Phosphorite concretions in a sediment core from a bathymetric high off Goa, western continental margin of India

Abstract

A sediment core collected from a bathymetric high off Goa on the western continental margin of India, has yielded phosphorite concretions with an average Pd2O5 content of 32.75%, the P2O5 concentrations being highest ever reported from the margins of India. These concretions vary in size from 1 to 5 cm, are subrounded, oval to irregular in shape, dark grey to yellowish grey in colour and consist of carbonate fluorapatite (CFA) as the single mineral phase. The concretions are present in the sediments at various levels below 110 cm from the core top and appear to be older than at least 250,000 yrs. Our study indicates that the phosphate released into the interstitial water due to decomposition of organic matter and dissolution of fish debris is precipitated as microgranular phosphorites which are consolidated and progressively become concretions with time.