The Norra Kärr complex is a zoned agpaitic, peralkaline, nepheline syenite - similar in many respects to other well-known peralkaline complexes, e.g. Ilimaussaq in Greenland and Lovozero on the Kola Peninsula of Russia.

The Norra Kärr intrusive is located close (2 km) to the eastern shore of Lake Vättern, a large riftcontrolled lake. Following the Tasman exploration efforts, the Norra Kärr complex is known to be an ovoid mass with an areal extent of some 1.3 km by 450 m.

The mineralisation at Norra Kärr is at once both simple and complex. Simple in mineralogical terms in that nearly all the REE mineralisation is hosted in the complex zircono-silicate mineral eudialyte. There are minor amounts of the (probably) secondary Ca LREE-F-silicate (britholite) and trace mosandrite. The eudialyte at Norra Kärr is, relatively rich in REE compared to most other similar deposits and also contains a very high proportion of HREO.

Various studies (e.g. Sjöqvist et al, 2013 (4)), have shown that within the resource, the TREO content of the eudialyte varies between 6 and 10 %. The percentage of HREO also varies from about 30 % in the more central GTM zone to above 70 % in more distal GTC zone. The total content and distribution of the REEs within the eudialyte also varies throughout the deposit. Sjöqvist et al (4) defined three compositional varieties of eudialyte group minerals at Norra Kärr:
- Fe-rich, REE-poor, classical pink eudialyte;
- Fe-Mn-bisected, HREE-rich eudialyte from “pegmatitic” grennaite; and
- Mn-rich, LREE-rich eudialyte from “migmatitic” grennaite.

This study supports the field and analytical evidence that there are varying types of eudialyte which can, to an extent, be differentiated by colour with the more vibrant pink variety being poor in REOs and the duller, brownish-red varieties containing higher values of REOs.

Open pit operations are planned to be conventional diesel hydraulic shovel and truck extraction, with drill and blasting of final benches at 20 m height. The mine life has been designed at 20 years. There is pre-stripping required of 600 kt waste and 60 days have been allocated for this task. The life of mine (LOM) mining rate averages 1.15 Mt/a ore and 0.84 Mt/a waste.

The mine plan has been developed using owner operated equipment in all aspects of mining. Hauling is scheduled to operate on a single eight hour shift per day, five days a week. This equates to 241 operating calendar days, less five days for weather delays. Blast hole drilling operates on two eight hour shifts at the same operating days due to drilling requirements. It has been assumed there will be 85 % operating availability of equipment.

Blast fragmentation was required to meet a maximum of 600 mm for a planned crusher and the blast design was made to ensure fly rock does not affect the E4 highway located to the west.

Blast hole drilling will be completed with a track mounted blast hole drill, such as an Atlas Copco Flex Roc D60. Final bench heights will be 20 m, fired in two lifts. Owing to the bulk nature and similarity of ore and waste, a blasting pattern has been designed for use in all materials. Vertical 110 mm (4.3”) diameter holes at a 2.75 m x 3.25 m staggered pattern are planned with 0.37 m sub-drill and 2.75 m stemming.

The overall blast design has a tight pattern with relatively small hole diameters and increased stemming, this is due to the fragmentation and fly rock constraints, whilst meeting targeted powder factors for the rock mass.

Loading will be undertaken using a hydraulic shovel and large wheel loader as a back-up. The primary excavator will be a 100 tonne class unit with a 6.7 m3 bucket, such as the Komatsu PC1250-8. The shovel has been planned in a face shovel configuration as this will allow good operator visibility, selectivity, and allow the unit to scale loose blocks either reaching upwards or downwards on the 20 m bench.

The wheel loader is planned for auxiliary tasks such as muck pile loading and bench clean ups, as well as acting as another loading unit in case of mechanical down time on the primary hydraulic excavator. The wheel loader will have a 6.9 m3 bucket, such as a Volvo L250G; this is sized to match 55 tonne payload trucks.

Haulage will be done using 55 tonne class haul trucks. CAT 773G (55.3 t, 35.8 m3 capacity) rigid body haul trucks were planned with the excavating units and for haulage profiles. Oversize or unmanageable blocks will be separated by the hydraulic excavator then transported using the wheel loader to a separate area.

