Overview
Status | Care and Maintenance |
Mine Type | Stockpile |
Commodities |
|
Mining Method |
- Cut & Fill
- Longhole stoping
|
Processing |
- Gravity separation
- ACACIA reactor
- Centrifugal concentrator
- Concentrate leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Merrill–Crowe
- Cyanide (reagent)
|
The Nevada Operations consist of Midas mine and mill, Fire Creek mine, Hollister mine, and Aurora mine and mill.
Development ceased at Fire Creek in the second quarter of 2019 when the decision was made to limit near-term production to areas of the mine where development was already completed. Mining of non-refractory ore at Fire Creek in areas where development had already been performed was completed in the fourth quarter of 2020. During 2021 production and revenue was generated from processing of the stockpiled non-refractory ore at the Midas mill and third-party processing of refractory ore in a roaster and autoclave facility, respectively. Fire Creek was placed on care-and-maintenance in the second quarter of 2021 after processing of the remaining non- refractory ore stockpile.
Production was suspended at the Hollister mine in the third quarter of 2019 and at the Midas mine and Aurora mill in late 2019. |
Source:
p. 7,150
Nevada Operations is 100% owned and was acquired on July 20, 2018 with the purchase of all of the issued and outstanding common shares of Klondex. Nevada Operations consists of three land packages in northern Nevada and containing operating or previously-operating mines with a history of high-grade gold production: Fire Creek, Hollister and Midas.
Deposit Type
- Epithermal
- Vein / narrow vein
Summary:
Mineralization at Fire Creek occurs in steeply dipping epithermal veins within Tertiary basalt flows and intrusive rocks. The mineralized basaltic rocks are a suite of mafic, extrusive rocks associated with the regional north-northwest-trending Northern Nevada Rift ("NNR") structural zone.
The deposit is a low-sulfidation epithermal deposit vertically-zoned within high-angle northwest striking structures, hosted in a mid-Miocene basalt package. Mineralization occurs as shallow structurally-controlled fault hosted gold mineralization in variably altered Tertiary basalts and as native gold in steeply dipping quartz-calcite veins or structures. A package of middle Miocene basalt and basaltic andesite flow has been cut by high-angle normal faults related to both NNR and Basin and Range extension that form grabens and half-grabens which are the structural controls in the district.
High-grade mineralization has been delineated between approximately 4,900 feet and 5,700 feet and is open both up and down dip as well as along strike. Lower-grade mineralization occurs from the surface and mineralization is open at depth. Vein textures, gangue minerals, and alteration seen at Fire Creek are typical of low-sulfidation epithermal systems. Widespread propylitic alteration changes to argillic alteration proximal to veins and/or other structural fluid conduits. Low-grade gold mineralization is often spatially associated with the argillic alteration zone surrounding the high-grade gold. Mineralization often occurs along discrete horizons within vein structures. An opaline silica cap is discontinuously preserved at surface above the main mineralization at Fire Creek.
Fire Creek is defined by two major north-northwest striking vein arrays, each comprised of several en-echelon veins. Several new target areas outside of the known vein arrays have been defined by both gradient-array and dipole-dipole induced polarization surveys as well as versatile time domain electromagnetic system geophysical surveys.
The Hollister mine is located along the NNR, and is on trend with the north-western end of the Carlin Trend, which is approximately 5 miles wide and 40 miles long. Mineralization is related to the Miocene period of magmatic activity associated with the NNR while gold mineralization on the Carlin Trend has been dated to late Eocene/early Oligocene magmatism.
The Hollister property also includes the Hatter Graben vein system, which is located approximately 2,500 feet east of the Hollister mine's underground development and has been down dropped approximately 800 feet lower than the current mine resource. The system of mineralized veins has a known vertical extent of 1,400 feet and strike length of 2,000 feet. This East-West trending zone is open along strike to the east and west and at depth and mineralization is strengthening in the east as historic high-grade intersections occur up to 4000 feet along strike to the east. Gold and silver mineralization is dominantly in the Ordovician quartzites, siltites and argillites. Higher grades are associated with banded quartz veins from inches to feet in width and extensive zones of quartz vein stockwork and quartz matrix breccias also contain significant mineralization. The first surface holes were initiated at Hatter Graben in the third quarter of 2018 with the intent to extend the current identified mineralized material east and west. Drill holes at 300-foot intervals have intersected swarms with multiple veins and mineralized breccias at the anticipated distance. Development of a drift from the Hollister mine's underground workings to the Hatter Graben area commenced in the third quarter of 2018.
Midas is a high-grade, epithermal vein deposit, and the land package covers approximately 30,000 acres (~47 square miles), which includes fee lands, federal unpatented mining claims, seven mining leases.
Gold and silver mineralization at Midas is hosted in several northwest-striking veins. The veins are divided into four principal groups based on their location and orientation. The two principal groups that host the majority of the identified mineralized material are the Main Veins and East Veins. The Main Veins dip easterly and are gold dominant, while the East Veins dip to the west and contain higher silver content than the Main Veins. The Main Veins produced more than 2.2 million ounces of gold and 26.9 million ounces of silver between 1998 and 2013, principally from the Colorado Grande and Gold Crown Veins. Initial development and production from the East Veins began in 2012. The third group of veins is comprised of the Queen and Trinity Veins located to the south of the existing workings and south of the regional South Owyhee Fault. They are defined by limited underground and surface drilling and there has been no mine production from them to date. The Queen Vein and Trinity Vein systems represent high-priority, near-mine exploration targets.
