GEOLOGY, GEOCHEMISTRY AND STRUCTURAL CONTROLS OF BERYL MINERALIZATION IN THE PRECAMBRIAN PEGMATITES OF PARTS OF IKARA SHEET 103 (NW AND SW), NORTHWESTERN NIGERIA
GEOLOGY, GEOCHEMISTRY AND STRUCTURAL CONTROLS OF BERYL MINERALIZATION IN THE PRECAMBRIAN PEGMATITES OF PARTS OF IKARA SHEET 103 (NW AND SW), NORTHWESTERN NIGERIA
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Date
2018-08
Authors
YUNUSA, Adamu
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Abstract
The geology, geochemistry and structural controls of beryl mineralization in pegmatites of parts of Ikara Sheet 103 was studied to determine their genesis and beryl mineralization. Petrographic studies on the rocks collected from the study area were carriedout using transmitted light microscope. Whole rock geochemical analysis of the rocks and mineral chemistry of beryl were carriedout using XRF and ICP-MS analytical techniques. Study of lineaments and structural attributes were carried out by remote sensing and field measurements using compass clinometer. The area is made up of granites, gneisses, schist and quartzite as major rock types. Structural elements such as foliation, joints, veins and dykes were measured. The major and trace element chemistry of beryl were used to determine the relative fractionation of the pegmatites. Structural imprints of NE-SW trending joints and pegmatite and lineament analysis data defines the structural trends of the area. The rocks originated from metaluminous to peraluminous magma (A/CNK ratio below 1.1) and were probably sourced from an extreme fractionation of syn- to late tectonic granites (Niobium (1.93 to 8.98ppm) and Yitrium (13.67 to 40.36ppm)). The marked negative Eu anomaly and the LILE enrichment (Ba (upto 727ppm), Sr (upto 565ppm) and Rb (upto 310ppm) in the rocks is a typical signature of continental crustal material. Concentrations of Rb (40.7ppm), Cs (1022.5ppm) and Na2O (0.3wt %) in the beryls analyzed are among the lowest measured in pegmatitic beryl of similar colours worldwide. Beryl from pegmatites of parts of Ikara are compositionally similar to beryl derived from intermediate zones characterized by a low degree of fractionation and formed in a geochemical environment poor in alkaline elements. The discrimination plots of beryl indicate that the formation of the pegmatite was controlled mainly by fractional crystallization. Trace element data shows that the subsequent crystallization of three intermediate zones reflects changes in melt composition with a general decrease in femic elements and an increase in alkali elements. An evolution was also marked in the beryls REE pattern with an increase in ΣREE from early beryl to late beryl increasing with fractionation.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE DEGREE IN GEOLOGY (MINERAL EXPLORATION) DEPARTMENT OF GEOLOGY FACULTY OF PHYSICAL SCIENCES AHMADU BELLO UNIVERSITY, ZARIA
Keywords
GEOLOGY,, GEOCHEMISTRY,, STRUCTURAL CONTROLS,, BERYL MINERALIZATION,, PRECAMBRIAN PEGMATITES,, IKARA,, SHEET 103 (NW AND SW),, NORTHWESTERN NIGERIA,