Critical Factors Controlling Pd and Pt Potential in Porphyry Cu–Au Deposits: Evidence from the Balkan Peninsula

Abstract

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.

Platinum-group minerals in the Skouries Cu-Au (Pd, Pt, Te) porphyry deposit

“…This study has confirmed that the PGE in Skouries are associated with the main vein stage of Cu deposition in this deposit. This agrees with work by Eliopoulos and Economou-Eliopoulos (1991), Eliopoulos et al (2014), who analysed whole rock samples for PGE content and found the potassic alteration zone to have Pd contents of 60-610 ppb and Pt contents of 5-150 ppb. Earlier work suggested that precious metal tellurides were formed in relatively shallow, cool environments, and that the PGE may have been redistributed during a late hydrothermal event Mutschler et al, 1985).…”

“…7; Sotnikov et al, 2001;Tarkian and Stribrny, 1999). These ratios either reflect the relative PGE contents in the source magma (Economou- Eliopoulos and Eliopoulos, 2000), or the fractionation of PGE in the mineralising fluid (Eliopoulos et al, 2014). PGE-enriched porphyry deposits globally have very similar Au/(Pd + Pt) of ∼90 and Pd/Pt of ∼10 (Fig.…”

“…Kalogeropoulos et al, 1989), however a recent study has shown them to have a trachy-andesitic composition (Siron et al, 2016). They have been suggested as a potential metal source for the Skouries deposit as they are very close in age, and similar units are present within the deposit (Eliopoulos et al, 2014;Siron et al, 2016).…”

“…PGE-enriched porphyry deposits globally have very similar Au/(Pd + Pt) of ∼90 and Pd/Pt of ∼10 (Fig. 7, Augé et al, 2005Augé et al, , 2002Eliopoulos et al, 2014;Eliopoulos and EconomouEliopoulos, 1991;Maier and Bowen, 1996;Steele, 1978;Thompson et al, 2001). However, it is worth noting that the company assay data provided in this study shows no correlation between Au and Pd + Pt (R 2 = 0.01), with an average Au/(Pd + Pt) of 310, meaning that Au grade should not be used as a proxy for PGE grade.…”

“…Palladium partitions strongly into semi-metal melts in the magmatic environment even in the presence of a strong sulphide collector mineral such as pentlandite (Helmy et al, 2007;Holwell and McDonald, 2010). Porphyry systems lack significant pentlandite, removing a potential sulphide host for Pd and increasing the tendency for it to combine with semi-metals in porphyry deposits, rather than be hosted in the sulphides (Eliopoulos et al, 2014;Tarkian et al, 2003;Tarkian and Koopmann, 1995;Tarkian and Stribrny, 1999;Thompson et al, 2001). The Pd-BiTe system is molten above 489°C (Cabri, 1981;Cabri and Harris, 1973), which is within the temperature range of porphyry system hydrothermal fluids generally (e.g.…”