Abstract
The Kuh-e-sefid phosphorite is located in Zagros fold-thrust belt, in the Ramhormoz area, northeast of Khuzestan province. Phosphorite mineralization occurred as phosphorite lenses of Eocene age hosted by the Pabdeh Formation. The aim of this study is to investigate the role of organic matter in trace metal portioning during phosphorite mineralization in the Kuh-e-Sefid deposit. Field observations and petrographic studies indicate that the host-rock of mineralization is mainly consists of shale, marl, and limestone with textures varying from wackestone to packestone. Phosphoritic components, such as authigenic apatite, pellets, intraclasts, fish skeletal fragments, and micro-fossils are present. Moreover, non-phosphorite minerals including calcite, glauconite, pyrite, iron-oxide and to a lesser extend montmorillonite with microcrystalline quartz occurred in phosphorite lenses. NASC-normalized patterns of REEs showed the enrichment of Heavy Rare Earth elements (HREE) and negative Ce anomaly with co-existence of slightly negative and positive Eu anomalies represent a transitional change from oxic to anoxic sedimentation conditions during mineralization. Importantly, Ni/Co versus V/Cr ratios and V/(V + Ni) diagrams confirmed dysoxic to anoxic conditions for the hydrocarbon-bearing phosphorite and hosted shales, while non-hydrocarbon-bearing phosphorites exhibit oxic conditions. The FTIR studies revealed qualitative information about the component bonds and nature of the organic matter and mineral-organic bonds like OH, carboxylic OH, carboxylic acid CO, CC alkaline, group CH2, CC aromatic, CH aliphatic, and aromatic stretching associated with phosphate mineralization. It seems that there is a link between a relatively high concentration of trace metals (i.e., REEs, U, Co, Zn, Ni, V, Sr and Mo) and phosphorites enriched in organic matter especially those of aromatic hydrocarbon groups.
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