The occurrence of phosphorites on the Calicut mount, off Kerala, Lakshadweep Sea, India

A highly altered carbonate rock was recovered from the mount, off Calicut, Kerala. Bulk chemical analysis of the rock showed that it contains ~ 21 % P2O5. The rock consists of fine to coarse lithic and bio-clasts embedded in brown to the yellow coloured phosphatic matrix. Detailed SEM-EDS of the rock piece indicates micro-globular and nodular growth of phosphorite around calcite to form a core-rim structure, with P2O5 as high as 31.67 weight percentage. The X-ray elemental mapping carried out using EPMA indicates highest P2O5 (29.87 %) on the altered surfaces. Microstructural and geochemical analyses suggest authigenic/diagenetic precipitation of phosphorite on the carbonate rock