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September-October 2016

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Spinel and Aspidolite from the Des Cèdres Dam Occurrence, Notre-Dame-du-Laus, Québec, Canada

The Parker mine in Notre-Dame-du-Laus, Québec, is well known among collectors for having produced substantial amounts of well-formed, lustrous black spinel crystals (rarely up to 6 cm) associated with euhedral, greenish forsterite (van Velthuizen 1993). This famous locality, however, is not the only source of aesthetic and idiomorphic spinel specimens in the area. The Des Cèdres Dam locality was first described by Aubert de la Rüe (1956) and later, in more detail, by Sabina (1986). Spinel is found in a marble exposure on the north shore of the Lièvre River, immediately downstream from the Des Cèdres Dam (fig. 1), just north of Notre-Dame-du-Laus (fig. 4). It can be accessed by taking Route 309 to Notre-Dame-du-Laus. Turn left on Chemin du Barage, just north of the town, followed by a left turn on a small gravel road that leads to a small parking area. The spinel-bearing rock can be found near the river (N 46.101783°, W 75.647055°) by walking down a short, steep trail from the parking area. Samples are difficult to extract from the outcrop, which likely contributed to the small production of specimens at this occurrence. The Des Cèdres Dam locality is of particular interest because the spinel has a purplish-blue color (with a hint of gray), and crystals as large as 6 cm have been found. They occur in a forsterite-rich rock surrounding fragments of feldspar-rich rock in marble. Aspidolite, the rare sodium analogue of phlogopite, is reported here as the first Canadian occurrence of the mineral. We present the specimen mineralogy of this occurrence and a short description of its origin. Mineral species have been confirmed with energy dispersive spectroscopy (EDS) and, where necessary, electron probe microanalysis (EPMA) at the University of Ottawa. Amphibole species are named according to the classification of Hawthorne et al. (2012) following formula calculation using the spreadsheet of Locock (2014).

Philippe M. Belley is a recent graduate of the University of Ottawa, now studying gem spinel and sapphire occurrences at the University of British Columbia.

Jonathan O'Neil is a professor in the Department of Earth Sciences at the University of Ottawa, specializing in petrology, isotope geochemistry, and geochronology.

Keiko Hattori is a professor in the Department of Earth Sciences at the University of Ottawa, specializing in geochemistry and mineral deposits.       

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