Europe's rare earth element resource potential: an overview of REE metallogenetic provinces and their geodynamic setting

Security of supply of a number of raw materials is of concern for the European Union; foremost among these are the rare earth elements (REE), which are used in a range of modern technologies. A number of research projects, including the EURARE and ASTER projects, have been funded in Europe to investigate various steps along the REE supply chain. This paper addresses the initial part of that supply chain, namely the potential geological resources of the REE in Europe. Although the REE are not currently mined in Europe, potential resources are known to be widespread, and many are being explored. The most important European resources are associated with alkaline igneous rocks and carbonatites, although REE deposits are also known from a range of other settings. Within Europe, a number of REE metallogenetic belts can be identified on the basis of age, tectonic setting, lithological association and known REE enrichments. This paper reviews those metallogenetic belts and sets them in their geodynamic context. The most well-known of the REE belts are of Precambrian to Palaeozoic age and occur in Greenland and the Fennoscandian Shield. Of particular importance for their REE potential are the Gardar Province of SW Greenland, the Svecofennian Belt and subsequent Mesoproterozoic rifts in Sweden, and the carbonatites of the Central Iapetus Magmatic Province. However, several zones with significant potential for REE deposits are also identified in central, southern and eastern Europe, including examples in the Bohemian Massif, the Iberian Massif, and the Carpathians

Palladium, platinum and gold concentration in porphyry copper systems of Greece and their genetic significance

Compilation of new and published data on precious metal and associated trace-element contents in mineralized porphyry copper intrusions of Greece indicates that the Pd content in the potassic-propylitic zone of the Skouries deposit is relatively high, ranging between 60 and 200 ppb (average 110 ppb), whereas in the porphyry copper intrusions of Gerakario and Pontokerasia, it is very low (3 ppb Pd). The oxidized zone of Fissoka (OP-65) exhibits low Pd and Cu contents, but higher Au, Te, As, Pb and Zn contents. The Pt content is much lower than Pd in the porphyry copper intrusions studied. The Pd/Pt ratio in the Skouries deposit ranges from 9 to 60, while it is much lower (< 2) in the mineralized samples from Fissoka, Gerakario and Pontokerasia. A decrease of the Pd content and Pd/Pt ratio with increasing Te, As, Pb and Zn content may indicate that the Pd distribution in porphyry copper systems is effected by the evolution of the magma-hydrothermal system. Also, mineralogical and geochemical data on the Skouries deposit, coupled with textural relations between base metal sulphides, PGM and Au-Ag tellurides, indicate that the main Pd-bearing mineral, merenskyite, is associated with the vein-type chalcopyrite or bornite, and was deposited during the main stage of mineralization. The high magmatic oxidation state and the magmatic features of the hydrothermal system (limited participation of meteoric portion) in the Skouries intrusion may be a strong control of its Pd potential. Assuming that Pd is mainly associated with chalcopyrite in the porphyry copper deposits, the calculated Pd (from measured Pd) contents in chalcopyrite (average 3300 ppb Pd) are relatively high, and comparable to that in the chalcopyrite concentrate made after the processing of large composite drill-hole samples (2400 ppb Pd to 21 wt.% Cu). It is considered to be an encouraging economic factor for Pd as a by-product, probably along with Au, although the main product is Cu. (C) 2000 Elsevier Science B.V. All rights reserved

Trace element distribution in magnetite separates of varying origin: Genetic and exploration significance

