Metamorphic phosphate deposits
• Evate. This large and probably metamorphic phosphate deposit lies within the Monapo structure, 100 km east of Nampula and close to the port of Nacala. The Evate apatite-magnetite-biotite mineralization occurs in the oval shaped 970 ± 23 million years old Monapo structure, composed of a metasedimentary sequence of biotite and graphitic gneisses with two separate marble horizons. The Evate marble deposit is 3 km long and 850 m wide. The phosphate-mineralized zones, 5-100 m thick, occur within the marble horizons. The phosphate-rich zones contain fluor-apatite as well as magnetite, forsterite, phlogopite, graphite and minor diopside (Cilek 1989; Manhica 1991). Preliminary reserve estimates indicate a resource of 155,413,000 tonnes of apatite ore at 9.32% P2O5, 5.76% Fe and 1.12%TiO2 (Manhica 1991; Ministry of Mineral Resources and Energy 1997). The reserves were calculated to a depth of 100 m above sea level. With approximately 14.5 million tonnes of P2O5 this is one of the largest phosphate deposits in east-central Africa.
The Evate apatite deposit is capped by a blanket of residual soil, 3-38 m thick, containing 4-64% apatite. The phosphate reserves of the residual apatite, calculated by Davidson (1986), reach 1.5 million tonnes of apatite concentrate. On a P2O5 basis, this would add another 525,000 tonnes P2O5 to the Evate deposit.
The magnetite- and apatite-rich residual soils might lend themselves to simple beneficiation and concentration of apatite and magnetite.