The geology, geochemistry and exploration of igneous phosphates northwest of Mumbwa (Big Concession) Central Province of Zambia
The syenites and quartz feldspar porphyries of the Mumbwa district occur as satellite bodies at the north east margin of the Hook Granite Massif, a large batholith dated 456 Ma, and intrude the pre-Cambrian Katanga metasediments. The composition of syenitic rocks varies from hornblende biotite syenite, through leucocratic porphyritic and microsyenite to pseudo-trachyte. Within the syenites occur large xenoliths of calc-silicate rocks. The syenites are quartz-bearing linked petrologically and chemically to alkaline magmatism formed during the final development of Pan-African batholiths. Geological, geochemical and geophysical investigations led to the discovery of a new type of phosphate deposit occurring as apatite pegmatite ore bodies N.E. Sugar Loaf, with estimated reserves of 0.22 X 106 tonnes at 12 percent P2Os . At Sugar Loaf Hill investigations are not complete. Resources of phosphate bearing material has been estimated in the range of 0.5 - 1.0 x 106 tonnes at 5 percent P2O5. Trace element studies show that the syenites are high level intrusions that resulted from differentiation of parental magma and assimilation of country rocks. Tectonic setting of the syenites has been classified as within-plate granite, of the attenuated continental crust. For future phosphate exploration locally and regionally, the most favourable target areas would be post-orogenic fractionated alkaline syenitic bodies occuring at the margin of large granitic batholiths associated with deep seated faults.
Geology -Mumbwa , Geochemistry , Exploration of igneous phosphates - Mumbwa