Janek Urbanski, MSc
J. Urbanski1, D. Jiang1, N. Banerjee1
1Department of Earth Sciences, Western University, London, Ontario, Canada
The Troilus deposit is hosted in the eastern Frotet-Troilus segment of the Frotet-Evans Greenstone Belt, of northern Quebec. Located approximately 120 km north of Chibougamau, Quebec, the deposit saw production of gold and copper as an open pit operation from 1996 to 2010. New ownership and exploration efforts from Troilus Mining Corporation has led to resource growth of over 12 Moz AuEq. While the deposit is understood to be structurally controlled, the genesis, evolution, nature, and relative timing of fabrics is poorly understood and should be considered in a broader tectonic and regional context.
This work employs a classical structural geology field mapping approach, integrating geometric and kinematic analysis at regional, outcrop, and microscopic scales. This has allowed for the establishment of multiple deformation events and their characteristic fabrics, the timing of mineralization, and for inferences to be made to regional tectonics.
The region has been divided into two structural domains based on geometric similarities between fabrics within each domain. Troilus Main comprises the area southwest of the Parker granitic pluton, while Troilus North comprises the area northeast of the Parker granite. The field area is characterized by fabrics developed during dextral transpression and shearing at upper greenschist to lower amphibolite facies conditions. Observations from the field are consistent with a pure-shear dominant style of transpressional tectonics in the southern domain, while the northern domain corresponds with a change to simple-shear dominant transpression.
The transpressive event is responsible for producing the main observed fabrics associated with deformation event D1, including a moderate to steeply NW dipping S1 foliation and steeply pitching L1 lineation in the Troilus Main domain, and a flatter NW dipping foliation with a more shallowly pitching lineation in the Troilus North domain. A later D2 deformation event is manifested by folded D1 fabrics and narrow shear zones which cut D1 features. Later events are recognized but not associated with mineralization.
Multiple styles of mineralization with variable timing are recognized to be hosted in the fabrics of the Troilus Main domain. The Troilus deposit is hosted within an anastomosing WSW-ESE trending mylonite zone defining a major regional lineament, within which ductile, brittle-ductile, and brittle structures host variable amounts and types of mineralization. Deposit scale controls include the syn-D1 shear zones and associated S1 foliation which acted as a major fluid pathway. There is also further enrichment corresponding to L1 and L2 lineation geometries.