Geochemical characteristics of the niobium-rich arfvedsonite granites, Younger Granites province of Nigeria |
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| Authors: | PO Ogunleye EC Ike |
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| Institution: | a Centre for Energy Research and Training, Ahmadu Bello University, P.M.B. 1014, Zaria, Nigeria
b Department of Geology, Ahmadu Bello University, Zaria, Nigeria |
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| Abstract: | Arfvedsonite granites are most prevalent in the northern sector of the Nigerian anorogenic ring-complex province wherein they form the main granitic rocks at Kudaru and Fagam and are important components of Kila-Warji, Ririwai and Dutsen-Wai ring-complexes. The albitized variety of these rocks hosts pyrochlore to varying extents depending on the degree of albitization and are, therefore, important targets for niobium investigation. Geochemical data of the granites reveal that niobium has a mean concentration of 111 ppm in the arfvedsonite granite, increasing to 168 ppm in the aegirine arfvedsonite granite and reaching 1568 ppm in the albite arfvedsonite granite. Niobium is thus enriched in the albite arfvedsonite granite by a factor of 8-11 relative to its mean value in the aegirine arfvedsonite and arfvedsonite granites, respectively. Uranium contents show a sympathetic trend with niobium, being also enriched in the albite arfvedsonite granite relative to its abundance in both the aegirine arfvedsonite granite and arfvedsonite granite by a factor of 15. The uranium abundance in the albite arfvedsonite granite is more than 48 times higher than the mean background values in low-calcium granite.The REE fractionation patterns in all three arfvedsonite granite varieties are characterized by enrichment of both the light (La-Sm) and heavy (Gd-Lu) rare earth elements and a significant negative Eu anomaly. The albite arfvedsonite granite is, however, preferentially more enriched in the heavy REE relative to the aegirine arfvedsonite and the arfvedsonite granites. A plot of the ∑REE against Na2O and niobium reveals positive correlation in the arfvedsonite granites. There is also a linear relationship and strongly positive correlation between Nb and Na2O because the pyrochlore is most abundant in the most extensively albitized variety of the arfvedsonite granites. |
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| Keywords: | Anorogenic ring-complexes Arfvedsonite granites Albitization Pyrochlore mineralization Nigeria REE patterns |
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