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Mines

Sedimentary Basins

Madagascar is composed of five basins covering a total 636.185 km² extending from the border of the basement till to the Exclusive Economic Zone (EEZ) in offshore.

The three most important basins, Ambilobe, Majunga and Morondava, lay in the western part of the island. The two remaining smaller basins, are both offshore : the Cap Sainte Marie basin in the South and the East Coast basin.

The sediments of Madagascar are constituted by two major systems:

  • the Karroo formation Permian to Eo-Lias in age containing thick continental sediments


  • the Post Karroo mainly deposited in marine environment.

The western basins have a common geological history, initiated by intra-cratonic rifts during the Neo Permian/Eo-Triassic period. They contain thick continental clastic sequences then overlied by Triassic to Lias sag deltaic to fluvial sequences.

Subsequent Toarcian rifting and southward drifting of Madagascar away from Somalia coast to its present location have controlled the Jurassic to Neocomian deposition. They have created a passive margin along the coast.

Continued subsidence and westward tilting in response to the rifting and drifting of India North-eastward during the Late Cretaceous, have led to a thickly developed Mesozoic and Cenozoic sequence in each basin.

The two latter basins are poorly understood:

    • the Cap Sainte Marie basin could have Permian and Mesozoic fills underlying the Neogene cover,
  • the East Coast basin may have thick Cretaceous section beneath the lava flow, cropping out along the onshore narrow sedimentary basin.
MADAGASCAR CHRONO-STRATIGRAPHICAL CHART
STRUCTURAL MAP OF MADAGASCAR (Dave Clark & al)

DRIFTING OF MADAGASCAR

The Majunga salt basin setting would have occurred just before Madagascar South-Westwards drifting.

Madagascar left the Somalia coast 165 millions years ago.

The drifting event lasted 65 million years, Madagascar has reached its present location since Aptian-Albian. (100 MY ago).

India North-Eastward drifting started at about 84 million years ago.

Madagascar, Somalia and Kenya share a common geological history through the Karroo system deposition : Permian to Early Lias.

Majunga and South-East Somalia basins were conjugate and Morondava basin were joint with Kenya and North Tanzania.

Sedimentation of Madagascar basins is controlled by the main tectonic events which have shaped Madagascar.

They are responsible of the major faulting trends. All Madagascar fault systems are inhe-rited from the basement. They have reacted through the geological times.

We record four main directions
  • N-S related to Permo-Triassic failed rift setting

  • NNE-SSW related to Toarcian rift setting and Cretaceous rift which has initiated India drifting

  • NNW-SSE corresponding to the direction of the Northern part of the Eat coast and the Ampasindava and Bemaraha trends.

  • NWN– ESE represented by Ranotsara trend in basement relaying by fault system in center Morondava underlined by gabbroic dykes

MADAGASCAR LOCATION 
PRIOR THE DRIFTING

modified from Reeves & al. (1987)

Uranium Potential

The Uranium occurrences in Madagascar are divided  into 4 mains areas. The exploration has been undertaken for several years:

  • The Neogene lacustrine basin of Antsirabe where secondary uranium mineralization occurs in small and erratic lenses. Several hundred tons of uranium have been reported in this area.
  • Uranium in pegmatitic formations (Betafo Faratsiho ,Near Soavinandriana Itasy ...) , and also in detrital or sedimentary formations (Vinaninkarena ...) The operating and ore processing tests were performed Vinaninkarena ; pegmatites were the operating object for niobotantalates uranium ( and other Betafite ) . Uranium can be held in several minerals such betafite , ampangabeite , samarskite , euxenite , fergusonite included pegmatites in Antsirabe - Faratsiho area .

Companies partners: PAMA (Pan African Mining Atomic) - PETRA Madagascar have allowed research on this region.

  • The region of Fort Dauphin, in the extreme south-eastern Madagascar, where uranothorianite occurs in calcomagnesian Shale Tranomaro Group.

Companies partners: URAMAD - PAMA (Pan African Mining Atomic ) - BLUE SUN MINING - ENERGY CORPORATION MADAGASCAR - MINERALS DEVELOPMENT CORPORATION - MADAGASCAR MINERALS FIELDS performed work Uranium exploration in this area

  •  Sedimentary system areas Karoo West , North West (Folakara) and southwest (Makay) , where the secondary uranium minerals are uranovanadate (carnotite) or francevillite ore.

Companies partners: PAMA (Pan African Mining Atomic) - URAMAD exploration campaign carried out the survey in this region

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