## 4 Results
### Trace Element Distribution in Fe-Ti-Oxides and Sulphides Mineralization Determined by EPMA  
EPMA analyses revealed that the most abundant trace elements in the sulphide mineralization were cobalt and nickel (Figure 12). These elements occurred mainly as substitutions in pentlandite, pyrrhotite, chalcopyrite, and pyrite, and as secondary minerals--thiospinels ((_Fe,Ni_) (\(Co\),\(Ni_{2}S_{4}\)), which formed as a result of pentlandite decomposition [41]. Cobalt and nickel substitutions in sulphides and thiospinels ranged from 0.1 to 40 wt% (Figure 12). The highest contents of Co were found in siegenite (29.7 wt%), and those of Ni were found in pentlandite (39.2 wt%) (Table 4). The contents of Co and Ni in siegenite averaged 22.0 wt% and 26.3 wt%, respectively. On the other hand, Co substitution in pentlandite was, in the vast majority of analyses, in the range of 2 to 7 wt% (Table A5). The remaining, definitely higher Co impurities in pentlandite (>14 wt%) should be interpreted as the presence of other thiospinels, most often identified as siegenite. The association of cobaliferous-pentlandite with thiospinels (Fe, Co, Ni) showing lower Co substitution, such as bravoite or talnakhite, was confirmed via EPMA. Bravoite showed nickel contents in the range of 26 to 30.4 wt% (mean = 28.1 wt%) and Co substitution from 1.4 to 3.4 wt% (mean = 2.7 wt%), (Table 4). In talnakhite, the mean values of Ni and Co substitutions were about 4 wt%. The presence of pentlandite and its decomposition products (thiospinels) was subordinate to that of pyrrhotite (approximately 1:10); therefore, much larger resources of Co and Ni should be associated with the presence of pyrrhotite, despite the fact that it contained much lower concentrations of these metals. The mean values of Co and Ni substitution in pyrrhotite were 0.16 and 0.61 wt%, respectively. The range of nickel substitution (0.2 to 4.0 wt%) in pyrrhotite was much higher than that of cobalt (0.05 to 0.3 wt%). In turn, the substitutions of Co and Ni in chalcopyrite were present at a similar level (mean = 0.11 wt%). The variability of Co and Ni substitution ranged from trace amounts up to 0.56 wt% (Table 3). Cubanite, which was formed as a result of the decomposition of a solid solution of magmatic chalcopyrite, contained traces of Co and Ni (with a maximum of 0.14 wt%). Figure 12 shows the diversity of the Co and Ni substitutions in pyrite. Pyrite was of secondary origin and replaced pyrrhotite. Co and Ni substitutions in pyrite ranged from trace amounts up to about 9 wt%, respectively. The mean value of the Co and Ni contents was 1.6 and 1.1 wt% (\(n\) = 37), respectively. It was possible to recognize a Co-rich pyrite with Co substitution >1 wt%. Cobalt showed a variable correlation with the Ni distribution in sulphides and thiospinels. A strong positive correlation of Co with Ni was observed in chalcopyrite and cubanite (\(r\) = 0.73, and \(r\) = 0.62, respectively) but no correlations occurred in other sulphides (Table 5). As an example, there were no correlation between distributions of Co with Fe in pyrrhotite and pentlandite, which indicates the possibility of mutual substitution by both elements (Figure 13A,B). Figure 12: Bivariate diagram of Ni vs. Co in sulphides and thiospinels from the Udryn and Krzemianka Fe-Ti-V deposits. Zero values and values below low-precision limits are not presented on the logarithmic axis. Note: gray dashed lines indicate the range of precision of measurements in the entire population for a given element and sulphide. Figure 13: Bivariate diagrams of trace elements in sulphides from the magnetite-imemite ores in the Udryn and Krzemianka Fe-Ti-V deposits. **(A)** Fe vs. Co in pentlandite; **(B)** Fe vs. Co in pyrrhotite. Magnetite is the major carrier of the critical element vanadium. The vanadium content in magnetite was in the range of 0.01 to 0.59 wt%, mean = 0.42 wt.% (Table 2, \(n\) = 81, Figure 14A).