Compositional features of precambrian pegmatites of Ago-Iwoye area South Western, Nigeria

Abstract

The increase in global demand for rare metal Ta-Nb deposits has caused a resurgence of interest in the search for economically viable deposits. Precambrian pegmatites occurring as near vertical dykes have been studied, with the aim of determining their compositional features and possible economic values. Four thin sections were prepared from the pegmatites of the study area for petrographic study. A total of twenty five samples comprising whole rock pegmatites and extracts of mica were analyzed for major and trace elements using inductively coupled plasma-atomic emission spectrometry analytical technique (ICP-AES). Petrographic study shows that quartz, microcline, plagioclase are the main mineral constituents under transmitted light. From the results, the whole rock pegmatite is considerably siliceous, but with noticeable depletion of silica in the mica extract. Average Fe 2 O 3 , Mgo, Mno, and TiO 2 values are low in all samples (< 2.00%). The samples are fairly enriched in Rb, Sr, Zr, but comparatively, poor in the rare metals Ta, Nb, W, Cs and Sn. Rare metal mineralization enrichment indices mainly, Ta vs Nb, Ta vs K/Cs, plots, show its depletion in rare metal mineralization, suggesting Ago-Iwoye pegmatites to be barren in rare-metal mineralization when compared with other rare-metal pegmatites across the world.

Petrochemical Evaluations of the Pan African Pegmatites of Apomu Area, Southwestern Nigeria

“…The analytical results are presented in Tables 2, 3, 4, 5 and 6. Major element distribution show that the pegmatites are siliceous; with SiO 2 content ranging between 46.03% and 73.54% with an average value of 69.31%; this is marginally lower than average values of rare metal Ta-Nb pegmatite of Nigeria (Okunlola, 2005) but comparable to the Ipetu ijesha barren pegmatites (Elueze, 1982), and Ago-Iwoye barren pegmatites (Akintola et al, 2011). From the analytical result of major element concentration, SiO 2 has the highest percentages in the pegmatite samples while P 2 O 5 , TiO 2 , K 2 O, Na 2 O, CaO and MnO are relatively low, in the same vein MnO (0.01-0.23%), TiO 2 (0.01-0.69%), P 2 O 5 (0.02-0.23%) values are generally low (Tables 2 and 4).…”

“…From the analytical result of major element concentration, SiO 2 has the highest percentages in the pegmatite samples while P 2 O 5 , TiO 2 , K 2 O, Na 2 O, CaO and MnO are relatively low, in the same vein MnO (0.01-0.23%), TiO 2 (0.01-0.69%), P 2 O 5 (0.02-0.23%) values are generally low (Tables 2 and 4). Mean contents of major oxides, Al 2 O 3 (14.34% ), Na 2 O (3.31%), Fe 2 O 3 ( 2.61%), CaO (1.63%), and K 2 O (4.80%) for the Apomu pegmatites compare favorably with the Ipetu Ijesha barren pegmatites , Kafin Maiyaki barren pegmatites and Ago-Iwoye barren pegmatites ( Elueze, 1982;Garba, 2003;Okunlola, 2005;Akintola et al, 2011). Trace and rare earth element data (Tables 3, 5 and 6) show that the following trace element Rb (540.1ppm), Cs (11.3ppm), Nb (26.6ppm), Ta (3.8ppm), Be (6.0ppm), Th (19.9ppm), Hf (8.3ppm), Y(108.9ppm), Sn (9.0ppm), Sr (531.7ppm) for the whole rock pegmatite samples of Apomu area has values that are significantly lower than the averages for the rare metal pegmatites of Ijero-Aramoko-Ara, Kushaka-Birni Gwari, Oke-Ogun, Isanlu-Egbe and Share but are comparable to the Ilesha barren pegmatites (Elueze, 1982;Okunlola, 2005) , Nasarawa-Kafin-Maiyaki barren pegmatites (Garba, 2003) and Ago-Iwoye barren Pegmatites (Akintola et al, 2011).…”

“…Mean contents of major oxides, Al 2 O 3 (14.34% ), Na 2 O (3.31%), Fe 2 O 3 ( 2.61%), CaO (1.63%), and K 2 O (4.80%) for the Apomu pegmatites compare favorably with the Ipetu Ijesha barren pegmatites , Kafin Maiyaki barren pegmatites and Ago-Iwoye barren pegmatites ( Elueze, 1982;Garba, 2003;Okunlola, 2005;Akintola et al, 2011). Trace and rare earth element data (Tables 3, 5 and 6) show that the following trace element Rb (540.1ppm), Cs (11.3ppm), Nb (26.6ppm), Ta (3.8ppm), Be (6.0ppm), Th (19.9ppm), Hf (8.3ppm), Y(108.9ppm), Sn (9.0ppm), Sr (531.7ppm) for the whole rock pegmatite samples of Apomu area has values that are significantly lower than the averages for the rare metal pegmatites of Ijero-Aramoko-Ara, Kushaka-Birni Gwari, Oke-Ogun, Isanlu-Egbe and Share but are comparable to the Ilesha barren pegmatites (Elueze, 1982;Okunlola, 2005) , Nasarawa-Kafin-Maiyaki barren pegmatites (Garba, 2003) and Ago-Iwoye barren Pegmatites (Akintola et al, 2011). The Rb/Sr ratio is low when compared to other rare metal mineralized pegmatites of Nigeria (Matheis & Emofurieta, 1987;Okunlola & Ocan, 2002;Okunlola, 2005, Elueze, 1980 but compares with the barren Nasarawa pegmatites (Garba, 2003).…”