Mineralogy, geochemistry of altered tuff from Cappadocia (Central Anatolia) and its use as potential raw material for the manufacturing of white cement

Abstract

The present study deals with mineralogy, geochemistry and uses of altered tuff from Cappadocia (Central Anatolia) as a potential raw material for the manufacturing of white cement. Mineralogical analyses show that altered tuffs are mainly composed of quartz and kaolinite. In some samples minerals such as jarosite, illite, smectite, sanidine and calcite have also been detected. A widespread, intensive hydrothermal alteration zone has developed across a NE–SW striking fault in the study area (Türkmenlik Hill). The field observations and the results of the analyses show that there are some changes in mineralogical and chemical composition across this fault zone. The central part of the fault zone shows an intensive silicification (> 85% SiO 2). The amount of kaolinite increases towards the outsides; the outermost zone is composed of smectite (illite) in association with quartz and kaolinite. This phase zonation supports the proposition that those minerals were probably formed by hydrothermal activity. The presence of jarosite in some samples indicates that the hydrothermal solution might have had acidic character. The geochemical analyses show that the major oxides such as K 2O, Na 2O, MgO, Fe 2O 3, CaO, MnO and P 2O 5 were leached out from parent rocks through hydrothermal alteration. The predominant number of the samples have very low concentrations (< 0.5%) of colouring elements such as Fe 2O 3 and MnO and thereby the material is very white. There is a strong correlation between Fe 2O 3 and whiteness-degree. The whiteness-degree value increases with decreasing Fe 2O 3 concentration ( r = − 0.9). Materials with Fe 2O 3 concentration lower than 0.5% have a whiteness-degree > 85%. These properties, which particularly depend on mineralogical and geochemical composition, allow the use of this rock as an industrial raw material for manufacturing white cement. The opportune geographical position of this material relative to the cement plants in Turkey offers very important advantages regarding transport cost, which can decrease the production cost of white cement by as much as 50%.