Geochemical Characteristic and Petrogenesis of Malumfashi Schist around Tandama Area , North - Western Nigeria

Abstract

Malumfashi schists which occur in association with migmatite - gneisses and biotite gr anite, occupy about 60% of Tandama area, north - western Nigeria . These rocks were studied with a view to evaluate their compos itional characteristics and their evolution. The lithology revealed from systematic mapping and petrographic examinations shows that the schist is mica schist, which is part of the Malumfashi Schist Belt of Nigeria. The mica schist consists of greater than 50% micaceous mine rals and less than 50% quartz and feldspar. It is light grey to silver grey in colour, well foliated and mostly weathered to rusty brown or reddish brown. Mineralogical determinations from optical studies show a high proportion of biotite and minor amounts of plagioclase and quartz. Chemical analysis of the samples obtained by Inductively Coupled Plasma Mass Spectrometry (ICPMS) instrumentation method, involving major and trace elements reveal s the nature of the mica sch ist. The A - C N - K diagram reveals a shale protolith which suffered moderate to high chemical weathering, prior to being metamorphosed. Obtained Rb/Sr ratio ( >0.4% ) and SiO 2 / Al 2 O 3 values support the shale protolith hypothesis for the schist, diagnostic geochemical featur es like the Na 2 O/Al 2 O 3 values, trace element ratios such as Th/U and REE patterns suggest that the protolith are predominantly derived from felsic igneous sources. Tectonically, SiO 2 /Al 2 O 3 versus K 2 O/Na 2 O plot revealed the protolith to have evolved within passive margin environment