A Review of the Distribution of Critical and Strategic Mineral Raw Materials in the Vein-Type Mineralizations of Vertiskos Unit, Northern Greece †

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Introduction
Critical mineral raw materials are essential for high-tech industries and the development of the low-carbon society [1].They are characterized by supply risk, economic importance, and, frequently, are restricted in terms of their geological availability; thus, their exploration and exploitation are of a high priority [1].The European Commission 2023 Critical and Strategic Raw Materials list includes the following critical and strategic metals and metalloids: Al, Sb, As, Be, Bi, Co, Ga, Ge, Hf, Li, Mg, Mn, Nb, Ni, Cu, Sc, Ta, W, V, the groups of heavy (HREE; including also yttrium) and light (LREE) rare earth elements and the platinum group metals (PGM) [2].In addition, rare metals (e.g., Ag, Au, Cd, Hg, etc.) are of specific significance.Previous publications have revealed new mineralogical and geochemical data on the base, precious, and critical metals incorporated in the Oligocene-Miocene magmatic-hydrothermal mineralization hosted in the Vertiskos unit (e.g., [3][4][5][6][7][8]) (Figure 1).This contribution to the literature constitutes a review of the critical, strategic, and rare metals hosted in the vein-type mineralization of the Vertiskos unit, as the future exploration and exploitation of the metals found in this region could facilitate the production of critical metals (e.g., Bi, Co, Te) as by-products of the main commodities produced (e.g., Cu, Au).commodities produced (e.g., Cu, Au).

Major Cenozoic Vein-Type Mineralization and Critical Metal Distribution at the Vertiskos Unit
The polymetallic mineralization is characterized by base metal sulfides, mainly chalcopyrite, arsenopyrite, and pyrite.In addition, a variety of Bi-sulfosalts, Bi-sulfotellurides, and tellurides associated with Au and Ag can be found [13,14] (Table 1).
At Laodikino, chalcopyrite hosts pilsenite (Bi 4 Te 3 ) and native gold inclusions, galena incorporates altaite, and tetrahedrite contains up to 7185 ppm of Ag (Figure 2a,b).At Kolchiko, native bismuth is commonly hosted in galena (Figure 2c,d).In the quartz veins at Koronouda, hessite, pilsenite, tellurobismuthite, and Bi 4 Te 2 S (Joseite-B) coexist with native gold, while the gold content after bulk geochemistry is up to 28.3 ppm [7].At Drakontio, the presence of native gold (Au < 22.5 ppm; bulk geochemistry) is correlated with the occurrence of matildite, emplectite, and aikinite [7].Argentopentlandite is found in the quartz veins at Stefania-Paliomylos and Koronouda [7].At Stanos, mineral phases of the bismuthinite-aikinite and lillianite-gustavite series, along with minerals of the Bi-Te-S-Se system (cf., Voudouris et al. [14]), represent a complex assemblage of Bi-sulfosalts, Bi-sulfotellurides, and tellurides [13].On the contrary, Bi-sulfosalts, Bi-sulfotellurides, and tellurides are lacking from the intrusion-related vein-type mineralizations enriched in Sb-W (i.e., Rizana and Philadelphio, [9]).In these mineralizations, Sb and W oxides and hydroxides are mainly found as minor mineral phases due to supergene processes (Table 1).Based on the published bulk geochemical data, the vein-type mineralization is enriched in Cu-As-Pb-Bi-Ag-Au-Te, with Au up to 28.3 ppm at Koronouda; Ag up to 2433 ppm at Laodikino; and Bi, W, and Co up to <995 ppm, <844 ppm, and <320 ppm, respectively, at Kolchiko [12].Other enrichments include Cd (<247 ppm), Hg (<187 ppm), Se (<59 ppm), and V (<10 ppm) at Laodikino, as well as Te (<3 ppm) at Kolchiko [12].Antimony is up to 7 wt.% in the polymetallic quartz veins from Laodikino and is mainly  The schematic model of the vein-type mineralization and the porphyry-epithermal systems found at the Vertiskos unit is shown in Figure 3.The vein-type mineralizations are hosted in metamorphic rocks and in shear zones and were formed under transpressional to transtensional tectonic settings mainly along the border between Vertiskos unit and the Circum-Rhodope belt.On the contrary, the porphyry-epithermal systems were formed in an extensional setting.Critical and rare metals are variably associated with this mineralization.Nevertheless, enrichments in Bi, Te, and Au can be found in both mineralization groups.For the vein-type mineralization, this may be an indication for concealed proximal and/or distal magmatic intrusions and magmatic-hydrothermal mineralizing processes set along or near shear zones [6,[12][13][14].
Author Contributions: Conceptualization, C.L.S., V.M.; writing-original draft preparation, C.L.S.; writing-review and editing, G.A.S., V.M., P.V.; All authors have read and agreed to the published The schematic model of the vein-type mineralization and the porphyry-epithermal systems found at the Vertiskos unit is shown in Figure 3.The vein-type mineralizations are hosted in metamorphic rocks and in shear zones and were formed under transpressional to transtensional tectonic settings mainly along the border between Vertiskos unit and the Circum-Rhodope belt.On the contrary, the porphyry-epithermal systems were formed in an extensional setting.Critical and rare metals are variably associated with this mineralization.Nevertheless, enrichments in Bi, Te, and Au can be found in both mineralization groups.For the vein-type mineralization, this may be an indication for concealed proximal

Figure 1 .
Figure 1.Cenozoic magmatism, structural setting, and mineralization types at the Vertiskos unit and the adjacent Kerdylion unit in Northern Greece [adapted from 10-12 and the references therein].

Figure 1 .
Figure 1.Cenozoic magmatism, structural setting, and mineralization types at the Vertiskos unit and the adjacent Kerdylion unit in Northern Greece (adapted from [9-11] and the references therein).

Figure 2 .
Figure 2. Photographs of hand-collected specimens from the polymetallic massive veins at Laodikino (a) and from the polymetallic quartz veins at Kolchiko (c).Photomicrographs (plane-reflected light: b,d) of the hypogene mineralization in these veins: (a) Massive pyrite (Py) and arsenopyrite (Apy); (b) native gold (Au) associated with pyrite (Py), as well as chalcopyrite (Cpy) from a polymetallic massive vein; (c) pyrite (Py) and chalcopyrite (Cpy) in quartz (Qtz); (d) pyrite (Py), sphalerite (Sph), chalcopyrite (Cpy), and galena (Gn) with inclusions of native bismuth (Bi) in a polymetallic quartz vein.Based on the published bulk geochemical data, the vein-type mineralization is enriched in Cu-As-Pb-Bi-Ag-Au-Te, with Au up to 28.3 ppm at Koronouda; Ag up to 2433 ppm at

Figure 3 .
Figure3.Schematic model showing the magmatic-hydrothermal mineralizing processes and tectonic settings at the Vertiskos unit during Cenozoic.Specific enrichments in critical and rare metals are highlighted for the porphyry-epithermal and the vein-type mineralization (modified after[13]).

Figure 3 .
Figure 3. Schematic model showing the magmatic-hydrothermal mineralizing processes and tectonic settings at the Vertiskos unit during Cenozoic.Specific enrichments in critical and rare metals are highlighted for the porphyry-epithermal and the vein-type mineralization (modified after [13]).