Magmatic-hydrothermal systems and associated magnetite-apatite-actinolite deposits, Echo Bay, Northwest Territories.

Abstract

Magnetite-apatite-actinolite deposits occur as pervasive replacement, veins, pods and breccias within wall rocks to the plutons of the Mystery Island intrusive suite at Echo Bay, Northwest Territories. The plutons and their altered wall rocks host previously-mined pitchblende, native Ag, Ni-Co arsenide veins. Although numerous studies were carried out on the pitchblende, native Ag, Ni-Co arsenide veins, the origin of the altered rocks which host them remains uncertain. Overall, this study reveals that the formation of magnetite-apatite-actinolite veins, pervasive replacement of rocks by albite and magnetite-apatite-actinolite, and hydrothermal brecciation by magmatic fluids is consistent with geologic and isotopic data. Thus, it is inferred that these deposits formed by replacement in a hydrothermal system dominated by magmatic fluids exsolved by cooling epizonal plutons of the Mystery Island intrusive suite. (Abstract shortened by UMI.)