The Mary River deposits can be described by the depositional model proposed for Algoma-type iron formation. The characteristic stratigraphy for Algoma-type iron formations comprise of a lower succession of typically intermediate volcanics interbedded with acid volcanics, volcaniclastic sediments, and their sedimentary derivatives. This succession is followed by banded iron formation comprised of alternating cherty bands and iron oxides or bedded or banded pure oxides ranging from metres to hundreds of metres in thickness, depending on depths of the original basins. This succession in turn is overlain by a sequence of volcanics and volcaniclastic sediments often intruded by ultramafics and granitic intrusive bodies.

Mary River Group greenstone belts across northern Baffin Island consist of variable amounts of banded iron formation (BIF), which are associated with metasedimentary, metavolcanic and metaigneous rocks (Jackson et. al., 1978a, b, c; Jackson and Morgan, 1978). The banded oxide and silicate facies iron formations comprise the lateral equivalents of the high-grade Mary River deposits, which are almost entirely composed of iron oxides, suggesting a significant enrichment of iron through secondary processes.

Duke (2010) suggests growing evidence for a secondary Fe enrichment mechanism associated with widespread retrograded mylonitic detachments along the base of the high grade and enriched BIF across north central Baffin Island in places such as the Mary, Turner, Cockburn and Rowley River areas. These detachment faults are marked by a chlorite retrograded mylonitic structural contact between underlying ductile rising domes of polydeformed mafic-felsic gneisses and overlying supracrustal sinking keels which host the Mary River iron deposits (Duke and McCleod, 2009). These detachments are thought to be post regional folding of the Hudsonian orogeny around 1,850 Ma (Duke, 2010).

The high grade massive and enriched iron oxide ores occur where Mary River BIF border directly on detachment schist that separates the mylonitic roof of infrastructural domes from the high strained keels of Mary River Group. At detachment schist contacts, magnetite BIF shows evidence of undergoing extreme pressure solution resulting in the highly efficient leaching of quartz from magnetite. In large deposits, the primary banding defining early isoclinal folding is completely destroyed by metamorphic differentiation and recrystallization, resulting in >100m thicknesses of massive magnetite/hematite. On the flanks of the high grade iron deposits, Feenrichment is marked by various degrees of silica loss due to continued silica removal. Several regional examples of exposed giant quartz veins occurring along detachment schist boundaries adjacent to high grade magnetite zones account for the removal of silica from the banded iron formations. Duke (2010) suggests that the hydrothermal removal of silica was likely facilitated by dewatering of the nearby footwall serpentinized komatiites.

The Mary River deposits are comprised of a number of iron formations which have been enriched and altered to varying degrees. Original banded iron formations comprised of alternating layers of magnetite and hematite, are preserved in several locations along strike of existing high grade deposits. The regional metamorphism and folding associated with the Hudsonian Orogeny resulted in significant crustal thickening. This period also resulted in zones of weak to very efficient leaching of silica. Subsequent hypogene and metamorphic events led to the alteration of magnetite to hematite and specular hematite. Surface outcrops differ in iron, silica and sulphur content and in the proportions of their main oxide minerals – hematite, magnetite and specularite. The microscopic examination of drill core specimens by R.A. Blais (1964) suggests that magnetite was the stable mineral of the iron formations during metamorphism (amphibolite facies), and was replaced to various degrees by hematite (martitization), resulting in a range of hematite-magnetite (martite) compositions. This alteration process occurred during a late stage of metamorphism, under conditions of localized stress and high oxygen pressure, and may have been associated with folding and faulting of the tabular high-grade magnetite iron formation.

The strong structural influence on channelling of oxidizing solutions is supported by the alignment of lineations produced by tubular pores in the hard high-grade hematite iron formation (i.e., parallel to the axial plane and plunge of the synform) and the concentration of high-grade hematite ore at the core of the fold. Euhedral specularite crystals in magnetite rock indicate that specularite did not form by a process similar to martitization, but through the possible metamorphic replacement of magnetite. It is also possible that the specularite and other hematite mineralization formed as a primary rather than secondary mineral. However, what caused the crystallization of flaky, course-grained specularite as compared to fine-grained massive hematite is not fully understood. Field evidence suggests that higher fluid or vapour pressures in zones of shearing may have facilitated the growth of specularite.

Ore and waste material is drilled and blasted using both large and small drill rigs drilling 4” to 6” diameter blast holes. The blasts are designed such that material can be mined out in 5m benches. An on-site explosives plant producing an emulsion product will be used to supply the explosives to the blast hole. The holes will be primed and tied together to a non-electric detonating cord that will be used to detonate the blast. Blasted material will generally be less than 800mm diameter. Any oversize will be drilled with a secondary drill and reblasted. Blast sizes will be maximized where practical to maintain large broken inventories in pit and reduce disruptions to mining operations. Blending requirements to ensure product quality will require multiple mining faces.

Hydraulic excavators and large front-end loaders are used to load 90 tonne haul trucks. A support fleet for motor graders, tracked dozers and excavators will be used to maintain the pit and waste dumps.

Waste material will be sent to a dump location Norwest of the pit. Ore will be delivered to the portable crushers at the base of the mountain. At an ultimate depth the pit will have walls that are more than 500m above the bit bottom and waste dumps of equivalent heights.

The capacity of the proposed mining, comminution and handling facilities are considered modest for iron ore operations. The subarctic location will necessitate thorough weatherproofing, but otherwise the crushers, screens and other processing and transfer equipment are conventional in their selections.

The process consists of sequential crushing by jaw and cone crushers in closed-circuit with vibrating screens. The plant will deliver two products, lumps and fines, to stockpiles for blending prior to transfer to the port for ocean transport.

Lump iron ore is expected to be the main product from the Project and will be about 75% of the total production by weight. This product will have high iron grade by world standard, and will have variable impurity content, depending on the mine plan and schedule. The lump product has been found suitable for blending as direct feedstock for blast furnace iron making. The minority fines product would also be saleable depending on its grade and market conditions.

The proportion of lump generated from laboratory crushing of core samples was high compared to other iron ores. This trend is likely to be confirmed from mined samples. Physical tests will be required on ore samples that represent mine deliveries to define the crushing and screening properties for detailed plant engineering and economic analysis of future production.

The process plant for the Mary River Project has been designed with the maximizing of lump product as a primary objective. It is a two-stage crushing and screening plant which produces two products, a -25 +6 mm lump product and a -7 mm fine product, each of which is then conveyed to storage piles ahead of the load out facility for road haul to Milne Inlet. Further work during the crushing and screening of the material during the bulk sampling program indicates that the physical attributes of the Mary River lump and fines are outstanding. The lack of undersize (~4% less than 6.3 mm) based upon screening at the discharge port indicates superior physical attributes that may allow tighter physical specifications of a lump ore sale product. It is important to note that the small portion of undersize was achieved without discharge port screening.

Material above this screen size is recycled to the secondary crusher. All material less than 7 mm will be shipped for sinter plant feed at the smelter, where it will be blended with other fine products.