almodovar, G., Gómez, C., & Escobar, J. M. (2015). The Las Cruces deposit, Iberian Pyrite Belt, Spain. Ore Geology Reviews, 66, 25–46.
• Mitjavila, J., Martí, J., & Soriano, C. (1997). Magmatic evolution and tectonic setting of the Iberian Pyrite Belt volcanism. Journal of Petrology, 38, 727–755.
• Munhá, J., Riberiro, A., Fonseca, P., Oliveira, J. T., Castro, P. & Quesada, C. (1989). Accreted terranes in Southern Iberia: Beja-Acebuches opjiolite and related oceanic sequences. In 28th International Geology Congress, Washington, USA. Abstract with programs, 2 (p. 481–482).

Ore Genesis and Mineralization

• Almodóvar, G.R., Sáez, R., Pons, J.M., Maestre, A., Toscano, M., Pascual, E. (1998). Geology and genesis of the Aznalcóllar massive sulphide deposits, Iberian Pyrite Belt, Spain. Mineralium Deposita, 33: 111-136.
• Barriga, F.J.A.S., Fyfe, W.S. (1988). Giant pyritic base-metal deposits: The example of Feitais (Aljustrel, Portugal). Chemical Geology, 69: 331–343.
• Sáez, R., Pascual, E., Toscano, M., Almodóvar, G.R. (1999). The Iberian Type of volcano-sedimentary massive sulphide deposits. Mineralium Deposita, 34, 549–570.
• Tornos, F., Solomon, M., Conde, C., Spiro, B.F. (2008). Formation of the Tharsis massive sulfide deposit, Iberian Pyrite Belt: Geological, lithogeochemical, and stable isotope evidence for deposition in a brine pool. Economic Geology, 103, 185–214.
• Almodóvar, G. R., Yesares, L., Sáez, R., Toscano, M., González, F., & Pons, J. M. (2019). Massive sulfide ores in the Iberia Pyrite Belt: Mineralogical and Textural evolution. Minerals, 9(11), 653.

Hydrothermal Alteration and Fluid Studies

• Barriga, F.J.A.S., Kerrich, R. (1984). Extreme 18O-enriched volcanics and 18O-evolved marine water, Aljustrel, Iberian Pyrite Belt: Transition from high to low Rayleigh number convective regimes. Geochimica et Cosmochimica Acta, 48: 1021-1031.
• Inverno, C.M.C., Solomon, M., Barton, M.D., Foden, J. (2008). The Cu-stockwork and massive sulfide ore of the Feitais volcanic-hosted massive sulfide deposit, Iberian Pyrite Belt, Portugal: A mineralogical, fluid inclusion, and isotopic investigation. Economic Geology, 103: 241-267.
• Munhá, J., Barriga, F.J.A.S., Kerrich, R. (1986). High 18O ore-forming fluids in volcanic hosted base metal massive sulphide deposits: Geologic, 18O/16O, and D/H evidence for the Iberian Pyrite Belt; Crandon, Wisconsin; and Blue Hill, Maine. Economic Geology, 81, 530-552.
• Relvas, J.M.R.S., Barriga, F.J.A.S., Longstaffe, F. J. (2006b). Hydrothermal alteration and mineralization in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal: II. Oxygen, hydrogen, and carbon isotopes. Economic Geology, 101: 753-790.
• Sánchez-España, J., Velasco, F., Boyce, A.J., Fallick, A.E. (2003). Source and evolution of ore-forming hydrothermal fluids in the northern Iberian Pyrite Belt massive sulphide deposits (SW Spain): Evidence from fluid inclusions and stable isotopes. Mineralium Deposita, 38: 519-537.

