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 comprised of rhyolite flows and tuffs, breccias, thin intervals of spherulitic and lithophysae tuffs, and fine-grained volcaniclastic rocks. The volcanic stratigraphy shows little continuity laterally and vertically, and is typically mapped as undifferentiated Rochester tuffs and flow banded rhyolites. The Rochester Formation is extremely fractured with a thickness estimated to be 1,800 feet in the Rochester Mine area.

Quartz veins and veinlets typically exhibit parallel and cross-cutting features, indicating multiple mineralizing events. Milky white quartz is typically overprinted by the ore carrying gray-to-tan cryptocrystalline quartz veins and stockwork. Tourmaline is rare in the milky white quartz at Rochester but can be seen in abundance outside of the property. High grade mineralization at Rochester is contained within discontinuous and anastomosing veins that range in thickness from 4 inches to 3 feet. These veins are steeply dipping at the surface (>60 degrees) but at depth become shallower (<30 degrees) and lower grade. Lower grade mineralization occurs as dissemination in veins, breccia stockwork, and throughout the rocks. Vein trends in plan strike northerly. In cross-section, mineralization associated with faults dips 35 to 65 degrees west while mineralization occurring near the formational contact exhibits shallow dips (0 to 30 degrees) both to the east and west.

All ore is hosted in the oxide zone where the Rochester-Weaver contact is the primary host for gold-silver mineralization, followed and influenced by mineralized fault zones with disseminations away from the faults. The contact is extensively brecciated post conglomerate lithification and healed by silica. Low grade mineralization is controlled by both hypogene processes and 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 ore grade typically drops off but can be found in narrowly focused quartz veins. The Rochester and Nevada Packard deposits are completely oxidized to a depth of 300-500 feet and partially oxidized to a depth of over 700 feet.

Currently identified mineralization at the Rochester deposit is discontinuous over an area of 5,100 feet north to south and 6,000 feet east to west. Mineralization dips to the west at an average of 300, nearly parallel with topography producing an average true depth of 700 feet. The discontinuous nature of mineralization increases near the edges of known mineralization.

Supergene processes are thought to be responsible for the remobilization and enrichment of silver at Rochester and possibly Nevada Packard. 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. Sulfide zone minerals in the hypogene profile include pyrite, sphalerite, galena, tetrahedrite, chalcopyrite, arsenopyrite, pyrargyrite, and possibly pyrrhotite and owyheeite (Vikre, 1981).

Mineralization at Nevada Packard is similar to that exploited in the Rochester pit in that northeast trending faults dipping to the west are the most dominant mineralized trends and silver and gold are associated with vein arrays. One difference in the Packard mineralization, however, is that silver tends to be of higher grade than at Rochester while the gold grades tend to be lower. The mineralized zones are broad and disseminated but smaller than those at Rochester, typically no larger than 200 feet wide. The discontinuous broad mineralized zones cover an area of 2,500 feet by 2,300 feet and up to 600 feet in depth. Mineralization below 300 feet rapidly decreases in number of occurrences and in width.

Since 1986, Coeur has mined at Rochester by conventional open pit, drill and blast, truck, and loader methods. The mining operation at Rochester is currently at planned capacity under the current PoO 10, and is expected to continue through the end of 2023. The planned mining areas have been cleared and grubbed and all pre-stripping has been completed. In 2017, Coeur plans to continue the process of obtaining permits for additional pad capacity, additional RDS facilities, and extensions of the Rochester Pit, which are expected to be received by mid-2021. This expanded capacity is anticipated to further extend Rochester’s active mine life, based on existing Mineral Reserve estimates through the end of 2029. Internal waste movement does occur as it is encountered and is placed in the mine’s RDS facilities.

Operations at Rochester consist of mining from in situ and stockpiled open pit sources that are either: (1) Fed directly into the primary crusher dump pocket; (2) Crushed at an in-pit crusher system; or (3) Placed directly onto a heap leach pad for ROM processing.

Ore extracted from the open pit mining operation is hauled to one of two crushing circuits. These circuits utilize three stages of crushing and are referred to as the X-pit and N-pit crushing systems.

ROM ore is utilized as a secondary ore source to be treated on the leach pads. ROM is classified as blasted but uncrushed ore and is directly transferred directly to the leach pads from the mining operations. ROM ore is transferred via 777 haul trucks to the active leach pad and is treated with lime from the N-pit lime silo for appropriate pH control during the leaching process.

Currently there are four dedicated valley-fill heap leach facilities at the Rochester Mine, referred to as Stage I, II, III and IV. The Rochester Mine leach pads are typically constructed in 30 foot lifts to heights of 300 feet above liner.

On the heap leach pads cyanide solution is applied via drip tube at a rate of ~0.004 gallons per minute per square foot,, and allowed to percolate down through the crushed material to leach metals. Efficient silver extraction occurs at a pH of 10.5 and cyanide concentrations maintained at 1.5 pounds per ton of solution. Metalladen ‘pregnant’ solution percolates downward to pad liner and migrates via gravity drain lines to a collection point (internal dike system). The pregnant solution from each of the active leach pads is processed at the Merrill-Crowe plant.

The Merrill-Crowe process is a separation method for removing dissolved metals from cyanide solution. At the Merrill-Crowe process plant - leaf filter clarifiers remove undesirable solid contaminants from the pregnant solution, and dissolved oxygen is removed using a vacuum de-aerator tower (Crowe tower). Following clarification and de-aeration, zinc dust is added to the solution causing precious metals to form solid precipitates. Zinc has a higher affinity for the cyanide ion in solution, causing the cyanide solution to give up the precious metals. The precious metal precipitates are separated from solution using plate and frame filter presses.

The metal precipitates are removed from the filter presses, placed into trays; and retorted to remove moisture and extract mercury. Retorting is followed by batch flux-smelting using a propane-fired furnace; slag impurities are skimmed from the top of the molten metal, and final product is poured from the furnace into half-round doré bars; each bar weighing approximately 350 pounds.