Mineralized material has been identified on the Main and East veins and other veins near the recently active mine workings. Active drill testing has recently taken place in these areas and has been prioritized based on ounce expectations, accessibility from existing development and geotechnical, ventilation, and hydrological considerations.
Mining Methods
- Cut & Fill
- Longhole stoping
Summary:
The Fire Creek mine is a trackless mine accessed by a decline, and has historically produced approximately 350 tons of ore per day. The mining method is primarily longhole stoping, with ramp access utilized.
Hollister includes an underground mine, former open pit mines, related mine support infrastructure, mining equipment, and administrative buildings, all of which are in operating condition.
The Hollister mine is a trackless mine accessed by a decline. Due to variability within the Hollister mine material, a selective mining approach is employed by matching mining methodology to stope characteristics. Hollister mining methods include cut and fill, ramp access and longhole stoping. The current Hollister mine plan primarily employs cut and fill stoping.
The Midas mine is a modern, mechanized narrow vein mine. The veins at Midas can vary in thickness from a few inches to over ten feet. Production at the Midas mine was suspended in the fourth quarter of 2019.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
30" x 40"
|
|
1
|
Cone crusher
|
|
53"
|
|
1
|
Ball mill
|
.......................
|
|
800 HP
|
1
|
Vertical mill / Tower
|
|
|
250 HP
|
1
|
Summary:
Underground mineralized material is extracted and delivered from Fire Creek and the Midas Mine to the run of mine (ROM) pad where it is placed on short term ROM mineralized material stockpiles. Typical mineralized material classifications are: low-grade less than 0.3 opt Au or less than six opt silver; high-grade (0.3 to 0.5 opt gold or six to 20 opt silver); and ultra-high-grade (more than 0.5 opt gold or more than 20 opt silver). Separate stockpiles are maintained for each mine. Underground mineralized material is hand-picked on the pad for scrap wire mesh and rock bolts before being fed to the crusher.
Mineralized material is crushed in two stages through a 30-inch by 40-inch primary jaw crusher and 53-inch secondary cone crusher. Both jaw and secondary crusher products are fed to a six feet by 20 feet Nordberg double deck vibrating screen fitted with two-inch top deck and one-half inch bottom deck screen panels to produce a 95% passing one-half inch product. Magnetic material is removed from the crusher screen feed by a continuous self-cleaning belt magnet to protect the cone crusher from damage. Screen undersize is conveyed to one of two 500-ton fine mineralized material bins.
Crushed and screened material is transported from the fine material bins by individual belt feeders into the 10.5 feet by 15 feet rubber lined Nordberg ball mill. The ball mill is charged with a blend of three-inch and two-inch grinding balls to maintain an operating power draw of 800 horse power (HP). Mill discharge pulp is pumped to a nest of four ten-inch Krebs cyclones (three duty and one standby) for classification. Cyclone overflow, at 80% passing 200 mesh, reports to the trash screen. Cyclone underflow reports to a two millimeters (mm) aperture scalping screen, with the screen undersize being distributed by three-way splitter to the ball mill, verti-mill, and gravity circuit. Lead nitrate solution is added to the ball mill feed chute to enhance silver leach kinetics.
Processing
- Gravity separation
- ACACIA reactor
- Centrifugal concentrator
- Concentrate leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Merrill–Crowe
- Cyanide (reagent)
Flow Sheet:
Summary:
Oxide ore from the Fire Creek, Midas and Hollister mines historically has been processed at the Midas mill, which has a design capacity of 1,200 tons per day. Fire Creek and Midas ore previously was processed using a counter current decantation ("CCD") circuit, with Hollister ore processed using a CIL circuit. However, all ore was subsequently processed using the CIL circuit beginning in April 2019.
Run-of-mine ore is crushed to 100% passing one-half inch in a conventional two-stage crushing circuit which utilizes a primary jaw crusher and a secondary cone crusher with the circuit closed by a double deck vibrating screen. The crushed product reports to the grinding circuit consisting of an 800 horsepower overflow ball mill and a 250 horsepower verti-mill. The circuit is closed using a bank of four (three operating, one standby) 10-inch cyclones. A portion of the cyclone underflow is sent to a gravity concentrator to remove coarse gold. The gravity concentrate is leached us ........

Recoveries & Grades:
Commodity | Parameter | 2021 | 2020 | 2019 | 2018 |
Gold
|
Head Grade, oz/ton
| ......  | ......  | ......  | 0.33 |
Silver
|
Head Grade, oz/ton
| ......  | ......  | ......  | 2.06 |
Reserves at December 31, 2021:
Category | Tonnage | Commodity | Contained Metal |
Measured
|
40 k tons
|
Gold
|
21 koz
|
Measured
|
40 k tons
|
Silver
|
115 koz
|
Indicated
|
259 k tons
|
Gold
|
123 koz
|
Indicated
|
259 k tons
|
Silver
|
674 koz
|
Measured & Indicated
|
299 k tons
|
Gold
|
144 koz
|
Measured & Indicated
|
299 k tons
|
Silver
|
789 koz
|
Inferred
|
77,223 k tons
|
Gold
|
3,458 koz
|
Inferred
|
77,223 k tons
|
Silver
|
15,265 koz
|
Aerial view:
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