Overview
Stage | Production |
Mine Type | Open Pit & Underground |
Commodities |
|
Mining Method |
- Truck & Shovel / Loader
- Overhand Cut & Fill
- Underhand Cut & Fill
- Longhole stoping
- Avoca
|
Processing |
- Carbon re-activation kiln
- Smelting
- Heap leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Carbon in column (CIC)
- Elution
- Carbon adsorption-desorption-recovery (ADR)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
Mine Life | 9 years (as of Jan 1, 2021) |
The project hosts both high grade open pit and underground mineral resources that remain open for expansion. The fully permitted Granite Creek underground represents the Company's most advanced project. Initial rehabilitation of the underground workings was completed in 2021 and additional levels are now being constructed and multiple levels are being prepared for mining. The test mining with a target of ramping up to production in H1-2022. Initially, material mined from Granite Creek will be trucked for processing at the nearby NGM's Twin Creeks processing facility through the interim processing arrangement that was entered into for processing until the Company's Lone Tree facility is operational. A Preliminary Economic Assessment for the Granite Creek Mine Project was completed in 2021 and a full feasibility study for the open pit project is planned to be completed in H2-2022. |
Latest News | i-80 Gold Corp.: Granite Creek Underground Drilling Intersects High-Grade Gold Mineralization August 3, 2022 |
Source:
p. 34
In April, 2021, i-80 Gold Corp (i-80) through its wholly-owned subsidiary, Premier Gold Mines USA (PGU), acquired Osgood Mining Company LLC (OMC) from Waterton Global Resources Management. OMC being the owner of the Granite Creek Mine Project.
Deposit Type
- Carlin-type
- Sediment-hosted
Summary:
The Property is located on the eastern flank of the Osgood Mountains within the Basin and Range tectonic province of northern Nevada. The Granite Creek Mine occurs within a northeast-trending structural corridor known as the Getchell gold trend. Gold mineralization at the Property is described as a Carlin-type, sedimentary-rock hosted system.
The Property geology comprises a sequence of Cambrian to Ordovician sedimentary rocks that form part of the Osgood Mountain Terrane and the Osgood Mountains. Much of the Property comprises shales, hornfels sedimentary rocks and limestone interbeds of the Preble Formation, and an overlying (or juxtaposed), alternating sequence of limestone, shale, and dolomite with tuffaceous shale and intraformational conglomerates belonging to the Comus Formation. The Preble and Comus Formations have been folded into a broad north-plunging anticline and have been intruded by large Cretaceous granodiorite stocks, resulting in irregular contact metamorphism.
Gold mineralization at the Property is strongly structurally controlled, occurring at favorable sites within a fault network occurring around the eastern edge of the Osgood granodiorite and predominantly within Comus Formation host rocks. Mineralization is commonly associated with the decarbonatization of carbonate rocks and the introduction of silica, fine grained pyrite, arsenian pyrite, and remobilized carbon. Continuity of mineralization is highly variable, ranging from 40 to 4,500 feet (12 to 1,372 meters) in strike extent, 250 to 1,800 feet (76 to 550 meters) in down-dip extent and 5 to 400 feet (1.5 to 122 meters) in thickness. The underground mineralization has a variable thickness between 5 and 30 feet (1.5 and 9 meters).
Oxidation reaches depths of up to 1,800 feet (550 meters) within shear zones. Oxide mineralization includes pervasive limonite, hematite, along with other iron and arsenic oxides. Historical production from the open pits was focused on the oxidized material. Underground mineralization displays pervasive argillization and decarbonatization of host lithologies, along with the formation of dissolution collapse breccias and intense shearing. Where the alteration is strongest, the altered zones consist of punky, spongy decarbonatized limestone in an argillically altered fine-grained, carbon-rich matrix (Gustavson, 2012). Silicification is minor and occurs as a broad overprint on the zone. Historical underground production included both sulfide and oxide material.
Mining Methods
- Truck & Shovel / Loader
- Overhand Cut & Fill
- Underhand Cut & Fill
- Longhole stoping
- Avoca
Summary:
Mine plans for the resource areas were designed and planned using conventional open pit mining method for the low grade, widely distributed gold. The open pit areas are suitable for phased designs. Mechanized over-hand cut and fill underground mining method for the narrow, high grade deposits. This method was chosen for its ability to mine narrow vein deposits with little dilution and reducing labor cost. The underground area utilizes the previously mined development and includes new development to replace the current access which will be destroyed when the CX pit is mined.
Open Pit
The Granite Creek Mine Project will employ conventional open pit mining techniques using front end loaders and rear dump rigid frame haul trucks. Open pit material will be treated using heap leach or CIL techniques, depending on grade and recovery of the material being processed. The mine plan is designed to deliver an average of 8,500 tonnes of high-grade heap leach material per day from the open pit to the crusher which will then be stacked on the heap leach pad, and 3,000 tonnes per day of CIL material to the mill. The average daily waste production rate over the life of the mine is 80,700 tonnes per day. Waste material would be either placed on waste rock storage facilities (WRSF) or as backfill in previously mined open pits. There are three distinct open pit production areas on the project: B pit, CX pit, and Mag pit. The CX and Mag pits were each designed with three phases, for a total of seven mining phases for the project.
