# Provenance and Paleo-Environment of the Late Carboniferous Bauxite Formations in Southern Shanxi
## 5 Discussion  
### Metallogenic Environment  
REEs exhibit good stability in sedimentary environments and throughout diagenesis, making them valuable for identifying sedimentary source rocks [33]. The occurrence of Ce anomalies is frequently observed in aluminium-bearing rock strata, similarly to the Wuchuan-Zheng'an-Daozhen bauxite deposit, the Zagrad karstic bauxite deposit, Montenegro, and the Apulian karst bauxite deposit, southern Italy. Ce anomalies serve as key indicators of redox conditions [34]. Under oxidizing conditions, Ce\({}^{3+}\) is converted to Ce\({}^{4+}\), resulting in a positive Ce anomaly, whereas under reducing conditions, soluble Ce\({}^{3+}\) predominates, leading to a negative Ce anomaly [35; 36; 37]. All samples from the Jinyu profile displayed negative Ce anomalies. In the Jinshi profile, all samples except for clay rock S7, which had a slightly positive Ce anomaly (1.04), exhibited negative Ce anomalies. These variations in Ce anomalies suggest that the primary diagenetic environment of the aluminous strata was reducing, with occasional weakly oxidizing conditions. The La/Y ratios can indicate the acidity or alkalinity of the bauxite depositional environment [36; 37]. When La/Y > 1, the environment is alkaline, while it is acidic when La/Y < 1 [34; 36; 38; 39]. In the Jinyu profile, La/Y values were all greater than 1; however, a significant difference was observed between bauxite Y8 and clay rocks Y7 and Y9 (Table 4). In the Jinshi profile, the La/Y ratios varied significantly, ranging from 0.11 (S2) to 7.18 (S9), with La/Y values less than 1 for the bauxite top S7 and the coal seam S6. This typically suggests that the diagenetic environment of the bauxite and its substrate was alkaline, whereas the top environment gradually became weakly acidic during diagenesis. XRD diffraction patterns reveal the presence of cookeite in S7, rutile in S8, quartz and mica in S9, and kaolinite and boehmite across all samples (Figure 5). Ruttile, primarily derived from the weathering of titanite and associated with REEs, particularly the Y group [40], suggests that the changes in the depositional diagenetic environment's acidity and alkalinity of the bauxite substrate are likely influenced by the source rock composition. This influence could be due to mixed materials from the in situ weathering of intermediate-acidic rocks and carbonates, indicating a genetic relationship between bauxite and acidic rocks, as well as carbonates. Sr and Ba are both prevalent in the crust and share similar chemical properties in some respects, but they behave quite differently in various sedimentary environments. Sr has a greater mobility in water than Ba. As water salinity increases, Ba precipitates first as BaSO\({}_{4}\) followed by the gradual accumulation of Sr, eventually forming SrSO\({}_{4}\). Consequently, the Sr/Ba ratio can indicate whether sediments are influenced by marine or terrestrial environments. Typically, when Sr/Ba > 1, it suggests saline deposits; when \(0.6<\) Sr/Ba < 1, it indicates brackish deposits; and when Sr/Ba < 0.6, freshwater deposits [41; 42]. The data in Table 2 signify that in the Jinyu profile, clay and bauxite rocks have Sr/Ba > 1, with the Y1 and mudstone Y4 bed having \(0.6<\) Sr/Ba < 1, and Y2 and Y3 having Sr/Ba < 0.6. Likewise, in the Jinshi profile, the clay and bauxite rocks exhibit Sr/Ba > 1, with the two coal layers and S1 layer having \(0.6<\) Sr/Ba < 1, and S3 and S4 having Sr/Ba < 0.6. These geochemical characteristics imply that during the diagenesis of the aluminum-bearing strata, the water body  
Figure 9: Standardized distribution curve of rare earth elements in the upper crust of the Pinglu aluminiferous strata. Note: (**a**) Jinyu profile strata, (**b**) Jinshi profile strata. was predominantly influenced by a marine environment, mainly saline, with transitional brackish and terrestrial freshwater environments within the strata.