Magmatic and hydrothermal prerequisites for porphyry-epithermal mineralisation in continental volcanic arc, Thrace, NE Greece

Supplying critical and energy critical elements (e.g., Te, Se, and Re) for the green transition is a growing challenge. and many of these commodities are understudied. The strong impact of these elements on the energy and economy sector of the European Union gives them a strategic importance. Thus, in order to reduce the dependency on imports the European continent needs to be re-explored to constrain economic zones enriched in critical and energy critical elements. The deposits of Thrace, NE Greece (Fig.1a and b), represent such an example, where zones with high metal and metalloid concentrations (e.g., Cu, Ga, Ge, Se, Mo, Sb, Te, Re, Au and Bi) occur at variable crustal depth in a mineralized continental arc setting in Europe (Voudouris et al. 2019; Voudouris et al. 2021). Regional variations in deposit mineralogy have been observed, but the ore-forming processes of the porphyry-epithermal deposits are still poorly constrained from a trace element perspective. The magmatic and hydrothermal prerequisites that lead to the formation of such a mineralised arc system are also still controversial, but essential to discover positive anomalies of critical and energy critical elements in the continental crust.

This project focuses on constraining the magmatic and hydrothermal prerequisites in continental arc settings which are needed to form economic valuable ore deposits. We will sample different plutonic and sub-volcanic/volcanic rocks in the Maronia-Leptokarya magmatic corridor (Thrace, NE Greece) which host porphyry-epithermal style mineralisations and represents a natural laboratory to investigate ore-forming processes in deposits emplaced at various crustal depth. Analyzing the whole element spectrum in these samples (XRF, ICP-MS, HG-AFS) combined with mineral chemistry (e.g., amphibole, magnetite, apatite) will allow us to investigate the effect of magma degassing, as well as sulfide saturation and segregation to form a pre-concentrate in the mid- to lower crust, as a possible source for metal scavenging by fluids exsolved from the magmatic systems. On the deposits scale we will focus on the chemistry of hydrothermal sulfides (e.g., pyrite and molybdenite, Fig.1c and d) in different vein-types of porphyry-epithermal style mineralization associated with various alteration assemblages and establish the hydrothermal processes forming the exotic mineralogy (e.g., Rheniite, Fig.1d) and element enrichments (e.g., Ga, Ge, Se, Sb, Te, Re and Bi). High-resolution trace element analyses on these minerals (EPMA, LA-ICP-MS) will provide insights into the processes of ore-formation from a 3D perspective, i.e. in a stratigraphic and regional context. The (in situ) S isotope composition of hydrothermal pyrite will help to better understand the interaction processes between the magmatic and hydrothermal system. Ultimately, we will define the fluid evolution in space and time on the deposit scale and combine our results with the magmatic evolution allowing us to create a comprehensive model for the enrichment of metals and metalloids in a mineralized arc segment.

Fig.1: a) The location of the Rhodope massif in NE Greece (white box) in the Aegean region. b) Geological map of the NE-SW trending Leptokaria-Maronia magmatic corridor consisting of age-regressive plutonic intrusions and associated volcanic eruptions. Major porphyry- and epithermal mineralisations occur at the Maroni, Sapes-Kirki, and Leptokaria areas. c) Molybdenite-pyrite mineralisation at the Maronia porphyry Cu-Mo-Au-Re prospect. d) rare occurrence of molybdenite associated with rheniite from Maronia.

References

Voudouris, P.; Mavrogonatos, C.; Spry, P.G.; Baker, T.; Melfos, V.; Klemd, R. et al. (2019): Porphyry and epithermal deposits in Greece: An overview, new discoveries, and mineralogical constraints on their genesis. Ore Geology Reviews 107, 654–691.

Voudouris, P.; Repstock, A.; Spry, P.G.; Frenzel, M.; Mavrogonatos, C.; Keith, M. et al. (2021): Physicochemical constraints on indium-, tin-, germanium-, gallium-, gold-, and tellurium-bearing mineralizations in the Pefka and St Philippos polymetallic vein-and breccia-type deposits, Greece. Ore Geology Reviews, p. 104348.