Geochemical prospecting in a greenstone-granite complex, South West Nigeria

• Main Author: Bammeke, B. O.
• Published: Swansea University 1986
• Subjects: 551.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636029

A low-density reconnaissance geochemical survey was made of the stream sediments and rocks in the Akaka/Ago-Iwoye, Egbe and Igbo-Ora districts of the southwestern basement complex, Nigeria. The areas are underlain by mainly Precambrian greenstone rocks in close association with granites, gneisses, metasediments (quartzites, quartz-mica schists) and pegmatites. Typical rain forest areas and streams are dissected by a closely and deeply developed dentritic-subdentritic drainage pattern. This study compares the three areas and includes recommendations for further prospecting. Field and mineralogical petrological evidence indicates sulphide mineralization, and geochemical trends in the amphibolites favour a tholeiitic affinity with ultrabasic igneous proliths overprinted by post-magmatic processes. The range of concentrations and geochemical characteristics of elements commonly found in rocks and sediments are reviewed. More than 350 samples were collected and analysed for 17 trace and 10 major elements by X-ray fluorescence, atomic absorption and inductively coupled plasma emission spectroscopy. Analytical precision was monitored using duplicates, standards and reference materials and the statistical basis of analytical quality control examined. Computer based univariate and multivariate statistical techniques are applied to the geochemical data. Initial univariate analyses clearly establish anomalous elemental abundances. Anomalously high Mo, significant Ni and Au values are characteristic of the areas investigated. Particular geochemical patterns of single-element distribution were found. In general, multi-element associations in the sediments were similar to those discerned in the associated bed-rocks. The application of multiple regression analysis to sediments from the Egbe area revealed enhanced Cu and Ni anomalous populations which were suppressed by iron-oxide coprecipitation. R-mode analysis identified models meaningful in terms of correlation either with underlying parent rock, secondary processes of the surifical environment and mineralization. However, there are no clearly defined indications of the ore potential of the Akaka area. The fourth-factor (Au-Sr) for rock samples in the Igbo-Ora complex confirms occurrence of gold mineralization. A clear-cut association of rare-earths are shown in all the areas. The most significant findings of the present work were the identification of exploration target areas worth further investigations. Other aspects highlighted were the possibility of reliable indicator elements for ore mineralization in these areas, significant anomalies being evident in the rocks and sediments.