Overview

Deposit type

• Porphyry
• IOCG
• Hydrothermal

Summary:

The Aitik, Salmijärvi, and Aitik East deposits occur along a largely continuous elongate mineralized trend (the Aitik-Salmijärvi mineralization) stretching approximately 5 km along strike from north to south averaging about 500 m in width.

Host rocks of the mineralization at the Aitik deposit consist mainly of paleo-proterozoic (ca. 1.89 billion years) muscovite schists, biotite gneisses, and amphibole-biotite gneisses of volcanic and volcanoclastic origin, crosscut locally by diorite intrusive units. In places the diorite intrusive make up a significant proportion of the mineralized volume, but typically at lower than average grade. Foliation is well developed in the host rocks, dipping at about 50 degrees to the west. The mineralization is mainly structurally controlled and the main mineralisation; Aitik is delineated by a hangingwall thrust and a footwall shear. Main sulfide minerals in the deposit are chalcopyrite, pyrite and pyrrhotite, with significant accessory minerals including magnetite, molybdenite and sulfates. The entire package has been metamorphosed to amphibolite grade resulting in significant recrystallization and coarsening of both sulfide and silicate minerals. Late granite pegmatite dikes crosscut the mineralized host rocks and are generally weakly mineralized to barren.

Mineralization at the Salmijärvi and Aitik East deposits is very similar in nature to the Aitik deposit, with the exception that host rocks are strongly dominated by amphibole-biotite gneisses and local diorite. Sulphide mineralization in these deposits is dominated by chalcopyrite, pyrite and pyrrhotite, although at typically lower grade than in the Aitik deposit.

About 3 km to the east, on separate and volumetrically smaller mineralized trend, sits the paleoproterozoic Liikavaara Cu-(W-Au) deposit. At Liikavaara the mineralisation is hosted by quartz±tourmaline-calcite veins, calcite veins and aplite dykes that cross-cut biotite-amphibole schists and gneisses, steeply dipping to the west. The mineralisation is mainly chalcopyrite, pyrrhotite and pyrite, accessory minerals are sphalerite, galena, scheelite, molybdenite and magnetite. Liikavaara shows slight enrichments in Au, Ag and Bi.

Mining Methods

• Truck & Shovel / Loader

Summary:

Aitik is a Palaeoproterozoic porphyry Cu-Au-Ag deposit, mined as an open pit complex consisting of the main pit, “Aitik”, and two satellite pits “Salmijärvi”, which was mined out during 2023, and “Liikavaara”, which will begin production in 2024. The mining in Aitik took place at three pushbacks of the main Aitik pit - designated S3, N6 and N7.

The ore is mined in two open pits along the same mineral deposit. The main pit is called Aitik and measures 4 km by 1.1 km at the surface, with the deepest point currently at 555 meters from the surface. In 2010, mining commenced in a second pit called Salmijärvi which has reached a depth of 305 meters below the surface, with a surface footprint of 0.9 by 0.6 km. The pit is being depleted during 2023 and no further expansions are planned for this area. The main pit will be expanded in all directions with five new pushbacks. Mining of pushback S3 in the southern part of the main pit started in 2016. Prestripping of pushback N7 commenced in 2019 to allow mining to start during 2020.

The ore and waste rock are blasted in 15-meter-high benches and are loaded on 300 tons capacity-size trucks by large rope shovels or hydraulic excavators. Ore from the deeper parts of the main pit is fed to an in-pit-crusher, while ore from pushbacks near the surface is transported to a surface crusher situated on the south-east side of the main pit. Waste rock is separated in the loading process and hauled by trucks to dumps at the surface where potentially acid-forming waste is dumped separately from non-acid-forming waste.

Holes for blasting are drilled with electric drills from Bucyrus and Atlas Copco. Hole depth: 16-17 m Hole diameter: 311 mm Drill attern: 7x9 m Between 200-300 holes are drilled for each round of blasting. A normal blast round produces around 700 000 tonnes of rock for extraction.

Boosters are loaded into the holes followed by emulsion explosives. Explosives: Emulsion explosives (Kemitti-610) from Forcit, about 1 tonne of explosive is used in each hole.

