Alkali-deficient tourmaline from the Sullivan Pb-Zn-Ag deposit, British Columbia

Mineralogical Magazine
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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 D???(Mg2Al)Al6Si6O18(BO 3)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.
Publication type Article
Publication Subtype Journal Article
Title Alkali-deficient tourmaline from the Sullivan Pb-Zn-Ag deposit, British Columbia
Series title Mineralogical Magazine
Volume 61
Issue 6
Year Published 1997
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Mineralogical Magazine
First page 853
Last page 860
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