Mineralogy and genesis of the Ni–Co lateritic regolith deposit of the Çaldağ area (Manisa, western Anatolia), Turkey

The Çaldağ Ni–Co deposit is characterized by a reddish brown oxide lateritic regolith, containing residual Ni deposit formed by the intense tropical weathering of peridotites. Nickel–Co ore is associated with transported ferricrete during the late Paleocene–middle Eocene, represented by colloform Fe oxides and residual lateritization during the Oligocene. The lateritic regoliths are developed over dunitic ultramafic rocks and consist mainly of smectite, berthierine, kaolinite, gypsum, pyrite, takovite, and pecoraite. These units were examined using polarized-light microscopy, X-ray diffraction, scanning and transmission electron microscopy, and geochemical methods. Mineralogical zonation from the base of the profile upwards has the following zones: ultramafic bedrocks, serpentinized ultramafic rocks (saprock), saprolite, carbonate- and sulfide-bearing zone, ferruginous saprolite zone, and silcrete. In addition, Fe oxides, smectite and opal-CT, and quartz increase towards the surface, whereas olivine, pyroxene, and serpentine decrease upwards in response to chemical weathering. Nickel–Co mineralization associated with Fe oxides and smectitic clays formed under wet and dry conditions, respectively, as a result of an increased Fe2O3 + Al2O3 + Ni + Co/MgO ratio. Field observations and mineralogical and geochemical analyses reveal that the smectite formed under basic conditions was controlled by multistage chemical weathering of ultramafic and volcanic rocks and by the concentrations of Si, Al, Fe, and Mg. Locally, concentrations of S in conjunction with Fe and Ca resulted in precipitation of goethite–hematite, gypsum, and pyrite in dissolution voids in association with smectite under acidic conditions that developed in a well-drained system. © 2018, Published by NRC Research Press.The study was supported by the Scientific and Technological Research Council of Turkey (TUBITAK). Mineralogy, micromorphology, and microchemistry studies of clay minerals were performed at Texas Tech University, Texas, USA. The authors are much indebted to Charles R.M. Butt (CSIRO Earth Science and Resource Engineering, Western Australia) and anonymous reviewers for their extremely careful and constructive reviews that improved the quality of the paper significantly. We are extremely grateful to Editor Ali Polat for his insightful editorial comments and suggestions. We are also grateful to Martin Wells (Mineral Resources, Kensington) and William L. Griffin (Macquarie University, Australia) for their critical and detailed reviews and suggestions on an early draft of the manuscript. We greatly thank Mehmet Yıldız and İ. Hakkı Karamanderesi for their help during the field studies. Mustafa Çiçek, Yasin Aydın, Okan Bektas¸, Tacit Külah, and Nergis Önalgil are also thanked for drafting assistance