Canadian Rockhound: Garnet and Iolite Gems in the Slocan Valley

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Garnet and Iolite Gems in the
Slocan Valley, British Columbia
By Willow Wight,
Canadian Museum of Nature,
Ottawa, Ontario

Anglo-Swiss Resources Inc. has been finding significant amounts of sapphire in the past three years on its properties in the Slocan Valley, B.C. A number of other gemstones have been found in the deposits, including pyrope-almandine garnet, iolite (cordierite), amethyst, clear, rose and star quartz, schorl and dravite tourmaline, beryl, spinel. Red pyrope-almandine garnet was discovered within feldspar-rich pegmatite sills and dikes on the Blu Starr group of claims in 1998. The top quality cranberry-red garnet has been faceted into several custom designs with impressive results. More than 300,000 carats of rough garnet have been extracted so far. Large, flawless pieces of rough are being faceted in Sri Lanka.

In November, 1998, a sampling program tested two gem quality iolite-bearing zones on the Blu Starr property Two zones outcrop about 1 km apart with excellent access. Iolite (cordierite) is a violet-blue colour similar to tanzanite. It is pleochroic: blue-violet, honey yellow, and pale blue grey. Correct orientation when faceting is critical to obtain the best colour. Cabochon cut material from this property displays a noticeable star effect. The iolite host rock is distinctive, dark green, fibrous metamorphic rock composed of biotite and fuchsite mica, tremolite-actinolite, iolite, quartz, feldspar, megacrystic almandine-pyrope garnets and amphibole. The iolite occurs as large crystals in quartz vein stocks and pegmatites, and as scattered masses throughout the host rock. It weathers to irregular masses but the deepest samples show euhedral, dark violet crystals with minimal alteration. A major factor in the value of the gems will be an attractive, saturated colour, and large enough size.

The deposit is in an area prone to freeze-thaw cycles that cause fractures. Approximately one tonne was taken from each outcrop, yielding roughly 25 kilograms of high-grade iolite each. The total yield was more than 100,000 carats of rough. The first iolite gemstones have been cut with very positive results. The chosen pieces have a "superb blue-violet colour, excellent clarity, and intense brilliance". Test lots are now being faceted by various cutters in Sri Lanka. Both garnet and iolite gems were exhibited at the recent Vancouver Cordilleran Roundup, where Anlgo's recent gem discoveries were considered one of the 1998 exploration highlights of the Kootenay Region.

Website: www.anglo-swiss.com

References:

"The Gemstones Report", Anglo Swiss Resources Inc.,
January, 1999.
"First Iolite Gemstones Cut", Press Release, Anglo Swiss Resources Inc., February 3, 1999.

This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, original source and the Canadian Rockhound, and include the website URL address of the Canadian Rockhound.

The preceding article was first published in the March 1999 issue of The Canadian Gemmologist, (Vol. 20, No. 1, p. 18.). The Canadian Gemmologist, is the official journal of the Canadian Gemmological Association. Reprinted in the Canadian Rockhound with permission from the editor.

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