Conference program
November 22, 2011 |
Geological revision of the Matagami region |
This work, which started in 2008, is part of a multidisciplinary project on the geologic and metallogenic understanding of the Matagami mining camp (1960-2005 production : 4.6 Mt Zn, 0.494 Mt Cu). The mapping component is under the direction of the MRNF. Geological revision work in the summer of 2011, at a scale of 1:20,000, covered the southern half of NTS map sheet 32F13, the northern half of 32F12, and some areas of 32E09 and 32E16, collectively covering the entire mining camp. A 3D geometric model of the region will be generated at the end of the project, with the objective of providing a better understanding of the stratigraphy, structural features, and distribution of VMS-type mineralization. This revision forms an integral part of a larger partnership involving the MRNF, researchers and students from INRS-ETE, UQAC and École Polytechnique de Montréal, and the mining companies Xstrata Zinc, Donner Metals and SOQUEM. The mapped region mainly belongs to the Abitibi Subprovince (ASP). It is underlain by various volcanic and plutonic rocks, the Rivière Bell Complex (RBC - a vast subconcordant ultramafic to mafic layered intrusion dated at 2724.6 ± 2.5 Ma) and a narrow band of sedimentary rocks (the Matagami Group - MaG, <2700 Ma) in faulted contact with the Opatica Subprovince (OSP) to the north and volcanics to the south. These lithologies are crosscut by Proterozoic gabbro dykes. Two volcanic groups are present: the Lac Watson Group (WatG, 2725 à 2723 ± 2 Ma) and the overlying Wabassee Group (WabG). The WatG consists mainly of rhyolite, rhyodacite and dacite. It is this group that hosts the majority of volcanogenic massive sulphide deposits in the camp. The Key Tuffite, immediately overlying the WatG rhyolites, represents an important marker horizon for VMS mineralization in this mining camp. The WatG is intruded by the CRB. The Wabassee Group is dominated by andesites and pillowed basalts, either massive or brecciated. The group includes the Rivière Bell Volcanics (tholeiitic affinity) and the Rivière Allard Volcanics (calc-alkaline to transitional affinity). Several geographical areas have been defined in the past: the South Flank, the North Flank, the Central Camp, and the West Camp. Our work has led us to propose a new subdivision into North and South domains, with the boundary marked by three shear zones named “Rivière Allard”, “Rivière Waswanipi” and “Lac Matagami”, all oriented 070°. They represent reverse sinistral shears ranging from 50 m to more than 100 m thick, dipping steeply to the north with a stretching lineation plunging steeply to the east. The South Domain will now comprise the historically defined North Flank and South Flank, the Central Camp and the West Camp. Our work demonstrates, just as several researchers have suggested in the past, that the South Flank, Central Camp and West Camp share the same stratigraphy, oriented NW-SE with a gentle to quasi-horizontal dip, developed in a relatively consistent and predictable manner. Mapping also reveals that the South Flank and Central-West camps are affected by a weak S1 cleavage and by three major F1 fold axes (two synclines and one large anticline), also oriented NW-SE. An E- to ESE-oriented S2 schistosity crosscuts S1 cleavage. The resulting geometry of the juxtaposed North and South domains calls into question the existence of the Galinée Anticline and has serious implications for the VMS potential in the areas described above. As for the North Flank, stratification is oriented 110° with a dip and general polarity to the north. An S2 schistosity oriented 090° to 110° affected the S0 surface and locally generated F2 folds. Shear zones, also oriented 110°, appear to repeat or truncate certain portions of the volcanic pile and the BRC. |
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