Taylor Mugford, MSc
T. Mugford1, B. Lafrance1, R. Sherlock1, G. Tuba1, D. Arriaga1, C. Evans2, P. Mercier-Langevin2, O. Côté-Mantha2, M. Oosterman2
1MERC, Laurentian University, Sudbury, Ontario, Canada
2Agnico Eagle Mines, Kirkland Lake, Ontario, Canada
The Kirkland Lake gold camp (>24 Moz gold), located within the Abitibi greenstone belt of northeastern Ontario, hosts the Macassa mine, one of the world’s highest-grade gold mines (9.18 g/t Au). Gold mineralization is localized along ENE-striking, orogen-parallel, reverse brittle faults, (e.g. Main Break, Amalgamated Break), which cut siliciclastic sedimentary and alkalic volcanic rocks of the Timiskaming assemblage (ca. 2679 – 2669 Ma) and co-genetic intrusions. These rocks are juxtaposed against older volcanic rocks of the Blake River assemblage (ca. 2704-2695 Ma) to the north and Tisdale assemblage (ca. 2710-2704 Ma) to the south. From the Blake River-Timiskaming contact to the north to the Amalgamated Break to the south, Timiskaming volcanic and sedimentary rocks form a south-younging, south-dipping homoclinal sequence overprinted by a steeply-dipping, NE-striking, regional S3 foliation, which is consistently oriented anticlockwise to bedding. Further south, from the Amalgamated Break to the Timiskaming-Larder Lake Group contact, the sequence becomes strongly folded by tens-of-meters-scale F3 folds. The S3 foliation is axial planar to those folds and becomes more pronounced within the Larder Lake-Cadillac Deformation Zone (LLCDZ), a 50 to 800 m wide ductile high-strain zone that straddles the Timiskaming-Larder Lake contact. The LLCDZ is a major structure that extends for over 250 km across Ontario and Quebec and hosts several world-class gold deposits east and west of the Kirkland Lake camp.
Several lines of evidence suggest that gold mineralization at Macassa is pre- or syn- D3 deformation, in contrast to many orogenic deposits along the LLCDZ in Ontario, which are commonly syn-D3. First, south of the Amalgamated Break, a reversal in structural facing towards the LLCDZ suggests that stratigraphy was tilted and rotated along pre-existing faults prior to D3. Second, the Timiskaming rocks young toward the LLCDZ and the older Larder Lake Group volcanics, suggesting that the LLCDZ originated as a north-directed thrust prior to the formation of the S3 foliation because observed S3-bedding relationships are inconsistent with thrusting. Third, gold mineralization within the Amalgamated Kirkland zone, situated in the field study area, is controlled by brittle fractures and breccias that predate the formation of the S3 foliation and LLCDZ. This study provides new insight into the relative timing of mineralization along brittle faults (Amalgamated Break and Main Break) and the ductile LLCDZ, as well as the structural controls on gold mineralization.