Phosphorite from the upper continental slope off Kachchh, northwest coast of India

Abstract

Flat slabs and irregular lumps (1 to 3 cm) of brown, grey, black phosphorites and creamy white limestone (2 to 4 cm) were recovered from 473 and 501 m depths from the upper continental slope off Kachchh. Phosphorites contain phosphatised skeletal fragments of shallow water origin, calcitic patches and phosphatised black peloids set in dark brownish microsphorite. Limestone contains fragments of foraminifera set in micrite. Carbonate fluorapatite, carbonate hydroxylapatite, ankerite, calcite in phosphorites and high magnesium calcite in limestone are the major minerals. Electron microprobe studies indicate the presence of Ca, P, Mg, Si, Al, K, Fe, S and Ti in phosphorites. P2O5 content of phosphorites and limestone are 29.42% and 11.76% respectively. It is suggested that the phosphatization is an;early diagenetic process took place in shallow wa ter condition most likely du ring the Quaternary period. Subsequently, tectonic changes brought them to the present site and thus occurring as relict phosphorites.