Geology and metallogeny of the Blake River Group (Abitibi): Status report and results of a joint GSC (TGI-3) – MRNF (Copper Plan) – OGS – Industry – University effort
Patrick Mercier-Langevin (GSC-Q), Pierre-Simon Ross (GSC-Q and INRS-ETE), Benoît Dubé (GSC-Q), Jean Goutier, Claude Dion, Marc Legault (MRNF), John Ayer (OGS), Thomas Monecke, John Percival, Vicki McNicoll, Bruce Taylor, Eric de Kemp, Gilles Bellefleur, Eric Grunsky (GSC-O), Phil Thurston, Harold Gibson (LU), Mark Hannington, Ryan Wilson, Joel Laurin (U of O), Bozwell Wing, Elisabeth Sharman-Harris (McGill), Patrice Gosselin (GSC-Q)

The Blake River Group (BRG) is the focus of a major project involving geological mapping, compilation, modelling, geochemistry and a metallogenic synthesis, jointly undertaken by the GSC (Targeted Geoscience Initiative TGI-3), the MRNF (Copper Plan), the OGS, industry and universities. The purpose of this project, comprising various geoscience activities undertaken in symbiosis and in complementary fashion, is to increase our knowledge, and develop and apply new concepts for base metal exploration.

Geoscience activities taking place within the BRG are, for the most part, in their first or second year. Geological and structural mapping, backed by an intensive U-Pb isotope geochronology program and 3D modelling, lead to more detailed global and local lithostratigraphic and lithotectonic frameworks for the various formations and faults within the BRG, whereas the study of volcaniclastic rocks throughout the BRG gradually sheds light on the variable nature (in terms of composition and facies) of these units and their association with certain hydrothermal alteration zones. Oxygen isotope mapping at the scale of the BRG and more detailed work in high-potential zones help define hydrothermal vectors related to volcanogenic systems, in parallel with the synthesis of alteration patterns observed in the field and a sulphur isotope study of various ore deposits. The ongoing characterization of mafic dykes suggests a complex emplacement sequence for intrusions of variable composition and timing throughout the volcanic and tectonic evolution of the BRG.

The study of the Horne ore deposit and the Horne West area illustrates the complexity of the volcanic setting in which this exceptional orebody formed, and outlines fertile stratigraphic horizons along the extensions of the Horne host sequence and metal zoning patterns, in order to guide exploration in this area. Similarly, the study of alteration systems around the Delbridge, D’Eldona and Pinkos deposits reveals the existence of a major carbonatation event, possibly volcanogenic in origin. Moreover, the metallogenic synthesis of the Doyon-Bousquet-LaRonde (DBL) camp documents major variations, at different scales and along different stratigraphic levels, in style of mineralization and alteration within the same volcanogenic hydrothermal system, something every exploration model should take into account.

This multidisciplinary approach has outlined at least five major volcanogenic massive sulphide ore-forming episodes within the BRG, thanks to a better understanding of global and local geological settings in the BRG.