Geology of Mozambique

South of the Save River, unconsolidated sediments are an important source of groundwater, overlying the Mozambique Basin. A 30 kilometer wide belt of dune sands occupies the southern coast of the country, atop Cretaceous and Paleogene rocks and form a moderately productive unconfined aquifer. Thick alluvium in the Limpopo River and Incomati River valleys forms a major aquifer in high porosity sands north of Maputo.

Marine and continental sandstones dominate deeper Cretaceous-Paleogene sedimentary aquifers and some also contain layers of limestone. These underlying rocks in the Mozambique Basin form the largest aquifer, beneath 21% of the country. Cut by large river valleys, arkosic sandstones give way to limestone closer to the coast. North of the Save River, the basin is moderately productive, but to the south it has high salinity nearly unusable groundwater for much of its extent. The Rovuma Basin is poorly studied, but impermeable marl and high incidences of brackish groundwater suggest it would not be a major potential source. As much as 57% of Mozambique is directly underlain by Precambrian basement rock, which forms some small and locally productive aquifers in weathered rock near the surface. Mountain areas tend to have thicker weathered mantle, with most productive locations near fault zones. In northern Mozambique, average weathered rock cover is less than 20 meters thick, rising to as much as 50 meters in valleys. Fractured volcanic rocks form locally productive aquifers, producing high quality water, often in 10 to 20 meter thick weathered rock near the surface. However, weathered basalt often ends up with high clay concentrations, limiting productivity.^[4]

Mozambique has extensive natural resources, although most remain undeveloped. The Manica Belt is a continuation of the Mutare-Manica Gold Belt from Zimbabwe and contains iron, copper, asbestos, gold, lead and nickel hosted in an Archean and Paleoproterozoic greenstone belt. Small mines in the region have targeted placer gold in sediments in the area and there is also a small, high-grade bauxite deposit. The metasediments of Gairezi Group and Umkondo Group both host limestone, copper and iron near the border with Zimbabwe. Mozambique has four asbestos deposits. One has chrysotile asbestos crystals, separated by serpentinite in the Zimbabwe Craton, near Manica. Others are in the Mozambique Belt, or associated with serpentinization south of Manica. Seven out of the nation's 10 provinces have graphite in Proterozoic rock associated with schist and gneiss. Semi-precious stones, feldspar, beryl (including aquamarine and morganite), mica and radioactive minerals are found with pegmatites in the Proterozoic rocks in Zambezia Province and Nampula Province. Elsewhere, in the northeast, pegmatite hosts lithium, bismuth, quartz, beryl, columbium, antimony and tantalum.

The Eocene Cheringoma Formation and the Miocene Jofane Formation contain limestone, halite and gypsum. Mozambique is also notable for beach sands between Quelimane and Angoche, laden with zircon, rutile, monazite and ilmenite. The country has 120 to 380 million tons of coal reserves in the bottom units of the Karoo Supergroup in the Rio Lunho Basin. The Cretaceous Grudja Formation in shows the most promise for potential hydrocarbons and Mesozoic sedimentary sequences in the north and south both have the possibility of future discoveries.^[5]