Enrichment regularities for iodine concentration in phosphorite of Doushantuo Formation of Late Ediacaran in Guizhou Province, SW China

Iodine was relatively enriched in the sedimentary phosphorite that formed during the Doushantuo period of Late Ediacaran, South China, especially in the Central of Guizhou Province, Southwest China. The resources of the associated iodine in the phosphorite are extremely high. The analysis and test of elements such as iodine in the phosphorus-bearing rock series reveal that iodine occurs only in the phosphorite and the iodine has positive correlation with P2O5 and CaO which are the main components of apatite, while has negative correlation with major oxides including MgO, Na2O, Fe2O3, TiO2 and K2O, which showed that the iodine is mainly rich in phosphorite. Meanwhile, it was observed that the iodine content is the highest in the gray-white clastic phosphorite, but is relatively low in the gray-black carbonaceous phosphorite. Discussion of the sedimentary environment in the research area showed that the gray, gray-white nest-like, particle-like, and fragmental algae-enriched phosphorite feature the most abundant iodine element, with the average content of 59 mg kg−1 and the maximum value of 98 mg kg−1. The compacted blocky phosphorite deposited in the neritic marine basin facies only has trace iodine, maybe due to the impact on the iodine absorption caused by the inhibition of algae propagation under anaerobic and reduction conditions. Results of correlation analysis illustrate that the relationship between iodine and the number of algae was suggested. Based on the aforementioned regulations and conditions for the iodine concentration in the phosphorite of the Late Edicanran Doushantuoian, the main iodine-enriched of ore, ore type, and facies belt were considered biogenic apatite, clastic phosphorite, and neritic marine platform facies, respectively.