The Porcupine mines are situated in the Porcupine Camp in Archean rocks of the western Abitibi Greenstone belt in the Canadian Shield. These consist of ultramafic and mafic volcanic rocks of the Keewatin subgroup overlain by sedimentary rocks of the Timiskaming group. The lands lie adjacent and to the north of the regionally significant Porcupine Destor Fault. Gold mineralization is found in a number of different structural settings and consists of continuous quartz carbonate veins, quartz tourmaline veins, quartz stockworks and gold associated with disseminated sulphides.

Mineralization at Hollinger and Hoyle, in Timmins, comprises multiple generations of quartzcarbonate-tourmaline albite veins, associated pyrite alteration envelopes, and disseminated pyrite mineralization. Mineralization at Borden consists of a shear zone containing quartz-vein hosted sulfides within a high-grade metamorphic greenstone package.

The Hoyle Pond.
The Hoyle Pond Main Zone and 1060 Zone deposits occur on opposite limbs of an open, northeast-plunging antiformal structure, hosted within carbonatized north-dipping tholeiitic basalts. The 7 Vein System occurs as a series of stacked, flat to gently northeast-dipping veins in the nose of the antiformal structure.

The Hoyle Pond Main Zone includes a series of generally northeast-striking, linked, quartz vein zones folded on a small scale with moderate west- and northeast-plunging axes.

The 1060 Zone consists of at least five main vein structures (1060 B1, B2 and B3 zones, A zone and Porphyry zone) with orientations ranging from north to northeast and a generally subvertical dip. The veins are strongly boudinaged, with the long axis of the boudin oriented from subhorizontal to shallow west–southwest plunging.

Alteration
The mineralization at Hoyle Pond occurs as coarse free gold in white to grey–white quartz veins with a variable ankerite, tourmaline, pyrite, and locally arsenopyrite, content. Alteration halos are generally narrow, consisting of mainly grey zones (carbon, carbonate, sericite, cubic pyrite) in the Hoyle Pond system and carbonate–sericite, plus fuchsite with pyrite, arsenopyrite and trace amounts of chalcopyrite and sphalerite within the 1060 structure.

Gold at the Hoyle Pond Mine predominantly occurs as coarse free gold in white to greyishwhite quartz veins with variable ankerite, tourmaline, pyrite, pyrrhotite and local arsenopyrite. Trace amounts of chalcopyrite and sphalerite have also been noted.

The Hoyle Pond Main Zone includes a series of generally northeast-striking, linked quartz vein zones. There are at least 11 veins of economic significance. These veins are folded on a small scale with moderate west and northeast plunging axes. The 1060 zone consists of at least five main vein structures with orientations ranging from north to northeast, are strongly boudinaged, and generally have a subvertical dip.

A series of auriferous zones occurs along what is termed the “South Trend”, stretching from the Bell Creek deposit (to the west of Hoyle Pond) for 6.4 km to the 1060 zone (includes Blackhawk–Vogel deposit, Owl Creek West, Owl Creek, Owl Creek East and the 950 zone). Mineralization in these zones consists of quartz–ankerite veining with varying amounts of pyrite, pyrrhotite and free gold.

The Borden Gold deposit.
Owing to its metamorphic grade, the Borden Gold deposit is markedly different from most known Archean-aged mesothermal gold occurrences. On the basis of visual evidence, which is yet to be supported by detailed petrographic studies, it is believed that the Borden Gold deposit is most closely associated with the disseminated gold sub-class.

The gold mineralization at the Borden Gold deposit occurs as a broad zone of disseminated and fracture-controlled sulphides within a volcano- metasedimentary package of variable composition. The main sulphides are pyrite and pyrrhotite, with the former typically dominating. The mineralization generally consists of low- to moderate-grade gold, with minor silver, and is characterized by a persistent higher-grade core surrounded by a lower-grade envelope. Results to date indicate that the higher-grade core improves in grade towards the southeast where it develops into a High-Grade Zone (HGZ) with average grades typically above 2.5 g/t Au.

The northwest portions of the deposit are characterized by local silicification but lack lithological control and quartz veining; while to the southeast a well-developed hydrothermal system consisting of local quartz flooding and potassic alteration predominates and defines the HGZ. The broad mineralized zone encompasses multiple/variable host rocks, dominated by metasedimentary horizons and subordinate intrusives of acidic to intermediate composition, all of which display feldspathic, chloritic and biotitic alteration. Outcropping in the northwest parts of the deposit, the lower-grade mineralization rarely exhibits visible gold grains, while in the southeast HGZ it is much more common, particularly in the quartz-rich core. A higher-grade core is also consistently present within the lower-grade zone, locally attaining very high grades reminiscent of the HGZ.

The deposit displays continuity and is consistently intersected along strike, reaching a current length of 3.7 kilometres, while remaining open in both the northwest and southeast directions. Structurally, the deposit is described by a consistent northeast dip and, locally, a shallow southeast plunge, which is mostly evident in the HGZ. Mineralization appears to be controlled by a ductile shear zone, which appears much better developed in the HGZ. The mineralized zone is up to 120 m wide, and has been confirmed to a vertical depth of approximately 650 m.

Porcupine, consists of the Hollinger open pit and Hoyle pond underground operations, located in the city of Timmins, Ontario, as well as the Borden underground operation, located near the town of Chapleau, Ontario. Borden mine is the world’s first all-electric underground mine.

