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. v 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.
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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
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