Archean Au Quartz Vein Mineralization Hosted in a Tonalite-Trondhjemite Terrane, Renabie Mine Area, Wawa, North Ontario, Canada
Published:January 01, 1989
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.
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The Geology of Gold Deposits: The Perspective in 1988
When the price of gold rose from about $200 (U.S.) an ounce in 1979 to nearly $700 an ounce by the end of the same year, the gold rush of the 1980s was under way. Gold production in the western world rose dramatically; from 1981 to 1986 production increased by 300 to 1,282 metric tons per year. Annual production may reach 1,500 to 1,600 metric tons by 1990 (Woodall, 1988). The major contributors to the increased stream of gold have been Australia, Canada, Brazil, and the United States together with other circum-Pacific countries. The increased price of gold and new methods of extraction have allowed many older deposits to be reopened, but the most important factor has been the high success level of exploration. This success has resulted in large part from the application of new genetic models and from the development of new exploration techniques.
There are hundreds of thousands of reported gold occurrences around the world. The majority are alluvial placers, but large numbers of bedrock occurrences have also been discovered. Most of these occurrences prove to be very small and are relatively unimportant in the overall world production level. Most mined gold has come from a small number of giant deposits, which were found by prospectors. It is becoming increasingly clear, however, that the discovery of giant deposits in the future will involve more than the sharp eyes and persistence of the old prospector. The use of sound geologic principles, and exploration programs based on those principles, is what the future holds. An example can be seen in the successful search for gold deposits in the South Pacific. There, exploration models have been based on principles developed in the study of modern geothermal systems. Giant deposits such as Lihir and Porgera have been the reward. Another example is the giant copper-gold-uranium deposit at Olympic Dam, South Australia, discovered beneath 300 m of cover using an exploration program based on models developed by Western Mining Corporation geologists for Zambian copper belt-type deposits.
Gold deposits are widely dispersed throughout many geologic settings and in virtually all kinds of rocks, but they do not seem to have formed at a uniform rate throughout geologic history. On the contrary, two very distinct metallogenic periods have been defined. The first is the Archean era, when most of the great deposits in greenstone belts were formed and the vast Witwatersrand basin deposits in