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Ibrahim Uysal, Karadeniz Technical University (Turkey)
Federica Zaccarini, Department of Applied Geological Sciences and Geophysics, University of Leoben (Austria)
M. Burhan Sadiklar, Karadeniz Technical University (Turkey)
Mahmud Tarkian, Institute of Mineralogy and Petrology, University of Hamburg (Germany)
Giorgio Garuti, Department of Earth Sciences, University of Modena and Reggio Emilia (Italy)
H. Juergen Bernhardt, ZEM, Institute of Geology, Mineralogy and Geophysic, University of Ruhr (Germany)
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Chromium is one of the essential elements of the modern industry, being used in the industry of steel, refractory and chemicals. Chromite ore is the only economic source of this element and Turkey has fairly large resources of this mineral and has been a major chromite producing country for many decades. Most of the Turkish chromitites are podiform-type and occur in the mantle sequence of ophiolites with suprasubduction zone affinity. Recent investigations had shown that platinum-group elements (PGE) concentrations in podiform chromitites are some order of magnitude higher than those of their host peridotites. This peculiarity makes these chromitites a potential target also for PGE recovery. In this work we present and compare the results of a mineralogical and geochemical investigation of different podiform chromitite occurrences, namely Kahramanmaras, Kop Mountains, Mugla and Eskisehir located in Turkey. The analysed chromites by electron microprobe, display a variable concentration of Cr2O3 wt% varying from 39.62-63.29. The maximum contents, as wt% of other elements are: of Al2O3 18.93, MgO 15.34 and total FeO 19.88. TiO2 wt% content is very low, being invariably less than 0.4. On the basis of the composition of chromite, in all the investigated localities refractory and metallurgical chromitites are present. PGE concentrations are low ranging from 28 to 1305 ppb. The general trend of the investigated chromitites resembles most mantle hosted ophiolitic chromitites, displaying an enrichment of Ru+Os+Ir over Rh+Pt+Pd. However, in the some samples a weak Pt and Pd enrichment have been observed.
All the investigated chromitites contain Platinum-group minerals (PGM). The PGM form single phase grains or they occur in polyphasic grains in association with base-metals sulfides, silicates and other PGM. They have a very small size, generally less than 10 microns, and occur enclosed in fresh and altered chromite crystals, along fissures and in the silicate matrix. The most abundant PGM discovered are Ru-Os-Ir phases (laurite, erlichmanite, Os-Ir-Ru alloys and irarsite), whereas Rh, Pt and Pd bearing PGM have been rarely encountered. Due to the small size of PGM, low PGE content (maximum total PGE = 1305 ppb), and the predominance of Ru-Os-Ir over the most valuable Rh-Pt-Pd, the investigated Turkish chromitites represent only a future potential target for PGE recovery.
Only few samples show a pronounced positive Pt anomaly, that is supported by identification of Pt specific phases. The Pt-bearing PGM were found exclusively included in fresh chromite, thus indicating primary magmatic origin. These chromitites represent a potential target for Pt recovery, therefore detailed study of the Pt mineralogy, distribution in the chromite ore, and identification of the mantle source of magmas anomalous in Pt and mechanisms of Pt concentration are necessary tools to future exploration.
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