THE BORON ISOTOPE GEOCHEMISTRY OF THE NEOGENE BORATE DEPOSITS OF WESTERN TURKEY

We have analyzed the boron isotope composition of 80 berate minerals ( major minerals: borax, colemanite, and ulexite; minor minerals: veatch ite-A, tunellite, kernite, terrugite, probertite, meyerhofferite, inde rite, inyoite, hydroboracite, howlite, and pandermite) from the main d eposits (Kirka, Bigadic, and Emet) and two smaller deposits (Kestelek and Sultancayir) in the western Turkish berate deposits. Forty-three s amples were also analysed for their Sr isotope composition. The data s pan a wide range in delta(11)B values from -1.6 parts per thousand to to -25.3 parts per thousand. The delta(11)B values of the main berate minerals are largely controlled by their mineralogy and the pH of the brines from which they precipitated. An inverse correlation between th e average delta(11)B and Sr-87/Sr-86 ratios of colemanite in the diffe rent deposits suggests there is some variation in the sources of boron and Sr to the deposits. Emet has the highest contribution from alumin osilicates and Kirka the highest contribution from Eocene carbonates, with Bigadic occupying an intermediate position. The delta(11)B values of the minor berate minerals distinguish between those which are prim ary precipitates from the original brines (or formed from primary bera tes without boron loss from the system) and those which formed from al teration of preexisting berate minerals with substantial loss of boron from the system. Copyright (C) 1997 Elsevier Science Ltd.