Louis Sautelli HBSc thesis abstract

The Hemlo gold deposit is located 41 km east of the town of Marathon in northern Ontario, Canada.  The deposit was discovered in 1980 and active mining in the camp was initiated in 1985.  The different lithologies hosting gold mineralization at this deposit were classified and assigned names that were acceptable at the time of its discovery and development.  This study revisits and re-interprets the classification and nomenclature of the rocks cropping out west of the C-zone open pit.  This lithological classification is reinterpreted using a modern comprehension of plate tectonic dynamics, in conjunction with, the effects of brittle and crystal plastic deformation mechanisms observed in recent material science studies.  Microstructural investigations of the samples collected suggest that the rocks are a mylonitized coarse-grained quartzo-feldspathic plutonic rock.  Microstructural analyses of the samples under transmitted and reflected light indicate that strain has been preferentially accommodated at different rates and that brittle-ductile deformation was progressive and occurred as numerous incremental events.  Such deformation resulted in rocks exhibiting different textures in hand samples but having homogeneous features when observed microscopically.  A weak schistosity results in abundant and relatively coarse-grained quartz and feldspar porphyroclasts, whereas a strong schistosity results in a low abundance and finer-grained quartz and feldspars porphyroclasts.  The magnitude of strain can be approximated using the porphyroclast size and their abundance.  This study also observed that gold mineralization in the Hemlo gold camp occurs at or near strain gradients and that gold mineralization has an affinity for competency contrast.