Magnetite is a widespread mineral, as disseminated or massive ore. Representative magnetite samples separated from various geotectonic settings and rock-types, such as calc-alkaline and ophiolitic rocks, porphyry-Cu deposit, skarn-type, ultramafic lavas, black coastal sands, and metamorphosed Fe–Ni-laterites deposits, were investigated using SEM/EDS and ICP-MS analysis. The aim of this study was to establish potential relationships between composition, physico/chemical conditions, magnetite origin, and exploration for ore deposits. Trace elements, hosted either in the magnetite structure or as inclusions and co-existing mineral, revealed differences between magnetite separates of magmatic and hydrothermal origin, and hydrothermal magnetite separates associated with calc-alkaline rocks and ophiolites. First data on magnetite separates from coastal sands of Kos Island indicate elevated rare earth elements (REEs), Ti, and V contents, linked probably back to an andesitic volcanic source, while magnetite separated from metamorphosed small Fe–Ni-laterites occurrences is REE-depleted compared to large laterite deposits. Although porphyry-Cu deposits have a common origin in a supra-subduction environment, platinum-group elements (PGEs) have not been found in many porphyry-Cu deposits. The trace element content and the presence of abundant magnetite separates provide valuable evidence for discrimination between porphyry-Cu–Au–Pd–Pt and those lacking precious metals. Thus, despite the potential re-distribution of trace elements, including REE and PGE in magnetite-bearing deposits, they may provide valuable evidence for their origin and exploration. © 2019 by the authors. Licensee MDPI, Basel, Switzerland

Geochemistry and origin of the asimotrypes carbonate-hosted mesothermal gold deposit, Pangeon Mt., N. Greece

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Geochemical and mineralogical characteristics of Fe-Ni- and bauxitic-laterite deposits of Greece

Contiguous vertical sample profiles from Ni-laterite deposits with in situ features (Kastoria, Profitis Ilias, and Tsouka) and allochthonous Ni- and bauxitic-laterite deposits in contact with basement limestone (Nissi) and bauxitic-laterites lying on peridotite (Parhari) were analyzed for major, trace (including Th and U), rare earth and platinum-group elements (REE and PGE, respectively). In addition, minerals with emphasis to chromite grains found as residual components in these laterites, inherited from the ophiolitic parent rocks, were analyzed by microprobe. Low Al2O3, TiO2, REE, Th and U contents are common features of the Kastoria, Bitincka and Tsouka deposits. In contrast, elevated REE contents are present in the karst-type bauxitic- and Ni-laterite ores of Nissi and bauxitic-laterites of Parhari. The bauxitic-laterite deposit of Nissi attains REE contents of thousands parts per million in samples from the contact between the lowest part of the bauxitic-laterite and the footwall limestone. Highest contents of Th and U are found in the bauxitic-laterites, with Th ranging from 4 to 28 ppm and U from 4 to 66 ppm. In general, increasing Al contents are accompanied by elevated Ti, REE, Th and U contents at the Parhari and Nissi laterite deposits. Goethite, is the dominant mineral in all Ni-laterite profiles studied, while boehmite co-existing with goethite is common in the bauxitic-laterites at Nissi and Parhari. Goethite exhibits variable Al contents, while the Al/Fe ratio increases towards the top of the profiles. The PGE concentrations are generally low, ranging from less than 100 ppb to a few hundred parts per billion. The lowest values - lower than in the bedrock - were recorded in the saprolite zone. A certain enrichment in Pt (up to 48 ppb), Pd (7 ppb), and Au (16 ppb) is recorded in the reddish altered peridotite overlying the saprolite zone at Profitis Ilias. The Fe-Ni ore overlying the reddish altered peridotite has the highest Os values (14 ppb), Ir (32 ppb), Ru (66 ppb), Rh (20 ppb), Pt (86 ppb), and Pd (186 ppb). Gold contents are below 36 ppb. An increasing Pt/Pd ratio from 3.0 in Fe-Ni-laterites to 6.0 in bauxitic-laterites is apparent. Both whole rock compositions and mineral chemistry of laterites indicate that major controlling factors of the composition of the bauxitic-laterites are the conditions during transportation/deposition of the weathered material and during diagenesis/metadiagenesis stage rather than parent mafic ophiolitic rocks. The comparison between the primary composition of chromite in the saprolite zone and the overlying Fe-Ni ore may provide evidence for the discrimination between Fe-Ni ore linked to in situ weathering and ore derived by transportation to some extent of clastic and chemical material. (C) 2000 Elsevier Science B.V. All rights reserved

