The New Afton deposit is a silica-saturated, copper-gold alkalic porphyry-style deposit. The porphyry intrusive bodies can comprise stocks, plugs, dikes, and dike swarms with a footprint of typically less than one square mile in area.

Mineralization results from late stage hydrothermal activity driven by remnant heat from the porphyry intrusion. Thermal gradients within these systems give rise to broadly concentric, although often complexly intermingled, zones of alteration and mineralization. The distribution of alteration and mineral facies are largely influenced by dikes, veins, and fracture systems which concentrate and control fluid flow.

The principal host rock for the New Afton deposit comprises crystalline and polymictic fragmental volcanics belonging to the Triassic Nicola Formation and lesser monolithic intrusive breccias. These rocks have been altered and mineralized by a monzonite intrusive consisting of a fault controlled elongated stock and related dike swarm. The monzonite is generally weakly mineralized to unmineralized and is interpreted as the causative intrusive phase that is less susceptible to the introduction of sulphide mineralization. Its geometry is best described as a narrow, elongated stock that remains open at depth and pinches down plunge to the west.

The primary mine site host lithologies are described by New Afton geologists as follows:
Polymictic Fragmental Volcanic Breccia: Comprising poorly sorted, variably coloured, massive to phyric, angular to sub-rounded, lapilli to block sized clasts of porphyritic diorite, andesite, basalt, picrite, and aphyric volcanics within coarse-grained crystal-rich matrix. Clast rock types are commonly porphyritic diorite, andesitic flows, mafic volcanics, picrite and aphyric volcanics within ash to coarse grained crystal dominated matrices.

Monomictic Volcanic Breccia: Contains subangular crystal-rich clasts of diorite or monzonite or Nicola Group volcanic rocks and are commonly located on the margins of intrusive bodies.

Crystalline Volcanic Rocks: Crystal tuffs and andesite flows dominated by very fine and fine to medium grained subhedral to anhedral, broken and or embayed phenocrysts of plagioclase ± pyroxene ± hornblende. Contains less than five percent by volume of coarse ash to lapilli sized lithic fragments within a variably altered fine grained to ash matrix.

Copper-gold-silver mineralization occurs as disseminations and fracture-filling sulphide grains occurring in three roughly tabular east-west striking, steeply dipping bodies. The Main Zone, as its name suggests, is the principal zone of mineralization. Present mining operations are located within the Main Zone. It is flanked to the east and south by two smaller bodies called the HW Zones.

The mineralization at New Afton is grouped into three broad categories: hypogene, secondary hypogene, and supergene. The term describing secondary hypogene mineralization has changed over time from mesogene to secondary hypogene and is now thought of as late hypogene/epithermal assemblage. Secondary hypogene has been retained for consistency in order to minimize confusion. Hypogene was originally ascribed to primary copper sulphide mineralization that had not undergone significant oxidation. Presently, hypogene refers to chalcopyrite and accessory bornite mineralization which forms the core of the deposit and is dominated by biotite alteration. This is noted to typically occur along the northern margins of the monzonite stock in the Main Zone and discontinuous monzonite dykes in the HW Zones. For logging purposes, hypogene mineralization is defined as having greater than 1% sulphides, or 0.5% sulphides in bornite-dominant zones.

Secondary hypogene is a later overprint of mineralization upon primary sulphide mineralization by tennantite-enargite + tetrahedrite with possible bornite and chalcocite. The secondary overprint is associated with pervasive kaolinite-rich argillic alteration localized along narrow fault zones and is responsible for the introduction of the deleterious elements: arsenic, antimony, and mercury. It is thought to be related to late-stage, lower temperature low-pH fluids that ascended along high-angle structures and remobilized copper from primary sulphides to form sulphosalts and high-sulphidation state sulphide minerals. Secondary hypogene mineralization appears as sooty steel grey to bluish grey reaction rims on chalcopyrite blebs and stringer fractures. The distribution of secondary hypogene mineralization is very narrow and discontinuous and commonly restricted to faults such as the HW, J, E and D faults, particularly where they intersect.

