Tindle, A. G.; Selway, J. B. and Breaks, F. W.
(2005).
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Due to copyright restrictions, this file is not available for public download |
| DOI (Digital Object Identifier) Link: | https://doi.org/10.2113/gscanmin.43.2.769 |
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| Google Scholar: | Look up in Google Scholar |
Abstract
Liddicoatite, a rare species of tourmaline, has been found in the McCombe pegmatite, of complex type and spodumene subtype, an example of the LCT (lithium, cesium, tantalum) family. It is one of a group of beryl- and complex-type pegmatites exposed along the Uchi–English River subprovincial boundary-zone, Ontario, in the Superior Province of the Canadian Shield. The mineral assemblage containing zoned "fluor-elbaite"�liddicoatite crystals was the last product of primary, near-solidus crystallization of the pegmatite and is unique not only to this subprovincial boundary, but also throughout the vast number of rare-element pegmatites distributed across Ontario. The most calcic composition of liddicoatite analyzed here corresponds to (Ca0.5Na0.40.1) (Li1.5Al1.2Mn0.2Fe0.1) Al6(Si6O18) (BO3)3 (OH3.4F0.6). Other calcium-enriched species found in the McCombe pegmatite include microlite (Ca1.2Na0.60.2)(Ta1.6Nb0.3Sn0.1)O6(F0.7OH0.3), Ca-enriched almandine (Alm44.6Sps26.4Grs26.2), Ca-enriched spessartine (Sps69.3Alm19.8Grs10.9), and fluorapatite. Evidence from progressively evolved units of the pegmatite and mineral zonation shows that contamination of the pegmatite-forming melt occurred, and that fluids from the pegmatite migrated out into the mafic metavolcanic host-rocks, creating a Li-, Cs-, and B-enriched metasomatic aureole. The evolution of the pegmatite-forming melt resulted in increased activity of fluorine, and the essentially in situ fractionation of the contaminated melt led to the crystallization of the rare-element-enriched minerals. Patterns of zonation seen in back-scattered-electron images show that primary crystallization of columbite–tantalite, garnet and tourmaline species involved multiple episodes of growth and dissolution in a dynamic system. Liddicoatite was able to form, not because of any one of these processes, but because they all acted together to concentrate both Li and Ca, a sequence of events that is apparently very rare in nature.
| Item Type: | Journal Item |
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| Copyright Holders: | 2005 Canadian Mineralogist |
| ISSN: | 0008-4476 |
| Academic Unit/School: | Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences Faculty of Science, Technology, Engineering and Mathematics (STEM) |
| Interdisciplinary Research Centre: | Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR) |
| Item ID: | 14939 |
| Depositing User: | Elizabeth Lomas |
| Date Deposited: | 23 Feb 2009 15:25 |
| Last Modified: | 06 Oct 2016 04:44 |
| URI: | http://oro.open.ac.uk/id/eprint/14939 |
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