A comparison of high-Au massive sulfide ores hosted in ophiolite complexes of the Balkan Peninsula with modern analogues: Genetic significance

Ophiolites of the Balkan Peninsula, of Upper Jurassic to Lower Cretaceous age, extend through the Mirdita zone (Albania) to the Pindos and Othrys complexes southern (Greece), and host massive sulfide deposits of Cu-Zn-(Pb) type. The deposits in Albania are hosted in intermediate to felsic-dominated volcanic successions of considerable thickness. These deposits are associated with ophiolites that were formed during the initial stages of an intra-oceanic westward-dipping subduction zone (arc, fore-arc, back-arc setting), and most closely resemble polymetallic sulfide deposits associated with felsic volcanic rocks at the modern seafloor. The massive sulfide ores are comprised of pyrite, chalcopyrite and lesser amounts of sphalerite, and are characterized by an increasing content of Au, Ag, As, Se, Sb, Mo and Hg from the Othrys to Pindos and Mirdita (Munella) ophiolites. In addition, the concentrations of these elements in both massive sulfide ores and Fe-Cu-Ni-Co type ores are higher in the Pindos compared to those in the Othrys complex. Sulfide mineralization associated with these complexes differs from the majority of Cyprus-type deposits in terms of: (a) host rock-type; (b) mineralogical composition, i.e., the presence of tennantite-tetrahedrite series minerals in the Mirdita sulfide ores, and the selenide clausthalite, hosted exclusively within later stage chalcopyrite and sphalerite intergrowths in the Pindos ores; and (c) their enrichment in Au. Gold in both Pindos and Mirdita ores occurs as submicroscopic gold, including solid solution gold, colloidal gold and surface-bound gold, in arsenian pyrite, chalcopyrite and bornite grains, and rarely as fine-grained electrum. The increasing Au content (up to 15.1 ppm) with decreasing crystal size in fine intergrowths between pyrite and sphalerite may be related to remobilization and re-deposition. However, submicroscopic gold in coarse-grained pyrite of the main mineralization stage (mean concentrations up to 1.01 ppm in the Pindos ores and 0.22 ppm in the Mirdita ones) may be co-precipitated into the structure of arsenian pyrite, reflecting the direct involvement of magmatic volatiles to the ore-forming hydrothermal system rather than recrystallization effects, and in turn the precious metal endowment in the hydrothermal systems. The Mirdita and Pindos massive sulfide ores are comparable to some modern seafloor deposits in terms of their association with andesitic pillow lavas and intermediate to felsic volcanic rocks and their bulk composition and mineralogy. © 2007 Elsevier B.V. All rights reserved

Platinum-group minerals and tetraauricupride in ophiolitic rocks of Skyros island, Greece

In the serpentinized ophiolitic rocks from Skyros island, two distinct assemblages of base metal sulphides (BMS) and platinum-group minerals (PGM) occur. The first (early) generation is associated with chromitites which are enriched in platinum-group elements (PGE). The highest values were recorded in samples from Achladones (Ru 1210, Ir 780, Os 630, Rh 228, Pt 208, Pd 22; all values in ppb). Mineral inclusions in chromite consist of Ni-Fe sulphides and Os-rich laurite, and crystallized at high sulphur fugacity (fS2) during chromite formation. The second (late) generation is closely associated with Au-rich, PGE-poor magnetite ores which host a complex assemblage of inclusions consisting mainly of graphite, Cu-Fe- and pure Cu sulphides, sperrylite and tetraauricupride. Their accompanying hydrous silicates are Cl-bearing. It is assumed that this mineral assemblage was deposited by hydrothermal processes during serpentinization. © 1992 Springer-Verlag

On the diversity of the PGE content in chromitites hosted in ophiolites and in porphyry-Cu systems: Controlling factors

