Castle Mountain is classified as a low-sulfidation epithermal gold deposit (Scott et al., 2018), a sub-type of the epithermal class of gold and silver deposits (Sillitoe and Hedenquist, 2003).

Mineralization
Structure and associated rock porosity-permeability characteristics are the first-order control on the distribution of gold. Flow-dome breccia margins, phreatic diatremes, fault cataclasite and fractures focused provided conduits for hydrothermal fluids and contain the highest gold grades. Unfractured coherent flow-dome facies, clay altered volcaniclastic facies, and clay altered phreatomagmatic diatremes with low or variable permeability are weakly mineralized due to lower fluid interaction. Lower permeability units that are mineralized have been cut by structures such faults, fractures, or phreatic diatremes that promoted hydrothermal fluid interactions.

Gold is focused along structures and margins of facies contacts. It is believed that sub-vertical structures acted as pathways for magma and are responsible for the emplacement of the felsic volcanic package. These same structures also acted as conduits for gold-bearing hydrothermal fluids. Intersections of the steep structures with more permeable volcanic rocks created an environment for enhanced gold precipitation from hydrothermal fluids, possibly due to processes of boiling and interaction with meteoric water.

Lithologic controls are dependent on the host rock texture. Tuff beds, auto-breccias, and hydrothermal breccias have permeable fragmental textures. Brittle rhyolite flows and intrusive equivalent rocks exhibit intense fracturing and are characterized by cooling joints, vesicular zones, spherulitic vugs, and flow foliations. Gold occurs within secondary silica in all these features. Major fault and fracture systems and intersections of fracture systems provided structural controls for mineralization. In the deposit area, north-northeast-striking, mineralized fracture zones are exposed in outcrop.

The morphology of mineralization follows two patterns. Firstly, gold is enriched along steep to vertical brecciated contacts of flow-domes and phreatomagmatic diatremes. Secondly, gold occurs in broad tabular zones that correlates with the general orientation bedding. The lateral extent of the mineralized bodies centered around fault zones are dictated by the intensity and extent of fracturing and faulting, in addition to the paleo-porosity of the host rocks.

Some faults and fracture zones are not gold-bearing since the structural regimes through the Project were active both pre- and post-mineralization. Gold seems to have precipitated during a single phase within a larger and longer-lived structural and hydrothermal event.

Silicification is commonly associated with gold occurring as pervasive silica flooding and quartz veining. Quartz veins can be vitric and “gel-like” or opaque white-gray opal. Vitric quartz veins typically occur in clusters as sheeted veins or stockwork in zones ranging from 3 to 35 ft (1 to 10 m) wide. Amorphous quartz occurs as discontinuous irregular veins and as open space filling quartz. The strongest silica alteration associated with gold is found along brecciated coherent rhyolite margins; this results in mosaic breccias where angular rhyolite clasts are within a hydrothermal-related silica matrix.

Gold on the Project occurs in oxidized fractures, faults, discontinuous veins, and breccia matrix. Gold mineralization correlates best with the deep red, red-brown and brown iron oxide that can range in color from pink to red-brown. The iron oxide intensity and appearance are commonly controlled by the volcanic facies occurring as discontinuous, fracture-controlled textures in coherent rhyolite facies, as matrix replacement in rhyolite breccias, wispy selvages and clast haloes in volcaniclastic rocks, and pervasive or matrix selective in diatremes. These iron oxide textures can be cut by fracture and vein filling iron oxide that ranges in color from brown-tan to red.

Visible gold is rarely observed in hand specimen and core. In petrographic samples collected near JSLA, visible gold is associated with iron oxide and silica and proximal to illite and adularia alteration (Cline, 2016). Gold deportment studies from Oro Belle by Chudy and Lane (2020) indicate that mineralization is roughly 79% native gold, 17% electrum and 4% silver minerals by frequency of grain count. Quartz may be intergrown with iron oxides/hydroxides, most commonly as hematite, which have formed as oxidation products of former sulfide minerals. There is a low abundance of sulfides observed on the Project. The most common sulfide mineral is pyrite, and varies from nil to 1%, which occurs within clasts and matrix.

Castle Mountain is being developed by Equinox Gold in two stages. Phase 1 construction was completed in 2020 with commercial production achieved in November 2020. Equinox Gold completed a feasibility study for the Phase 2 expansion in March 2021, outlining plans to extend the mine life and expand production to more than 200,000 ounces of gold annually. Phase 2 permitting is expected to commence in Q1 2022.