Pit Design
Based on previous engineering analysis performed by Golder (Golder Associates, 2014), Ms. Lane of GRE used a triple bench format consisting of triple 20-foot vertical benches with a horizontal 30- foot catch bench every three vertical benches. In less competent zones of safety, benches will be wider or placed at more frequent intervals to reduce the slope angle.
Underground
The Granite Creek Mine Project has a zone of high grade material suitable for underground mining. The zone exists near the intersection of the Range Front, Adams Peak, and Cx West Faults. The steep hill nearby makes a pit for this resource untenable due to a very large stripping ratio.
Three methods were considered for the Granite Creek Mine Project: Overhand Cut and Fill, Underhand Cut and Fill, and Longhole Stoping. Each method has a situational usefulness that can be applied when criteria are met. Underhand Cut and Fill will be used when the ground conditions are very poor. Overhand Cut and Fill will be used when the ground is stable, and the stope is narrow. Longhole Stoping will be used when rock quality is good and the stope is wide.
Overhand Cut and Fill
The underground mining method at Pinson will involve mining stopes sized 50 feet in height and 100 feet in length. Mining is fully mechanized with mobile equipment. An access drift is driven through the bottom of the stope. Then, blast holes are drilled in the back of the drift and blasted. Once this mineralized material is mucked, backfill is placed to use as a working platform for the next cut and to stabilize the hanging wall and footwall of the open stope. This method was chosen for its ability to mine a semi-narrow deposit with little dilution from the low grade or barren wall rock. Development required to access stopes consists of ramps, level drifts, and ventilation excavations. The previous underground workings at the site will provide initial access and fulfill ventilation requirements in the early stages of the mine.
Underhand Cut and Fill
Underhand mining is used in areas of poor rock quality. The reason being that mining work takes place under a cemented, reinforced backfill that will remain intact when the surrounding wall rock fails. This method costs more, but is a far safer alternative.
Longhole Stoping
Longhole Stoping will be used in areas of the mine where the average stope width is wide enough to allow full stope recovery and where the surrounding wall rock is competent enough to permit large, open stopes. Alternative bulk underground mining methods that can be used include long hole stoping with delayed fill, and AVOCA stoping methods.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
|
|
2
|
Cone crusher
|
.......................
|
|
|
1
|
Cone crusher
|
.......................
|
|
|
1
|
Ball mill
|
|
|
|
1
|
Summary:
Crushing Circuit (Heap Leach)
The crusher has been designed to process approximately 9,370 short tons per day (tpd) (8,500 metric tonnes per day) on a 24-hour basis. The design crushing rate would be 389 short tons per hour (354 metric tonnes per hour). The run of mine feed would pass over a vibrating grizzly with a 6-inch (150-mm) opening. The undersize would report directly to the jaw crusher discharge conveyor while the oversize would feed the jaw crusher. The jaw crusher would crush to a nominal 6-inch (150-mm), with the crushed product reporting to a vibrating screen for scalping undersize prior to secondary crushing. The double-deck screen would be equipped with a top deck with 4-inch (100-mm) openings and the lower deck with 2-inch (51-mm) openings. The screen undersize would report to the final product conveyor, and the screen oversize would be fed to a HP 500 crusher, or equivalent, with a closed side setting of 1 inch (25 mm). The discharge from the crushers would fall onto the final product conveyor. The secondary crushing circuit would be operated in open circuit. This crushing circuit would be capable of achieving a product of 100% passing two inches or a P80 of approximately 1½ inches (37.5 mm).
CIL Crusher Circuit
The crusher is designed to process approximately 4,150 tpd (3,750 metric tonnes per day) on a 24-hour basis. The design crushing rate is 172 short tons per hour (156 metric tonnes per hour). The run of mine feed would pass over a vibrating grizzly with a 6-inch (150-mm) opening. The undersize would report directly to the jaw crusher discharge conveyor while the oversize would feed the jaw crusher. The jaw crusher would crush to a nominal 4-inch (100-mm), with the crushed product reporting to a vibrating screen for scalping undersize prior to secondary crushing. The double deck screen would be equipped with a top deck with 3-inch (75 mm) openings and the lower deck with 2/3-inch (17 mm) openings. The screen undersize would report to the final product conveyor and the screen oversize would be fed to a HP 800 crusher, or equivalent, with a closed side setting of 1 inch (27 mm). The discharge from the crushers would fall onto the final product conveyor. The secondary crushing circuit would be operated in open circuit. This crushing circuit would be capable of achieving a product of 100% passing 17 mm or a P80 of approximately ½-inch (11mm).
