Structural and lithological controls on gold mineralization at the Cheminis mine: implications for the formation of gold deposits along the Larder Lake - Cadillac deformation zone, Ontario

Abstract

The Larder Lake-Cadillac deformation zone (LLCDZ) is a major deformation zone within the southern Abitibi subprovince of the Archean Superior Province. It hosts several gold deposits, including the Cheminis and the giant Kerr Addison - Chesterville deposits in Ontario. The two deposits occur along a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma), bounded on both sides by younger, less deformed, Timiskaming turbidite (2680-2670 Ma). Gold was emplaced during D2 closure of an extensional Timiskaming basin, following the formation of early F1 folds. D2 deformation was a progressive compressive deformation event that began with regional F2 folding and the formation of a regional S2 cleavage, and ended with the localization of the deformation along the band of older volcanic rocks, the formation of the LLCDZ, and the introduction of gold during south-side-up reverse-slip faulting along the LLCDZ. The presence of weakly deformed syenite dykes suggests a minor magmatic contribution to the gold-bearing hydrothermal fluids. Thus, gold was deposited as hydrothermal fluids flowed upward along the LLCDZ during D2 south-side-up shearing.