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