Deformation and Structural Controls on Gold Mineralization in the Clarence Stream Shear Zone, Southwestern New Brunswick, Canada

Abstract

The Main zone of the Clarence Stream gold deposit is hosted by a shear zone adjacent to the Saint George batholith in southwestern New Brunswick. The mineralization history relates to progressive deformation in the shear zone and the intrusion of the Magaguadavic granodiorite. Of three phases of deformation that have affected the area (D 1 –D 3 ), D 1 is not observed in the Clarence Stream shear zone. Two suites of igneous rocks intrude the shear zone: post-D 2 , pre-D 3 gabbro; and granitic dikes, which crosscut the gabbros. Granitic dikes show a diverse range of relationships to D 3 features, from pre-syn-D 3 mylonitic fabrics in transposed and highly deformed enclaves, to nondeformed and entirely discordant dikes (post-D 3 ). A variety of veins occur within this shear zone. Zoisite-bearing and later, crosscutting epidote-bearing veins are preserved as relics in quartz-mylonites, and predate quartz veins that host gold mineralization. The epidote-bearing veins are associated with pseudotachylitic cataclasite dikes, consistent with transient brittle failure during ductile deformation. Deformation relates to right-lateral strike-slip motion across the shear zone, and subhorizontal and near-vertical stretching lineations imply transpression. A late (late- or post-D 3 ) dip-slip phase of motion is also apparent, and cooling followed a metamorphic peak early in D 2 –D 3 history. Deformation of the shear zone, and more localized transient brittle failure, provided the permeability for fluid movement and vein emplacement. This scenario is similar to the findings of other studies, in which geochemical, tracer isotopic, and age-dating (U/Pb, 40 Ar/ 39 Ar) results suggest that the adjacent Magaguadavic granodiorite provided heat and metals.