Archean Au Quartz Vein Mineralization Hosted in a Tonalite-Trondhjemite Terrane, Renabie Mine Area, Wawa, North Ontario, Canada
N. J. Callan, E. T. C. Spooner, 1989. "Archean Au Quartz Vein Mineralization Hosted in a Tonalite-Trondhjemite Terrane, Renabie Mine Area, Wawa, North Ontario, Canada", The Geology of Gold Deposits: The Perspective in 1988, Reid R. Keays, W. R. H. Ramsay, David I. Groves
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Economically significant Archean Au quartz vein mineralization in the Renabie area, north Ontario, is hosted entirely within a tonalite-trondhjemite terrane which is marginal to a greenstone belt and constitutes a part of an exposed, 120-km-wide (∼26 km estimated true thickness) uplifted Archean crustal section. Mineralization shows marked structural control and is confined to variably oriented, brittle-ductile shear zones showing oblique displacements. Host shear zones are superimposed on a regional foliation and appear to have formed under a bulk stress field which was reoriented with respect to the stress field responsible for earlier regional flattening. Strain features shown by the mineralization, together with evidence for reaction-enhanced ductility associated with hydrothermal fluid-rock interaction within shear zones, indicate that mineralization and hydrothermal alteration were synchronous with deformation. Banded quartz vein geometries are interpreted to be the result of repeated hydraulic fracturing in response to fluid overpressuring, with fracture orientation largely controlled by shear fabric anisotropy. On a microscale, gangue and opaque minerals show variation in style and intensity of deformation. Gold and closely associated tellurides, together with galena and chalcopyrite, appear to be paragenetically late with respect to pyrite and fill brittle dilational sites which developed during shear deformation.
The δ34S data and vein mineralogy reflect the oxidized nature of the fluid system at Renabie. Carbonate δ13C and δ180 data suggest a close relationship between fluids associated with gold mineralization and more pervasive fluids active within tonalite remote from mineralization in the Renabie area. The carbonate δ13C data (x = — 4.2 ± 0.2; 1< T, n = 14) are consistent with fluid derivation from a magmatic source and/or a juvenile (i.e., mantle) source.
The Renabie mine, though a rather unusual tonalite-trondhjemite-granodiorite-hosted Au deposit by virtue of its size and grade, exemplifies the potential of tonalitic-trondhjemite-granodiorite terrane-hosted Au quartz vein mineralization, given the correct combination of geologic conditions. Renabie-type deposits should therefore be considered viable exploration targets.