Conclusions
The platinum-group elements (Os, Ir, Ru, Rh, Pd and Pt) or PGEs, are the most valuable elements in the nature, due to their growing use in advanced technologies and automobile catalyst converters. Also, they provide valuable evidence for the mineralizations associated with ophiolites complexes, such as chromitites and sulfides and the origin of ophiolites themselves, due to differences as far as the geochemical behavior between IPGE (Os, Ir, Ru) and PPGE (Pt , Pd ± Rh), during partial melting in upper mantle and fractionation processes.
The PGE contents in economic chromite deposits such as the Vourinos and Othris ophiolite complexes, which are dominated by high-Cr and high-Al ores, respectively, are low (less than 200 ppb). They are characterized by relatively high IPGE and low PPGE) contents, resulting in PGE-patterns with a negative slope, and low Pd/Ir ratio.
Chromite occurrences in the Pindos complex, which are PPGE-enriched, show smooth sloped to positive slope PGE-patterns, comparable and that of the UG2 in the Bushveld complex and high Pd/Ir ratios. The whole ore PGE content is consistent with the dominated Pt- and Pd-bearing PGM, including Pt–Pd alloys, PGM arsenides and sulfarsenides, sperrylite, which were identified exclusively in the serpentinized matrix of chromitite.
The PPGE enrichment in chromitites towards the petrological moho has been attributed to the presence of only a small amount of immiscible sulfide liquid, and is considered be a sensitive fingerprint for the orientation in the mantle sequence of the ophiolite complexes and hence the exploration for chomite deposits.
The enrichment in IPGE (Os, Ir, Ru), such as the Pindos (Milia), Skyros and Veria in small chromite occurrences, reaching 25 ppm total PGE, may be related to episodes of partial melting and subduction-related crustal recycling, at relatively lower temperatures (800 to 900oC), during a period of deformation, beginning with plastic deformation to brittle deformation in the crust along the permeable shear zones.
The most targeting for PGE locations general in ophiolite compexes may be (a) for the chromitite-IPGM associations exclusively small chromite occurrences along shearing zones of ophiolite complexes, postdating their initial/magmatic PGE deposition, and (b) for PPGE the uppermost parts of the mantle and the lowest crust sequence.
Although the potential for PGE mineralization, associated with such large Cu and Au-Cu porphyry deposits is still unknown, the association of the Pd-telluride, merenskyite, which is the main PGE mineral in porphyry Cu–Au–Pd–Pt deposits, with chalcopyrite and bornite, the obtained recovery percentage (~90%) and the estimated value of the Net Present Value suggest that the recovery of Pd and Pt, as by-products (Cu and Au being the main products), may contribute significantly to the economic attractiveness for certain porphyry-Cu deposits.