Rochester is a complex deposit, with structurally controlled and disseminated silver-gold mineralization occurring within extensive zones of QSP-type alteration and silicification. In addition, many high-grade (>3 opt Ag) silver-gold vein occurrences hosted in faults exhibit chalcedonic or vuggy, crystalline quartz. These textures indicate an epithermal origin, possibly related to the later Cretaceous Rocky Canyon intrusion event. Low tenor, but persistent gold values distributed throughout the deposit appear to be associated with disseminated pyrite. The Rochester District exhibits characteristics of both low-sulfidation and intermediate-sulfidation precious metal systems, complicated by supergene enrichment processes and significant oxidation in much of the deposit.

Supergene enrichment is commonly found in porphyry copper deposits, but some recent work has shown supergene enrichment in silver-rich deposits (Anderson, 2016). This appears to be the case at Rochester. Supergene enrichment is a process where meteoric waters percolate through pyrite-rich rocks that contain acid-soluble, metal-bearing minerals. Dissolved sulfide minerals then re- precipitate at or below the water table, which enriches sulfide mineralization and associated metals. Oxidized pyrite at Rochester could have provided the acid needed to remobilize and redeposit silver.

Silver and gold mineralization at the Rochester and Nevada Packard mines is hosted by the Rochester and Weaver Formation volcanic and epiclastic rocks of the Koipato Group. The Rochester Formation exposed in the Rochester pit is composed of rhyolite flows and tuffs, breccias, thin intervals of spherulitic and lithophysae tuffs, and fine-grained volcaniclastic rocks. Erratic intervals of conglomerate-breccia up to 100 ft. thick, occur at various places in the stratigraphy. Volcanic stratigraphy shows little continuity laterally and vertically, and is typically mapped as undifferentiated Rochester tuffs and flow banded rhyolites. Thickness of the Rochester Formation in the Rochester Mine area was estimated to be 1,800 ft., although recent estimates by Chadwick and Robinson (2015) estimate the thickness at approximately 1,380 ft. The Rochester Formation is also highly fractured, as described in a report by Golder Associates (2015).

The Weaver Formation consists of spherulitic tuffs, air fall and water-lain ash, shale/siltstone, fine-grained volcaniclastic rocks, tuffs, and lithic tuffs. The RochesterWeaver contact is marked by a discontinuous lithic tuff with up to cobble sized clasts. Basal units of the Weaver Formation (W1t, W1lt) are the most favorable mineralized host rocks at Rochester. These units consist primarily of tuffs and lithic tuffs. Mineralization occurs within high and low angle faults, related breccias and veins. Mineralization may extend up to 500 ft. laterally away from the structures when in the vicinity of the WeaverRochester contact. A discontinuous ash layer (W1a) is sometimes found along the base of the Weaver Formation. This W1a ash layer is typically lens-shaped and is not a favorable host to mineralization. A volcaniclastic unit (W1c) lies stratigraphically above W1a and is relatively thin, approximately 60 ft. in thickness. Unit W1c is composed of sandstones interbedded with lithic tuffs and minor siltstone. Overlying W1c is a siltstone unit (W2), followed by the uppermost Weaver unit (W3), which is a predominately dark siltstone with a discontinuous spherulitic tuff at its base.

Units W2 and W3 do not host mineralization at Rochester, but unit W3 is the dominant host at the Nevada Packard deposit, particularly the spherulitic tuff facies. Unit W3 at Nevada Packard shows much greater structural preparation, although it exhibits a similar structural domain when compared to the same unit at Rochester.

The Rochester ore deposit mineralization is largely structurally controlled by the prevailing fracture system (Caddey and Cato, 1995a). Fracture intensity is poorly developed in the upper two units (W2 and W3) of the Weaver Formation. The lack of fracturing resulted in poor mineralization in these units. Basal Weaver (W1t) and upper Rochester units (Rt) are extremely fractured, which prepared these units for mineral emplacement by permitting hydrothermal fluids extensive access in these hosts.

Quartz veins and veinlets typically exhibit both parallel and cross-cutting features, indicating multiple mineralizing events. Milky white quartz is typically overprinted by mineralized gray-to- tan cryptocrystalline quartz veins and stockwork. Tourmaline, possibly related to an early QSP alteration phase, is rare in the milky white quartz at Rochester, but can be seen in abundance outside of the property. High-grade precious metal mineralization at Rochester is contained within discontinuous and anastomosing veins within compressional and extensional fault structures that range in thickness from a few inches to 3 ft. These veins are steeply dipping at the surface (>60°) but at depth become shallower (<30°) and lower grade. Lower grade precious metal mineralization occurs in fractures, narrow veins, stockwork breccia stockwork and in disseminated zones associated with structures. In plan view, veins strike north and northeast with dominate orientations at approximately 0, 10, 30, 55 and 70° azimuth. The highest-grade, best-developed historical underground silver stopes were located on the East Vein, a conjugate 30°- striking shear between splays of the 10°- or northerly-striking Black Ridge Fault. In cross-section, mineralization associated with faults dips 35 to 65° west, while mineralization occurring near the formational contact exhibits shallow dips (0 to 30°) both to the east and west.

Based on current projections, economic mineralization is hosted mainly in the oxide zone, where the Rochester-Weaver contact is the primary host for silver-gold mineralization, followed and influenced by mineralized fault zones with associated fracture, stockwork and disseminated mineralization away from the faults. The contact is extensively brecciated and healed by silica in both the Rochester and Weaver Formations. Low grade mineralization is controlled by hypogene processes and possible supergene enrichment. These low-grade systems vary in width (both along strike and down dip) from tens to hundreds of feet. Below the oxidation zone, metal grade typically drops off, but high grades of silver-gold with minor base metal content can be found in narrow quartz veins. The Rochester and Nevada Packard deposits are strongly oxidized to a depth of 200-500 ft. from the current pit bottom and partially oxidized to a depth of over 700 ft.

