Muir (2002) interprets the Hemlo deposit to be an atypical, mesozonal-orogenic, disseminated-replacement-stockwork deposit, broadly synchronous with D2 and “middle” stage granitoid plutonism, prior to or synchronous with peak regional metamorphism, and involving magmatic ± metamorphic fluids.

The Hemlo deposit is approximately three kilometres long by two kilometres deep and averages 20 m wide with a very small surface expression.

Mineral Reserves at the Williams Mine are currently grouped into two main areas: the B Zone and C Zone. The A Zone has been mined out. The A and B Zones are geologically the same continuous zone, with the B Zone being the down-plunge westerly extension of the A Zone, which sub- cropped at surface. The B Zone is further divided into the main zone and footwall zone. The C Zone represents multiple sub-parallel lenses of irregular, generally narrow, gold mineralization. C Zone mineralization is stratigraphically different from the main zone and occurs in two broad geological domains, the porphyritic felsic metavolcanics (Moose Lake porphyry) and the intermediate to felsic volcaniclastic sediment unit. Interlake is the down dip extension of the C Zone.

The B Zone extends to a depth of at least 1,300 m below surface and has a strike length of approximately 1,200 m. Main Zone mineralization occurs at or near the contact with the hanging wall sediments in a strongly feldspathized rock unit. The zone dips at 60° to 70° to the northeast and plunges to the northwest at approximately 45°. The horizontal thickness of the mineralization varies from three metres to 45 m. The maximum thickness of ore is located adjacent to the Golden Giant boundary. Moving west from that property boundary, the mineralization generally declines in width and grade. The western portion of B Zone Mineral Reserves includes two or three mineralized zones within the typical host lithology. Internal waste pillars of at least 10 m horizontal thickness separate these zones. This mineralization represents the fringe of the Hemlo deposit and as such, continuity of grade and thickness becomes increasingly erratic.

The B Zone Footwall (BZFW) zone is a series of lower grade mineralized lenses 20 m to 50 m south of the B Zone main zone. It diverges from the main zone above the 9200 elevation and westward from the former Newmont property boundary which is part of the Hemlo Property following the acquisition in 2014. The BZFW Zone is hosted in a series of structures subparallel to the main B Zone mineralization. Mineralization is hosted within a muscovite schist unit which can be traced from the David Bell Mine in the east part of the Hemlo area, through the Golden Giant Mine, to the western rim of the Williams Pit. Four of the seven FW lenses occur in mineable widths from two metres to nine metres over a strike length of up to 150 m and 125 m vertically. FW mineralization is characterized by rapid pinch-outs (within 20 m), but where present, the mineralization is often high grade (10 g/t Au to 30 g/t Au). Associated minerals are molybdenite, pyrite, realgar, orpiment, arsenopyrite, tourmaline, and green mica .

The C Zone mineralization is approximately 400 m to 600 m west of the B Zone and distinctly different from the B Zone. Several zones or lenses are typical; most of which are thin, low to medium grade mineralization. These extend eastward roughly 700 m from the western boundary of the Williams property and vertically from surface to a depth of at least 1,300 m. The Interlake resource is the down dip extension of the C Zone mineralization.

The C Zone mineralization strikes at approximately 100° azimuth, dips 68° to the North, and plunges at 45° to 60° to the west. The higher-grade cores of the lenses are mined by underground methods where ore body widths are generally less than 10 m. Mineralization in the C Zone generally occurs along contacts between the fragmental units or as lenses that parallel the foliation. Individual lenses display pinch and swell features and large variances in grade can occur within each lens. Pre-existing geologic structures appear to have exerted the strongest controls on mineralization. The influence of later deformational events is not well understood. All of the major rock units are highly deformed with multiple events of deformation. Regional metamorphism is up to amphibolite grade. A muscovite schist, which is a key marker, pinches out at depth, between the porphyry and the fragmental unit.