The supergene mineralization type consists of native copper and chalcocite that formed through oxidation of primary sulfides within the uppermost portion of the deposit that were exposed to weathering and erosion during the Eocene to Quaternary. The domain is roughly conical in shape and centered below the New Afton pit, limited to the east by the M fault. The supergene domain is defined for logging purposes as having 0.5% or greater native copper, or, in the absence of native copper, intervals of strong oxidation with a threshold assay of 0.2% Cu.

The mineralized zone, as it is delineated to date, is a sub-vertically dipping, generally continuous, tabular body extending downwards from the base of the existing pit. The body plunges to the southwest at an angle of 50°, extending 1,570 m from surface to the lowest drill hole intercept. The Main Zone measures approximately 220 m across strike at its widest point, and it tapers with depth and along strike. Two smaller satellite bodies are located on the hanging wall side of the Main Zone, bringing the maximum width of mineralization subtended by all bodies to just over 470 m.

New Afton is an operating block cave mine. As of the year-end 2019, the mine operated at a rate of approximately 15,600 tpd. Ore is all from the B1 and B2 Caves with development underway towards the B3 and C Zones. Ore is transported from the drawpoints on the extraction level, by a load haul dump unit (LHD), to an ore pass. The ore is then re-handled on the haulage level by an LHD and loaded into a haul truck for transport to the underground gyratory crusher. The crushed ore is conveyed to surface.

There are four general zones at the mine, located beneath and to the west of the Afton open
pit. Production is coming from the B1 and B2 Zones (Lift 1) where there are two panel caves (west and east) in operation.

New Afton is a block cave mine which utilized an undercut with an apex level and an undercut level for Lift 1. The Lift 1 extraction level at New Afton employs straight-through drawpoints. This layout was selected for simplicity, ease of development, geotechnical, ventilation, and access reasons. The extraction level consists of a west and east cave with six and five strike drives respectively separated by a central pillar.

Lateral development is advanced using standard hard-rock development techniques. Mine development totalled 1,427 m in 2017, zero in 2018, and 3,203 m for year-end 2019. Development in 2018 was curtailed by New Gold as a cost saving measure. In 2019, development towards the B3 and C Zones was re-started. The advance rates used are 75 m per month for single headings and 110 m per month for the main ramps to the C Zone. Large heading sizes are 5.8 m to 6.0 m high by 5.8 m wide while small heading sizes are 4.3 m to 5.0 m high by 4.2 m to 4.5 m wide. RPA considers these advance rates to be achievable and within industry norms.

Vertical raises are used as a means of ventilating between multiple levels and as ore passes between the extraction and undercut levels down to the haulage level. Vertical development has been completed with raise bore machines. Primary ventilation raises were bored to a 3.5 m diameter and secondary ventilation raises as well as ore passes were bored to 2.4 m diameter.

B3 development consists of two ventilation raises and two ore passes. The raises were completed in 2019, with the truck loading chutes to be installed in the ore passes in 2020.

Run-of-mine (ROM) ore is crushed to minus 150 mm through a 1,100 mm x 1,800 mm FLSmidth gyratory crusher located at the cave extraction level. The ore is then transported to surface via five conveyor belts. The final conveyor belt has a plow, which allows waste and low-grade ore to be diverted from the mill feed. The remaining ore discharges onto a 120,000 wet metric tonne (wmt) live capacity stockpile. Underneath this stockpile, two 1.8 m x 11 m apron feeders regulate the flow of ore onto the SAG mill feed conveyor. The SAG mill is an 8.5 m diameter x 4 m long Farnell-Thompson mill, driven by a 5,220 kW GE motor with a variable speed drive. The SAG mill discharge is screened over a 2.4 m x 6.1 m Deister doubledeck screen with 6 mm x 28 mm apertures on the lower deck. The screen-deck was upgraded from single to double deck in 2015 to allow for an increased milling rate. Both the upper and lower deck oversize are recycled to the SAG mill feed conveyor, with the option of crushing this recycle stream using an FLSmidth XL600 Raptor cone crusher.