Processing
- Carbon re-activation kiln
- Smelting
- Heap leach
- Agitated tank (VAT) leaching
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Carbon in column (CIC)
- Elution
- Carbon adsorption-desorption-recovery (ADR)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
Heap Leach Process Description
The Granite Creek Mine Project would employ open pit mining with a conventional heap leach system on a 365 day per year 24 hour per day basis. The heap leach will use crushed ROM material at a nominal size of 2 inches (51 mm). The crushed material would be agglomerated with lime and cement, as necessary, and transported to the heap leach via conveyor belt.
The heap leach would consist of a suitable area lined with a containment system, typically a linear lowdensity polyethylene (LLDPE) liner with an over liner of sized material to facilitate drainage and to protect the liner during initial stacking. Drainage pipes would be placed within this over liner to conduct the leach solution to the centralized solution collection ponds. The crushed material would be stacked in lifts on the lined pad by a radial stacker. The stacker would be fed by a series of jump or grasshopper conveyors that would be fed from the agglomeration. The lifts are targ ........

Production:
Commodity | Units | LOM (Projected) |
Gold
|
oz
| 1,245,900 |
All production numbers are expressed as metal in doré.
Reserves at May 4, 2021:
Open Pit Mineral resources are reported at a 0.35 g/t cutoff, an assumed gold price of 1,800 $/tr. oz, using variable recovery, a slope angle of 41 degrees, 6% royalty, heap leach processing cost $9.92 per tonne (includes admin), CIL processing cost of $17.63 per tonne (includes admin).
Underground Mineral Resource Cut-off is 5 gpt based on Mining Cost of $100/ton, Process Cost of $106/ton, recovery of 92%, and a gold price of $1600/t. oz.
Mineral resources are reported at a 0.35 g/t cutoff for .
Cut-off is 5 gpt for Underground Mineral Resource.
Category | OreType | Tonnage | Commodity | Grade | Contained Metal |
Measured
|
In-Situ (OP)
|
20,857 kt
|
Gold
|
1.47 g/t
|
988 koz
|
Measured
|
In-Situ (UG)
|
483 kt
|
Gold
|
10.07 g/t
|
156 koz
|
Indicated
|
In-Situ (OP)
|
7,448 kt
|
Gold
|
1.27 g/t
|
304 koz
|
Indicated
|
In-Situ (UG)
|
525 kt
|
Gold
|
10.7 g/t
|
181 koz
|
Measured & Indicated
|
In-Situ (OP)
|
28,306 kt
|
Gold
|
1.42 g/t
|
1,291 koz
|
Measured & Indicated
|
In-Situ (UG)
|
1,008 kt
|
Gold
|
10.4 g/t
|
337 koz
|
Inferred
|
In-Situ (OP)
|
1,531 kt
|
Gold
|
1.26 g/t
|
62 koz
|
Inferred
|
In-Situ (UG)
|
741 kt
|
Gold
|
13.41 g/t
|
319 koz
|
Corporate Filings & Presentations:
Document | Year |
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|
2021
|
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|
2021
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2021
|
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News:
News | Date |
i-80 Gold Corp.: Granite Creek Underground Drilling Intersects High-Grade Gold Mineralization
|
August 3, 2022
|
i-80 Gold Begins Shipping of Granite Creek Ore to Nevada Gold Mines
|
July 5, 2022
|
i-80 Gold Intersects High-Grade Gold in Drilling of the Ogee Zone at Granite Creek - Provides Initial Results from 2022 Underground Program
|
June 1, 2022
|
i-80 Gold Drilling Expands High-Grade Mineralisation At Granite Creek
|
May 24, 2022
|
i-80 Gold to Expand Granite Creek Property with Key Land Acquisition
|
May 9, 2022
|
i-80 Gold Intersects High-Grade Gold in Initial Drilling of the Ogee Zone at Granite Creek
|
May 5, 2022
|
i-80 Gold Drilling Returns Best Intercept To-Date in the South Pacific Zone at Granite Creek 16.3 g/t Au over 15.7m and 33.7 g/t over 3.7m in hole iGS21-18
|
May 3, 2022
|
i-80 Gold Continues to Intersect High-Grade Gold in Expansion Drilling at Granite Creek
|
April 20, 2022
|
i-80 Gold Intersects High-Grade Gold in Underground Drilling at Granite Creek
|
April 6, 2022
|
i-80 Gold Intersects 73.2 m of 7.4 g/t Au in Step-out Drilling at Granite Creek
|
February 8, 2022
|
i-80 Gold Intersects High-Grade Gold in Underground Drilling at Granite Creek
|
January 26, 2022
|
i-80 Gold Reports Final Results from Phase 1 Drilling Targeting Open Pit Mineralization at the Granite Creek Mine Project in Nevada
|
December 8, 2021
|
i-80 Gold Intersects High-Grade Gold in Expansion Drilling at Granite Creek
|
November 16, 2021
|
i-80 Completes PEA for Granite Creek, Nevada
|
November 9, 2021
|
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