Garnierite Mineralization of the Nickel Laterite Deposit in the East Sulawesi Ophiolite, Indonesia

Abstract

Indonesia retains many resources in diverse type of deposits that resulted from complex subduction tectonic settings. One of the main islands of Indonesia, Sulawesi, also surrounded by subduction zones having large ophiolite zone, the East Sulawesi ophiolite. With the large extent of ophiolite and tropical climate of Indonesia make nickel laterite deposits by weathering process. Nickel is a critical metal for making secondary battery and metal alloy, therefore, the production of nickel in the laterite deposits becomes having attention. In this study, we focus on the development of nickel laterite profile in the study area and the related mineralization of nickel ore mineral called garnierite. The location of the study area is Morowali, the eastern part of the East Sulawesi ophiolite. The profile of Morowali nickel laterite deposit is divided into saprolite, limonite and ferruginous cap from bedrock to surface showing difference in chemical composition and mineralization. Since the bedrock was exposed to the surface, laterization began and weathering progressed from top to bottom making ferruginous cap, limonite and saprolite horizons in regular sequence. As a result, immobile elements such as Fe, Al, Cr and Ti are enriched and alkaline elements are depleted in upper horizon. In case of Ni, it is enriched in saprolite horizon where the nickel containing mineral, garnierite, occurred in different colors, is abundant. Relatively high amount of nickel also can be observed in limonite zone. This might be due to the amount of nickel contained in goethite in limonite horizon.

The results of these garnierite analyses (XRD and EPMA) indicate that Morowali garnierites can be classified into serpentine-like and talc-like garnierites. The serpentine-like garnierites are creamy yellow and grass green garnierite having different Ni concentration. The creamy yellow garnierite has low NiO contents (2.63 wt.% NiO in average) and the grass green garnierite has the high amount of NiO contents up to 38.26 wt.% (17.01 wt.% in average). The talc-like garnierite is jade green in color garnierite and it has moderate NiO contents (6.37 wt.% in average). The serpentine-like garnierites were made during laterization by exchanging Mg with Ni in serpentine and the talc-like garnierite is secondary originated garnierite.