THE GEOLOGY, GEOCHEMISTRY AND MINERALIZATION OF THE ARUFU-AKWANA-UGBA AREA, MIDDLE BENUE TROUGH

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Date
1992-06
Authors
CHUKU, DANIEL UKAEGBU
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Abstract
Geological mapping of the Arufu-Akwana-Ugba area of the Middle Benue Trough indicates that it consists of Cretaceous sediments deposited in a series of depressions formed by the defferential subsidence of the Pan-African basement confined by the trough. Some of these sediments are continental in origin and may have fluviodeltaic members while the majority are marine Inside the trough isolated differentially faulted blocks outcrop at the present erosion level as horst-like inliers, sometimes in the form of ridges which are separated by narrow local basins filled with sedimentary series upto 3,000 metres thick. Both the inliers and the sediments are elongated along the NE-SVV direction of the main axis of the trough. Among the sediments the oldest is the Pre-Asu River Sediments which are Pre-Aptian in age, and intruded by Aptian rhyolitic sills, while unconformably resting on the Basement Complex. The succeeding Asu River Croup consists of two formations, namely, the Middle-Upper Albian coral - and mollusc-bearing shallow marine Uomba Formation consisting of limestones, shales and siltstones, and Late Albian to Early Cenomanian Awe Formation which marks the beginning of the regressive phase of the Albian sea, with transition beds of shales and sandstones. It is overlain by the continental sands of the Keana Formation, followed by the marine strata of the Eze-Aku Formation. Structural analysis indicates that the Cretaceous sedimentary formations were subsequently folded, with fold axis parallel to the NE trending boundaries of the trough and apparently affected by later folding at right angles to the trough thus imparting a characteristic regional sinuosity of the fold axes similar to that found in the Lafia- Awe area by previous workers. The dominant NE trend coincides with the disposition of the Benue rift structure. The north-easterly trending fractures and faults are exploited by most of the galena-fluorite mineralization which occured in the area investigated. The fractures and faults are localized along the edges of the trough. The significance of the deeply penetrating Cretaceous marginal and axial basic intrusive rocks in relation to the galena mineralization and their possible relationship to the medial gravity anomaly and r i f t structure of the Middle Benue Trough, is explained. The economic potential of the area is studied with particular reference to the stratigraphic and structural controls of the mineralization. About 2,000 stream sediment samples were collected and analyzed mostly for Pb, Zn, and PH. The conclusions drawn from the interpretation of the geochemical data show that reconnaissance stream sediment survey proves a useful tool in exploring for blind ore mineralization in the Middle Benue Trough and that detailed investigation on suitable areas should concentrate on the marine Albian limestone-black shale-siltstone-fine sandstone Asu River Group proximal to major fault zones. Criteria for distinguishing the three episodes and types of galena mineralization can be best defined according to crystal morphology as follows: (c) Crystalline galena (Early Cenomanian) (b) Massive galena (latest Albian) (a) Galena specks and fibrous stringers (Late Albian). Prospects for tapping the brine resources, limestones, and stone aggregates are shown to be high
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A Dissertation submitted to the Postgtraduate School, Ahmadu Bello University, In partial fulfillment of the requirements of the degree of: Doctor of Philosophy (Ph.D) Department of Geology Faculty of Science Ahmadu Bello University, Zaria JUNE, 1992
Keywords
GEOLOGY,, GEOCHEMISTRY,, MINERALIZATION,, ARUFU-AKWANA-UGBA,, MIDDLE BENUE
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