Petrographie, geochimie et potentiel economique en fer-titane-phosphore du secteur du Lac a Paul, partie nord de la suite anorthositique de Lac-Saint-Jean, province de Grenville, Quebec

This master's project is a study of the geochemistry, the petrography and economic potential of iron-, titanium-, and phosphorus-rich rocks (Fe-Ti+/-P) of the lac a Paul area, located in the northern part and on the margins of the Lac Saint-Jean anorthositic suite (LSJAS). The LSJAS is part of the Grenville province, which is characterized by numerous proterozoic AMCG-type anorthositic suites. This type of Fe-Ti+/-P enrichment is characteristic of these suites.;The minerals analysed by microprobe (olivine, plagioclase, orthopyroxene, clinopyroxene, ilmenite, magnetite, spinel and apatite) all display evolved compositions. The plagioclase is mostly andesine (An27 to An 50) and the forsterite content of the olivines varies from Fo46 to Fo63. Unlike the other lithologie, which are characterized by ilmenite, the ferrodiorites contain hemo-ilmenite.;The evolved nature of the different rock types of the lac a Paul area, illustrated by the petrographic and geochemical studies, indicates that the parental magma of these rocks is also evolved. Moreover, the ubiquitous distribution of apatite indicates that the parental magma had a composition where apatite was on the liquidus. The REE composition of the parental magma was calculated using the REE composition of separated apatites analyzed by INAA. This (calculated) composition is similar to the composition of ferrodioritic rocks often associated with anorthosite massifs. The formation of the anorthositic and troctolitic rocks is possible by crystal fractionation, from a magma of ferrodioritic composition. The origin of the nelsonitic peridotites remains problematic and liquid immiscibility cannot be excluded. The Fe-Ti oxide rocks were probably formed by migration of the ilmenite and magnetite in low-pressure zones during emplacement of the rocks of the study area or during subsequent deformation. The ferrodiorites have higher LREE enrichment than the calculated magmatic compositions of the lac a Paul area but they are probably genetically related to the Fe-Ti+/-P-rich rocks of the study area.;The nelsonitic peridotites, with 10 to 25% apatite, have the highest economic potential in terms of phosphorus (4 to 10% P2O5). They have a widespread distribution in the study area and they could also represent a secondary economic potential in ilmenite and magnetite. The Fe-Ti oxide rocks display the highest concentrations in iron and titanium. Unfortunately, they have an erratic distribution in the study area.;The Fe-Ti+/-P enrichment of the different types of rocks in the lac a Paul area reflects their variable enrichment in magnetite, ilmenite and apatite. The sampled rocks that show this type of Fe-Ti+/-P enrichment were divided into six lithologies: (1) Fe-Ti oxides- and apatite-bearing anorthosites, leucogabbros, leuconorites and leucogabbronorites; (2) Fe-Ti oxides- and apatite-bearing troctolites and leucotroctolites +/-; (3) nelsonitic peridotites; (4) Fe-Ti oxides rocks; (5) Fe-Ti oxides-bearing pyroxenites, and; (6) Fe-Ti oxides-bearing dunites. Some ferrodiorites, in the form of crosscutting dykes, were also sampled.