EXPLORING NICKEL GEOCHEMISTRY IN IRANIAN NI LATERITE DEPOSIT

Nickel (Ni) is a critical metal, playing a vital role in various modern technologies. Due to the rapid growth of Iran's steel industry, the country is actively on the lookout for Ni deposits. The primary source of the world's Ni supply is from nickel-laterite deposits. Chah-Gheyb is the first and only explored Ni deposit in Iran with a reserve of ~102 kt of Ni (purity = 0.92 %). Nickel originated from the weathering of serpentinized ultramafic rocks. It is situated as 1-meter-thick lateritic zone over serpentinites. After thorough characterization of the sapropelic, limonitic, and lateritic zones, a systematic sampling approach was employed. Sequentially, samples weighing approximately 1 kg were taken at regular intervals from the bottom to the top of the sequence.

To determine the mode of occurrence of Ni, a mineralogical study was carried out using microscopic and microanalytical techniques. Chemical compositions of chromite, magnetite and goethite were determined by Electron Probe Micro Analysis (EPMA) (15 nA, 15 kV). In the lateritic zone, chromites showed ~51 – 63 wt% Cr₂O₃, ~11 –21wt% Al₂O₃, ~7 – 11 wt% MgO and Cr#= 0.77-0.94. Chromites in limonitic zone showed 48 -55 wt% Cr₂O₃, 9 -18 wt% Al₂O₃, 9-14 wt% MgO, and Cr# of 0.60-0.89. Magnetite minerals in lateritic samples are mostly composed of FeO (~85 wt%) with very small amounts of Cr₂O₃ (~0.2 wt%). FeO content in goethite ranged from 59 to 82 wt%. Lateritic samples contain ~0.4 – 4.6 wt% NiO while the content of NiO in limonitic samples is ~1.5 wt%. Concentration of Ni in all the chromites and magnetites was below the detection limit. Back Scatter Image (BSI) and EPMA analyses showed that Ni does not present in spinel phase whilst being enriched in goethite. This indicates the higher partition coefficient of this element, which favors its incorporation into olivine lattice. Therefore, they have been able to be liberated readily during serpentinization and transferred into the newly-formed weathering products, especially goethite. Our results show the absence of discrete Ni minerals, such as garnierite, in this deposit and support the development of an ore processing strategy based on Ni being associated with goethite.