With the help of shovels from Bucyrus, P&H, Komatsu and wheelloaders from Caterpillar, the blasted rock is loaded on to trucks for further tranportation. The largest trucks, CAT 795F, holds about 313 tonnes. A bucket can hold 45 m³ rock (Komatsu 26 m³). The ore is transported to the crusher and the waste rock to a waste rock dumpsite. The machines are equipped with the positioning system Minestar.

In Aitik, ore haulage has been automated to a high degree, which enables for largescale production while also ensuring a safe workplace with good climate performance. In 2023 the open pit’s reserves and planned production will provide a further 27 years of mining.

The start-up of production at Aitik’s Liikavaara deposit drew closer with the relocation of the E10 public road and the building of a road between the new open pit and the crusher.

Comminution

Crushers and Mills

Summary:

Aitik currently operates in-pit and near-surface crushers to facilitate ore transport. As part of the Aitik 36 expansion project, two gyratory crushing stations with a combined capacity of 8000 t/h were installed inside the pit to allow for the crushing of ore mined from deep parts. To further increase production, the Aitik 45 expansion project included the construction of an additional crushing plant consisting of two gyratory crushers located between the two open pits on the surface, each with an approximate capacity of 9000 t/h.

Ore handled by the crushers in pit is transported on conveyor belts to an intermediate storage on surface, where it is mixed with ore from the surface crusher fed in by a separate conveyor line. From the intermediate storage another conveyor belt transports the ore up to the main ore storage beside the processing plant. The main ore storage has a storage capacity corresponding to about one day’s production, providing buffer for the production.

In the processing plant the ore is ground in two stages, with autogenous grinding in the primary stage and pebble mill grinding in the second. The milled ore is classified using a spiral classifier.

Two grinding lines are present in the mine, both of which are fully autogenous. The grinding lines are operated in a closed circuit consisting of a primary AG mill, a secondary pebble mill and a screw classifier. The AG primary mills are the largest in the world, having a power rating of 22.5 MW, diameter of 11.6 m, length of 13.7 m and volume of 1400 cm3 (June 2011). Grinding capacity ranges from 2,500-3,200 ton/hr while operating work index ranges from 9.7 to 12.4 kWh/ton. These values are highly dependent on the hardness of the ore. The grinding line targets a P80 size of 175 µm for the downstream process. This particle size is based on the liberation analysis of sulphides, mainly chalcopyrite, in the ore.

Also, each primary AG mill operates in a closed circuit with a cone crusher to crush salient pebbles aiming at increasing the AG mill’s throughput .

Regrinding circuit is consist of autogenous mills that operate in a closed-circuit configuration with hydro cyclones.

Processing

• Crush & Screen plant
• Flotation
• Dewatering
• Filter press

Summary:

The milled ore is sent for concentration through a series of froth flotation stages, namely, rougher, scavenger and four cleaning stages.

Milled ore is classified using a spiral classifier. Mineral separation is done by flotation and a copper concentrate is produced. The tailings are separated into a high-sulphur (cleaner tail) and a low-sulphur (rougher tail) fraction, deposited separately at the tailings management facility. The copper concentrate is dewatered using thickeners and air pressure filters. The precious metals also report to the copper concentrate. The copper concentrate is trucked to an on-site railway terminal and reloaded for further transport by rail to the Boliden Rönnskär smelter in Skelleftehamn.

The plant produces a final concentrate containing 20-23% copper with gold, silver and molybdenum. Copper recovery is at 85-95% while silver and gold is at 65% and 50%, respectively. Molybdenum is currently not being recovered.

Production

Operational metrics

Personnel

Job Title	Name	Phone	Email	Profile	Ref. Date
Environmental Manager	Åsa Sjöblom	0970-729162	asa.sjoblom@boliden.com		Jun 12, 2023
General Manager	Thomas Sundqvist	0970-729011	thomas.sundqvist@boliden.com		Jun 8, 2024
Project Manager	Johanna Lundin				Jun 8, 2024
Technical Services Manager	Patrik Gillerstedt				Jun 8, 2024
Technical Services Superintendent	Åsa Bergstrand				Jun 8, 2024