Sediment-Hosted Kaolin Deposit from Çakmaktepe (Uşak, Turkey): its Mineralogy, Geochemistry, and Genesis

Abstract

Because of their geochemical properties, the Ç akmaktepe (Us°ak) kaolin deposits have been considered as primary. New sedimentological, mineralogical, and geochemical data suggest that the Ç akmaktepe kaolins are secondary deposits of sedimentary processes after hydrothermal alteration of the source rocks. The kaolins in the Ç akmaktepe deposit were formed from the hydrothermal alteration of calcalkaline Karaboldere volcanics (KBV). The kaolinized materials were then reworked and accumulated in a lacustrine basin. The argillic alteration zones were associated with faults, and lateral zonation of minerals was observed in the KBV. Smectite was the major phyllosilicate in the 'outer zone'. The alteration mineralogy of the 'inner zone' was similar to that of the Ç akmaktepe kaolins and consisted mainly of kaolinite with minor amounts of smectite and alunite. The trace-element abundances in the kaolinized volcanics and the Ç akmaktepe kaolins indicated hypogene conditions. The d 18 O values of the Ç akmaktepe kaolins ranged from 0.2 to 5.92%, which indicated that the Ç akmaktepe kaolinites were formed at temperatures between 92 and 156ºC, and the dD values ranged from À91.68 to À109.45%. The irregular edge-to-face morphology, the variation in grain-size, a few broken crystals of kaolinite, the deficiency of dissolution-replacement and crystallization mechanisms, and the the low sphericity, very angular, and poorly sorted quartz crystals in the kaolins all result from transport processes. The sedimentary structures, including trough cross-lamination, tool marks, and load casts, indicate transportation by turbulent waters and deposition of kaolin layers in a shallow lake.