Iron ore deposits associated with Hormuz evaporitic series in Hormuz and Pohl salt diapirs, Hormuzgan province, southern Iran

Abstract

Three types of iron ore, including banded ore, hydrothermal-metasomatic ore and earthy hematite ochre occur in Hormuz and Pohl salt diapirs. Primary banded ores of upper Neoproterozoic age contain alternating iron-rich and silica-rich bands, which characterized by the presence of folded hematite-rich bands and glacial diamictite fragments of quartz, dropstone and other clastics. Hematite as specularite and oligist is the major mineral in the iron-rich bands with minor goethite, pyrite, magnetite and rare siderite. Textural relationships between the ore and gangue minerals indicate that these ores are Rapitan-type sedimentary banded iron deposits. This is supported by the geochemical data of iron ores, such as low concentration of Al2O3, TiO2, Ba, V, Cr, Co, Ni, Cu and other trace elements, plus high value of MnO, Fe/V and Fe/Ti ratios, and REE patterns. Subsequent to the formation of iron ore deposits, an immense thickness of evaporitic rocks was formed in the oceanic marginal basins. Negative δ13C and δ18O values of the cap carbonates and strong positive δ34S values of the underlying sulfates are similar to the isotopic patterns of Ediacaran Rapitan-type iron deposits. Due to salt diapirism in the upper Mesozoic and Cenozoic eras, secondary iron deposits were formed by the activation of hot hydrothermal fluids during salt rising. High contents of some indicative elements such as Sr, Zr, U, Th, Pb, Zn, Sn, W and Mo in the metasomatic iron ores showed that they are the products of iron ore remobilization–redeposition in a hydrothermal system. The nearness of these ores to the fault zones is consistent with the scheme of migration and redeposition of iron compounds as metasomatic deposits under oxidizing conditions. Finally, earthy ochre was formed following the weathering and erosion of pre-existent iron ores.