Summary:
The Lac Doré Property is located at the northeast end of the Abitibi greenstone belt, which is host to several Archaean mafic intrusions, including the Lac Doré Complex (LDC) near Chibougamau, which has been emplaced into volcano-sedimentary host rocks and has in turn been intruded by the felsic Chibougamau Pluton.
The LDC is a layered mafic complex and is comparable (albeit smaller) to other better-known complexes, such as the Bushveld Complex in South Africa. The Lac Doré Property area (located in the Layered Zone of the LDC) is underlain by anorthosite, gabbro, magnetitite, and pyroxenite in varying proportions.
The Lac Doré Complex is a lopolith, a sub-tabular intrusive body of mafic to anorthositic composition, strongly differentiated near its top. The lopolith is emplaced within the Waconichi Formation, a felsic volcanic and sedimentary pile, and folded along by the regional anticlinorium. The deposit is hosted in a homoclinal sequence of magnetite bearing layers within the South flank of the Lac Doré Anorthositic Complex. Top of stratigraphy is to the south.
According to Allard (1967), the Lac Doré Complex is divided in four major units. From top to bottom they are:
- The border zone (top, South-East);
- The granophyre;
- The layered zone;
- The Anorthositic zone (base, North-West).
The layered zone hosts the vanadiferous titanomagnetite deposit, while the anorthosite and the granophyre host most of copper-gold mineralization of the mining camp (outside the current project). The anorthosite zone (approximately 3660 m in observed thickness) is composed of anorthosite, gabbro and titanomagnetite-bearing gabbro, plus some minor pyroxenite. The titanomagnetite abundance as well as the vanadium content increase in the upper 150 metres of the unit, toward the layered zone.
The layered zone, which hosts the vanadiferous titanomagnetite deposit, consists up of 450 to 900 metres of rhythmically layered beds rich in pyroxene, titanomagnetite plus ilmenite, intercalated with layers of anorthositic gabbro. The vanadium mineralization is located in the lowermost part, namely the P1, P2 and P3 units. Vanadium strongly partitions into magnetite, and thus into the first titanomagnetite layers. Abundance of titanomagnetite decrease upward (Allard, 1967).
Local stratigraphy is presently defined as follow, from bottom (North) to top (South), and more recently refined by Arguin (2017):
- Footwall anorthosite, free of magnetite.
- P0: Anorthosite with small scattered beds of magnetite.
- P1: Anorthosite with abundant and thick beds of magnetite.
- P2: Magnetite and layered gabbros, main ore body.
- P3: Magnetite-ilmenite bearing pyroxenite.
- Hanging wall, mainly gabbro and pyroxenite.
Lenses of anorthosite, metres to tens of metres in thickness, are intercalated within the above units, which were considered as stratigraphic units by Allard (1967).
Vanadiferous mineralization at Lac Doré is composed of titanomagnetite and ilmenite, hosted in anorthosite, anorthositic gabbros and gabbros, within the layered series of the Lac Doré Complex. Magnetite and ilmenite, associated in various proportions depending on stratigraphy, are found either as massive beds, decimetres to metres thick, or as dissemination within anorthositic and gabbroic facies. Overall, the deposit contains about 30% magnetite, the main reservoir for vanadium, plus 10% ilmenite. Oxides are best described as orthocumulate phase in the massive beds, or intercumulate while disseminated in host rock. Typical abundances and vanadium grades for the various units as estimated from McKenzie Bay Resources channel samples.
Mineralization is in the form of vanadiferous-titanomagnetite (VTM), which forms a significant proportion of the lithologies and in some cases, may make up close to 100% of the lithological unit. Each mineralized zone varies in thickness across the 3 km of strike, as outlined, and the entire mineralized zone varies between 200 m and 300 m in thickness. The lithologies and overall magmatic stratigraphy dip at approximately 50--60° to the southeast and have been drill-tested to depths of at least 220 m below the surface.
The concentration of vanadium and titanium within the magnetite varies with stratigraphic elevation. The magnetite from stratigraphically lower units (P1, P2-LOW) are more enriched in vanadium and has relatively low titanium levels, whereas stratigraphically higher levels (P3) have lower vanadium and higher titanium in magnetite. Titanium and vanadium levels in magnetite remain relatively constant within units and along strike.