In the Aley deposit, niobium occurs in pyrochlore that formed as early-stage mineral precipitates in primary magma. Alteration of the dolomite carbonatite by unknown factors created the Nb bearing alteration minerals fersmite and columbite. The changes are believed to have occurred largely in situ, and as such there has been less scope for transport or concentration of Nb by secondary processes. The type of deposit is considered to be that of magmatic segregation.

The Aley Carbonatite complex intrudes Cambrian to Ordovician sedimentary rocks of the Kechika (limestone), Skoki (dolomite to volcaniclastics) and Road River Group formations (clastic sedimentary rocks). The intrusion is ovoid in plan view with a diameter of approximately 2 km and surrounded by a fenite aureole up to 500 m thick that has previously been mapped as “amphibolite” (Pride, Cominco Ltd., 1987) and “syenite” (Mäder, 1986). The intrusive contacts are parallel to bedding and lie at a uniform stratigraphic level near the base of the Kechika Formation. Three principal units within the carbonatite have been identified:

1) a volumetrically dominant fersmite- and pyrite-bearing dolomite-apatite carbonatite unit that forms the core of the sill;
2) a magnetite, pyrochlore, phlogopitebearing calcite-apatite carbonatite unit that forms the margins of the sill where it is in contact with the Kechika Formation; and
3) a banded magnetite-apatite unit in the dolomite core.

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The Aley open pit will be mined by a conventional truck and shovel operation. Due to the production rate, location of the deposit and the width of the mining cuts, the equipment utilized in this operation will be approximately one third of the size of typical equipment found in today’s large open pit operations.

The production rate of 10,000 tpd ore was selected as a base case for project design and costing on the basis of balancing economies of scale and niobium market conditions.

Designs for the Aley pit phases use a fixed face slope angle of 65 degrees and safety berm widths of 10m for every two vertical 10m benches, for a standard inter-ramp slope angle of 46 degrees. Knight Piesold’s recommended inter-ramp pit slopes for different sectors of the pit are:
- 10m vertical benches, double benching configuration (safety berm every 20m);
- North Sector: 70 degree face angle, 50 degree inter-ramp angle, berm width of 9.5m;
- North-East Sector: 65 degree face angle, 48 degree inter-ramp angle, berm width of 9m;
- South-East Sector: 70 degree face angle, 50 degree inter-ramp angle, berm width of 9.5m;
- West Sector: 65 degree face angle, 45 degree inter-ramp angle, berm width of 11m.

The following parameters were used to drive the production schedule and equipment requirements:
- Annual mill feed of 3,650 ktpa is targeted based on 10,000 tonnes/day ore milling;
- Year 1 milling target of 7,500 tonnes/day;
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