The present study on the diversity of the platinum-group elements (PGE) content in chromitites and porphyry-Cu deposits from Greece and everywhere (literature data) aims to define factors controlling precious metal enrichment in ophiolite complexes and the unknown Pd and Pt potential in porphyry Cu systems, through an integrated set of mineralogical and geochemical approaches. The PGE content in chromitites associated with ophiolite complexes is commonly low (a few 100 s of ppb). However, a significant PGE-enrichment (up to 10 s of ppm) is a feature of relatively small chromite occurrences, regardless their major element composition. Plots of the Pd/Ir versus normalized Pt/Pt∗ ratios defined separate fields corresponding to various chromitite types. Large chromite deposits exhibit low Pd/Ir values, reflecting low degree of fractionation (primitive magmas), negative (Pt/Pt∗ < 1) Pt/Pt∗ (partial melting of already depleted mantle) and increasing partial melting trend from high-Al towards to high-Cr deposits. The association with hydrous silicates (Cr-bearing hydrogrossular, chlorite and serpentine) and texture features of Os, Ir, Ru-rich (compatible) or IPGE-minerals, coupled with very low Pd/Ir and negative Pt/Pt∗ values were attributed to an origin by partial melting of already depleted mantle and increased partial melting degree, during a subsequent crustal/mantle recycling stage, via fluid-driven processes. Assuming that the increasing Pd/Ir reflects a fractionation trend of parent magma, a significant enrichment in Pt and Pd (incompatible) or PPGE, occurring in small occurrences (either high-Cr or high-Al type) may be a sensitive fingerprint for the orientation in the mantle sequence of the ophiolites and exploration for chromite. Commonly the PGE content in porphyry Cu-Mo-Au deposits is less than 10 ppb. However, elevated (Pd + Pt) contents (over 6 ppm in sulfide-rich samples) are a characteristic feature of certain porphyry Cu-Au alkaline intrusions. Evidence of a favorable tectonic setting (post-collisional) for the origin of porphyry Cu-Au-Pd-Pt-elevated porphyry deposits include elevated (up to hundreds of ppm) contents in Cr, Co, Ni and Re, and elevated 187Os/188Os ratios, reflecting mixing and contribution to the magma composition. The oxidized nature of parent magmas (abundant magnetite) and the evolved mineralized fluid system in porphyry deposits are considered to be critical requirements for the transportation and deposition of sufficient Au and PGE. Elevated Pd, Pt and Au contents in porphyry deposits combined with the association of the major Pd-mineral (merenskyite) with bornite and chalcopyrite (major Cu-minerals) are encouraging economic factors for the contribution to the global (Pd + Pt) production. © 2017 Elsevier B.V

Critical factors controlling Pd and Pt potential in porphyry Cu-Au deposits: Evidence from the Balkan Peninsula

Porphyry Cu-Au-Pd±Pt deposits are significant Au resources, but their Pd and Pt potential is still unknown. Elevated Pd, Pt (hundreds of ppb) and Au contents are associated with typical stockwork magnetite-bornite-chalcopyrite assemblages, at the central parts of certain porphyry deposits. Unexpected high grade Cu-(Pd+Pt) (up to 6 ppm) mineralization with high Pd/Pt ratios at the Elatsite porphyry deposit, which is found in a spatial association with the Chelopech epithermal deposit (Bulgaria) and the Skouries porphyry deposit, may have formed during late stages of an evolved hydrothermal system. Estimated Pd, Pt and Au potential for porphyry deposits is consistent with literature model calculations demonstrating the capacity of aqueous vapor and brine to scavenge sufficient quantities of Pt and Pd, and could contribute to the global platinum-group element (PGE) production. Critical requirements controlling potential of porphyry deposits may be from the metals contained in magma (metasomatized asthenospheric mantle wedge as indicated by significant Cr, Co, Ni and Re contents). The Cr content may be an indicator for the mantle input. © 2014 by the authors; licensee MDPI, Basel, Switzerland