Mining will be an open pit operation using conventional diesel-powered truck and shovel mining equipment. The current Phase 1 operation consists of a 14,000 ton/d (12,700 t/d) ROM operation with a focus on mining backfilled material that was placed in the JSLA pit from the previous mining operation 20 years ago. The Phase 2 expansion will increase production to 53,500 ton/d and extract hard rock material from open pits which will be drilled, blasted, and loaded to mine trucks using hydraulic shovels and wheel loaders. Phase 2 mine production is split with 50,000 ton/d (45,400 t/d) to the heap leach and 3,500 ton/d (3,200 t/d) to the mill.

There are five pit areas with pits at JSLA (3 phases), Jumbo, Oro Belle, East Ridge (2 phases) and South Domes (2 phases). There is a total of nine phases of open pit mining starting with JSLA backfill and moving north, and then to South Domes to complete the operation. The mining sequence of the phases allows for backfilling of waste as the pit reaches final limits.

Phase 1 mining is being conducted by contract mining services. Mine supervision and technical management are handled by the CMV mining team while all other mining functions are the contractor’s responsibility. A transition to operator owned mining services or fleet will start prior to Year 5 in parallel with Phase 2 mining. Full Phase 2 mining production coincides with the start of the fully expanded processing facilities, estimated to be in Year 6.

Phase 1 mining will be focused on mining backfilled material in the JSLA pit.

The JSLA Phase 1 pit is based upon the Pre-feasibility Study plan to mine backfill at a rate of 14,000 ton/d (Scott et al., 2018). The design reflects use of the existing final ramp in hard rock from the backfilled pit. The Phase 2 design, shown in Figure 16-1, developed in this study has a double access ramp system that allows the pit to be split for scheduling of two phases. These ramps will exit the pit on the south side at 4,300 ft elevation. The pit bottoms will be at 3,480 ft elevation on the east and west sides. The pit will be 3,700 ft across in the east-west direction and 3,750 ft in the north-south direction. The overall wall height will be 1,200 ft on the east side.

The mining equipment will operate on 30 ft (9.1 m) high benches with double benching in waste, up to 60 ft (18.2 m) high. Berms will be left on alternate benches in hard rock. Wall slope design recommendations have been implemented for inter-ramp slopes with variable berm widths and bench face angles. Inter-ramp slope angles are determined by geological domains which vary from 48 to 52°, with modified slope angles within structural domains of 40 to 46°. Bench face angles vary from 60 to 79° depending on the domain and host lithology.

Alluvium, backfill, and waste dump material will be free-digging. Hard rock will require drilling and blasting. Ore grade control will utilize rotary blast holes drilled across a full bench height of 30 ft (9.1m). Blastholes will be grid drilled to facilitate breakage and will be loading with ammonium nitrate and emulsion explosives. The blastholes will be sampled to provide analytical results for planning. Drilling will be in advance of the mined benches to allow proper short-term planning.

Heap leach ROM ore will initially be hauled to the existing Phase 1 leach pad. In Phase 2 of the LOM plan, ROM will be hauled to a new, adjacent Phase 2 leach pad that will be developed progressing from South to North, then towards the West. Mill feed will be placed in a stockpile adjacent to the primary crusher and re-handled by wheel loaders to feed the crusher.

Conceptual designs for waste dumps and waste backfill plans have been developed to accommodate volumes scheduled over the life of mine. The lift height between berms will be variable over time. The face slope during construction of the dumps was assumed to be 38° and overall final reclamation slopes will be 26.5°.

The current operation consists of a 14,000 ton/d (12,700 tpd) ROM heap leach operation with gold recovery in carbon columns. Crushing and agglomeration is being introduced in 2022 to improve leach time and recoveries. The planned expansion for Phase 2 will include a 50,000 ton/d (45,350 tpd) ROM heap leach and a new 3,500 ton/d (3,175 tpd) crushing, milling and leach/CIL plant for recovering gold and silver from mill grade ore. Optimization studies are underway and the application for permit amendment is planned for late Q1, 2022.

The processing plan has been divided into two stages:

- Stage 1 (Years 1-3) considers processing 14,000 tons per day of ROM backfill material from the JSLA pit, where it was stored from the previous operation. Excavated backfill material will be loaded into 100-ton haul trucks and stacked in 50- ft lifts. Quicklime (CaO) will be added to the material in the trucks for pH control before the ore is stacked and leached in two stages using a ........