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

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.

The significance of Mn‐rich ilmenite and the determination of P–T paths from zoned garnet in metasedimentary rocks from the western Cape Breton Highlands, Nova Scotia

“…Although a volumetrically minor phase, ilmenite can incorporate significant amounts of Mn (e.g. Jiang, Palmer, & Slack, ; Mitchel & Liferovich, ; Suwa, Enami, Hiraiwa, & Yang, ), such that an investigation of ilmenite in relation to the highly Mn‐dependent nature of garnet stability is warranted.…”

The influence of microscale lithological layering and fluid availability on the metamorphic development of garnet and zircon: insights into dissolution–reprecipitation processes

“…11). In the mica-rich matrix either: (a) ilmenite recrystallises at the garnet isograd releasing Mn for garnet growth (Woodsworth, 1977; Jiang et al , 1996) and Zr for zircon; or (b) finer grained fragments of the more metamict detrital zircon are more reactive and dissolve further as fluid is released during garnet forming reactions (Dempster and Chung, 2013). Formation of abundant micro-zircon in garnet is therefore a result of micro-zircon encapsulation from the matrix but also formation of new micro-zircon where the Zr is derived from dissolution of detrital and micro-zircon at the garnet growing face and potentially the recrystallisation of ilmenite.…”

Occurrences of Foitite and Rossmanite From the Koktokay No. 3 Granitic Pegmatite Dyke, Altai, Northwestern China: A Record of Hydrothermal Fluids

“…Foitite may be found as hair-like crystals in pockets of granitic pegmatites and some hydrothermally affected rocks (e.g., Foit et al 1989, Pezzotta et al 1996, Aurisicchio et al 1999, Francis et al 1999, Novák & Taylor 2000, Medaris et al 2003, and in some cases, it is described as the initial generation of fibrous tourmaline that replaces elbaite (e.g., Dutrow & Henry 2000) and as the fibrous tourmaline of replacement origin in fractured pre-existing tourmaline (e.g., Henry et al 2002). However, magnesiofoitite has been reported in only two localities, the Sullivan Pb-Zn-Ag deposit, British Columbia (Jiang et al 1997) and the Kyonosawa area, Japan (Hawthorne et al 1999), and rossmanite has been described only at the type locality (Selway et al 1998); recently, "oxy-foitite" was described from the Baraboo quartzite, Wisconsin (Medaris et al 2003). Clearly, investigations of X-site-vacant tourmalines are rather limited.…”