## 3 Critical and Rare Metals in Greece
### Platinum Group Elements (PGE)  
An increased worldwide usage of platinum group elements (PGE = Pt, Os, Ir, Pd, Ru, Rh) has been observed during the last decades, due to their unique physical and chemical properties that make them critical to many emerging technologies. Consequently they have become essential commodities and are considered as strategic metals because of their specialized applications in chemical, petroleum, high-tech, electrical, medical, and aerospace industries [19]. They also have important uses in environmentally related technologies, such as automobile catalytic converters and fuel cells. The global reserves of PGE are mainly concentrated in South Africa, followed by Russia and Canada, where they are by-products of nickel processing [19].  
In Greece there are two target mineralization groups that contain elevated PGE grades: Porphyry-type deposits and chromite ores. A significant Pd-Pt enrichment has been determined in the Skouries porphyry Cu-Au deposit of NE Chalkidiki peninsula, in the copper ore, as well as and in the flotation concentrates [44; 45]. The Pd content in the mineralized samples (stockwork veinlets from the potassic alteration and from the oxidation zones) ranges from 45 to 490 ppb and up to 3300 ppb in chalcopyrite concentrates, suggesting that Pd (in the form of the telluride merenskyite) is mainly associated with chalcopyrite [44]. The leaching process of the final concentrate (21 wt % Cu, 22 ppm Au, 2.4 ppm Pd, 0.04 ppm Pt) resulted in the recovery of 96.6% Au, 97.7% Pd and 100% Pt [45]. Since the intended investment in the Skouries deposit focuses on gold and copper mining and metallurgy, the recovery of Pd and Pt has a positive economic potential for a future sustainable development.  
The second target mineralization group for PGE exploration in Greece is associated with the ophiolites of Veria, Pindos and Skyros Island. High PGE concentrations, reaching 25 ppm total PGE's (Os = 7400, Ir = 6020, Ru = 9700, Rh = 310, Pt = 760, Pd = 750, all in ppb) were determined in chromitites hosted in the Veria ophiolites, northern Greece [46; 47]. These elevated PGE contents are associated with a great number (>100) of different PGM grains, mainly Os-Ru-Ir-Fe alloys, reaching 1 mm in size [47]. They are concentrated along a shear zone of strongly brecciated chromite ore. In Korydallos area, Pindos the PGE-mineralization is associated with several PGM grains (Pd-Cu alloys, sperrylite, Pt-Fe-Ni alloys, naldrettite, bismuthotelluride, native Au, _etc._) [48]. The total PGE + Au content in the chromitites with low Cr# chromian spinel is 28 ppm (Pt = 17100, Pd = 7860, Ru = 2100, Rh = 1140, all in ppb) among the highest ever measured in ophiolitic chromitites worldwide, and the highest ever mentioned for chromitites from Greece [48]. It is assumed that a sulfur bearing melt played an important role in scavenging the PGE + Au content of the silicate magma from which chromian spinel had already started to crystallize [48].  
The ophiolitic complexes of Thessaloniki (Triadi, Vassilika) and Chalkidiki (Vavdos, Gerakini-Ormylia) contain relatively low PGE contents (<0.5 ppm) and so they are not of economic significance [49].