Abstract:

The study of variations of uranium and thorium abundances in the Guidong granite body suggested that the insitu melting resulted in enrichment of uranium and thorium elements at the top of the crustal granite layer, and caused spatial separation of the two elements which is shown by the fact that the maximal abundance zone of uranium in a granite body is generally located over that of thorium. Multiple insitu melting led not only to the formation of a composite granite body (CGB), but also to the enrichment of uranium in the younger members of the CGB. Characteristics of relatively higher uranium and lower thorium contents in the eastern part of the Early Yanshanian granite of Guidong CGB are considered to be related to the original buried depth of the sourcelayer of uranium (the SinianPrecambrian strata) while the difference of uranium abundance from south to north of the CGB is related to the attitude and erosion of the MI of the latest stage. It is concluded that the coexistence of high uranium content and high U/Th ratio usually indicates the possibility of a concealed granite body, which is of practical significance for exploration of concealed uranium deposits.

Key words:  uranium and thorium abundances, insitu melting, composite granite body (CGB), North Guangdong Province