Investigation of the Ni-rich regolith in Bavanat region, Fars province, Iran: Constraints from mineralogy, geochemistry and Ni isotopes

A nickel-rich regolith outcrops discontinuously in varying thickness between the Sedimentary Zagros Orogenic (SZO) and Metamorphic Sanandaj-Sirjan (MSS) belts in Fars province, southwest Iran. It is the only known Ni-bearing regolith in the country. The laterites occur as residual and transported regolith in the Bavanat region. Profiles of the residual regolith from bottom to top include protolith, hard and soft saprolite, and oxide horizon. The parent rock is a highly serpentinized harzburgite containing relicts of olivine and orthopyroxene. From the hard saprolite to the oxide horizon, the proportions of hematite, goethite, talc, dolomite, and quartz increase, while chlorite, olivine, serpentine, and pyroxene decrease. Hematite and goethite are the dominant mineral phases in the oxide horizon. Part of the profile of transported regolith, especially oxide horizon has moved downslope due to landslide, slip, creep, and likely faulting. The Ni concentration varies gradually along the laterite profiles, with a maximum grade of 1.2 wt% in the oxide horizon. SEM-EDS data show that Ni released from serpentine group minerals in the parent rock was concentrated in the hematite of the oxide horizon. The isotopic fractionation of Ni along the soil profiles is controlled by the circulation of meteoric water and the intensity of weathering with formation of secondary minerals.

Automated summary

A nickel-rich regolith is discontinuously distributed between the Sedimentary Zagros Orogenic (SZO) and Metamorphic Sanandaj-Sirjan (MSS) belts in Fars province, southwest Iran. The nickel concentration varies along the laterite profiles, with the highest grade in the oxide horizon. Nickel release from serpentine group minerals in the parent rock is concentrated in the oxide horizon, influenced by meteoric water circulation and intensity of weathering.