STRUCTURAL DATA INTEGRATION IN 3D GEOLOGICAL MODELS OF A POLYDEFORMED BANDED-IRON FORMATION DEPOSIT IN THE NORTHEASTERN GRENVILLE PROVINCE, QUEBEC

Three-dimensional geological models of parts of the Mount Wright iron mine in Fermont, north-eastern Quebec, were built using structural and drilling data. This work aims at documenting the deformation pattern of the mine, which will decrease the probability of finding waste rock in unexpected flanks of map-scale folds. It further fills a gap in our knowledge of the tectonic evolution of the northeastern Parautochtonous Belt, because it constitutes one of the first modern structural analysis in the Central Grenville Province of Quebec.

The mine site is located in the Gagnon Terrane, in the northeastern part of the Grenville Parautochthonous Belt. The ore deposit consists of a Lower Proterozoic banded iron formation in a foreland basin sequence that were deformed and metamorphosed during the Rigolet phase (ca. 1.0 Ga) of the grenvillian orogeny.

Our geological models show that the geometry of the deposit is controlled by three episodes of ductile deformation (D1 to D3) overprinted by one episode of brittle deformation (D4). The D1 episode is associated with NE-SW trending isoclinal F1 folds. The D2 event produced ENE-WSW trending tight F2 folds with SE vergence. Folding of F1 and F2 by the steeply-dipping, close to open, NW to NNW-trending F3 folds produced map-scale dome-and-basin interference patterns. Additionally, a series of late NNE and ENE trending normal brittle faults subsequently affected the deposit.

D1, D2, D3 structures could be interpreted as the result of NW thrusting of the foreland rocks on Laurentia, of backfolding and backthrusting related with the geometry of the underthrusting Archean basement rocks, and of late transtensional folding, respectively. Finally, the D4 extension faults orientations are consistent with the continental break-up of Rodinia and the opening of the Iapetus Ocean.