## 4 Results
### Metallic Mineralization in Light of the Microscopic and EPMA Studies
Our metal-rich ore samples mainly contained the hexagonal form of pyrrhotite, accompanied by chalcopyrite and pentlandite. The pyrrhotite grains were most often xenomorphic in size, ranging from 0.005 to 0.05 mm in diameter. They usually made up polycrystalline aggregates of up to 2-3 mm in diameter. Some pyrrhotite exhibited lamellar structures, resulting from decomposition products of a high-temperature pyrrhotite. EPMA showed that pyrrhotite had a low Fe content (mean = 59.5 wt%) and a high S (mean = 39.1 wt%) content, as well as constant substitution of Ni and Co (Tables 3 and 4). In pyrrhotite, there were oval or lenticular exsolutions--products of pentlandite or chalcopyrite--with diameters  
Figure 8: The composition of Fe-Ti oxides plotted in a TiO\({}_{2}\)-FeO-0.5 Fe\({}_{2}\)O\({}_{3}\) ternary diagram in ore samples from the Krzemianka and Udryn Fe-Ti-V deposits in NE Poland. Explanation of calculation (in atomic proportions): TiO\({}_{2}\)–Ti (IV); FeO = Fe (II) + Mg (II) + Mn (II) + 2O (II); Fe\({}_{2}\)O\({}_{3}\) = Fe (III) + Cr (III) + Al (III) + V (III) + 3O (II). from a few to several hundred micrometres (Figure 11A,B,D,F). They arranged themselves parallel to the planes of separation in pyrrhotite (001). Moreover, star-shaped exsolution products of pentlandite in pyrrhotite were observed. Pentlandite and chalcopyrite were also found in the form of intergranular fillings between the pyrrhotite grains. They exhibited xenomorphic crystals with distinctive cleavage, which were up to 0.5 mm in length. The decomposition of pentlandite in pyrrhotite showed a variable chemical composition, on average 34.9 wt% Ni, 27.2 wt% Fe, and 33.3 wt% S, as well as the constant substitution of Co (Tables 4 and A5). The other secondary sulphides were also observed crystallizing along the fractures or cleavage of primary minerals (e.g., pyrrhotite and pentlandite). They formed as a result of the decomposition of high-temperature pentlandite-pyrrhotite solid solutions into their low-temperature products. They were represented mostly by thiospinels from the (Fe, Ni) (Co, Ni)\({}_{\text{S}}\)4 terms [41]. EPMA showed that the proportions of metal contents indicated the presence of diadochid substitutions and/or micro-overgrowths of several transition phases in these minerals. Siegenite (_(Ni,Co)\({}_{3}\)S\({}_{4}\)_), bravoite (_(Fe,Ni,Co)\({}_{S2}\)_), mackinawite (_(Fe,Ni)S\({}_{0,g}\)_), and probably smithithite (_(Fe,Ni)S\({}_{1I}\)_) were identified. The average composition of siegenite was 26.3 wt% Ni, 22.0 wt% Co, 10.8 wt% Fe, and 41.1 wt% S (Tables 4 and A6). Bravoite had much higher Fe and lower Co contents, compared to siegenite (Table 4). Bravoite occurred inside pentlandite along its cleavage, in the form of veinlets or lattices up to approx. 30 um thick. Moreover, lenticular or lancelonic exsolutions of mackinawite were also observed in pentlandite. Chalcopyrite accounted for about 10% of the sulphide contents in the investigated magnetite-immetite ones. It created small overgrowths with pyrrhotite or pentlandite, up to several hundred um in diameter. The adhesive desorption of these sulphides by gangue minerals was visible. Chalcopyrite was more commonly observed as a thin (30-100 um thick) lamellae exsolution in pyrrhotite. The chemical composition of chalcopyrite contained, on average, 34.5 wt% Cu, 30.5 wt% Fe, and 34.4 wt% S and the constant substitution of Co, Ni, and Zn (Table A7). Exsolutions of regular cubanite lamellae or sporadically millerite were also observed in the decomposition product of chalcopyrite in the pentlandite (Figure 7H). Cubanite was also found in the form of tiny xenomorphic crystals associated with pyrrhotite. The chemical composition of cubanite included 41.0 wt% Fe, 23.2 wt% Co, and 35.0 wt% S (Tables 3 and A8).