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,*Université du Québec à Montréal, Département des Sciences de la Terre, C.P. 8888, succ. Centre-ville, Montréal, Québec, Canada H3C 3P8
Laboratoire de Tectonique Quantitative, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris 05, France
Terra Sancta Inc., 48 Peoples Avenue, Gooseberry Hill, Western Australia, Australia 6076
Corresponding author: e-mail,
acarrier{at}lino.com
Late orogenic gold-bearing quartz vein deposits within
the Rouyn-Noranda mining district occur mainly within Archean tonalitic
plutons of the Blake River Group (southern Abitibi belt). The Silidor
deposit is a representative example of a pluton-hosted lode gold deposit.
The Silidor mine contained 2.95 million tons (Mt; mined and estimated
reserves), grading 5.1 g/t Au (~15 t Au). The mineralized zone is 900 m in
length and has a vertical extent of 900 m, an average thickness of 3.5 m,
and trends northwest-southeast with a dip of 50° to 70° NE. Its alteration
envelope consists of a red hematite-altered trondhjemite. Measured 
18O
values for quartz veins (7.7–10.9
) and 34S
values for pyrite (–6.1 to –9.4) imply oxidizing conditions during
gold deposition. The mineralized zone comprises: vein quartz (white, gray,
and smoky varieties), beige mineralized trondhjemite, and green
carbonate-sericite-fuchsite breccia, which resulted from shearing and
metasomatism of an early northwest-southeast dioritic dike.
A quantitative microtectonic study (>400 measurements)
was carried out on the Powell tonalitic sill in the Silidor mine area to
reconstruct the deformation before, during, and after the mineralizing
events. The reduced stress tensors display large variations in 
1
orientation, trending successively northwest-southeast, northeast-southwest,
and finally north-south. The Silidor deposit is the result of several
vein-filling events, which occurred during evolution from strike-slip
faulting to reverse faulting regimes, with 1
remaining northeast-southwest but with exchange of orientation of 2
and 3. Such
variations may reflect an oblique collision and processes of stress
permutation.
Paleostress mapping of Archean terranes can be used as a targeting tool for mesothermal lode gold deposits. Reduced stress tensors were used for the computation of paleostress maps, using a distinct element model. The Silidor Au quartz mineralization appears on these paleostress maps in an area characterized by low mean stress throughout the deformation history of the area near the Horne Creek fault. This study emphasizes the role of second-order faulting in the location of low- and high-pressure zones in the Archean crust and the possible role of a tectonic indentor in the location of Au mineralization.
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