## 3 Analytical Methods  
### The Whole-Rock Geochemistry  
In total, 39 samples, representing a variety of Fe-Ti-V oxide and sulphide mineralizations, were the subject of the whole-rock geochemistry and point analyses. Samples were collected from the archive core materials of boreholes drilled during the 1970s and 1980s. Twenty-three samples were collected from the Krzemianka deposit (boreholes: Krzemianka \(-24\), \(-50\), \(-56\), \(-63\)) and 16 samples came from the Udryn deposit boreholes (Udryn \(-7\), \(-10\), \(-11\)) (Figure 4). The ore-grade economic intervals of the drill cores were analyzed for their metallic element contents using a portable pXRF spectrometer (Olympus Delta  
Figure 3: Geological cross section (without Cenozoic sedimentary rock cover) of the Udryn Fe-Ti-V ore deposit (modified after [39]). Abbreviations: 1—anorthosite; 2—norite; 3—limeinte-magnetite ore; 4—fault. T1—Lower Triassic; P—Perman; Cm—Cambrian. The geochemical analyses were performed at the Polish Geological Institute--National Research Institute, using international and internal standards, and included duplicate analyses. The contents of trace elements were determined in pressed powder samples (As, Ba, Bi, Br, Cd, Ce, Co, Cr, Cu, Ga, Hf, La, Mo, Nb, Ni, Pb, Rb, Sn, Sr, Th, U, V, Y, Zn, and Zr) and the major element oxides were determined in fused samples (SiO\({}_{2}\), TiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), MnO, MgO, CaO, Na\({}_{2}\)O, K\({}_{2}\)O, P\({}_{2}\)O\({}_{5}\), SO\({}_{3}\), Cl, and F), (Table 1). All analyses were performed using the wavelength dispersive spectrometry (WDS-XRF) X-ray fluorescence method, using a Philips PW-2400 spectrometer. Additionally, the contents of the rare earth  
Figure 4: Location of boreholes sampled and studied in the Krzemianka and Udryn Fe-Ti-V deposits in NE Poland. Note: the boundaries of the deposits are projected onto the ground surface. Figure 5: Schematic geological profile of the Krzemianka 63 drill hole, together with the results of analyses carried out with a portable XRF spectrometer to assess the content of Cr, V, Ti, and Fe (as a percentage) in the selected ore interval. elements (REEs: Sc, Y, La, Ce, Pr, Nd, Eu, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and trace elements (Ag, As, Bi, Cd, Co, Cu, Hf, In, Mn, Mo, Ni, Nb, Re, Sb, Se, Sn, Ta, Te, Th, Tl, W, and V) were determined after decomposition with a full mixture of HCl, HNO\({}_{3}\), HF, and HClO\({}_{4}\) acids using a Perkin Elmer ICP-MS Elan DRC II mass spectrometer by means of inductively-coupled plasma mass spectrometry (ICP-MS). Au, Pd, and Pt were measured using a Perkin Elmer model 4100 ZL spectrometer and the graphite furnace atomic absorption spectrometry (GF AAS) method. In the case of gold analyses, samples were preroasted and reconstituted with a mixture of HCl and HNO\({}_{3}\) acids. Liquid-liquid extraction to methyl isobutyl ketone (MIBK) was performed to separate the matrix and concentrate the test solution. The platinum and palladium samples were digested with aqua regia, and then they were isolated on activated carbon using formic acid. The basic statistical parameters (arithmetic mean, geometric mean, median, and standard deviation) of the content of elements in bulk-rock samples from Fe-Ti-V deposits were determined, as well as the correlation matrices between elements in the considering deposits. The degree of correlation of parameters was interpreted as follows. \(r\leq 0.5\): no correlation, \(r>0.5\) to 0.7: weak correlation, \(r>0.7\) to 0.9: strong correlation, and \(r>0.9\): very strong correlation. Datasets containing values below the limit of detection (LD) can lead to underestimates or overestimates of both the mean value and standard deviation, and therefore to correct this influence statistical substitution methods are commonly used to replace a value below the minimum limit of detection with a value equal to half the limit of detection (LD/2).