Canadian Rockhound: Cubanite, a Rare Mineral from Thompson, Manitoba

Cubanite, CuFe₂S₃, is an interesting copper-iron sulphide mineral that occurs in copper-zinc deposits. It is brassy to bronze-yellow in colour, metallic, and has a hardness of 3.5. The mineral can differentiated from chalcopyrite on the basis of magnetism, which is strong in Cubanite. It is non-fluorescent. As a crystal, cubanite forms a 6-point star, with the points radiating from a common centre. Cubanite is a rare mineral, and well-crystallized specimens are extremely rare.

Cubanite is found in copper-zinc deposits. In Canada, cubanite is known to occur at a number of localities. These are the Henderson II Mine in Chibougamau, Quebec, the Strathcona Mine in Sudbury, Ontario, the Advocate Mine at Baie Verte, Newfoundland, specific localities in British Columbia, and at the Thompson Mine in Manitoba.

INCO's Thompson Mine in Thompson, Manitoba, is a large nickel mine. Many interesting minerals have been found in the nickel sulphide ores. Serious mineral collectors that are familiar with Canadian minerals may recall the recent discovery of well-crystallized millerite specimens from a small pocket found at the Thompson Mine in the early 1990's. Dave Joyce was the first to recover the millerite specimens from this locality. It is unfortunate that overcollecting by other individuals has resulted in the depletion of this mineral from this locality.

Besides millerite, several beautiful and well-formed cubanite crystals were recently found at the Thompson Mine. Sadly, not many cubanites were saved from this locality, especially in recent years. In the early 1990's, when the mine used the cut and fill mining method, many specimens of various crystals were recovered. After the mine switched to open stoping, VBM, and "slot and slash", very few specimens were recovered. The photograph below shows what one of the Thompson Mine cubanites look like (Figure 1).

Figure 1. Cubanite crystal from the Thompson Mine, Thompson, Manitoba. This photograph was taken using a Nikon Coolpix 950 camera. The crystal is 1.6 cm in diameter. Photo by Dave Joyce.

Cubanite occurs elsewhere in Manitoba, but in lesser quantities. References to other localities were reported in the two volume series, "Minerals of Manitoba", published in 1978 and 1979. Localities where cubanite is known to occur include the copper-zinc mine near Sherridon, situated 65 km northeast of the city of Flin-Flon, and the Ruttan Mine, a large open-pit mine east of Leaf Rapids. According to Minerals of Manitoba, Vol. II, "tiny blebs of cubanite" were found in sphalerite at the Ruttan Mine. To our knowledge, the best cubanites in Manitoba have only been found at the Thompson Mine. It is hoped that some day well-crystallized specimens will be found again.

References:

Phillips, K.A. Minerals of Manitoba, Volume II: Metallic Minerals. Province of Manitoba Department of Mines, Natural Resources and Environment, MRD Educational Series 78/2. 1979.
Richard V. Gaines, H. Catherine Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig. Dana's New Mineralogy, 8th edition. John Wiley & Sons, Inc. 1997.

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