Geochemistry and K-Argeochronologyof Rare Metal Pegmatite, Osogbo-Okinni Area, Southwester

Abstract

Osogbo-Okinni pegmatite bodies intruded gneissic granite, quartzite, amphibolite, and granite as low-lying, thin, and massive dykes, sometimes up to 500mx150m in size. Quartz (25.0%), microcline (34.0%) and plagioclase (24.0%) were the main mineral constituents, with muscovite(5.0%), biotite (5.0%), and tourmaline (7.0%) as minor constituents. The mean concentration of SiO Al O Na O, K O and TiO were 70.92, 15.95, 3.5, 4.23, and 0.02wt%, 2, 2 3, 2 2 2 respectively. Average whole pegmatite trace elements contents (ppm) were 283.95, 101.94, and 70.35 for Ba, W, and Ta. LREE sum (18.92ppm) greater than HREE sum (2.22ppm), Low K/Rb (50.37-340.77) and Mg/Li (1.23-36.54) ratios indicated fractionated pegmatites.The mica extracts average trace elements contents (ppm) was 510.86, 104.86, 376.88, 1101.97, and 272.41 for Sn, Sc, Li, Rb, Nb, respectively. Na O+K O versus SiO , Al O /Na O+K O 2 2 2 2 3 2 2 versus Al O /CaO+Na O+K O and K/Rb versus Cs plots indicated an igneous origin, peraluminous nature and 2 3 2 2 placement in the muscovite class of lithium-caesium-tantalum pegmatite family.The unspiked K-Ar dating, (Cassignol technique) yielded an absolute age of 774-692 Ma for the pegmatites, corresponding to evolution during the early Pan-African orogeny. This agrees with the early Brasiliano orogeny of South America (790Ma; 730- 700Ma), both of which were created during the Gondwana formation between the Neoproterozoic and Cambrian evidenced by the presence of post-collisional granitoid plutons.

Publication Info:

Author: Owoyemi, K.A. , Okunlola, O.A. and Hollanda, M.H.B.M.

Volume: 59

Issue: March

Published By: Journal of Mining and Geology Vol. 59(1) 2023. pp. 19 - 35, 2023-03-01