## 3 Analytical Methods
### The Ore Microscope and Microprobe Studies  
Mineralogical and petrographic examinations, together with photo-micrographic documentation, were carried out on a NIKON ECLIPSE LV100 POL microscope (Tokyo, Japan) with NIS-Elements software (Version 3.0). The quantitative examination of ore minerals on the electron microprobe was preceded by a preliminary investigation using a ZEISS LEO-1430 scanning electron microscope with an EDS (energy-dispersive spectrometry) detector. Electron microprobe analysis (EPMA) was performed using a Cameca SX-100  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & & \\ \hline As & Ba & Bi & Br & Cd & Ce & Co & Cr & Cu & Ga & Hf & La & Mo \\ \hline
3 & 10 & 3 & 1 & 3 & 5 & 3 & 5 & 5 & 3 & 3 & 5 & 2 \\ Nb & Ni & Pb & Rb & Sn & Sr & Th & U & V & Y & Zn & Zr & \\
2 & 3 & 3 & 3 & 2 & 2 & 3 & 2 & 5 & 3 & 2 & 3 & \\ \hline \multicolumn{11}{c}{**ICP-MS [ppm]**} & & & & & & & & & & & & \\ \hline Sc & Y & La & Ce & Pr & Nd & Eu & Sm & Au & Pd & Pt & \\
0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.5 & 0.05 & 0.05 & 0.001 & 0.005 & 0.01 & \\ Gd & Tb & Dy & Ho & Er & Tm & Yb & Lu & & & & & \\
0.05 & 0.05 & 0.05 & 0.05 & 0.05 & 0.05 & 0.05 & 0.05 & & & & & \\ \hline \multicolumn{11}{c}{**ICP-MS [ppm]**} & & & & & & & & & & \\ \hline Ag & Cd & In & Mn & Re & Sb & Se & Sn & Ta & V & Te & Tl & W \\
0.1 & 0.5 & 0.05 & 1 & 0.05 & 0.5 & 2 & 1 & 0.05 & 5 & 0.5 & 0.05 & 0.1 \\ As & Bi & Co & Cu & Hf & Ni & Nb & Mo & Th & & & & \\
2 & 0.05 & 0.5 & 0.5 & 0.05 & 0.5 & 0.5 & 0.05 & 0.05 & & & & \\ \hline \multicolumn{11}{c}{**WDS-XRF [\%]**} & & & & & & & & & & \\ \hline 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 & F \\
0.1 & 0.01 & 0.05 & 0.01 & 0.001 & 0.01 & 0.01 & 0.01 & 0.01 & 0.001 & 0.01 & 0.001 & 0.01 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The minimum detection limits of element measurements via the applied methods.  
microphe (Paris, France) equipped with five WDS detectors. The following parameters were used during the EPMA analyses: HV accelerating voltage: 15 kV, beam current: 20 nA, a focused beam (<1 \(\upmu\)m in diameter), acquisition time at the peak position: 20 s, at the background position: 10 s, and carbon sputtering. International (commercial) standards from the SPI-53 set from SPI and from the sulf-16 set from P&H were used for instrument calibration.  
The determination of low concentrations in small phases with an electron microprobe is not straightforward and uncertainties differ according to the acceleration voltage, counting statistics, background subtraction, sample heterogeneity, beam drift, and other analytical factors (e.g., stray X-rays and surface contamination). Although the precision of each single measurement for a given element was different due to the specificity of the method, it was possible to determine the variability of measurement precision. In the case of trace elements, such as V in magnetite and ilmenite, the variations in measurement precisions ranged from 450 to 650 ppm (with an average of approximately 550 ppm) and from 200 to 300 ppm (with an average of approximately 250 ppm), respectively. In the case of cobalt and nickel, the variations in measurement precision ranged from 800 to 1000 ppm (with an average of approximately 900 ppm) in pentlandite, pyrrhotite, chalcopyrite, and pyrite. The statistics of the elements presented in this article include values above or close to the level of precision of a single measurement.