GEOLOGY, GEOCHEMISTRY AND PETROGENESIS OF GRANITE SUITES AND PEGMATITES IN THE NORTHERN PART OF MANDARA HILLS GWOZA SHEET 114, NORTHEASTERN NIGERIA
GEOLOGY, GEOCHEMISTRY AND PETROGENESIS OF GRANITE SUITES AND PEGMATITES IN THE NORTHERN PART OF MANDARA HILLS GWOZA SHEET 114, NORTHEASTERN NIGERIA
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Date
2015-02
Authors
GIREI, BALA MUSA
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Abstract
This research work focused on the petrological and geochemical characteristics of the granites and pegmatites in the northern part of Mandara Hills part of sheet 114 (Gwoza), so as to constrain their evolutionary history and to determine their mineralization potential, based on new sets of petrological and geochemical data. The area is underlain by low-lying migmatite gneiss, amphibolites, granite suites, aplite and pegmatites. The granite suites vary in texture and composition and comprise of diorite, mediun grained biotite hornblende granite, porphyritic biotite granite, coarse grained biotite granite, medium grained biotite granite, fine grained biotite granite and tectonised granite (cataclasite). Two types of pegmatites have been mapped in the area. Type-I pegmatite occurs as large oval-shaped bodies trending in E-W directions, and type-II occurs mainly as veins often cross-cutting their host rocks and strike mainly in the NE-SW direction.
The results obtained revealed that the migmatitic gneiss is metaluminous, cal-alkaline and was derived from igneous protoliths. The amphibolite has tholeiitic chemistry and TiO2 versus SiO2 discrimination plot shows that it was derived from igneous protoliths. The granite suites on the othe-r hand, are ferroan, calc-alkaline, metalumnous to slightly peraluminous I-type granites. The high Th/U (greater than 2.5), high K and Rb contents, as well as negative distribution trends of Ba, Sr and Nb on trace elements spider diagram suggest crustal source for the granites. The strong negative correlation of most major element with increasing acidity (SiO2) on the Harker diagram suggest that fraction crystallization has played a significant role in the evolutionary history of the granite suites.
The two types of pegmatites mapped in the study area differ significantly not only in their field occurrences but also in chemistry. The type-I pegmatite shows negative Ce anomaly and has high Rb but low Sr and Ba contents. This pegmatite is also moderately fractionated but barren with respect to rare-metal mineralization. However, the pegmatite hosts “ferroan pyroxmangite” which contains 10.00 wt. % of MnO, 28.33 wt. % Fe2O3 and 33.20 wt. % of SiO2. The mineral is considered as a potential ore of manganese. This pegmatite probably formed from fractional crystallization of a flux bearing granitic melts and is co-magmatic with the granite suites. The type-II pegmatite, on the other hand is characterized by low Rb but high Ba and Sr contents. This pegmatite is primitive and barren and probably formed from the anatexis of granitic rocks at shallow depth.
Description
A THESIS SUBMITTE TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD
OF A MASTER DEGREE IN GEOLOGY
Keywords
GEOLOGY,, GEOCHEMISTRY,, PETROGENESIS,, GRANITE,, SUITES AND PEGMATITES, NORTHERN PART,, MANDARA,, HILLS GWOZA,, SHEET 114,, NORTHEASTERN,, NIGERIA.