Canadian Rockhound: Bernic Lake Minerals

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The Pegmatite Minerals
of Bernic Lake
By Dirk Schmid and Marjorie Reynolds,
Winnipeg, Manitoba

On Saturday, May 20, 1995, members from both the Rock & Mineral Club of Winnipeg and the Mineral Society of Manitoba, and non-members paid a visit to the famous TANCO mine at Bernic Lake to collect minerals. The trip, hosted by the Rock & Mineral Club, was attended by 17 people, including Marjorie Reynolds, president of the Rock & Mineral Club, and Jack Bauer, president of the Mineral Society of Manitoba. In this feature article, we will present a brief background of the TANCO mine, its geology and minerals, and a summary of the minerals we found there this year.

Mining History
TANCO, which stands for Tantalum Mining Corporation of Canada, Ltd., is situated about 180 km northeast of Winnipeg and is privately owned by Hudson Bay Mining and Smelting and Cabot Corporation.
The existence of the mine today is due to the discovery of tin in the pegmatites below Bernic Lake. The mine originally was founded in 1929 by Jack Nutt Mines Ltd. to exploit the area's tin potential. A mill was constructed to produce tin concentrates, but in the end the low quantities of tin ore extracted from the operation made further processing unfeasible. As a result, tin operations stopped and the mine site was abandoned. While in operation, though, further drilling revealed measurable concentrations of lithium in the pegmatite rock. When the value of lithium increased in the late 1950s, a short-lived attempt was made to exploit the pegmatite for its lithium content. In 1960 the mine again was abandoned, but not for long. The mine resumed operations again in 1969, this time for tantalum minerals in response to increased demand for tantalum. A drop in the value of tantalum and poor markets caused mining operations to cease in 1982. During the time it operated, about 500 or more tons per day of tantalum ore was mined. The fourth phase in the life of TANCO began in 1984 when the mine began extracting its lithium reserves again. According to TANCO, the lithium reserves are in the form of very low iron spodumene-quartz intergrowths, or SQUI. The chief mineral extracted today is spodumene.

Geology
The TANCO mine and neighboring Bernic Lake are situated on top of a pegmatite. It is this pegmatite which contains the minerals of interest. The pegmatite forms part of the Bird River greenstone belt (is a member of the Superior geological province). According to TANCO, the pegmatite is composed of metavolcanic and derived metasedimentary rocks and synvolcanic metagabbro intrusives. Eight separate mineralogical zones have been identified, each containing a different type of ore, such as tantalum, spodumene, cesium and rubidium.

Common Minerals
More than 80 different minerals have been found at TANCO. Some of the minerals found there were first discovered at TANCO. Major minerals include spodumene, amblygonite, wodginite, microlite, pollucite, lepidolite, and K-feldspars. Other minerals include beryl, hornblende and other amphiboles, tourmaline, petalite, montebrassite, the micas (muscovite, phlogopite and biotite), quartz and tantalum minerals. Please remember that prior permission must be obtained from TANCO to enter the compound and collect to minerals.

Applications
Many minerals possess unique and useful properties. The minerals found at TANCO can be used for a variety things, ranging from electrical components to biomedical engineering. Spodumene, a pyroxene, is typically used in the specialty glass and ceramics industries such as Corning cookware. Tantalum minerals are primarily used in the electronics industry and tantalum alloys such as tantalum carbide, from which cutting tools are produced. Tantalum alloys help make pipes resistant to corrosion. Hip-joint replacements would not be possible without tantalum, since it is the only known metal not rejected by the human body. Pollucite is a source of cesium. Its major use is in biomedical engineering, but is also effective in the sterilization of sewage.

Field Trip Summary
Despite the rain, members collected a variety of minerals from the tailings outside the main gates. In fact, the rain made it easier to spot the different minerals in the rocks. White blades of spodumene, up to 5 inches long, accompanied by quartz and feldspars were found. Tourmaline crystals in the form of black schorl were also present in many rocks, but can also be confused with hornblende, a black mineral that is softer (hardness 5) than tourmaline (hardness 7). Massive, purple coloured lithia mica (probably muscovite) was found by several people and was easy to find. It is possible however that lepidolite is present in small quantities in rocks containing lithia mica. Muscovite and "nailhead" mica were found in many rocks at one end of the compound. The pale yellowish muscovite crystals occurred in book form and were up to 2 inches in diameter. Grey crystals of muscovite were also present in book form, but this species is interesting in that the books taper towards one end, thus giving a "nailhead" like appearance. Also, this form of muscovite has a shiny metallic lustre. It is unlikely that zinnwaldite, a rare mica, is present at TANCO. Blue specks of apatite were often present in many rocks. One large pile contained individual chunks of pollucite. Other minerals found include quartz, lithiophyllite, albite, cleavelandite (a variety of albite), amblygonite, wodginite and various feldspars. Unfortunately, no beryl was found.
Overall, the trip to TANCO was a success and was enjoyed by all who came out. It also was great to see members and non-members help one another and share their mineral specimens.

References:

Brochure, "Tantalum Mining Corporation of Canada Ltd" (no date).

Phillips, K. A. 1978. Minerals of Manitoba.
Vol. 1: Non-metallic and pegmatitic.

Acknowledgements:
Special thanks is given to Dr. Petr Cerny of the University of Manitoba's Geological Sciences Department who provided additional information and helped identify some of the minerals specimens collected at Bernic Lake.

Copyright ©1997 Dirk Schmid and Marjorie Reynolds
E-mail: dirk_schmid@hotmail.com
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 May 1995 issue of the Mineral Society of Manitoba Newsletter. Reprinted in the Canadian Rockhound with permission from the authors and editor.

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