# Provenance and Paleo-Environment of the Late Carboniferous Bauxite Formations in Southern Shanxi
## 5 Discussion
### Source of Metallogenic Materials  
The metallogenic materials of weathering sedimentary type bauxite originate from multiple exogenous sources [7; 13; 34; 48; 49]. Any igneous, metamorphic, or sedimentary rock exposed to a warm and humid environment can contribute metallogenic materials essential for bauxite formation [50]. The Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratio remained relatively stable during sedimentation and can be utilized for provenance analysis. The Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) values in basic rocks are 3-8, and those of intermediate rocks are 8-21, and those of acidic rocks 21-70, and occasionally above 70. The Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratios of the Pinglu bauxite (Table 1) indicate that, except for S5, the Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratios of other bauxite and clay rocks are all greater than 21, with coal seam S2 reaching 25. The other rock samples, particularly the upper sandstone, had Al\({}_{2}\)O\({}_{3}\)/TiO\({}_{2}\) ratios between 8 and 21. Furthermore, the Al\({}_{2}\)O\({}_{3}\)-TiO\({}_{2}\) diagram (Figure 10a) reveals that nearly all points fall within the provenance areas of intermediate and acidic rocks, especially the bauxite and their top and bottom beds. This suggests that the source of metallogenic material for the Pinglu bauxite is closely related to acidic igneous rocks, whereas the source for the overlying rock layers transitioned gradually to intermediate rocks. Studies indicate that Th, Sc, and Zr are minimally impacted by later diagenesis and are primarily related to the rock composition of their source areas, with Zr being particularly stable. The element Zr is predominantly found in highly stable zircons and exhibits enrichment in sediments through recycling processes. The ratio of Zr/Sc can serve as an indicator for the degree of recycling. Felsic rocks tend to be rich in La and Th compared to basic rocks, whereas Sc and Co are more abundant in mafic rocks [50]. Consequently, relatively stable trace elements such as La, Th, Zr, Sc, Co, and their ratios--like Zr/Sc, Th/Sc, La/Sc, and Th/Co--can provide insights into potential source areas and lithology, thereby offering source information [51; 52]. In the Zr/Sc-Th/Sc and La/Sc-Th/Co diagrams (Figure 10b,c), the sample points cluster around intermediate-acidic igneous rocks, further suggesting a close relationship between the metallogenic materials of the bauxite and clay rocks and intermediate-acidic igneous rocks. The lack of a significant increase in Zr in Figure 9b implies that the diagenetic materials of the Pinglu bauxite series may not have undergone sedimentary recycling. Compatible and incompatible elements serve as essential parameters for the differentiation of felsic and mafic rocks. Acidic rocks typically exhibit Th/Sc values exceeding 1, while intermediate rocks range from 0.6 to 1, and basic rocks less than 0.6 [53]. Tables 2 and 3 show that the Th/Sc values for the aluminum-bearing strata samples in Pinglu are all greater than 1.0, suggesting that the clastic source rocks are predominantly felsic igneous rocks. For the upper layer samples (except for coal seam S6), the Th/Sc values are all greater than 0.6, indicating that the source rocks of the overlying beds of the aluminum-bearing strata are likely to be intermediate rocks. Previous research on U-Pb dating and Hf isotopes of detrital zircons from the Late Carboniferous bauxite on the southern margin of the North China Craton points out that the primary metallogenic materials of the bauxite originated from the Neoproterozoic Kuanping Group and the Mesoproterozoic Qinling Group of the North Qinling orogenic belt [13]. It is well-established that the North Qinling tectonic belt underwent granittoid magmatism between 500 and 410 Ma prior to the Early Devonian. Nevertheless, the final collision and subsequent amalgamation of the North China and Yangtze blocks along the Mianlue suture, resulting in the formation of the Qinling orogenic belt, occurred in the Early Mesozoic [54; 55].