Bolkardağı bauxite deposits at Ayrancı, Karaman, Central Turkey. Part I. Geological setting

The region investigated is located 15 km southeast of the Ayrancı district (Central Turkey), covering an area of about 300 km². The aim of this study is to investigate the stratigraphical setting and erosional surface of bauxite deposits and examine their age in relation to host rocks. Thus, the geological evolution of the area and formation of bauxite deposits are discussed on the basis of geologic, tectonic and stratigraphic data. Permian–Cretaceous rocks of the Bolkardağı unit, which is one of the main tectonic associations comprising the Central Taurides, are found at the basement, and overlain by Miocene units. Sequence starts with the Upper Permian Dedeköy formation, which is composed of dolostone at the bottom and limestone to the top. It is conformably overlain by schist, phyllite, metasandstone and marble of the Lower Triassic Saraycık formation. Middle Triassic vein rocks of diabase composition (Kasır diabase), with a maximum diameter of 100 m, divide the Saraycık formation units. The Saraycık formation and all other old units are unconformably overlain by the Jurassic–Cretaceous Berendi formation. Karamanoğlu Ophiolite is pushed over the Berendi formation, seen as a thick carbonate sequence. This ophiolite was probably emplaced during the Late Cretaceous period. Karamanoğlu Ophiolite is unconformably overlain by Miocene Mazı and Divlek formations, which are represented by conglomeratesandstone and clayey limestones, respectively. The bauxite deposits are found within the Upper Permian Dedeköy formation, and between the Gerdekesyayla Dolostone and Bulgardede Limestone member, and also in the limestone. Geological setting and degree of metamorphism of these bauxites indicate that they were formed during the Late Triassic–Early Jurassic (?) period on Upper Permian carbonate rocks and Lower Triassic shale–sandstone–limestone units and before being transported into the dolines and caves of carbonate rocks. The fact that bauxites are formed on top of dolostone and on the top, base and within limestone may indicate that these two carbonate units response differently to karstification.