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Geology of Kakanda, D.R.C.: implications for lithological and structural controls of Cu-Co mineralization of the Roan group, The
Twigg, Helen C.
Twigg, Helen C.
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2019
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2020-02-12
Abstract
The Neoproterozoic metasedimentary rocks of the Central African Copperbelt (CACB) host the world’s largest reserves of stratiform copper and cobalt and significant deposits of zinc, lead, gold, nickel and uranium. Models for development of the Congolese Copperbelt (CCB) basin including mineralization events and basin inversion remain controversial despite advances in basin system models pioneered in the petroleum industry. The role of halokinesis in CCB basin development and subsequent basin inversion is generally accepted, although still controversial. This study used district scale models of the Katangan Supergroup sediments, lithofacies studies of the Mines Subgroup and deposit scale geological models of lithology and mineralization of Mines Subgroup blocks to investigate local basin development, mineralization and inversion in the Kakanda mine area, DRC. Contrary to previous interpretations, the location of Mines Subgroup host rock blocks are not random. Their distribution is consistent with halokinetic processes mobilizing intrasalt blocks. The geology of Kakanda reflects salt tectonic processes. Common salt related structures found in the Kakanda area are: minibasins of suprasalt stratigraphy, breccia resistate after salt walls rooted stratigraphically below the Mwashya Formation, intrasalt blocks formed by encapsulating a diapir carapace, intrasalt blocks of syn-salt sediments, chaotic breccia resistate after allochthonous salt wings or salt sheets, and autochthonous carapaces of suprasalt formations. The Kakanda megabreccia complex is the surface exposure of two intersecting salt walls. The main salt wall, a splay from the Tilwezembi structure, is located over a southwest-down spoon shaped normal fault. The remainder of the Kakanda breccia complex trends northwest to intersect the Tenke-Fungurume breccia complex and southeastwards along the Kakanda-Luisha lineament. Mines Subgroup blocks in the Kakanda breccia complex are highly broken and disarticulated, but examination of variations of thickness and deposition environment among the blocks indicate little movement relation to one another. The distribution and deformation style of the Mines Subgroup rocks into disaggregated anticlines and synclines at Kakanda indicates that the Mines Subgroup was deposited between thick evaporites in the Roche Argilo-Talqeouses (R.A.T.) Subgroup below and in the Roches Greso Schisteuses (R.G.S.) Formation above. The distribution of copper and cobalt within the allochthonous Mines Subgroup Formation blocks initially appeared unpredictable. This study indicates that hypogene copper and cobalt distribution and trends within and between Mines Subgroup blocks at Kakanda is related to specific lithofacies groups as well as to proximity to up flow zones in the relict salt walls. Six endmember styles of mineralization controlled by host rock facies variability and fluid pathways were identified. Proximity to district scale basin faults is the primary indicator for mineralization. Most Cu-Co deposits in the Kakanda breccia complex are spatially located above the zone of maximum throw of a pre-salt spoon shaped listric normal fault which may have served as a major fluid conduit.
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