john robert mcarthur hbsc thesis abstract
the thunder bay amethyst mine is composed of vein and breccia mineralization, containing amethyst, colourless quartz, prasiolite and citrine. the mine occurs in a strike-slip fault situated within a archean batholitic intrusion of granodiorite.
during the present study fluid inclusions in amethyst indicated temperatures on the order 60 to 90°c during vein deposition. eutectic temperatures in fluid inclusions suggest the solution composition consisted of a cacl2 + nacl system. salinity of the solution decreases in the direction of vein growth from 22.9 to 15.3 equiv. wt.% nacl. the presents of na in the system may assist in the production of hole and electron colour centers by allowing for a charge compensation in the substitution of fe3+ for si4+ in the crystal lattice of quartz. variations in salinity in the direction of growth may reflect changes in amethystine colour density.
eh-ph conditions, calculated on the basis of paragenetic sequence within cu-sulfide inclusions, suggest a reducing thrend during deposition.
sulfur isotopic composition of pyrite in amethyst (delta34s = -0.6 to -0.4) was compared to the sulfur isotopic composition of lead-zinc-barite veins in the dorion area (delta34 s = -0.1). the similarity in isotopic signature suggest that both types of deposit have similar origin.