A petrographic study of samples from cassiterite bearing localities in Central New Brunswick, Fontao, Spain and Echassieres, France

Abstract

The cassiterite deposits of Central New Brunswick, Fontao Spain, and Echassieres France have been studied petrographically. Comparison of these deposits with those in Cornwall, South West England and Thailand indicated that the Sulpetro, Rocky Brook Main, some parts of Dungarvon, Falls Brook, Todd Mountain, and Burnthill deposits are similar to the Cornwall type deposits. Tin Hill, some parts of Dungarvon, and Fontao deposits are similar to the Thailand deposits. Temperature information, based on cassiterite crystal habit, indicated a range from 600°C to 450°C for the depositional temperature of the cassiterite. Depth of emplacement and lithostatic pressures, based on Strong's (1981) classification of tin deposits, indicated a range from 12,000 to 2,000 meters and from 3.5 to 0.5 kilobars respectively. The activities of K20 and Na20, based on the stability relations in the K20-Na20-A1203-Si02 -H20-HCl system, are highest in the potassium feldspar rich veins of Salpetro and Rocky Brook Main. They were lowest for the muscovite rich samples from Fontao, Tin Hill greisen, and Cleveland greisen. Because a geological report on the Central New Brunswick area indicated the possibility of a common magmatic source for the granite stocks (Irrinki, 1981), a unifying model was devised to explain the genesis of the cassiterite deposits of Central New Brunswick. The origin of each cassiterite deposit and its relation to the other cassiterite deposits in the area, could be explained using this model. From the model, it is suggested that the Cornwall type complex hydrothermal lode deposits like Sulpetro were produced by fractional crystallization of a late stage granite stock. Smaller deposits like at Rocky Brook Main, may be associated with earlier less trace element rich granite stocks