Geology, mineralogy and geochemical properties of the Çaldag Ni-Co laterite deposits [Çaldag (turgutlu-manisa) lateritik Ni-Co yatagının jeolojisi, mineralojisi ve jeokimyasal özellikleri]

Çaldag Ni-Co deposit covers an area approximately 10 km2 on the Çaldag horst of Gediz Graben. This world class Ni-Co deposit has recently started to be exploited. Extensive exploration drilling on the mineralization proved a reserve of 38 million tonnes, with a grade of 1.14% nickel and 0.05% cobalt. Showing complex and zoned structures, Çaldag mineralization is analogous to the New Caledonian type residual nickel deposits that are formed by the intense tropical weathering (lateritization) of the peridotites which consist of trace amounts of nickel. Çaldag Ni-Co mineralization is developed over the ultramafic rocks of Late Cretaceous-Early Paleocene ophiolitic mélange. The ophiolitic mélange consists of limestone blocks, radiolaria, and serpentinized ultramafic rock masses set in a matrix composed of interbedded sandstone-shale, spilitic volcanic rocks with pelagic limestone and shale intercalations. Peridotites with variable serpentinization are mainly composed of dunite, harzburgite and pyroxenite. The ophiolitic mélange was emplaced tectonically on the basement rocks of Menderes masif. The whole succession is uncomformably overlain by Upper Miocene-Lower Pliocene lacustrine sediments. Whole rock, trace and REE analysis on volcanic rocks implies that they have tholeiitic magmatic source and they formed in intra oceanic-arc environment. The primary Ni-bearing ore phases in serpentinized peridotites are pentlandite and associated nickel-sulfide alloys. In Çaldag mineralization, lateritic profile consists of serpentinized peridotites (% 0,2-1,2 Ni; % 0,04-0,11 Co), ironoxide and clay-rich saprolite (% 0,02-5,6 Ni; % 0,02-5,2 Co), carbonate and gypsum-bearing laterite (%0,2-1,2 Ni; % 0,04-0,11Co), and silica rich laterite (% 0,2-1,2 Ni; % 0,04-0,11 Co) with different Ni-Co contents. Two different lateritization stages are determined in the enrichment of Ni-Co ore; 1) Colloform goethite, limonite and hematite, Ni-Co asbolane and manganese oxides are mainly formed during the first lateritization stage (Upper Paleocene-Middle Eosene). Laterite was carried tectonically towards north to its present place by thrust faults during Upper Eocene. 2) The second lateritization took place in Oligocene, beside the colloform ore, takovite, pecoraite, manganese oxides, gypsum, bravoite, pyrite, marcasite and clay minerals such as nimite, halloysite, montmorillonite were deposited either as fracture infills or brecciated masses. Following the second lateritization event, the Çaldag lateritic deposit was covered by Mio-Pliocene terrestriallacustrine sedimentary units. During the Neotectonic period, the region was dissected by high-angle normal faults resulted in NW-SE trending horst and graben structures. The Çaldag horst was uplifted during this stage and the Plio-Quaternary alluvial fans were formed around the Çaldag Horst due to erosion of the rising blocks. Finally, the latest event resulted in erosion of the cover series and the Çaldag lateritic deposit cropped out over the Çaldag Horst