Contrasting styles of alteration and metamorphism in shear zones at Wawa, Ontario.

Petrographic and chemical analysis of sheared rocks from seven narrow deformation zones in Archean-age rocks near Wawa, Ontario reveal different styles of alteration and deformation. The strained rocks are classified into protomylonite, mylonite and ultramylonite using feldspar grain-size measurements and clast/matrix ratios. Hydrothermal alteration and gold mineralization result in complex chemical patterns in some of the shear zones. Typically mineralizing fluids add SiO$\sb2$, alkalis, copper, gold and arsenic. Early alterations are overprinted by the chemical changes accompanying formation of mylonites and post-deformation alterations are generally constrained to the most deformed rocks. Evidence of multiple deformation and alteration events in the study area leads to a proposed model of the temporal relationship among the deformation and mineralization events. The northeast-striking shear zones show evidence of an early mineralization that is disturbed and altered during mylonitization. In some cases the shear zones act as conduits for a later mineralizing event. A set of northwest-striking shear zones offset the northeast-striking set. The northwest set show a less complex history with a single mineralizing event following deformation. (Abstract shortened by UMI.) Source: Masters Abstracts International, Volume: 31-03, page: 1174. Adviser: W. H. Blackburn. Thesis (M.Sc.)--University of Windsor (Canada), 1992