Ore mineralogy and metal deportment of Fe-Ni-Co laterite deposits from Sebuku Island, SE Kalimantan, Indonesia

Indonesian laterite deposits are a major source of Ni and Co. Here, we present new geological data on the Sebuku laterites (SE Kalimantan, Indonesia), with a resource of ~390 Mt at 42.5 wt.% Fe, 0.9 wt.% Ni, and 0.15 wt.% Co. The deposits are mostly limonitic, oxide-dominated Fe-Ni-Co-rich horizons, which formed by weathering of Jurassic-Cretaceous ophiolitic units. Although the Fe ore has been mined since 2006, little mineralogical and geochemical data are available, which would allow optimizing beneficiation and recovery of Ni and Co.

Typical laterite profiles at Sebuku consist of: 1) weathered bedrock composed of serpentinized dunites and harzburgites overlain by 2) a 0.2-7 m-thick saprolite zone, 3) a 2-8.5 m-thick yellow limonite zone, and 4) a 1-3.5 m-thick red-limonite zone.

Preliminary XRF, XRD, and mineral liberation analysis (MLA) data show a decrease in Mg and Si and an increase in Fe moving upwards through the laterite profile, corresponding to a transition from silicate- to oxide-rich mineralogy. Oxides and (oxy)-hydroxides comprise goethite, maghemite, hematite, magnetite, chromium spinel, gibbsite/bayerite, and various Mn-minerals, whereas silicates consist of serpentine, chlorite, talc, quartz, pyroxene, olivine, and clay minerals. Ni is hosted by various minerals, which include goethite, Mn-oxides, serpentine, and clays, whereas Co is mainly hosted by Mn-oxides.

Mineral chemical analyses (EPMA) are planned to further understand critical metal variability and distribution within the host minerals and throughout the deposits. Our ultimate goal is to characterize and quantify the distribution of Ni and Co in order to develop more efficient beneficiation processes.