REE GEOCHE ISTRY IN THE WEATHERING PROCESS OF GRANITES IN LONGNAN COUNTY, JIANGXI PROVINCE
Wu Chengyu, Huang Dianhao, (Institute of Mineral Deposits, Chinese Academy of Geological Scienses, Beijing) Guo Zhongxun (Geological Survey Party of South Jiangxi, Jiangxi Bureau of Geology and Mineral Resources)
Warm and humid climate with an annual rainfall of 1582 mm and gentle hilly geomorphology (300—400 m above sea level) have provided favourable conditions for the development of the weathering crust (a few m to 30 m) of the Zudong and Guanxi granite intrusions, Long nan County, Jiangxi Province. Most of REE but Ce are depleted in the surface soil zone which consists of the kaolinite-halloysite (7)-gibbsite-goethite assemblage. In the wholly weathered zone, where the main clay minerals are hallcysite (7) and kaolinite, REE are obviously enriched with significant negative Ce anomaly. Exchangeable REE account for 48—86%. Leacbing experiments and stable isotopic study of clay minerals suggest the downward ,penetration of meteoric water and increasing gradient of pH values have played an important role in the enrichment of REE during the progressive weathering process. Slight fractionation among individual REE cannot change their distribution patterns in the sections, which are inherited from parent rocks.