A reconnaissance of the boron isotopic composition of tourmaline

A preliminary investigation of the boron isotopic composition of tourmaline from some boron-rich associations has been made. The results for tourmaline from metasedimentary parageneses ( n = 12) range from δ 11B = −22 to +22 per mil. These data mainly fall between the boron isotopic compositions of normal marine sediments with δ 11B = −2 to +5 per mil and seawater with δ 11B = +39.5 per mil. Tourmaline samples from granitic pegmatites ( n = 6), on the other hand, range from δ 11B = −12 to −5 per mil. The data provide a rudimentary indication of the range of boron isotopic variation in tourmaline, some of the processes leading to this range, and some possible geochemical tracer applications.