Chemical composition (EPMA)

The chemical composition of 28 samples (nos. 1–26, 30, 32) was determined at the Polish Geological Institute—National Research Institute in Warsaw using a Cameca SX-100 electron microprobe (EPMA). The amount of metallic material in sample no. 31 was too small for testing. Therefore, it was excluded from further analyses. Metal samples were obtained using a micro-drill and HSS drills with a diameter of 1–2 mm. Drilling chips or small pieces up to 1.0 mm in length were mounted in epoxy resin in 1-inch discs. Samples were then polished with diamond paste and carbon coated to obtain electrical conductivity. Detailed photographs were taken, using both optical and scanning electron microscopes. Analytical conditions of the EPMA were set to 15 kV of accelerating voltage and 20 nA beam current. The diameter of the electron beam (spot size) was set to 50 μm (samples 1, 3, 4, 5, 18, 19, 20, 24, 25) and 10 μm (2, 6, 7–17, 21, 22, 23, 26, 30, 32), depending on the available homogeneous area of the samples. Due to a variable composition at the μm-scale, approximately 20 areas (15–22) were analysed per each sample. The following standards used and corresponding X-ray lines were used: Si Kα wollastonite, Al Kα orthoclase, S Kα pyrite, Ca Kα wollastonite, Ag Lα hessite, Sb Lα InSb, Sn Lα cassiterite, Cl Kα vanadinite, Bi Mβ Bi2Se3, PbMβ galena, Zn Kα ZnS, Se Lβ ZnSe, As Lβ FeAsS, Cu Kα CuFeS2, Ni Kα Ni metal, Co Kα Co metal, Fe Kα pyrite, Mg Kα diopside, Au Mα Au metal, Hg Mβ cinnabar.