Hemlo has produced more than 21 million ounces of gold and has been operating continuously for more than 30 years. It consists of the Williams mine — an underground and open pit operation —located about 350 kilometers east of Thunder Bay, Ontario.

Hemlo, which transitioned to a fully underground operation during 2020, remains firmly on track to becoming a Tier Two asset. A new underground portal is currently under development to access the Upper C Zone, with mining expected to start in the second half of 2021. Improving flexibility with a third mining front at Hemlo will allow underground throughput to ramp-up to a steady state of 1.9 million tonnes per annum from 2022 onwards.

The Hemlo open pit mine was a typical truck and loader/hydraulic shovel operation. The pit design was based on 10 m bench heights.

The underground mine at Williams is accessed via a vertical shaft equipped to move personnel and material, and also ore and waste from the underground to the surface. The Williams Mine is equipped with a 4.6 m diameter double drum hoist with 22 t capacity skips and a 3.7 m diameter service hoist with cage and counterweight.

Two stoping methods are utilized at the Williams Mine, including the longhole and Alimak methods. Longhole “Longitudinal” stopes are typically 20 m to 25 m high and 15 m to 20 m along strike, with an average ore width of three to eight metres. Longhole “Transverse” stopes are between 15 m to 20 m along the strike, typically 25 m to 30 m high and stope widths ranging from three to thirty metres wide. Production drilling is performed with ITH (In-the Hole) drills using 4.5 in. diameter holes or Stopemaster drills using 3 in. diameter holes.

Alimak stoping, involves mining from the Alimak platform, after the slot raise has been driven in ore and the ground support installed. The Alimak method is a specialized method and carried out by a mining contractor (Manroc Developments Inc.).

Generally speaking, the Alimak method includes driving a three metre by three metre raise to create an initial opening in the ore. The raise is driven to breakthrough on an upper level or it can be stopped without breakthrough. The hanging wall is then cable bolted, providing support in the middle of the raise opening. Once the support is completed, a longhole drill is set up on the Alimak platform and the stope is drilled off, along strike. If the stope length is 14 m, for example, the drill holes are drilled for seven metres from each side of the raise centre line. Once completed the longhole rings are loaded with explosives and blasted, either in a series of rings (i.e. two to four rings) or the stope can be blasted entirely in two shots using high precision electronic delays such as the iKon delays.

The inherent advantage with Alimak stopes is the unlimited stope height that can be achieved. At Williams, stope heights up to 180 m have been used. The Alimak technique is used mainly in the C Zone area between the 9450 level and the C Zone open pit. The Alimak stopes are typically 14 m to 15 m in length and a 1.5 m pillar is left between the stopes in order to comply with the ministry regulations regarding drilling near previously blasted ground.

BACKFILL
Approximately 30% of the mill tailings are used to prepare paste backfill for the Williams underground mine. The Williams backfill plant has a capacity of 100 m3/hr. A typical mixture includes 1.5% cement and 1.5% fly ash, up to 4% each. The paste fill is delivered at 75% to 80% solids.

Barrick Hemlo is a combination of three mine properties (Golden Giant Mine, David Bell Mine and Williams Mine). All of the major cyanide facilities are associated with the Williams Mine. The David Bell Mine has been decommissioned since the last certification and there are no longer any mining operations occurring there. The Golden Giant Mine has been decommissioned and there are no longer and mining operations occurring there. Some infrastructure supporting items such as stormwater management remain in place. The operation refers to itself as Barrick Hemlo (Hemlo).

The active cyanide facilities at the Hemlo operation include:
- Grinding Circuit
- Gravity Concentration Circuit
- Pre-Leach Thickener
- Cyanide Storage Tank and Offload Facility
- Cyanide Leach Circuit (re-built in kind, 2 done)
- Tanks (9)
- Carbon-In-Pulp (CIP) Circuit (6 tanks)
- Carbon Strip Circuit
- Barren Solution Tank
- Loaded Solution Tank