Abstract
The Çaldağ nickel laterite deposit located in the Aegean region of W. Turkey contains a reserve of 33 million tons of Ni ore with an average grade of 1.14% Ni. The deposit is developed on an ophiolitic serpentinite body which was obducted onto Triassic dolomites in the Late Cretaceous. The deposit weathering profile is both laterally and vertically variable. A limonite zone, which is the main ore horizon, is located at the base of the profile. A hematite horizon is located above the limonite, which in the south of the deposit is capped by Eocene freshwater limestones and in the north by a siliceous horizon. The deposit is unusual in lacking a significant saprolite zone with little development of Ni-silicates. The boundary between the limonite zone and serpentinite below is sharp with a marked decrease in concentrations of MgO from 13 to 1 wt.% over a distance of 2 mm representing the ‘Mg discontinuity’. Ni concentrations within goethite, the main ore mineral, reach a maximum of ~3 wt.% near the base of the limonite zone. Silica concentrations are high throughout most of the laterite with up to 80 wt.% silica in the upper portion of some profiles. The combination of a serpentinite protolith and a high water table at Çaldağ, in association with an aggressive weathering environment in a tropical climate, resulted in the formation of an oxide-dominated deposit. The precipitation of silica may coincide with a change in climate with silica precipitation linked to an increase in seasonality. Additional variations within profile morphology are attributed to transportation during and after laterite development as a result of faulting, pocket type laterite formation and slumping, each of which produces a contrasting set of textural and geochemical features.
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Acknowledgements
This study was funded by a National Environment Research Council PhD studentship to R. Thorne, NER/S/A/2006/14212. Field work at Çaldağ was made possible by the support of European Nickel Plc. The authors also express gratitude to J. Spratt for his assistance with microprobe analysis at the Natural History Museum, R. Pearce for his aid with SEM imaging, and I. Croudace for his assistance with XRF analysis. This paper has also benefited from comments and suggestions by D. Teagle, B. Lehmann, and G. Paterson.
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Thorne, R., Herrington, R. & Roberts, S. Composition and origin of the Çaldağ oxide nickel laterite, W. Turkey. Miner Deposita 44, 581–595 (2009). https://doi.org/10.1007/s00126-009-0234-6
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DOI: https://doi.org/10.1007/s00126-009-0234-6