## 5 Discussion  
### Provenance Analysis  
Al, Ti, Nb, Zr, and REY are resistant to alterations during weathering, transportation, and diagenesis [58; 59]. This makes them valuable geochemical indicators for determining the source of detrital materials in coal-bearing strata [6; 53; 60] and the composition of source rocks [61; 62; 63]. [PERSON] et al. (2016) demonstrated Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) and Zr/TiO\({}_{2}\) vs. Nb/Y ratios [64], and believed that the distribution pattern of REY changed minimally during the weathering-sedimentation-diagenesis process, which can be used as reliable geochemical indicators for determining the source of detrital materials [64]. The Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratio is particularly useful for identifying the source rocks of coal seams [58; 65] and for inferring the source rock composition of coal seams and interbeded volcanic ash. [PERSON] et al. (1997) classified the Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratios of different source rocks into three numerical intervals ranging from 3-8, 8-21, and 21-70, which represent mafic, intermediate, and felsic igneous rocks, respectively [58; 66; 58]. The sample points of the C1 and C2 layers of the No. 15 coal fall within the mafic rock region, the C5 and C6 sample points fall within the intermediate rock region, and the remaining sample points fall within the felsic igneous rock region (Figure 11A). The La/Yb-\(\Sigma\)REE source rock discrimination diagram [68] by [PERSON] and [PERSON] (1978) provides further insights (Figure 11B). Five coal samples (C1-C2 and C7-C9) fall within the central part of the basalt area, indicating that continental tholeiitic basalts are the source rock. In contrast, samples C3-C6 and the roof sample fall within the sedimentary rock region. The parting and floor samples fall near the intersection of alkali basalts and sedimentary rocks. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Samples** & **Eu\({}_{\rm N}\)/Eu\({}_{\rm N}\)** * & **Ce\({}_{\rm N}\)/Ce\({}_{\rm N}\)** * & **(La/Lu)\({}_{\rm N}\)** & **(La/Sm)\({}_{\rm N}\)** & **(Gd/Lu)\({}_{\rm N}\)** & **Type** \\ \hline
15R & 1.16 & 1.05 & 0.67 & 1.03 & 0.68 & H \\ C1 & 1.37 & 1.05 & 0.14 & 0.87 & 0.20 & H \\ C2 & 1.29 & 1.01 & 0.21 & 0.45 & 0.52 & H \\ C3 & 0.95 & 1.06 & 0.76 & 1.27 & 0.77 & H \\ C4 & 1.00 & 1.05 & 0.61 & 0.93 & 0.70 & H \\ C5 & 1.06 & 1.04 & 0.41 & 0.72 & 0.57 & H \\ C6 & 0.88 & 0.85 & 0.66 & 1.40 & 0.62 & H \\ C7 & 1.09 & 1.01 & 0.22 & 0.44 & 0.50 & H \\ C8 & 1.18 & 0.98 & 0.17 & 0.30 & 0.56 & H \\
15P & 1.04 & 0.90 & 0.51 & 0.99 & 0.55 & H \\ C9 & 1.25 & 0.91 & 0.19 & 0.52 & 0.37 & H \\
15F & 0.99 & 0.98 & 0.38 & 0.68 & 0.58 & H \\ \hline \end{tabular} Note: Eu\({}_{\rm N}\)/Eu\({}_{\rm N}\)* = Eu\({}_{\rm N}\)/(0.5\times\) Sm\({}_{\rm N}\) + 0.5 \(\times\) Gd\({}_{\rm N}\); Ce\({}_{\rm N}\)/Ce\({}_{\rm N}\)* = Ce\({}_{\rm N}\)/(0.5\times\) LaN + 0.5 \(\times\) PrN).  
\end{table} 
Table 6: REY parameters of Gaoping No. 15 coal and non-coal samples. [PERSON] and [PERSON] (1977) suggested that the source rock types in the provenance region could be traced based on the relationship between Zr/TiO\({}_{2}\) and Nb/Y [7; 69; 70; 62]. However, Yttrium (Y) is mobile in low-temperature aqueous solutions, and its easy migration properties may affect the reliability of this method [71]. Therefore, we employed the Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) vs. Zr/TiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) vs. Nb/Yb discriminant diagrams optimized by [PERSON] et al. to analyze the material sources [72]. The potential provenance [73; 74; 75; 76; 77; 78] of the coal measure strata (Figure 12) shows that the sample points mainly fall in the region of Yinshan diorite and granite and partly fall in the region of Zhong-tiao Mountain. No sample point falls in the Paleozoic granite region of the North Qinling Mountains, indicating that the sediments in this region mainly originate from the Yinshan diorite and granite and the Zhongtiao Mountain. [PERSON] et al.