Geological Information
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Deposit Type
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Metasomatite
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Geological Setting
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The Kitongo deposit area is part of the Pan-African Mobile Belt and is located between the Guinea and Congo cratons.
The Lower Proterozoic basement N'tem Complex consists of magmatic and metamorphic rocks and is characterized by high-grade metamorphism with partial to complete anatexis. It is overlain by the Middle-Upper ? Proterozoic Poli Group (schists, gneisses, metavolcanics) of lower grade of metamorphism, probably of the Kibaran Orogeny (1800-1200 Ma). They are in turn overlain by the Paleozoic to Mesozoic Mangbei Group, the clastic lithologies of the Cretaceous in the Benue Basin and the tertiary ring complexes and basalts.
Several granite intrusions of various ages cut through the older formations. The « Old Intrusions » are of Lower to Middle Proterozoic age, while the « young intrusions » are of Pan-African age (around 550 Ma). The Kitongo granite has not been dated, but it is suggested that it belongs to the « young p».
The oldest prominent regional structure is the northeast strike of the trough N 50°) containing the Poli Group. This structural direction was dominant during the Pan-African Orogeny and is expressed primarily by fracturing and shearing movement as well as magmatic activity, which played a very important rôle in in the emplacement of the Kitongo granite.
The predominent rock type is a light grey, medium-grained, hornblende-biotite granite with porphyritic alcali feldspars and a pronounced parallel texture (gneissose granite). Close to the uranium mineralization, the granite is progressively altered by an increase in the albite content and a decrease in quartz and K-feldspar content.
Lithology: Panafrican granite in schist of Poli Series; Stratigraphy=Mid-Upper Proterozoic
Tectonics: Contact fault zone between granite and schist
Alteration: Albitization, desilicification, hematitization
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Age of Mineralization
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Pan-African ?
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Mineralization
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The uranium mineralization occurs at the intersection of the Kitongo and Dombulko N 50° faults and the N 150° Ninga fault, on the northwest margin of the intrusion. It is located within a pink albitite developping along the faults.
The ore is mainly of the disseminated type and is thick, but with low value. The cataclastic type associated with the shear zones is the most economic and has locally a considerable thickness. This type is occasionnally associated with sulphides like galena, sphalerite, chalcopyrite, covellite and bornite. The vein type is subordinate, with very thin veinlets (< 1 cm), but with higher grades (> 0.1%)..
The primary uranium mineral is uraninite found between albite crystals as very small grains together with magnetite or hematite, frequently on the margins of mafic minerals. Secondary minerals are uranophane and beta-uranophane.
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MetallogenicAspects
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The Kitongo uranium deposit is the result of a metasomatic replacement of the country rocks:
- structurally controlled, syn-orogenic granitic intrusion of the Pan-African Orogeny along a deep-seated fault,
- late phase hot solutions (residual liquids of the magmatic differentiation) circulating along the fault zone and enriched in Na, Fe, U and O.,
- Na-rich solutions affecting large portions of the Kitongo granite and surrounding country rocks (albitization),
- as U is less mobile than Na, it remained restricted close by the Kitongo fault with the formation of the uraninite-albite-magnetite mineral association. It totally replaced the feldspars and quartz of the granite and changed the normal hornblende to Na-hornblende (arfvedsonite).
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Age of Mineralization
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Pan-African ?
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DepositShape
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steeply dipping prismatic bodies
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DepositDimensions
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Three mineralized zones have been defined:
- A (Kitongo fault): lengh 1050 m, height 250 m, width 10m (6563 tU),
- B (Ninga fault): 1500 m x 250 m x 5 m (4690 tU),
- C (Domboulko fault): 300 m x 250 m x 10 m (1875 tU).
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GeologicalRemarks
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Metallogenic Aspects
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The Kitongo uranium deposit is the result of a metasomatic replacement of the country rocks:
- structurally controlled, syn-orogenic granitic intrusion of the Pan-African Orogeny along a deep-seated fault,
- late phase hot solutions (residual liquids of the magmatic differentiation) circulating along the fault zone and enriched in Na, Fe, U and O.,
- Na-rich solutions affecting large portions of the Kitongo granite and surrounding country rocks (albitization),
- as U is less mobile than Na, it remained restricted close by the Kitongo fault with the formation of the uraninite-albite-magnetite mineral association. It totally replaced the feldspars and quartz of the granite and changed the normal hornblende to Na-hornblende (arfvedsonite).
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