Scandium geochemistry of phosphorites, Guizhou, southwest China.

Phosphorite accounts for about 30% of world and 26% of Chinese Sc resources, with many deposits concentrated along the western margin of the Yangtze Platform. A study was made of Sc geochemistry and correlation with chondrite-normalised REE patterns in Late Sinian and Early Cambrian P-bearing formations. A comparison between the phosphorites, tuffs and other strata showed that Sc and REE were most likely to have been derived from earlier or contemporaneous marine volcanics or tuffs, with no indication of a genetic link to purple shales, siltstones and dolomites in the area. Enrichment in heavy S isotopes suggested that the Sc-bearing phosphorites had formed in a relatively closed basin environment, far from the coast and characterised by abundant plankton. Apatite in the high-grade phosphorus ores had probably formed in a system with a low Ca/P ratio at a pH between 7 and 7.8; the other major minerals suggested slightly reducing conditions with Eh between 0 and -0.3.
Phosphorite accounts for about 30% of world and 26% of Chinese Sc resources, with many deposits concentrated along the western margin of the Yangtze Platform. A study was made of Sc geochemistry and correlation with chondrite-normalised REE patterns in Late Sinian and Early Cambrian P-bearing formations. A comparison between the phosphorites, tuffs and other strata showed that Sc and REE were most likely to have been derived from earlier or contemporaneous marine volcanics or tuffs, with no indication of a genetic link to purple shales, siltstones and dolomites in the area. Enrichment in heavy S isotopes suggested that the Sc-bearing phosphorites had formed in a relatively closed basin environment, far from the coast and characterised by abundant plankton. Apatite in the high-grade phosphorus ores had probably formed in a system with a low Ca/P ratio at a pH between 7 and 7.8; the other major minerals suggested slightly reducing conditions with Eh between 0 and -0.3.