Currently identified mineralization at the Rochester deposit is discontinuous over an area of 5,100 ft. north to south and 6,000 ft. east to west. Mineralization dips west at an average of 30°, and mineralization is nearly parallel with topography, with an average true depth of 700 ft. Silver mineralization becomes erratic with increasing distance from favorable fault intersections, unit contacts, and structures.

Supergene processes are thought to be responsible for the remobilization and enrichment of silver at Rochester and possibly at Nevada Packard (Vikre, 1981). Supergene oxide minerals present include acanthite, chlorargyrite, embolite, hematite, kaolinite, halloysite, goethite, amorphous iron oxides, chalcanthite, chalcophanite, melanierite, jarosite, manganese oxides, and native silver. Acanthite and chlorargyrite are the most abundant oxide silver phases. Below the oxidation zone, the hypogene profile is preserved, consisting of pyrite, sphalerite, galena, argentiferous tetrahedrite, chalcopyrite, arsenopyrite, pyrargyrite, and possibly pyrrhotite and owyheeite (Vikre, 1981).

Precious metal mineralization at Nevada Packard is like that at Rochester in that northeast trending, west dipping faults with associated disseminated metal, veins, and

Since 1986, Coeur has mined at Rochester by conventional open pit, drill and blast, truck, and loader methods.

Operations at Rochester consist of mining from in situ and stockpiled open pit sources that is fed directly into the primary crusher dump pocket and crushed product is placed directly onto a heap leach pad for processing.

Blasting services are contracted at the Rochester Mine. The contractor is responsible for obtaining, securing explosive agents, loading blast holes, and initiating the blasts.

Blast patterns and locations are laid out by Coeur Rochester engineers and surveyors. Three blast hole drills are used to drill the typical square blast pattern of 15 × 15 ft. on a 30 ft.-high bench, with 3 ft. of sub drill. Shots typically consist of 350 to 450 holes. Three row trim shots are used near highwalls to protect the highwall from blast damage. Trim shots are laid out on a 15 × 15 ft. pattern.

Current blasting practices at Rochester employ the use of Ammonium Nitrate and Fuel Oil (ANFO). Emulsion blends are used where necessary. Non-electric detonators are used for initiating and timing the blast. Stemming depth with crushed rock varies but is typically 11 ft. deep

All waste rock is placed either inside the pit perimeter as backfill, or outside the pit in the approved RDSs. Waste rock is defined as material below cut-off; however, it could still contain some mineralization. It is then further evaluated to determine if it is Potential Acid Generating (PAG).

Rochester historically utilized a three-stage crushing circuit with cone crushing in the tertiary position to produce a nominal 3/8-inch product of ore from 1986 through mid-2019. In 2019 Rochester adopted HPGR crushing technology to replace cone crushers in the tertiary position. The product gradation and operational parameters of the HPGR are being optimized for gradation, permeability, and recovery.

Ore extracted from the open pit mining operation is hauled to the primary crushing circuit. This circuit utilizes three stages of crushing and is referred to as the X-pit crusher.

X-pit Crusher
The original ore crushing facilities were installed in 1986. A closed-circuit tertiary crushing
system was in place at Rochester from 1986 to 2003 to achieve a 3/8-inch product; however, in 2003, the closed-circuit tertiary system was replaced with two Nordberg MP800 crushers in open-circuit configuration to achieve a nominal 3/8-inch product at approximately 9.5M tons per year. In 2019 the open circuit tertiary cone crusher system was replaced with a single HPGR crusher. The HPGR operating parameters are being optimized to achieve ideal gradation, throughput, and recovery from heap leaching. The crusher is permitted to operate 24 hours per day 365 days per year.

Currently, material from the mining operations is enddumped from Komatsu HD1500 150-ton haul trucks into a dump hopper where material is then processed via three stage crushing; jaw crushing, screening, and secondary crushing, followed by tertiary crushing. Pebble lime is added to the final crushed product belt to control pH during heap leach processing. A series of overland conveyors deliver final crusher product to the load out area stockpile, located near the Rochester Mine’s
Stage IV leach pad.

As part of POA 11, the X-pit crushing facility will be removed and replaced with the Limerick crushing facility.

Limerick Crusher
The Limerick crusher will be permitted to operate at approximately 78,000 tpd and approximately 28.5 million tons per year. This traditional three stage crushing circuit is designed and engineered to produce a nominal 3/8” product that will be placed on the Stage VI HLP for heap leaching.

Rochester historically utilized a three-stage crushing circuit with cone crushing in the tertiary position to produce a nominal 3/8-inch product of ore from 1986 through mid-2019. In 2019 Rochester adopted HPGR crushing technology to replace cone crushers in the tertiary position. The product gradation and operational parameters of the HPGR are being optimized for gradation, permeability, and recovery. Crushed material, and at times ROM ore, is placed on heap leach pads. Cyanide heap leaching is used to extract silver and gold from mineralized ore. Metal laden pregnant solution is then collected from a drain system and Merrill-Crowe processing is utilized to recover the precious metal doré.

Currently, there are four dedicated valley-fill HLPs at the Rochester mine, referred to as Stage I, II, III, and IV. The Rochester leach pads are typically constructed in 30 - 60 ft. lifts with ultimate heights ranging from 200 - 400 ft. above liner.

Leaching on the heap leach ........