Mobilization and redistribution of phosphate and rare earth elements in the weathering zone above Panda Hill carbonatite, SW Tanzania

Petrographic and geochemical studies of a 12m deep weathering profile above the Cretaceous Panda Hill carbonatite, southwest Tanzania, indicate that leaching of calcite from the primary carbonatite has led to the accumulation of apatite in the saprolite zone. Ba, Sr and REEs from the carbonatite, and Al, Fe and Si from country rocks have been transported by groundwater and redeposited in secondary phosphates, Fe oxides, and secondary quartz.Most of the phosphate at Panda Hill is contained in apatite. Alteration of apatite has enabled Ba, Sr and the REEs to substitute for Ca, and S04 for P04 in the apatite structure. Such substitutions, along with the addition of Al, have led to the formation of goyazite and svanbergite. Rhabdophane was also identified. All of these minerals are concentrated in the saprolite zone. Synchysite was identified in the carbonatite.