Secondary grinding is accomplished using a 5.5 m diameter x 9.8 m long Farnell-Thompson fixed speed ball mill, driven by a 5,220 kW motor, in closed circuit with seven (five operating) Krebs GMax-26 hydrocyclones. Approximately 7% of the cyclone feed is diverted to a Gekko inline pressure jig and magnetic separation circuit for native copper and gold recovery and magnetite rejection, with concentrate reporting to the concentrate thickener. Approximately 15% of the secondary underflow feeds an Outotec Skim-Air 500 flash flotation cell with concentrate reporting to the rougher concentrate regrind circuit, and the tails reporting to the ball mill feed. The cyclone overflow reports to the tertiary circuit.

The tertiary grinding circuit was added as part of the 2015 mill expansion project. Prior to this, the ball mill cyclone overflow reported directly to rougher flotation. Tertiary grinding is accomplished using a Metso Vertimill 3000 in closed circuit with seven (five or six operating) Krebs GMax-26 hydrocyclones. The tertiary cyclone overflow reports to the rougher flotation cells. Approximately 15% of the tertiary cyclone underflow reports to a continuous CVD42 Knelson concentrator for native copper and gold recovery with concentrate reporting to the cleaner inline pressure jig feed. Both the SAG and ball mill circuit control is supported with an expert control system.

A mill expansion was completed in 2015 to add a tertiary stage of grinding and additional flotation cleaning capacity. This allowed throughput to increase to a peak average of 16,420 tpd in 2017. Throughput for 2019 averaged 15,300 tpd.

FLOTATION
The tertiary grinding cyclone overflow flows by gravity into the rougher flotation circuit, which consists of two staged flotation reactor (SFR) cells in series followed by six 100 m3 flotation tank cells in series. The two SFRs were commissioned in Q2 2017. The concentrate from the rougher flotation cells is collected in launders and flows by gravity to the regrind circuit; the tailings from the final rougher cell is discharged into the tailings pumpbox.

The regrind circuit grinds the rougher flotation concentrate, to decrease the particle size to 80% passing 35 µm to 40 µm, prior to it being processed in the cleaner flotation cells. The regrind circuit consists of a 932 kW Vertimill in closed circuit with the regrind cyclopac. The underflow stream from two of the operating regrind cyclones is processed through two XD-40 Knelson concentrators to recover liberated gold and native copper from the regrind circuit. The Knelson concentrate discharges to the 3rd cleaner concentrate pumpbox, where it is pumped to the concentrate thickener. The Knelson concentrator tailings are discharged back to the regrind cyclone feed pumpbox. The regrind cyclone overflow discharges into the cleaner flotation circuit and the tailings flow to cleaner scavenger flotation. Cleaner scavenger tailings report to the tailings pumpbox. Three SFR cells were added to the head of cleaner flotation as part of the mill expansion project in 2015 to increase cleaner flotation capacity. The concentrate from these three cells is combined with the inline pressure jig final concentrate, 3rd cleaner concentrate, and regrind Knelson concentrates to produce the final copper concentrate for dewatering.

DEWATERING
The final concentrate is pumped to the concentrate thickener, where the solids achieve an underflow slurry density of approximately 55% solids. The slurry is pumped to an agitated tank and subsequently pumped into one of the two filter presses, where the concentrate is dewatered to less than 9% moisture. The dewatered concentrate is discharged from the filter presses directly into the concentrate storage shed, before being loaded onto trucks and transported to the Port of Vancouver for shipping.

TAILINGS
Currently, tailings streams from the rougher flotation and cleaner-scavenger flotation circuits are discharged into the tailings pump box and pumped to the tailings storage facility (TSF). The tailings are cycloned at the TSF for use in internal tailings dam construction.