Petrology and Geochemistry of Calc-Silicate Schists and Calc-Silicate Reaction Bands In The Jakura Marble, Western Nigeria
The Jakura Marble deposit is located ca. 50 km northwest of Lokoja, southwestern Nigeria. Calc-silicate schists occur as intercalations and lenses within the marble. The schists consist of hornblende, biotite, actinolite, plagioclase, quartz, accessory epidote, sphene, zircon, chlorite and apatite. Calc-silicate reaction bands developed at the contacts between the marble and calc-silicate schists consist of diopside, plagioclase, scapolite, late actinolite and epidote.
Chemically the calc-silicate schists are characterized by relatively high CaO, MgO, Cr, Ni, Sr, La, Ce and Nd contents compared with the mica schist regionally associated with the marble as well as the Post-Archean Australian Shale (PAAS). Relative to the ultramafic schist the calc-silicate schists are characterized by higher contents of K2O, Ba, Pb, Rb, La and Ce and lower MgO, CaO, Fe, Na2O, Cr and V. The calc-silicate reaction bands have higher contents of CaO and Sr and lower concentrations of K2O, Rb, Ni, and Ba relative to the calc-silicate schists; and relatively higher SiO2, TiO2, Al2O3, Fe2O3, MgO, Na2O, K2O and P2O5 and lower CaO contents compared to the marble.
These features suggest that the protoliths of the calc-silicate schists were admixtures of carbonate material with some ultramafic detritus, and the reaction band was produced by diffusion of elements from the calc-silicate schists into the marble contact zone.