## 1 Introduction
The Kilks ore district in northern Greece belongs in the Vertiskos unit and is part of the Serbo-Macedonian metallogenic province that is a potential region for future exploration projects targeting critical and rare metals [25; 26; 27; 28; 29; 30; 31; 32; 33] (Figure 1). This district hosts Cenozoic deposits and prospects enriched in Cu and Au, as well as in critical and rare metals (e.g., Sb, W, Te, Bi, Ga, Co, Ag, and REE) [25; 26; 27; 28; 29; 30; 31; 32; 33]. Oligocene to Miocene porphyry deposits (Vathi, Gerakario, Pontokerasia, Koryfi, Doirani) are clustered in the northern part of the district [23; 24; 32; 33]. Ancient mining galleries indicate the importance of these mineralization for gold and copper during antiquity. Several other deposits, including skarn/carbonate replacement, epithermal and vein type mineralization in metamorphic rocks are found proximal or distal to magmatic intrusions, at the central and southern parts of the Vertiskos unit, as well as in the adjacent Kerdylion unit [23; 24; 32; 33] (Figure 1). For deposits distal to magmatic rocks, the regional metallogenic model, the local structural setting, the character of the hydrothermal fluids, and their ore geochemistry (i.e., enrichments in chalcophile elements, such as Au, Bi, Co, Te) relate their genesis to a combination of factors, including the relationship to buried magmatic intrusions, shear zones, and brittle deformation [23; 34; 35]. The most important Sb deposits in the region are found at Rizana, Philadelphia, and Gerakario [23, 31, 32] (Figure 1). The Rizana (also known as Lachanas) shear-zone hosted deposit is found in sheeted quartz veins crosscutting two-mica gneiss and schist of the Vertiskos unit [28, 36, 37, 38]. Sericitization and silicification are observed in the basement rocks [36]. The ore mineralization is enriched in Sb and W and the ore assemblage includes stibnite, wolframite, sphalerite, pyrite, and bertheriite, and traces of chalcopyrite, arsenopyrite, marcasite, and native antimony, arsenic, and gold [36, 37]. Gagne minerals are quartz and barite, while alteration minerals include quartz, seritic, chlorite, calcite, and dolomite [36]. Between the 1930s and 1950s, 9000 tons of stibnite ore, with up to 40% of Sb in the produced concentrate, were extracted from underground mines [28]. Wolframite was also mined between the 1910s and 1940s. The measured reserves of stibnite (0.3 wt.% Sb in average) are 5000 t, and the indicated reserves vary between 50,000 and 100,000 t, including also 1000 t of wolframite [28]. At Philadelphia, Sb mineralization occurs in shear-zone hosted massive and discordant stibnite veins, crosscutting the metamorphic rocks of the Vertiskos unit [29] (Figure 1). Hydrothermal alterations include sericitization and chloritization of the host rocks [22]. The ore assemblage consists of stibnite, arsenopyrite, chalcopyrite, chalcopstibite, traces of scheelite, kermesite, marcasite, pyrite, pyrrhotite, sphalerite, stibiconite, tetrahedra,  
Figure 1: Geological setting of the Cenozoic magmatic rocks and the related ore types in the Kilkis ore district, northern Greece (modified after References [23, 31, 32, 24, 33]). The studied area in Gerakario is also shown. covellite, wolframite, zinkenite, melnikovite, and native gold, while quartz is the gangue mineral [22]. Indicated resources include 10.08 Mt of ore, grading 3.36 wt.% of Sb [22]. The Gerakario area has been explored for Cu, Au, Mo, and base metals between the 1970s and the 1990s [39]. The exploration of the Cu-Au porphyry deposit included soil geochemistry, geophysical surveys, and drilling [39; 40]. Stibnite is hosted in quartz veins found at the periphery of the porphyry deposit. Stibnite was mined in the 1930s with underground galleries and wells, but the amount of the extracted ore is unknown. Probable and indicated reserves are up to 0.13 Mt of ore, grading 0.3% Cu and 1.4 g/t Au for the porphyry deposit [28]. Estimations on Sb resources and reserves are yet to be determined.