Mineralogical characterization of low-grade nickel laterites from the North Oman Mountains: Using mineral liberation analyses – scanning electron microscopy-based automated quantitative mineralogy

Afterwards to the Late Cretaceous obduction of the Tethyan Semail ophiolite suite intense chemical weathering involved the Oman Mountains region. This weathering produced complex mineral and chemical assemblages that led to the formation of a Ni lateritic paleosol. In the present study, five laterite sections were sampled and studied by using a quantitative mineralogical and petrographic approach. Mineral liberation analyses (MLA) were carried out for the first time for several selected samples. The MLA results, supported by the Electron probe micro-analyzer (EPMA) and Energy-dispersive X-ray spectroscopy (EDX) analyses, revealed that the main ore minerals of the analyzed laterite are chlorite and goethite as the main Ni-bearing hosts. Magnetite and chromite are also present as by-product minerals. The Ni-bearing chlorite in the Saqah-3 and Al Russayl profiles have coarser grains compared to those in the other Saqah localities, while the goethite grains are coarse in most of the analyzed samples. The presence of approximately 60 to 80% of both the Ni-bearing minerals (chlorite and goethite) as liberated phases (>95% free) is a potential indicator for their future exploration. Chromite and magnetite grains are present in a wide range of grain sizes. Seventy percent of the chromite grains in Saqah-4 and Al Russayl profiles and 70% of the magnetite in Saqah-2 occur as liberated phases (>95%) compared to their presence in other profiles, where only half of them occur as liberated phases. The grain-size-liberation class relationships showed that Ni-bearing mineral phases (chlorite and goethite) are present as liberated phases (high-grade materials) followed by chromite and magnetite, which are interlocked with other phases to lower grade materials. A better understanding of the mineralogical and geochemical quantitative characterization, such as grain size, modal analyses, mineral association, and percentage of interlock between minerals in the deposit, can avoid the metallurgical problems, thus possibly reducing the operational costs and improving the recovery of metals. The above-obtained MLA parameters can build a good feasibility study during the exploration stage of these low-grade Ni deposits in the Northern Oman Mountains, as well as later during their beneficiation and processing methods, if other economic and mining factors are deemed favorable.