BORON ISOTOPE VARIATIONS IN NATURE - A SYNTHESIS

The large relative mass difference between the two stable isotopes of boron, B-10 and B-11, and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes. Published deltaB-11 values (relative to the NBS SRM-951 standard) span a wide range of almost-equal-to 90 parts per thousand. The lowest deltaB-11 values around - 30 parts per thousand are reported for non-marine evaporite minerals and certain tourmalines. The most B-11-enriched reservoir known to date are brines from Australian salt lakes and the Dead Sea of Israel with deltaB-11 values up to + 59 parts per thousand. Dissolved boron in present-day seawater has a constant world-wide deltaB-11 value of + 39.5 parts per thousand. In this paper, available deltaB-11 data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects, including possible tracer applications of boron-isotope geochemistry, are summarized.