Geological Setting of the Marbridge Mine: Komatiite Hosted Ni-Cu Ore Deposit

English Abstract:

The Marbridge Mine is located in the southeastern part of the Abitibi Sub-province, at the base of the Malartic Group within the La Motte-Vassan Formation (2714 Ma). The mine was in operation from 1962 to 1968 with a production of 700,000 tonnes of ore at 2.28% Ni and 0.17% Cu, from four lenses associated with komatiites. The study area is surrounded by various plutonic rocks (Preissac pluton; 2681-2660 Ma; La Corne pluton; 2680-2642 Ma and La Motte pluton; 2647 Ma). Regional metamorphism reaches the amphibolite grade and surrounding rocks are part of an intense deformation zone which is characterized by L-tectonites. The main schistosity (S1) is commonly oriented NW-SE and is overprinted by a subvertical crenulation cleavage (S2) generally EW associated with Z-shaped P2 folds. The lithogeochemical analyses of the various units has allowed to recognize two distinct suites: (1) a calc-alkaline suite consisting of andesitic, dacitic, rhyolitic units and various associated volcanic rocks; and (2) a tholeiitic suite, consisting mainly of komatiitic flows, basalts and ultramafic intrusions. The presence of intense sericitic and chloritic alteration in felsic volcanic units and strong epidote alteration in mafic volcanic units is compatible with an early “VMS” hydrothermal system in this sector. Finally, these data will be used to reconstruct the sequence of geological events that have affected the Marbridge mine area. This reconstruction will allow the definition of exploration tools in such metamorphosed ultramafic-mafic environments.