Mining haul ramps are designed at 10 % gradient and at 18 m width, a rolling resistance of 2 % has been assumed (2 % is equivalent to a hard, smooth surface stabilised surface, watered and maintained). Although the haul trucks are capable of descending at over 50 km/h, a site speed limit for heavy plant of 30 km/h on ramps and 40 km/h on the flat is recommended. The mine model has set the haul truck descending speed to match the inclined speed to ensure a constant cycle, thus avoiding trucks waiting to be loaded.

An apron feeder will reclaim Run of Mine (ROM) material from the ROM bin onto a vibrating grizzly screen. Oversize material reports to a jaw crusher where the material is comminuted before recombining with the grizzly screen undersize and fed to the secondary crushing screen. Similarly, oversize from the secondary crushing screen will report to the secondary cone crusher where the material will be comminuted before reporting to the tertiary crushing screen. Screen undersize from the secondary and tertiary screens will then be transferred to the fine ore bin. Oversize material from the tertiary crushing screen will report to a tertiary crusher where it will be comminuted before being recycled to the tertiary crushing screen for classification. All material transfers between process units will be by conveyors.

Discharge from the fine ore bin will be delivered for primary grinding, via a conveyor, to an open circuit rod mill. Rod mill discharge will be screened with the oversize reporting to a tower mill for secondary grinding. Tower mill discharge is combined with rod mill discharge and classified over the same screen in a closed circuit.

Undersize from the mill screen will be fed to a low intensity magnetic separator to remove any residual grinding media, before reporting to a wet high gradient magnetic separator. The magnetic separator will produce two product streams:
- the magnetic concentrate enriched in aegirine and eudialyte; and
- the non-magnetic concentrate depleted of iron bearing minerals.

Each concentrate will report to their respective thickeners to recover water. Thickener underflow from the non-magnetic thickener reports to the tailings discharge tank for disposal and thickener overflow returns to the process water tank. Thickener underflow from the magnetic concentrate reports to the leach conditioning tank and the thickener overflow is returned to the magnetic separator.

Fresh sulfuric acid will be added to the slurry in the leach conditioning tank. Additional sulfuric acid will be recycled from the solvent extraction plant. In order to maintain the pH set-point sulfuric acid will be added in each of the leach tanks.

After leaching, the pH of the solution will be raised through the addition of magnesium oxide. A pH value is established in order to reject various impurities, which will be precipitated, allowing their removal from the solution via thickening and filtration (filter cake reports to tailings tank). Following impurity removal the temperature of the pregnant leach solution (PLS) is raised and the pH reduced, using sulfuric acid, to enhance solvent extraction characteristics.

PLS will report to solvent extraction to recover the REE. Solution will be contacted with a suitable solvent, into which the rare earths will preferentially exchange. The loaded organic solvent will then be scrubbed with dilute sulfuric acid to remove most of the loaded impurities. The REE will be stripped from the pregnant solvent using oxalic acid. The precipitate will then be removed by a combination of centrifugation and filtration of the insoluble rare earth oxalates.

The REE oxalate filtercake is then dried and calcined in a calciner to produce a REE rich mixed oxide. The oxide will then be cooled and packed in preparation for dispatch to a refinery for metals separation.

Raffinate from solvent extraction will contain various dissolved metals, the concentration of which will build up in the system when recycled. Ultimately, these dissolved species will interfere with the recovery of rare earths if their concentration gets too high. As such, a portion of the waste water will be sent for treatment, involving the addition of lime, nanofiltration, reverse osmosis (RO) and brine evaporation. The gypsum sludge resulting from the addition of lime reports to the tailings discharge tank for disposal. The neutralised effluent will then undergo a series of nanofiltration and reverse osmosis stages producing a permeate (water) and a brine. The RO water reports back to the raw water tank and the brine will then be further subjected to thermal evaporation to remove the contained water to produce a solid salt residue (predominately magnesium and sodium sulfates) and a water vapour condensate. The condensate reports back to the raw water tank and the salt is transported to a licenced storage facility for long term management.

The principal reagents required in the process are sulfuric acid, magnesium oxide, lime, oxalic acid, flocculant, primary amine solvent, iso-decanol (diluent) and Shellsol 2046.