Petrography and Geochemistry of the Banded Iron Formation of the Gangfelum Area, Northeastern Nigeria

摘要

The Gangfelum Banded Iron Formation (BIF) is located within the basement complex of northeastern Nigeria. It is characterized by alternate bands of iron oxide and quartz. Petrographic studies show that the BIF consist mainly of hematite, goethite subordinate magnetite and accessory minerals including rutile, apatite, tourmaline and zircon. Chemical data from inductively coupled plasma optical emission spectrometer (ICP-OES) and inductively coupled plasma mass spectrometer (ICP-MS) show that average Fe 2 O 3(t) is 53.91 wt.%. The average values of Al 2 O 3 and CaO are 1.41 and 0.05 wt.% respectively, TiO 2 and MnO are less than 0.5 wt. % each. The data suggested that the BIF is the oxide facies type. Trace element concentrations of Ba (67-332 ppm), Ni (28-35 ppm), Sr (13-55 ppm) and Zr (16-25 ppm) in the Gangfelum BIF are low and similar to the Maru and Muro BIF in northern Nigeria and also the Algoma iron formation from North America, the Orissa iron oxide facies of India and the Itabirite from Minas Gerais in Brazil. The evolution of the Gangfelum BIF involved metamorphism of chemically precipitated or rhythmically deposited iron-rich sediments into hematite-quartz rocks. The banding of the BIF suggested a break in iron precipitation probably due to iron oxide deficiency. ?