Geochronology and Isotope Studies

• Barrie, C.T., Amelin, Y., Pascual, E. (2002). U-Pb geochronology of VMS mineralisation in the Iberian Pyrite Belt. Mineralium Deposita, 37: 684-703.
• Mathur, R.; Ruiz, J.; Tornos, F. (1999). Age and sources of the ore at Tharsis and Rio Tinto, Iberian Pyrite Belt, from Re-Os isotopes. Mineralium Deposita, 34, 790–793.
• Munhá, J., Relvas, J.M.R.S., Barriga, F.J.A.S., Conceição, P., Jorge, R.C.G.S., Mathur, R., Ruiz, J., Tassinari, C.C.G. (2005). Os isotope systematics in the Iberian pyrite belt. In: Mao, J., Bierlein, F.P., (eds.). Mineral deposit research: Meeting the global challenge, v. 1, Proceedings of the 8th Biennial SGA Meeting, Beijing, China, August 2005: Berlin, Germany, Springer-Verlag, p.: 663-666.
• González, F., Moreno, C., Sáez, R., Clayton, J. (2002). Ore genesis age of the Tharsis Mining District, Iberian Pyrite Belt: a palynological approach. Journal of the Geological Society, 159, 229-232.
• Pascual, E., Maestre, A., Pons, J. M., Sáez, R., Almodovar, G. R., & Toscano, M. (1996). Geoquímica de los halos de alteración hidrotermal relacionados com los yacimientos de sulfuros mas-sivos de Aznalcóllar-Los Frailes: Criterios de evaluación de la intensidad de alteración. Boletin Geológico y Minero., 107(5), 551–557.
• Nieto, J.M.; Almodóvar, G.R.; Pascual, E.; Sáez, R.; Jagoutz, E. (1999). Estudio isotópico con el sistema Re-Os de las mineralizaciones de sulfuros de la Faja Pirítica Ibérica. Geogaceta, 27, 181–184.

Specific Deposit Studies

• Barrett, T.J.; Dawson, G.L.; MacLean, W.H. (2008). Volcanic stratigraphy, alteration, and seafloor setting of the Paleozoic Feitais massive sulfide deposit, Aljustrel, Portugal. Economic Geology, 103, 215–239.
• Gaspar, O.C. (2002). Mineralogy and sulfide mineral chemistry of the Neves-Corvo ores, Portugal: Insight into their genesis. Canadian Mineralogist, 40: 611-636.
• Ruiz, C.; Arribas, A.; Arribas, A., Jr. (2002). Mineralogy and geochemistry of the Masa Valverde blind massive sulphide deposit, Iberian Pyrite Belt (Spain). Ore Geology Reviews, 19, 1–22.
• Oliveira, D.P.S.; Matos, J.X.M.; Rosa, C.J.P.; Rosa, D.R.N.; Figueiredo, M.O.; Silva, T.P.; Guimarães, F.; Carvalho, J.R.S.; Pinto, Á.M.M.; Relvas, J.R.M.S.; et al. (2011). The Lagoa Salgada Orebody, Iberian Pyrite Belt. Economic Geology, 106, 1111–1128.
• Yesares, L.; Sáez, R.; Nieto, J.M.; Almodóvar, G.R.; Gómez, C.; Escobar, J.M. (2015). The Las Cruces deposit, Iberian Pyrite Belt, Spain. Ore Geol. Rev., 66, 25–46.

Other References

• Pinedo Vara, I. (1963). Piritas de Huelva. Summa: Madrid, Spain.
• Large, R.R. (1992). Australian volcanic-hosted massive sulfide deposits: Features, styles, and genetic models. Economic Geology, 87: 471-510.
• Franklin, J.M.; Gibson, H.L.; Galley, A.G.; Jonasson, I.R. (2005). Volcanogenic massive sulfide deposits. In Economic Geology 100th Anniversary Volume; Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J., Richards, J.P., Eds.; Economic Geology: New Haven, CT, USA; pp. 523–560.
• Relvas, J.M.R.S., Tassinari, C.C.G., Munhà, J., Barriga, F.J.A.S. (2001). Multiple sources for ore-forming fluids in the Neves Corvo VHMS deposit of the Iberian Pyrite Belt (Portugal): strontium, neodymium and lead isotope evidence. Mineralium Deposita, 36: 416-427.