Albitization in the Inkisi Sandstones, Republic of Congo: Characterization and Interpretation

Abstract

Albitization appears to be one of the most important transformations affecting aluminium silicates in the superficial zone of the Earth’s crust, occurring in a variety of different formations. However, this process has not yet been clearly recognized in Africa. In this paper, we present the process of albitization in the context of an African sedimentary basin, in particular the Neoproterozoic to Palaeozoic arkosic sandstones of the Niari basin in the Republic of Congo. Differents faciès, mineral parageneses associated, chemical compositions of these albitizations are presented. The morphology of these albitization textures, which are often developed as a peripheral halo composed of pure albite surrounding (with a sharp contact) the practically unaltered potassium feldspar, would argue in favour of in situ albitization. In the same way, the presence of calcium-rich zones sometimes surrounding the albitized domains would support this hypothesis, the calcium being exsolved at the outer grain boundary during in situ formation of the albite. Thus, the presence of in situ albitization in the Inkisi sandstone could indicate an important marine influence on the sedimentary environment and diagenesis of these sandstones.

Keywords: Albitization, Sandstone, Inkisi, Congo, Feldspar