Geochemistry of colemanite deposit of Kestelek, Bursa, Turkey

The known borate deposits of the Turkey were deposited in the lacustrine environment during Miocene when the volcanic activity occurred since Tertiary to Quaternary. All of the Turkish borate deposits are classified as volcanic related deposits. The Neogene sediments which contain the borates in the Kestelek region rest unconformably on the Paleozoic and Mesozoic basement complex. These sediments were deposited during a tectonically stable period accompanied by extensive volcanic activity. During this period, the volcanic activity gradually increased and produced tuff, tuffite, and agglomerate, and andesitic, trachytic, and rhyolitic volcanic rocks are interbedded with sediments. The borate zone consists of marl, limestone, tuffaceous limestone, tuff, and borate layers.
The borate minerals occur interbedded with clay minerals. Colemanite is present as masses from nodule to boulder size and as thin layers of fibrous and euhedral crystals. Colemanite is the predominate borate in the Kestelek deposit and calcite, quartz, aragonite, smectite, chlorite, illite, heulandite, and rarely corrensite are the associated minerals in the deposit. Results of geochemical analyses of the Kestelek colemanite deposits are the following: major elements are Ca, Si, Mg, Al, Fe, K, Na, Ti, P, Mn, Cr. Trace elements are Li, Cs, Sb, As, Sr, Se. Among these elements, Se is significantly enriched. Ca, Mn, Sc, Bi are constant according to the depth. Na, Mg, Al, Si, Fe, Ti, K are similar. The trace elements Cu, Zn, As, Rb, Zr, Co, Ni, Th, Cs form the first group; and Sb, Ga, U, Nb, Ag, Y, La, Hg forms the second group. Te, Ba, Mo, Au, Cd, Sc, Se, Bi move dependently both of this two groups and each other. Results of the REE discrimination diagrams of these two groups indicate at least two different precipitation regimes. Magnetic features of boron samples (2CaO.3B2O3.5H2O) from Kestelek (Bursa) region were investigated. Ca+2 magnetic centers were observed in boron samples. Spectra of Ca+2 magnetic centers were measured by Electron Paramagnetic Resonance (EPR). EPR parameters were determined independently from temperature. It was found that the results of this study are in good agreement with those of literature.