Rare Earth Element Geochemistry Of Groundwaters From The Fogang Granitoid Weathering Crust, Guangdong Province

Groundwater from the granitoid weathering crust is broadly distributed in Southern China. It is an important drinking water resource for people who live there. During the weathering of granite, groundwater from the granitoid weathering crust have special chemical compositions. In this thesis, we research into the geochemical data of the groundwater from the granitoid weathering crust of the Fogang granite in Baisha region, Guangdong Province. In particular, the rare earth element (REE) concentrations and REE distribution patterns are studied in detail for different degrees of weathered granitic samples. Our results indicated that REE concentrations of groundwater within the granitoid weathering crust in Baisha area are high relative to many groundwater samples within granite weathering crust worldwide. The highest total REE concentration we determined is 114 g/L, about one to two orders higher than those from other places worldwide. So the safety of drinking water deserves great attention.In the thesis, the REE concentration and REE distribution patterns are also studied for stream water, granite fissure water and water from carbonatite around the Baisha region. There is a weak negative correlation between REE concentrations and pH values in these groundwater samples. Weathering degree and REE concentrations of the parent rocks are the main factors affecting the concentration of REE in the groundwater. On the PAAS-normalized plots, the parent granite and the granite weathering crust are enriched in LREE without Ce anomaly. While the groundwaters are also enriched in LREE, they display significant negative Ce anomaly, indicating the fractionation of Ce during water-rock interaction. Based on the study of two profiles of granitoid weathering crust, we concluded that REE concentrations in the groundwaters from the granitoid weathering crust are likely related to the continued chemical weathering, as well as the REE concentrations in the crust near the water table, clay concentration and the water pH values.