Hydrothermal fluids responsible for the formation of precious minerals in the Nigerian Younger Granite Province     

S. I. Abaa 《Mineralium Deposita》1991,26(1):34-39

Preliminary investigations in the Younger Granite Province of Nigeria have revealed that precious and semi-precious minerals like rubies, sapphires, emeralds, aquamarine, zircon and fluorite can be found in the region. The gem minerals are shown to have been produced either by direct deposition along fissures, veins and greisens by hydrothermal fluids or as a result of hydrothermal fluids reacting with wall-rocks. These wall rocks are either biotite granites from which the hydrothermal fluids originated or basement rocks or any other rocks which the biotite granites intrude and their residual hydrothermal fluids have invaded. The hydrothermal fluids appear to have been rich in alkalis (Na⁺, K⁺, etc.), rare elements (Be, Zr, F, REE, etc.) and siliceous. As these fluids rose through fractures and channel ways through the rocks, they either deposited the gem minerals in the fractures at the appropriate stability conditions or reacted with the wall-rocks producing the gem minerals at the expense of elements like Ca and A1 in the minerals of these rocks.  相似文献   

Petrographic composition and depositional environments of Cretaceous coals and coal measures in the Middle Benue Trough of Nigeria     

N.G. Obaje  B. Ligouis  S.I. Abaa 《International Journal of Coal Geology》1994,26(3-4)

Cretaceous coals and coal measure sequences in the area around the Obi/Lafia part of the Middle Benue Trough of Nigeria were studied petrographically. The Turonian-Santonian Awgu Formation and the Maastrichtian Lafia Formation constitute the sedimentary successions in both outcrop and borehole profiles of this area.Maceral analyses of 32 coal samples from this area allow subdivision of the coal beds into three different coal facies: the vitrinite-fusinite coal facies, the trimaceritic coal facies and the shaly coal facies. In the vitrinite-fusinite coal facies, vitrinite constitutes, on average 67.3%, liptinite 4.2%, inertinite 17.1% and mineral matter 11.4%. The trimaceritic coal facies has 42.3% vitrinite, 22.4% liptinite, 23.8% inertinite and 11.5% mineral matter. In the shaly coal facies, vitrinite constitutes 29.9%. Liptinite, inertinite and mineral matter are 13.8%, 22.0% and 34.3%, respectively.Correlation of the distribution of microfossils in the interseam sediments with the tissue preservation, gelification, groundwater and vegetation indices of the coal facies indicates that the vitrinite-fusinite coal facies was deposited in wet forest swamp subenvironments along and within lagoons. The trimaceritic facies was deposited in limno-telmatic clastic marsh subenvironments in lower delta plains. The shaly coal facies shows characteristics of various subenvironments but generally tends to be more marine than the other two facies.  相似文献