- journal_title：The Canadian Mineralogist
- Contributor：Julie B. Selway ; Petr Černý ; Frank C. Hawthorne ; Milan Novák
- Publisher：Mineralogical Association of Canada
- Date：2000-
- Format：text/html
- Language：en
- Identifier：10.2113/gscanmin.38.4.877
- journal_abbrev：Can Mineral
- issn：0008-4476
- volume：38
- issue：4
- firstpage：877
- section：Articles
The zoned petalite-subtype Tanco granitic pegmatite, located about 180 km east-northeast of Winnipeg, near the Manitoba–Ontario border, intrudes amphibolite. Tourmaline is not abundant, but is widespread in most of the pegmatite zones. Tourmaline is black, brown or rarely green in the border zone (10), wall zone (20), aplitic albite zone (30) and central intermediate zone (60); it is pink and rarely green in the petalite-bearing lower and upper intermediate zones (40) and (50). On the basis of paragenesis and compositional zoning within individual tourmaline crystals, tourmaline at Tanco is characterized by the following sequence of crystallization: foitite – schorl → (± schorl – foitite) → Al-rich schorl (±Mg) → schorl (±Mg) → schorl – elbaite (±Mg) → “fluor-elbaite” – schorl (±Mg) → Fe-rich “fluor-elbaite” → Mn-bearing “fluor-elbaite” → rossmanite – elbaite → elbaite –rossmanite → (± Ca-bearing “fluor-elbaite”, Ca-bearing “fluor-elbaite” – rossmanite). The dominant substitution at the X site is Na ⇌ □, and there is a positive correlation between proportions of Na and F. The dominant substitution at the Y site is 3Fe2+ 1.5Al + 1.5Li, which is controlled by fractionation of the pegmatite-forming melt. Magnesium and Ti incorporated from the host amphibolite into the pegmatite-forming melt generated endomorphic Mg-bearing schorl to Al-rich Mg-bearing schorl to Mg-bearing schorl – elbaite to Mg-bearing elbaite – schorl in zones (10), (20) and (30). Sodium, Mn and F all increase from foitite –schorl to “fluor-elbaite” – schorl and Fe-rich “fluor-elbaite” in zones (10), (20), (30) and (60). In late-stage tourmaline, Ca and F increase from rossmanite–elbaite to Ca-bearing “fluor-elbaite” – rossmanite to Ca-bearing “fluor-elbaite”in zones (40) and (50). Late Ca-enrichment is due to sequestering of Ca in the melt as fluoride complexes. This is the first occurrence of foitite, rossmanite and late-stage Ca-enrichment in tourmaline reported a petalite-subtype pegmatite.