THE GEOLOGY, GEOCHEMISTRY AND MOLYBDENITE MINERALISATION OF THE KIGOM COMPLEX
THE GEOLOGY, GEOCHEMISTRY AND MOLYBDENITE MINERALISATION OF THE KIGOM COMPLEX
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Date
1992-09
Authors
JOSEPH, ITAH OMADA
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Abstract
Field, geological and geochemical studies of the Kingdom
complex and the associated molybdenum mineralization have been
undertaken.
The Kingdom complex, one of the late Jurassic contraindication
granitic intrusions into the Nigerian-Niger basement, consists of
four categories of granite with gravitational contacts between them:
the fatality-bearing Reginae micro-granite (oldest), the
arfvedsonite granite, the Beiderbecke granite and the riebeckiteaegirine-
biotech granite (youngest). The granites are hypersonic
containing micrometeorites with modified ex-solution textures of the
coexisting feldspar's. Close to the amphibious, the perquisites are
enriched in K-feldspar. This modification may reflect the local
removal of Na consumed in the late growth of sonic amphibious
suggesting that the K+ for Na+ ion exchange was most active in the
rocks as late magmatic minerals were being deposited. The
amphibious, optically both arfvedsonite and Beiderbecke, but
com-positionally Beckie arfvedsonites, are aristocratic
containing inclusions of Perth and quartz. Late hydrothermal
alterations along cleavages and at margins of the amphibious
produced Reginae, magnetite, and biotech as the K-rich fluid had
long reaction time with the sub-solidus minerals; a process that
becomes prevalent in-the-latter granites. Astrophyl1ite, fluorite,
tho-rite, and zircon are common accessory minerals in the rocks.
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The Kingdom granites typically display enrichment patterns
characteristic of per-alkaline androgenic A-type granites: high
Si02, Na20, K20, Fe203 (total Fe), Zr, Rb, Nb, F, and Y, and low Sr
and Ba. Differentiation indices clearly show that the perquisites
differentiated early in the crystallization history and that the
degree of per-alkalinity increases from the older to the younger
fancies following the trend of final consolidation of the magma
responsible for the Kingdom complex. This is related to the later
alkali metastasis by an alkali-rich fluid into the system such
that the more altered rocks are the most enriched in trace
elements. The trace element ratios are those characteristic of
late-granites, while their high values are indicative of shallow-level
sub-volcanic intrusions. The granites of the Kigom complex
have very low Mg/Mg+Fe ratio indicating a crustal source.
Molybdenum mineralization is of low-grade and occurs
disseminated in riebeckite granite at the contact between it and
the Samsonite granite, and the basement mitigate. The
molybdenum generally has inclusions of Perth with which it, in
places, has blunt contacts. Pyrite, which essentially constitutes
the outer zone of the mineralization, as well as chalcopyrite,
galena, Helvetica, and hairsplitter are also common in the ore zone.
Whole-rock and trace element studies of the ore zone indicate that
the Mo mineralisation, like most of the trace elements, represent
rest concentrations of elements which were initially present in the
magma but incompatible with the silicates and were therefore
deposited at relatively lower Eh/pH conditions at which stage the
vapour phase was supersaturated in Mo. The Mo in the melt was
introduced into it from the source. Molybdenite mineralisation
elsewhere in the world also are typically known to be associated
with calm-alkaline and per-alkaline magma series at a contact with
earlier granites and or the host rocks.
The Kigom has evolved as a peralkaline water-saturated and
F- and volatile-rich shallow-level subvolcanic magma; a condition
favourable for Mo enrichment.
Description
IN FULFILLMENT OF THE REQUIREMENTS OF THE POSTGRADUATE SCHOOL,
AHMADU BELLO UNIVERSITY, ZARIA, FOR THE AWARD OF A Ph.D GEOLOGY
(MINERAL EXPLORATION) IN THE DEPARTMENT OF GEOLOGY, AHMADU BELLO
UNIVERSITY,ZARIA
DEPARTMENT OF GEOLOGY
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA
SEPTEMBER, 1992
Keywords
GEOLOGY,, GEOCHEMISTRY,, MOLYBDENITE,, MINERALISATION,, KIGOM COMPLEX