## 4 Results
### Elemental Geochemical Analysis
#### 4.4.3 Rare Earth Elements and Yttrium (REY)  
Rare earth elements are stable during deposition and their distribution pattern can be used to judge the changes in paleoclimate, water salinity, redox conditions, and supply of material sources in coal depositional environments to study the depositional mechanisms of abnormal enrichment or depletion of the elements in the coal [54]. The REY content varies from 68.97 ug/g to 386.99 ug/g (Table 5). The average REY content in the coal samples is 102.77 ug/g, which is higher than that in world hard coal (68.41 ug/g) and Late Paleozoic coals of the Qinshui Basin (80.30 ug/g) [55], but lower than that in China coals (135.89 ug/g). The REY content is higher at the bottom and lower at the top seam, and it is the highest in C9 coal. Furthermore, the REY content in the roof, parting, and floor is higher than that in the coal. [PERSON] and [PERSON] (2012) classified REY into three types [56]: light rare earth elements (LREY: La, Ce, Pr, Nd, and Sm), medium rare earth elements (MREY: Eu, Gd, Tb, Dy, and Y), and heavy rare earth elements (HREY: Ho, Er, Tm, Yb, and Lu). The REY data were normalized by the Upper Continental Crust (UCC) [57] to generate the REY distribution pattern of the Gaoping coal (Figure 10). The REY parameters (Table 6) show that \(\delta\)Eu (Eu\({}_{\rm{N}}\)/Eu\({}_{\rm{N}}\)*) is 0.88-1.37, with an average value of 1.11. The coal sample C6 is an Eu-negative anomaly (0.88); the C3, C4, 15P, and 15F samples have no anomalies; the C1, C2, and C9 samples are positive anomalies. \(\delta\)Ce (Ce\({}_{\rm{N}}\)/Ce\({}_{\rm{N}}\)*) is 0.85-1.06, with an average of 0.99, and there is no anomaly, excluding C6, 15P, and C9, which are less than 0.95, which is a negative anomaly. C3 is higher than 1.05 (1.06), which is a slightly positive anomaly. The others have no anomalies. [PERSON] and [PERSON] classified the distribution patterns of REY [56] based on the UCC-normalized La\({}_{\rm{N}}\), Lu\({}_{\rm{N}}\), Sm\({}_{\rm{N}}\), and Gd\({}_{\rm{N}}\), including the following:  
1. Light rare earth-enriched type (L-type): La\({}_{\rm{N}}\)/Lu\({}_{\rm{N}}\) > 1.0;
2. Medium rare earth-enriched type (M-type): La\({}_{\rm{N}}\)/Sm\({}_{\rm{N}}\) < 1.0 and Gd\({}_{\rm{N}}\)/Lu\({}_{\rm{N}}\) > 1.0;
3. Heavy rare earth-enriched type (H-type): La\({}_{\rm{N}}\)/Lu\({}_{\rm{N}}\) < 1.0. Figure 10: Distribution pattern of REY of No. 15 coal and non-coal samples. (**A**) roof, parting, and floor samples; (**B**) C1–C2, C7–C9, coal samples; (**C**) C3–C6, coal samples. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline
**Element** & **15R** & **C1** & **C2** & **C3** & **C4** & **C5** & **C6** & **C7** & **C8** & **15P** & **C9** & **15F** & **WA–C** & **World 1** & **Chinese 2** \\ \hline Th & 9.26 & 1.14 & 1.59 & 14.00 & 5.73 & 6.97 & 13.80 & 3.73 & 1.22 & 34.40 & 4.06 & 38.90 & 5.80 & 3.20 & 5.84 \\ U & 3.52 & 6.82 & 0.69 & 5.18 & 2.87 & 3.25 & 9.67 & 2.16 & 0.70 & 12.50 & 5.89 & 35.60 & 4.14 & 1.90 & 2.43 \\ Nb & 14.60 & 1.53 & 2.01 & 17.30 & 6.82 & 12.90 & 2.110 & 3.60 & 0.81 & 24.20 & 5.56 & 20.00 & 7.96 & 4.00 & 9.44 \\ Ta & 1.07 & 0.06 & 0.14 & 2.03 & 0.39 & 0.92 & 1.60 & 0.16 & 0.07 & 0.06 & 0.36 & 1.23 & 0.64 & 0.30 & 0.62 \\ Zr & 125.00 & 20.60 & 19.00 & 105.00 & 84.20 & 107.00 & 154.00 & 73.80 & 42.40 & 287.00 & 214.00 & 379.00 & 91.11 & 36.00 & 89.50 \\ Hf & 5.03 & 0.45 & 0.62 & 3.80 & 2.60 & 3.25 & 5.21 & 2.27 & 1.33 & 10.90 & 6.73 & 11.40 & 2.92 & 1.20 & 3.71 \\ REY & 127.33 & 79.84 & 68.97 & 96.17 & 93.64 & 86.50 & 143.22 & 70.48 & 104.09 & 267.48 & 176.66 & 386.99 & 102.18 & 68.41 & 135.89 \\ \hline \end{tabular} Note: WA–C, the weighted average for all coal samples; 1 World coals, data from [PERSON] and [PERSON] (2009) [14]; 2 Chinese coals, data from [PERSON] et al. (2012) [52].  
\end{table} 
Table 5: _Cont._In addition, there are mixed enriched types such as light and medium rare earth-enriched types (L-M-type) and medium and heavy rare earth-enriched types (M-H-type). The (La/Lu)\({}_{\rm N}\) values of the No.