The ore in the Mustavaara deposit is around 60 m in thickness, and is located in the lower part of the magnetite gabbro layer. The magnetite gabbro comprises small to medium-grained plagioclase, pyroxene (augite) and titaniferous magnetite (ilmenomagnetite) as the main rock forming minerals. The vanadium, iron and titanium grades of the rock correlate with the amount of the ilmenomagnetite. Depending on the amount of ilmenomagnetite, the ore is divided into four distinct sub-layers that are, from bottom upwards: Ore Lower Layer (5 m thick; 20-35 wt% oxide minerals), Ore Middle Layer (15-50 m thick; 10-15 wt% ilmenomagnetite), Ore Upper Layer (10-40 m thick; 18-25 wt% ilmenomagnetite) and Ore Disseminated layer (<10 wt% ilmenomagnetite). The footwall contact of the ore is very sharp, but towards the hanginwall there are huge anorthositic blocks, thus making the upper contact gradational.
Figure 3. Cross-section of the Mustavaara ore interpreted on the basis of three diamond drill holes (MV-063, R-047 and R-048)
The ore reserves in the proven and probable categories are 99 million tonnes, grading 14.0 wt% ilmenomagnetite on average, with a cut-off value of 8.0 wt% for ilmenomagnetite. These reserves are minable by open pit, providing a minimum mine life of 30 years at the envisaged annual mining rate of 3.25 million tonnes.