Surveys Conducted in Isolated Areas with Some Road Access
Geological mapping is carried out by working teams consisting of a geologist and a geological assistant. Access to most of the territory is by helicopter. Nonetheless, vehicules are used locally where roads cross the study area. Teams are deposited at their point of entry from which they make 5 to 14 km-long line transects. Spacing between the lines and their length, as well as spacing between described outcrops depend on the mapping scale, thickness of surface deposits, density of vegetation, topography, outcrop extension, its quality of exposure and the geological complexity of the area. The shores and islands of large bodies of water and rivers are routinely mapped by boat. Areas difficult to access with low outcrop density are also covered by helicopter, spot stops or the“leapfrog” technique.
Outcrops are described using electronic tablets to capture field data in the “Geofiches” module (see MB 98-05 and DV 2013-07 documents). Data is then integrated into the SIGÉOM database. To better characterize geological units, representative samples are analyzed using the following techniques:
- Petrographic description of thin sections (covered and polished) to characterize mineral assemblages and textures of rock units;
- Lithogeochemical analyses for major, minor, trace and rare earth elements to define the composition and characterise the geochemical signature of units. Mineralized samples are analyzed for metals of economic in order to enhance the mineral potential of the sector;
- Sodium cobaltinitrite staining of the sawed-off surface of sedimentary, ignous or metamorphic rock samples to estimate the modal proportions of plagioclase, K-feldspar and quartz. Estimation of modal proportions is done by eye or by image analysis (see method described in RG 2001-15);
- Geochronological analyses of uranium and lead isotopes from zircons, monazites, baddeleyites or titanites to determine the ages of inheritance, crystallization, deposition or metamorphism of units.
The stratigraphic nomenclature of the mapped area meets the standards of the North American Stratigraphic Code (DV 86-02, MNR, 1986; North American Commission on Stratigraphic Nomenclature, 2005; Easton, 2009) and the already-established nomenclature. Units were defined in terms of rock composition, age, cross-cutting relationships, structures and textures, and regional distribution.