The gold mineralization at Macassa is found along breaks or faults, in veins as quartz filled fractures, as breccias and as sulphide (pyrite) zones.

The gold mineralization is located along the breaks and subordinate splays as individual fracture fill quartz veins, from several inches thick to as much as 12 ft. thick. Veins may be of single, sheeted or stacked morphology. Several generations of quartz deposition are evident from colour and textural variability and vein quartz is generally fractured.

The presence of a fault splay is often a prerequisite for gold deposition. Broader zones of mineralized, brecciated and fragmented quartz are found in the footwall and hanging wall of major faults.

Gold is usually accompanied by 1% to 3% pyrite and sometimes is associated with molybdenite and/or tellurides of lead, gold, gold-silver, silver, nickel and mercury (altaite, calaverite, petzite, hessite, melanite, coloradoite). Silver is present amalgamated with the gold and in the minerals petzite and hessite.

The presence of pyrite and silicification does not guarantee gold, however, higher grade gold is almost always accompanied by increased percentages of pyrite and silica. Hematization or bleaching with carbonatization and silicification are commonly alterations of the wall rocks. Sericitization is a more local feature. The alteration has enriched the rocks in K2O and depleted them in Na20.

The new discoveries in the South Mine Complex (SMC) generally are of a different style of mineralization with wide sulphide systems rather than the quartz vein mineralization that is found in the Main Break complex. Tellurides appear to be more prevalent in the SMC, compared to the historical mineralized systems, in particular the occurrence of the gold telluride mineral calaverite.

These new, wide, hydrothermally altered zones could represent a new plumbing system for a southern mineralized part of the Camp parallel to the Main Break, fed by a deep porphyry body. The gold mineralization is found in carbonate altered conglomerate, tuff and porphyry, mineralized with up to 10% disseminated pyrite. The SMC may also be characterized by quartz veining and silicification when hosted within the porphyry.

The Macassa Mine employs conventional drill and blast mining methods to extract the ore. Mining is by mechanized cut and fill, normal cut and fill or long hole methods.

Access to the mining areas is by shafts. The cut and fill is carried out using mechanized scoop trams, or conventionally with slushers in the stope.

The long-hole blocks are accessed by Alimak driven or bored raises or with sub-level drifts from ramps. The mucking is by remotely driven scoop trams.

Macassa has started to employ battery powered scoops and battery powered trucks for use in the SMC zones. The working conditions (heat and air) will be greatly improved by using this equipment. Level trains move the ore to the main ore passes for hoisting to surface.

All of the stopes are now being filled with paste backfill. Previously the stopes were filled with cemented rock fill.

These mining methods recover about 94% of the ore.

The Corporation’s long-term projections are for the mining to be carried out on the basis of approximately 10% long-hole, 60% mechanized cut-and-fill, 20% conventional cut and-fill and 10% development, although these percentages will vary as circumstances warrant.

Underground mining is carried out from the 3400, 3835, 4250, 4500, 4750, 4900, 5025, 5150 and 5300 Levels of the '04 Break region and the 5000, 5300 and 5400 Levels of the SMC in the Macassa Mine.

The underground production is hoisted to surface by the No. 3 Shaft of the Macassa Mine.

The ore is crushed down to 11 mm at a maximum throughput rate of 180 tph and then ground to 40-45 microns; cyanide is added at the grinding stage. It is then delivered to two pre oxidation tanks before being pumped to the thickener. The overflow reports to the carbon columns (where over 75% of the gold is recovered) and the underflow to the leach circuit. Leaching takes place in seven tanks during a retention time of 100 hours. The carbon-in-pulp circuit (CIP) consists of six tanks. Following electro-winning, the concentrate is melted in an induction furnace to produce doré grading 85% to 88% gold and 8% to 10% silver. The capacity of the plant is 2,000 tpd.

The company’s mill was built in 1986 at a capacity of 725 tpd. Modifications over the years increased the throughput capacity to 2,000 tpd in 2013.