The Mount Pleasant tin deposit in New Brunswick is mineralogically complex and contains a wide variety of minerals. The tin-bearing minerals are cassiterite and stannite. Cassiterite is the chief tin mineral, and it occurs in sulphide veins, wall-rock and in a kaolin body containing fluorite. The cassiterite in the sulphide veins and wall-rock is present as small grains, whereas that in the fluorite-bearing kaolin body is present as relatively large grains in massive fluorite. Stannite has been found only in sulphide veins where it occurs as grains, veinlets and minute inclusions in sphalerite, and occasionally as borders around cassiterite.

Sphalerite is the most abundant ore mineral. It is black and contains minute exsolution bodies of chalcopyrite and stannite. Analyses of sphalerite concentrates give Fe 8.2-14.3%, Cu 1.3-5.5%, Sn 0.15-0.40%, In 0.03-0.30%, Cd 0.12-0.19%, and Mn 0.06-0.08%.

Sphalerite geothermometry indicates that the depositional temperatures of the sphalerite fall between 335° C. and 700° C., and arsenopyrite geothermometry gives depositional temperature up to 500° C.

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