Bauxite and Nickel-Cobalt Lateritic Deposits of the Tethyan Belt
Richard Herrington, Nicola Mondillo, Maria Boni, Robert Thorne, Metin Tavlan, 2016. "Bauxite and Nickel-Cobalt Lateritic Deposits of the Tethyan Belt", Tectonics and Metallogeny of the Tethyan Orogenic Belt, Jeremy P. Richards
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Laterites are regoliths developed under tropical to subtropical conditions and are host to key deposit types, notably bauxites (major sources of Al, derived from weathering of aluminosilicate rocks) and Ni-Co laterites (derived from ultramafic rocks). Research on the western Tethys region, where bauxites and Ni-Co laterites developed during the Mesozoic and Cenozoic, probably peaking at the Paleocene-Eocene thermal maximum when geology, paleogeography, and climate were ideal for the deep weathering of favorable lithologies, is reported in this article.
Bauxites were developed on the rocks forming the continental margins to the various branches of the Tethys Ocean and were already forming in the Triassic, whereas the Ni-Co laterites developed on fragments of obducted ophiolite from the Tethys Ocean, which were only uplifted and exposed to weathering after the Jurassic. Residual lateritic bauxites are known in the region but karst bauxites are much more common.
Ni-Co laterites are found as residual profiles, ranging from oxide, to clay-silicate, to hydrous-silicate types, but are also represented by distinctive, extensively redeposited clay-oxide ores. This diversity of styles probably reflects differences in topography and uplift history because the deposits all formed within a similar, restricted climatic time window. The bauxite belt extends from Spain in the west, through the type locality of Les Baux in France, and intermittently through the Balkans, Greece, and Turkey to Iran and beyond. Bauxite resources in Europe constitute around 2% of the world’s current known stock. Significant Ni-Co laterites are found in a more restricted geographic area stretching from Serbia to Turkey.
The bulk of both Al and Ni-Co production currently comes from Greece, today accounting for around 1% of world production of both Ni and bauxite, and with published resources on the order of 650 Mt @ >50% Al2O3; other mines are located in Turkey, Albania, and Kosovo. Ferronickel plants are located in Greece, but also in the Former Yugoslav Republic of Macedonia, and Kosovo. The region has significant potential for the discovery of additional bauxite resources, although they would most likely be karst bauxites, less suited to large-scale mining efforts. Many undeveloped Ni-Co deposits are recorded in the region, with a recent focus to unlock the potential of oxide mineralization using novel hydrometallurgical technologies. Particularly noted is the potential for large low-grade redeposited lateritic Ni-Co-Fe deposits: Mokra Gora in Serbia, for example, has a resource of more than 1 Gt @ 0.7% Ni and 0.05% Co.
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Tectonics and Metallogeny of the Tethyan Orogenic Belt
The Tethyan orogenic belt stretches from the Alps, through the Carpathians and Balkans, Taurides and Caucasus, Zagros, Makran, and Himalayas, to Indochina and into the southwest Pacific Ocean. It represents a complete Wilson Cycle, from opening and closure of the Paleotethys Ocean in the mid-Paleozoic to the Late Triassic, opening of the Neotethys Ocean in the Permian-Early Triassic, and its progressive closure throughout the late Mesozoic and Cenozoic eras. The current state of the orogen includes all stages of convergence from active subduction beneath the Makran and eastern Mediterranean, through advanced continental collision in the Caucasus/Taurides and Zagros, to syn- to postcollisional readjustment in the Carpathians, Balkans, Himalayas, and Indochina (Richards, 2015).
The region has been the focus of significant recent attention from geologists interested both in its tectonic evolution and metallogeny, made possible by increased accessibility to many of the geographic sections of the orogen. Key breakthroughs in understanding its tectonic history have come through improved geochronological techniques and expansion of the database of samples and events dated, combined with more accurate paleogeographic and tectonic models. In parallel, an improved understanding of the subtle relationships between tectonomagmatic and metallogenic processes have refined interpretations that were once based on simplistic assumptions (e.g., that porphyry deposits only form above active subduction zones). Indeed, economic geologists have been among the key drivers of these advances by demanding more accurate and predictive tectonomagmatic models for ore formation that can reliably inform mineral exploration.
Consequently, the Tethyan orogen is now understood to be the best preserved global example of a collisional orogen, where all stages of convergence can be observed in real or recent geological time, and the detailed relationships to ore formation, commonly reflecting tectonic changes measured on submillion-year timescales, can be accurately documented and modeled.
In this volume, we present a selection of papers that showcase this advancement in knowledge, with examples from Eastern Europe to South Asia.Beginning in the Balkans, Knaak et al. (2016) describe the variety of mineral deposits that occur in the emergent worldclass Timok region of eastern Serbia. The origin of the Late Cretaceous Timok Magmatic Complex remains debated, but the authors propose that arc magmatism was focused by dextral transtensional structures, followed by complex structural rearrangement in the Cenozoic. Porphyry Cu-Au deposits, polymetallic replacement deposits, and sedimentary rockhosted Au deposits occur in close spatial, and possibly genetic, relationship to the Late Cretaceous arc rocks. A key contribution of this study is the detailed reconstruction of later Cenozoic fault movements that led to structural dislocation and oroclinal bending, complicating geologic and metallogenic correlations in the region.
- aluminum ores
- Balkan Peninsula
- bauxite deposits
- cobalt ores
- Iberian Peninsula
- metal ores
- nickel ores
- Southern Europe
- Western Europe