THE PETROLOGY OF BASEMENT ROCKS AND ASPECTS OF GOLD MINERALIZATION IN KUTCHERI AREA, WONAKA SCHIST BELT, NORTHWESTERN NIGERIA
THE PETROLOGY OF BASEMENT ROCKS AND ASPECTS OF GOLD MINERALIZATION IN KUTCHERI AREA, WONAKA SCHIST BELT, NORTHWESTERN NIGERIA
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Date
2014-05
Authors
AMUDA, Abdulgafar Kayode
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Abstract
The study area forms part of the Precambrian to Early Paleozoic Nigerian Basement complex. Multispectral images from Landsat 7 ETM+ were utilized to complement lithological mapping, elucidate lineaments and clearly outline alteration zones. Field mapping in Faskari and Chafe was carried out using topographical map of Funtua NW sheet 78 on a scale 1: 50, 000 and the area of gold mineralization around Kutcheri were further mapped on a scale of 1: 25, 000 to study it in more detail. Petrographic studies of 16 samples were conducted using transmitted light microscope. The geochemical analysis of 10 representative samples for major and trace elements was carried out using X-ray fluorescence technique, inductively coupled sector field mass spectrometry. Also, 13 quartz vein samples were analysed for target (Au) and pathfinder elements (Pb, Hg, Cu, Ag and Zn) using Atomic Absorption Spectrophotometer. The dominant rock types are gneisses, metasediments, granites and serpentinite with minor quartz-tourmaline rock, aplite dyke, quartzofeldspathic and quartz veins. Petrographic studies have shown that the gneisses include banded gneiss, porphyroblastic and granite gneiss that mainly composed of quartz, feldspar, biotite ± pyroxene. The metasediments include biotite schist and phyllite that are composed of quartz, biotite, feldspar, ± muscovite, ± chlorite. The granites include medium to coarse grained to porphyritic varieties and are mainly composed of quartz, feldspar and biotite.
These rocks have been deformed; sheared with joints and foliation. The dominant foliation trend NNE-SSW to NE-SW, follows the general trend of structures resulting from Pan-African Orogeny. Traces of other trend directions thought to be pre-Pan African are also observed.
Exfoliation and tectonic joints with non-orthogonal joint pattern are observed. Both dextral and sinistral strike slip faults are observed on granites. Folds mainly had NNE-SSW axial trend. Geochemical analyses results show that SiO2 in gneisses range from 72.2-64.2 wt.%, and metasediments from 68.5-58.0 wt.%. The K2O in gneisses ranges from 5.32-1.52 wt.% and metasediments from 5.42-1.98 wt.%. The Na2O is generally higher in gneisses 5.18-3.39 wt.% than in the metasediment 3.35-0.71 wt.%. The CaO content of all lithologies overlaps (1.07-2.86 wt%) except for phyllite (0.61 wt%). The alkali and alkali earth elements are enriched in the gneisses with Sr varying from 574.0-103.1 ppm, Rb from 336.9-67.6 ppm and Ba from 1415-215 ppm compared with the metasediments with Sr varying from 213.1-60.0 ppm, Rb from 170.4-58.9 ppm and Ba from 1155-419.0 ppm respectively. Similar trend occurred in rare earth element being significantly enriched in the gneisses with La from 392.3-14.2 ppm, Ce from 690.5-29.0 ppm, Eu from 2.55-0.74 ppm and Lu from 0.72-0.15 than in the metasediments with La from 29.0-20.2 ppm, Ce from 60.3-41.8 ppm, Eu from 1.31-1.08 and Lu from 0.50-0.36 ppm respectively. Moderate to high mobility of alkali elements K and Na confirms low grade metamorphism for the metasediments (greenschist facies) and low to medium grade for the gneisses (greenschist to lower amphibolite facies). The gneisses are of igneous parentage except granite gneiss that may be sedimentary. The gneisses have granitic to granodioritic composition related to granite that originated from magma enriched in alumina relative to alkalis. Paleoweathering estimates point to relatively moderate to intense chemical weathering of the metasedimentary source rocks that are immature.
Normalised trace element shows a striking parallelism with upper continental crust for the metasediments while the gneisses are more evolved. Relative depletion of HREE and enrichment of LREE with significant negative Eu anomaly in the gneisses and metasediments shows that plagioclase feldspar fractionates. Negative Ce anomaly in granite gneiss indicates absence of zircon while negative Ce anomaly characteristics of the metasediments indicates anoxic to suboxic condition during metamorphism. Alluvial/elluvial gold grains with pristine, modified and reshaped morphology occur in sediments while primary gold mineralization is presumed to occur in quartz veins. Geochemical investigation for target (Au) and some pathfinder elements (Pb, Hg, Cu, Ag and Zn) show Au concentration to range between < 1-4.8 ppm, Pb (<2-28 ppm), Hg (<0.5 ppm), Cu (6.2 to 61.4 ppm), Ag (<0.5 ppm) and Zn (8.8 to 39 ppm). There is no significant statistical difference between the Au, Pb, Cu, Ag and Zn content in Dutsen Burka and Gidan Boss area. Pearson correlation coefficient shows Cu and Pb are indicator elements for Au in the area.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA; IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF A MASTER OF SCIENCE DEGREE IN GEOLOGY DEPARTMENT OF GEOLOGY FACULTY OF SCIENCE AHMADU BELLO UNIVERSITY, ZARIA NIGERIA MAY, 2014
Keywords
BASEMENT,, PETROLOGY,, ROCKS,, ASPECTS,, GOLD MINERALIZATION,, KUTCHERI AREA,, WONAKA SCHIST BELT,, NORTHWESTERN NIGERIA.