Alkali-Deficient Tourmaline from the Sullivan Pb-Zn-Ag Deposit, British Columbia

Shao-Yong Jiang1, 2, Martin R. Palmer1 and John F. Slack3
1 Department of Geology, University of Bristol, Bristol, BS8 1RJ, UK
2 Max-Planck-Institut für Chemie, Abt. Geochemie, Postfach 3060, 55020 Mainz, Germany
3 U.S. Geological Survey, National Center, MS 954, Reston, VA 20192, USA

Abstract: Alkali-deficient tourmalines are found in albitized rocks from the hanging-wall of the Sullivan Pb-Zn-Ag deposit (British Columbia, Canada). They approximate the Mg-equivalent of foitite with an idealized formula □(Mg2Al)Al6Si6O18(BO3)3(OH)4. Major chemical substitutions in the tourmalines are the alkali-defect type [Na*(x) + Mg*(Y) = □(x) + Al(Y)] and the uvite type [Na*(x) + Al(Y) = Ca(x) + Mg*(Y)], where Na* = Na + K, Mg* = Mg + Fe + Mn. The occurrence of these alkali-deficient tourmalines reflects a unique geochemical environment that is either alkali-depleted overall or one in which the alkalis preferentially partitioned into coexisting minerals (e.g. albite).

Some of the alkali-deficient tourmalines have unusually high Mn contents (up to 1.5 wt.% MnO) compared to other Sullivan tourmalines. Manganese has a strong preference for incorporation into coexisting garnet and carbonate at Sullivan, thus many tourmalines in Mn-rich rocks are poor in Mn (<0.2 wt.% MnO). It appears that the dominant controls over the occurrence of Mn-rich tourmalines at Sullivan are the local availability of Mn and the lack of other coexisting minerals that may preferentially incorporate Mn into their structures.

Keywords: alkali-deficient tourmaline • Mn enrichment • hydrothermal alteration • Sullivan mine • Pb-Zn-Ag deposit • British Columbia

Mineralogical Magazine; December 1997 v. 61; no. 409; p. 853-860; DOI: 10.1180/minmag.1997.061.409.08
© 1997, The Mineralogical Society
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