John Robert McArthur HBSc thesis abstract

Thesis Title: 
Fluid Inclusion and Stable Isotopic Studies on Amethyst, Thunder Bay Amethyst Mine, Thunder Bay District, Ontario

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.