Summary:
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