Introduction
Platinum was formally discovered only in 1751, although it was used since the 7th century BC in Egypt. Platinum was originally called “platina” or “little silver” in Spanish, as it was considered a poor-quality by-product of silver mining operations 400 years ago in Colombia. The platinum-group elements (Os, Ir, Ru, Rh, Pd and Pt) or PGEs, which are the most valuable elements, traditionally are associated with mafic-ultramafic complexes, and have been described in a wide range of geotectonic settings. On the basis of their geotectonic environment they can be classified in (a) ophiolites and zoned Alaskan-Ural type (targets of exploration and sources of significant economic platinum placer deposits) emplaced in orogenic zones, (b) layered intrusions, for example the Bushveld Complex (South Africa), the Great Dyke (Zimbabwe) and the Stillwater Complex (USA), characteristic of a cratonic environment, and (c) komatiites which are an important portion of the Archaean greenstone belts. Also, on a variety of criteria, magmatic PGE deposits may be classified into several types. In this review they are classified into two groups, sulphide-poor and sulphide-rich. In the group of the sulphide-poor mineralization belongs the largest known platinum group metal (PGM) deposit in the world, the Bushveld complex in South Africa. The second type contains sulphide deposits, from which Ni, Cu and Co are extracted, the PGE being by products. The majority of the world supply of PGE is produced from magmatic ores derived from basaltic magmas. Major Pt and Pd economic mineralization is hosted in well-defined stratiform reefs of large layered intrusions, as is exemplified by the Bushveld Complex (South Africa), the Great Dyke (Zimbabwe) and the Stillwater Complex (USA) [Lee and Tredoux 1986; Cowden et al. 1986; Barnes and Campbell 1988; Cawthorn 1999; Barnes and Maier 1999, 2002; Cawthorn 1999; Naldrett and Duke 1980; Campbell et al. 1983].
The type of mafic-ultramafic complexes dominated in Greece, belongs to ophiolites associated with orogenetic zones, such as the Balkan-Carpathian system, which is part of the Alpine-Himalayan system, extending from western Europe through Iran and the Himalaya to China and Malaysia. Although chromite is major collector of the PGEs, their content in large chromite deposits, such as the deposits hosted in the Othrys and Vourinos complexes, is relatively (a few hundreds of ppb). However, PGE-enrichment: (a) in all PGE, (b) only in Os, Ir and Ru or (c) in Pt and/or Pd, are a common feature of disseminated chromite and/or relatively small chromite occurrences, of both high-Cr and high-Al type, in the uppermost parts of the mantle and/or in the lowest crust sequence. Examples of PGE-enrichment include the ophiolites of Pindos, Skyros Island and Veria (Greece) [Auge 1985, 1988; Economou et al. 1986; Auge and Legendre 1994; Auge et al. 2005; Konstantopoulou and Economou-Eliopoulos 1991, Economou-Eliopoulos 1996; Economou-Eliopoulos et al. 1999; Ohnenstetter et al. 1999; Economou-Eliopoulos 1996, Kaptiotis et al. 2006, 2009; Prichard et al. 2008; Grammatikopoulos et al. 2009].
Recently, elevated levels of platinum group elements (PGE), particularly Pt, have been reported in sea-floor massive sulfides related to ophiolite complexes indicated that elevated platinum, up to 1000 ppb Pt in an occurrence of brecciated pipeform diabase, underlying the massive ore from the Pindos ophiolite complex [Economou-Eliopoulos et al. 2008]. Elevated levels of Pd and Pt, have been reported in several alkaline porphyry deposits, such as the Skouries porphyry deposit (Greece), Cordillera of British Columbia (Copper Mountain Galore Creek), Allard Stock, La Plana Mountains and Copper King Mine in USA, Elatsite (Bulgaria), Santo Tomas II in the Philippines and elsewhere [Werle et al. 1984, Mutschler et al. 1985, Eliopoulos and Economou-Eliopoulos 1991, Eliopoulos et al. 1995, Tarkian and Koopmann 1995, Tarkian and Stribrny 1999, Economou-Eliopoulos and Eliopoulos 2000, Tarkian et al. 2003; Auge et al. 2005].
This paper focuses on (a) the mineralogical and geochemical characteristics of numerous PGE-sources in Greece, (b) the application of the current state of knowledge on the solubility of PGE in hydrothermal systems, related to ophiolite complexes and porphyry Cu-Mo-Au±Pd±Pt deposits, toward a better understanding of the PGE mineralization in hydrothermal systems (c) the factors controlling precious metal enrichment the PGE mineralization in ophiolite complexes and the unknown Pd and Pt potential in porphyry Cu systems, and (d) the establishment of a probable relationship between the potential in ore deposits and their geotectonic setting at which noble metals become concentrated in Greece.