Summary:
The deposit is hosted in the Sept-Îles Anorthosite Complex (SAC): a large, layered, unmetamorphosed, matie intrusive suite of Cambrian age. The tunnel shaped intrusion displays concentric layering. Mineralization occurs above the Critical Zone in what is termed the Mine Series Stratigraphy. At the base of the deposit massive olivineilmenite magnetite-apatite rocks occur in bands up to several meters thick in gabbro (Nelsonite Layer). Stratigraphically above the Nelsonite horizon, ilmenite, magnetite, and apatite are disseminated, throughout the host gabbros in varying quantities, in three principal layers referred to as the Railroad, Upper and California layers. The layers have shallow dips ( -20 o to -40 °) to the southeast.
Chlorine (Cl), a contaminant in the process of apatite concentrate, is found in the host rock and in the ore composing the Sept-Îles deposit. This particularity is a major concern for Mine Arnaud due to the tact that the Cl content of the produced concentrate cannat exceed 0.14 (VARA specifications). To this date the relationship between the Cl in the head assays and in the concentrate are not perfectlly understood.
A sub-vertical fault system crosses the mineralized body without significant displacement and two other longitudinal, sub vertical faults have displacements that vary from nil up to 50 meters and mimic a horst-and graben type structure. These structures are visible iin the magnetic gradient. Since the apatite encountered appears to be associated with magnetism, and the magnetic anomaly continues to the northeast, there is potential for more mineralization in that direction and will be the target of subsequent exploration efforts. lndeed, four widely-spaced drill holes have been completed along the northeastern strike extension and have intersected the phosphate-bearing stratigraphy.
The Project hasts three types of mineralization. 1) The first is hosted in the stratigraphie footwall to the deposit (i.e. below the footwall contact of the Nelsonite unit) and is composed of numerous oxide-rich zones hosting bands of stratiform, nearly massive magnetite plus ilmenite that are hosted by gabbros. These zones are poor in apatite mineralization. Surface magnetic patterns suggest these rocks have significant lateral extent and thicknesses, up to 50 m. Within the deposit, iron-titanium-phosphorous mineralization takes two forms. 2) At the base of the deposit massive olivine-ilmenite magnetite-apatite rocks occur in bands up to several meters thick in gabbro (Nelsonite Layer). 3) Stratigraphically above the Nelsonite horizon, ilmenite, magnetite, and apatite are disseminated, throughout the host gabbros in varying quantities, in three principallayers referred to as the Railroad, Upper and California layers.
Apatite concentrations are linked to the magmatic differentiations which enhances concentration within residual magma otherwise present as trace elements in the initial magmatic fluid. High phosphate grades are associated with coarse to very coarse grain sizes and high concentrations of iron and titanium oxides. Law phosphate grades are generally associated with fine to very fine grain size and law concentrations of iron and titanium oxides (Met-Chem, 2002).