Borate Minerals and Related AutMgenic Silicates in Northeastern Mediterranean Late Miocene Continental Basins

Exploration & Mining Geology, Vol. 2, No. 2, 1993

C. HELVACI Dokuz Eyliil University, Bornova Izmir, Turkey, M.G. STAMATAKIS Athens University, Department of Geology, Athens, Greece, C. ZAGOUROGLOU and J. KANARIS Institute of Geology and Mining Exploration, Athens, Greece

Borate minerals, such as colemanite, ulexite and borax, have been reported in Tertiary continental basins of West Anatolia, Turkey, and Samos Island, Greece. Tuffaceous rocks interbedded with the berates are rich in authigenic silicate minerals such as zeolites, potassium feldspar and opal-CT, all of which have a genetic association with the borates. Chemical analyses of the tuffaceous rocks show variation in major elements due to the varying percentage of carbonaceous, detrital, and volcanic derived material. The volcanic activity in the vicinity of each particular lacustrine basin created ion-rich fluids from which a series of borates were precipitated under arid climate. Additionally, the saline-alkaline character of these fluids was responsible for the diagenesis of the silicic glass of the tuffaceous rocks, altering them to silicates and silica polymorphs.