Evolution of gold-bearing splays of crustal-scale fault zones of the south-central Archean Abitibi subprovince: Constraints from the Kirana deformation zone, Kirkland Lake, Ontario, Canada

摘要

We explored the effects of brittle-ductile deformation processes on the localization of strain and hydrothermal fluid flow throughout the formation and evolution of a fault zone. This was accomplished through detailed structural analysis of the Kirana deformation zone (Kdz), a splay of the Archean crustal-scale, orogenic gold-hosting Larder Lake-Cadillac deformation zone (LLCdz) in Ontario, Canada. Investigations included mapping, quantification of fault-related breccia by particle size distribution analysis, microstructural and petrographic characterization, and kinematic analysis of brittle-ductile structures. The Kdz records three principal evolutionary stages. Stage 1 involved seismogenic processes that resulted in the formation of a > 50 m wide fault core and damage zone. Stage 2 is characterized by transpressional ductile shear localized along texturally favorable, mechanically weakened zones that formed during stage 1 and/or along zones where coeval fluid flow facilitated reaction weakening. Native gold is observed within the mylonitized fault core that is interpreted to have formed syn-to late-ductile shear. All structures are crosscut by small-scale faults and shear veins with disseminated alteration halos, defining stage 3. The Kdz demonstrates how early fault processes may control the spatial pattern and temporal progression of strain and hydrothermal fluid localization in orogenic gold-bearing fault splays.