Timing of Gold Introduction in the Late Archean Tectonic Framework of the Canadian Shield: Evidence from U-Pb Zircon Geochronology of the Abitibi Subprovince
Soussan Marmont, F. Corfu, 1989. "Timing of Gold Introduction in the Late Archean Tectonic Framework of the Canadian Shield: Evidence from U-Pb Zircon Geochronology of the Abitibi Subprovince", The Geology of Gold Deposits: The Perspective in 1988, Reid R. Keays, W. R. H. Ramsay, David I. Groves
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The maximum age of gold mineralization and the chronostratigraphy of the Timmins and Kirkland Lake-Matheson areas in the external zone and the Detour Lake mine in the internal zone of the Abitibi subprovince, Ontario, are established through U-Pb zircon geochronology. In the Timmins area, two episodes of felsic volcanism are determined at 2,727 ± 1.5 and 2,698 ± 4 Ma which support existing stratigraphic interpretations. In the Kirkland Lake area, three periods of felsic volcanism are dated at 2,747 ± 2 (J. K. Mortensen, pers. commun., 1988), 2,705 ± 2, and 2,701+3−2 Ma. In the area south of the Kirkland Lake-Larder Lake break, the dates do not correspond to the current stratigraphic interpretation, rather, they indicate reversals which possibly resulted from stacking. In the Matheson area, north of the Destor-Porcupine break, an episode of felsic volcanism is determined at 2,714 ± 2 Ma. The dates in this area indicate structural repetition of some units. Therefore, caution is exercised in stratigraphic correlation across structural discontinuities.
The youngest lithologies hosting gold mineralization consist of late Archean intrabelt intrusions which cut the youngest, folded and/or tilted volcanic rocks. They are silica-saturated quartz porphyries which in the Timmins mines are 2,691 to 2,688 Ma and silica-poor or undersaturated monzonites and lamprophyres(?) which are 2,678 to 2,673 Ma.
In the Detour Lake mine, feldspar porphyry which is the youngest lithology hosting gold-bearing structures dates at 2,722+3−2 Ma. An apparent age difference between the late plutonic event of the internal and the external zones of the Abitibi subprovince suggests a different timing of cratonization of the two terranes.
Gold mineralization shows a distinct spatial and temporal association with major deformation zones such as the Destor-Porcupine and the Kirkland Lake-Larder Lake breaks, and the silica-poor or undersaturated intrusions, emplaced along these breaks. Gold is temporally separated from volcanism by 25 Ma and from emplacement of quartz porphyries by 13 to 15 Ma. Along the Destor-Porcupine break, gold is synchronous with or later than 2,673+6−2 Ma.
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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