Summary:
Deposit Types
Globally, there are two main types of phosphate mineral deposits: 1) igneous rock hosted; and 2) sedimentary rock hosted (Pufahl and Groat, 2017). There are two types of igneous rock hosted phosphate mineral deposits: 1) igneous carbonatite hosted; and 2) igneous massif-type anorthosite hosted. Lac à l’Orignal is an anorthosite massif-hosted phosphate (apatite) mineral deposit.
Anorthosites are plutonic igneous rocks that contain 90% to 100% plagioclase and 0% to 10% mafic silicate and (or) oxide minerals. The most common mafic minerals present are pyroxene (orthopyroxene and clinopyroxene), olivine, Fe-Ti oxide minerals (e.g., magnetite, ilmenite) and apatite. Plagioclase-rich rocks that contain.
Mineralization
Phosphate and Fe-Ti mineralization in the Lac à l’Orignal region is restricted to the AMCG suites and associated mainly with anorthositic rocks. Mineralization in the Pipmuacan Anorthositic Suite (“PAS”) occurs in the Vanel Anorthosites, particularly along fault or shear zones. Three main types of mineralization have been recognized: 1) Fe-Ti (massive magnetitite) mineralization; 2) Fe-Ti-P mineralization (nelsonite or disseminated oxides); and 3) disseminated apatite (phosphate) mineralization. The Fe-Ti-P and P mineralization is restricted to andesine anorthosites. This type of anorthosite was recognized initially in the LSJAS. Previously, these rocks were considered to be labradorite anorthosites. The recognition of anorthosite, leuconorite and andesine apatite-enriched norite containing 5% to 8% P2O5, in the absence of iron and (or) titanium oxides, constituted an important discovery.
The two main mineralized showings on the Lac à l’Orignal Property are the Lac à l’Orignal Showing itself and the Lac Vanel Showing. At the Lac à l’Orignal Showing, phosphate mineralization is located in an oxide gabbro (ultramafic rock I4Za) unit >1 km long and approximately 50 m to 70 m thick. This unit strikes east-west and dips approximately 30° north. The Lac Vanel Showing is situated approximately 2 km north of the Lac à l’Orignal Showing. The mineralization of the Mirepoix Showing is associated with a late-phase of the Mattawa Anorthosite that intruded along fault planes within the Vanel Anorthosite.
The X-ray powder diffraction analysis and petrographic thin section studies of 35 drill core samples from four drill holes (LO-14-02, LO-14-022, LO-14-23 and LO-14-24) from Lac à l’Orignal indicates that these rocks contain mainly plagioclase, orthopyroxene, clinopyroxene, ilmenite, magnetite, apatite, and biotite (Banerjee, 2022) (Figure 7.16). The relative proportion of these minerals varies from one sample to another, such that the host rocks of the apatite mineralization can be gabbro, pyroxenite, norite, nelsonite or anorthosite.