Currently, approximately 60% of the gold comes from the Hoyle Pond underground mine, where mechanized cut and fill and longhole mining methods are used to extract the ore, and the remaining ore comes from the Hollinger Open Pit mine. The Dome Underground mine ceased operations in 2017.

Hollinger Open Pit mine
There is sufficient grade at specific gold price-points to mine a 150m deep pit, with the rock being processed at the nearby Dome Mine mill. The voids (sub-vertical stopes, shafts, and connecting drifts/drives) are sometimes spaced nearly 20-50m apart extending several hundred metres deep in a 2km square area beneath the City. The pit design was constrained by a regional highway (and the City’s water tower) along the northern wall, with homes and businesses on all other sides of the Property.

The Hollinger is being mined using three 6m and two 9m cuts making up 18m high benches in mostly FAIR to GOOD ground. All blasting is done with blast-mats to reduce fly-rock and noise. Because the mine is in-town, damage needs to be minimised. Earlier, blast trials were conducted to determine the depth of blast-damage induced by varying sizes of confined blasts. These trials indicated that a three-row trim shot onto a pre-sheared final wall would not induce excessive damage. To reduce the damage further, the pre-shear drill-hole spacing is adjusted for ground conditions within the immediate vicinity of voids.

This strategy sufficiently decreases the back-wall damage to less than 4m. The multi-use of probe holes to presupport the rock mass before blasting is part of the production cycle. Grouting cables into the final slopes, above and alongside voids, before blasting reduces the amount of final wall crown and wall rehabilitation required. This pattern has 8m cable-bolts on 4m spacing, drilled at -45° and -05° from the pre-shear line. On the North Wall, the dominant fabric (72/155°) is the main control on the bench face angle. This highly foliated rock mass tends to delaminate when blasted. To reduce the bench-crest attrition from delamination, pre-support is applied using 6m cables on a 6m spacing, drilled at -45° into the crest from the pre-shear line.

For each of the larger multi-bench voids encountered, individualised support designs are being implemented.

Hoyle Pond underground mine
Access to the underground workings is by means of two ramps, one at either end of the ore body and a four-compartment shaft.

Conventional cut and fill, shrinkage and panel mining methods are typically employed to excavate the narrower gold bearing vein structures. Each of the preceding mining methods is used to extract vein structures with vertical and/or near horizontal attitudes. Veins mined by these methods typically range from 0.20 meters to 2.0 meters thick and are usually higher grade material. Mucking is accomplished using appropriately sized slushers.

Longhole methods with paste backfilling are used in wider stoping areas. Longhole levels are advanced at 60 meter intervals with sub levels at a 20 m interval. Haulage drifts are driven in the footwall about 12 meters offset from the ore zone. Backfilling methods were traditionally a combination of rock fill and cemented slag but these methods have been replaced with high quality paste backfill delivered through holes from surface and distributed with a network of underground piping.

Borden mine is the world’s first all-electric underground mine.
Commercial gold production at Borden began in October 2019.
The Borden Gold Mine has an ore production capacity of 4000 tonnes per day over a mine life of up to 15 years.

Mining method:
- Sub-level retreat
- Cemented rock fill with waste backhaul from PGM for waste requirement.
- 15m longhole retreat – factored 24% dilution
- ~2000tpd ore @ 7gpt to mill using proven production rates
- 5x5m main haulage drifts
- Diesel trucks & tethered (electric) scoops until quick-charge battery alternate is viable.
- Battery electric equipment

At the Dome mill, ore from PGM’s mining operations is crushed in three stages to produce a product size of 80% passing ½". Primary and secondary crushing is achieved in a 400 HP 42"x 65" gyratory and 400 HP 7' standard cone crusher, respectively. The latter feeds a 10' x 24' double deck screen in a closed circuit with a HP700 cone crusher. The screen undersize reports to two 4,000 tonne fine ore bins and the oversize is conveyed to a 75 tonne tertiary surge bin feeding the HP700 cone crusher. Due to the limited fine ore bin capacity, an external fine ore stockpile and reclaim conveyor system provide for supplemental mill feed during extended shutdowns of the crushing plants.

Minus 1/2" material is fed to a grinding circuit that consists of two parallel grinding lines. Circuit A consists of a 10.5' diameter x 14' 700 HP rod mill and 13.5' x 20' 2200 HP ball mill while Circuit B consists of a 15' diameter x 20' 2200 HP rod mill and a 16' x 28.5' 4500 HP ball mill.

At the Dome mill, ore from PGM’s mining operations is crushed in three stages to produce a product size of 80% passing ½".

Gold is recovered using a combination of gravity concentration and cyanidation techniques. The circuit consists of primary, secondary and tertiary crushing, rod/ball mill grinding, gravity concentration, cyanide leaching, carbon-in-pulp gold recovery, stripping, electro winning and refining.

Gravity gold is recovered by the use of five Knelson CD-30 Concentrators fed from the cyclone underflow. A Consep CS6000 Acacia Reactor is used to intensively leach the Knelson concentrate. The Acacia loaded solution has a dedicated electrowinning circuit. Gravity recovery accounts for up to 45% of the recovered gold, depending on ore type.

The cyclone overflows reports to a 155' thickener where the slurry density is increased to 55-60% solids. The thickener underflow feeds six leach tanks in series, which provide about 32 hours residence time.< ........