The geology and geochemistry of the Maru Banded Iron-Formation, northwestern Nigeria

Abstract

Narrow units (< 1–30 m thick) of banded iron-formation (BIF) occur in the low-grade schist belt of the Maru district, northwest Nigeria. The schist belt consists of a deformed sequence of pelitic to semi-pelitic phyllites with subordinate iron-formation and quartiztes, and also amphibolites of inferred tholeiitic volcanic origin. The Maru BIF is commonly interlayered with phyllites within an antiformal fold. It consists essentially of a magnetite oxide facies with sporadic silicate facies composed of grunerite, garnet and rare stilpnomelane. In the BIF, Fe 2O 3 (as total Fe) ranges from 44.07 to 58.41 % and SiO 2 from 24.74 to 42.67%. Relatively high values of Al 2O 3 (2.00–8.97%) and MnO (2.29–9.37%) are characteristic of the iron-formation. On the basis of bulk geochemical affinity and rock association, the Maru BIF is similar to the Lake Superior-type BIFs. However, it differs from them in containing comparatively high amounts of Al 2O 3 MnO, TiO 2 Ba, Sr, Co and Zr. The close association of the BIF with metasediments, supported by geochemical evidence, suggests its derivation from a deeply weathered peneplaned hinterland. The BIF precursor materials were probably transported by sluggish flowing rivers and deposited under mixed river fresh water-sea water conditions in a restricted or sheltered basin.