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

Katie A Mcfall,Jonathan Naden,Stephen Roberts,Tim Baker,John Spratt,Iain Mcdonald

doi:10.1016/j.oregeorev.2018.06.014

Abstract

The Skouries deposit is a platinum-group element (PGE) enriched Cu-Au porphyry system located in the Chalkidiki peninsula, Greece, with associated Ag, Bi and Te enrichment. The deposit is hosted by multiple porphyritic monzonite and syenite intrusions, which originated from a magma chamber at depth. An initial quartz monzonite porphyritic intrusion contains a quartz–magnetite ± chalcopyrite–pyrite vein stockwork with intense potassic alteration. The quartz monzonite intrusion is cross cut by a set of syenite and mafic porphyry dykes and quartz–chalcopyrite–bornite ± magnetite veins which host the majority of the Cu and Au mineralisation. Late stage quartz–pyrite veins, with associated phyllic alteration crosscut all previous vein generations. Electron microprobe and scanning electron microscopy shows that the PGE are hosted by platinum-group minerals (PGM) in the quartz-chalcopyrite–bornite ± magnetite veins and within potassic alteration assemblages. The PGE mineralisation in Skouries is therefore part of the main high temperature hypogene mineralisation event. Platinum-group minerals at Skouries include: sopcheite [Ag4Pd3Te4], merenskyite [(Pd,Pt)(Te,Bi)2] and kotulskite [Pd(Te,Bi)], with rare telargpalite [(Pd,Ag)3Te], isomertieite [Pd11Sb2As2], naldrettite [Pd2Sb], testibiopalladite [PdTe(Sb,Te)] and sobolevskite [PdBi]. The most common platinum-group mineral is sopcheite. The PGM in Skouries are small, 52 µm2 on average, and occur as spherical grains on the boundaries between sulphides and silicates, and as inclusions within hydrothermal quartz and sulphides. These observations support a “semi-metal collector model” whereby an immiscible Bi-Te melt acts as a collector for PGE and other precious metals in high temperature hydrothermal fluids. This mechanism would allow the formation of PGM in porphyries without Pt and Pd fluid saturation.

Highlights

Porphyry deposits can contain appreciable amounts of platinumgroup elements (PGE), in particular Pt and Pd, with the economic extraction of these valuable by-products of increasing interest (Economou-Eliopoulos, 2010, 2005; Tarkian and Stribrny, 1999)
The Serbomacedonian metallogenic province (SMP) is associated with Late Cretaceous to Tertiary magmatism (Jankovic, 1977), and is a subdivision of the Tethyan Metallogenic Belt, which incorporates all deposits associated with the closure of the Tethyan Ocean (Jankovic, 1997; Richards, 2015)
The Skouries Cu-Au deposit is a multi-stage alkali porphyry system with multiple overprinting intrusions, each associated with hydrothermal vein sets

Summary

Introduction

Porphyry deposits can contain appreciable amounts of platinumgroup elements (PGE), in particular Pt and Pd, with the economic extraction of these valuable by-products of increasing interest (Economou-Eliopoulos, 2010, 2005; Tarkian and Stribrny, 1999). The SMP is associated with Late Cretaceous to Tertiary magmatism (Jankovic, 1977), and is a subdivision of the Tethyan Metallogenic Belt, which incorporates all deposits associated with the closure of the Tethyan Ocean (Jankovic, 1997; Richards, 2015) These include the Cretaceous PGE-enriched Elatsite porphyry deposit in Bulgaria (Tarkian et al, 2003), as well as post-collisional deposits such as Skouries (Siron et al, 2016). Exhumation of the Rhodope core complex is closely related to post collisional magmatism and mineralisation (Marchev et al, 2005)

Results

Discussion

Conclusion