• journal_title：Mineralogical Magazine
• Contributor：B. M. Shabaga ; M. Fayek ; F. C. Hawthorne
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2010.074.2.241
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：74
• issue：2
• firstpage：241
• section：Research Articles

The Li and B isotopic compositions of gem-quality Cu-bearing tourmalines were used (1) to distinguish among Paraiba tourmalines from Brazil and Cu-bearing tourmalines from Nigeria and Mozambique; and (2) to identify the likely source of Li and B for these gem-quality tourmalines. The δ¹¹B values of tourmaline from Paraiba, Brazil, range from -42.4‰ to -32.9‰, whereas the δ¹¹B values of Cu-bearing tourmaline from Nigeria and Mozambique range from -30.5‰ to -22.7‰ and -20.8‰ to -19.1‰ respectively. Tourmalines from each locality have relatively homogeneous δ¹¹B values and display no overlap. There is slight overlap between δ⁷Li values of Paraiba tourmaline (+24.5‰ to +32.9‰) and Cu-bearing tourmaline from Nigeria (+32.4‰ to +35.4‰), and δ⁷Li values of Cu-bearing tourmaline from Nigeria and Mozambique (+31.5‰ to +46.8‰). Nevertheless, Cu-bearing tourmalines from each locality can be fingerprinted using a combination of their δ¹¹B and δ⁷Li values. The very small δ¹¹B values are consistent with a non-marine evaporite source, and are among the smallest reported for magmaticsystems, expanding the global range of B isotopic composition for tourmaline by 12‰. The corresponding large δ⁷Li values are among the largest reported, although they are less diagnosticof the source of the Li. The large δ⁷Li values in conjunction with the small δ¹¹B values suggest a non-marine evaporite or brine as a source for Li and B, either as constituent(s) of the magma source region or, by assimilation during magma ascent. The large range in δ¹¹B and δ⁷Li values suggests that B and Li isotope fractionation occurred during magmatic degassing and late-stage magmatic-hydrothermal evolution of the granite-pegmatite system.