## 4 Results
### Geochemistry  
The major and trace element concentrations of the sedimentary rocks from the Madzaringwe Formation are presented in the Supplementary Materials Data (Tables S1 and S2). The mineralogy of the Madzaringwe Formation shale and mudstone is reflected by their major element abundances. The major elements found in the collected samples include SiO\({}_{2}\), TiO\({}_{2}\) Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\), MnO, MgO, CaO, Na\({}_{2}\)O, K\({}_{2}\)O, and P\({}_{2}\)O\({}_{5}\). The summary of the abundances of the aforementioned oxides is shown in Table 2. In general, SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\) Fe\({}_{2}\)O\({}_{3}\), and K\({}_{2}\)O are more abundant in the mudroks (shale and mudstone) and sandstones, whereas CaO is more enriched in the coal samples. On the other hand, the trace elements in the samples include Ag, As, Ba, Bi, Br, Cd, Ce, Co, Cr, Cu, Ga, Ge, Hf, La, Mo, Nb, Ni, Pd, Rb, Sb, Sc, Se, Sn, Sr, Ta, Th, Ti, U, V, W, Y, YB, Zn, and Zr. The trace element compositions are divided into large ion lithophile elements (LILE), high field strength elements (HFSE) and transition trace elements (TTE). The summary of the abundances of some trace elements is depicted in Table 3. Rb, Sr, and Nb are more abundant in the coal and shale samples, while Cr and Ni is more abundant in the sandstones. In general, the studied samples have a high concentration of Ba, Zn, Zr, Rb, and Ce.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Oxide** & **Coal** & **Shale** & **Mudstone** & **Sandstone** \\ \hline SiO\({}_{2}\) (\%) & 9.64–24.13 & 62.93–69.48 & 62.52–71.90 & 39.99–65.63 \\ \hline TiO\({}_{2}\) (\%) & 0.14–0.30 & 0.76–0.87 & 0.75–0.88 & 0.20–0.85 \\ \hline Al\({}_{2}\)O\({}_{3}\) (\%) & 3.17–7.20 & 16.45–20.48 & 5.51–19.98 & 3.32–20.00 \\ \hline Fe\({}_{2}\)O\({}_{3}\) (\%) & 0.42–2.17 & 1.67–2.87 & 1.07–3.53 & 3.03–29.33 \\ \hline MnO (\%) & 0.01–0.02 & 0.01–0.02 & 0.01–0.04 & 0.01–0.02 \\ \hline MgO (\%) & 0.17–0.50 & 0.43–0.90 & 0.43–1.16 & 0.16–0.92 \\ \hline CaO (\%) & 0.49–2.20 & 0.32–0.75 & 0.26–0.86 & 0.44–3.55 \\ \hline Na\({}_{2}\)O (\%) & 0.03–0.08 & 0.32–0.84 & 0.35–0.60 & 0.05–0.30 \\ \hline K\({}_{2}\)O (\%) & 0.42–0.82 & 2.09–2.62 & 2.15–2.92 & 0.36–0.76 \\ \hline P\({}_{2}\)O\({}_{5}\) (\%) & 0.03–0.05 & 0.06–0.13 & 0.04–0.15 & 0.03–0.11 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Abundances of the oxides in studied samples.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Trace Elements** & **Coal** & **Shale** & **Mudstone** & **Sandstone** \\ \hline \multirow{4}{*}{LILE} & Rb (ppm) & 131–173 & 93–156 & 24–163 & 19–147 \\ \cline{2-6}  & Ba (ppm) & 260–761 & 276–324 & 129–513 & 294–377 \\ \cline{2-6}  & Th (ppm) & 20–20 & 10–20 & 2–19 & 2–19 \\ \cline{2-6}  & Sr (ppm) & 98–211 & 140–201 & 60–208 & 90–183 \\ \hline \multirow{4}{*}{HFSE} & Zr (ppm) & 43–290 & 212–427 & 63–432 & 139–217 \\ \cline{2-6}  & Y (ppm) & 5–55 & 24–49 & 5–51 & 21–50 \\ \cline{2-6}  & Nb (ppm) & 20–24 & 15–24 & 4–24 & 3–22 \\ \hline \multirow{4}{*}{TTE} & Sc (ppm) & 11–17 & 9–15 & 4–16 & 6–15 \\ \cline{2-6}  & V (ppm) & 7–108 & 45–84 & 5–99 & 76–86 \\ \cline{2-6}  & Cr (ppm) & 53–105 & 53–108 & 50–243 & 57–340 \\ \cline{2-6}  & Ni (ppm) & 11–70 & 10–16 & 7–50 & 16–101 \\ \cline{2-6}  & Zn & 4–108 & 49–107 & 4–132 & 22–59 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Abundances of some trace elements in studied samples.