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United States
Stibnite Project

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 Location:
159 km NE from Boise, Idaho, United States

  Project Contacts:
13181 HWY 55
PO Box 429
Donnelly
Idaho, United States
83615
Phone208-901-3060
Fax208-325-9273
EmailEmail
WebsiteWeb
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Overview

StagePermitting
Mine TypeOpen Pit
Commodities
  • Gold
  • Silver
  • Antimony
Mining Method
  • Truck & Shovel / Loader
On-Site Camp 300 people
Mine Life14.3 years (as of Jan 1, 2020)
Latest NewsPerpetua Resources Corp. : U.S. Forest Service Comment Period Closes for Proposed Stibnite Gold Project with Strong Public Support     January 11, 2023


Owners

Source: p. 9,60
CompanyInterestOwnership
Midas Gold Idaho Inc. (operator) Indirect
Perpetua Resources Corp. 100 % Indirect
Ownership Tree
Through a series of name changes and consolidations, the various subsidiaries have been consolidated into three entities: Idaho Gold Resources Company, LLC, an Idaho limited liability company; Stibnite Gold Company, an Idaho corporation and wholly owned subsidiary of Idaho Gold Resources Company LLC which is turn is a wholly owned subsidiary of Midas Gold Corp. Midas Gold Idaho, Inc., an Idaho corporation and wholly owned subsidiary of Midas Gold Corp. holds no real property ownership interests but is the operating company for the landowning interests.

Feb. 16, 2021 - Midas Gold Announces Name Change to Perpetua Resources and Approved Nasdaq Listing.

Contractors

ContractorContractDescriptionRef. DateExpirySource
unawarded or unknown Mine Development Mine development pre-production work activities are envisioned to be performed by contractors selected through a pre-qualification and pre-tendering process, beginning with the water diversion tunnel, the site access road construction, and power transmission line. Dec 22, 2020


Deposit Type

  • Replacement
  • Vein / narrow vein
  • Epithermal
  • Breccia pipe / Stockwork
  • Skarn
  • Intrusion related

Source: Source p.112-115,122

Summary:

Gold-antimony-silver-tungsten deposits of the Stibnite Mining District (the District) are not readily categorized based on a single genetic deposit model due to complexities associated with multiple overprinting mineralization events and uncertainties regarding sources of mineralizing hydrothermal fluids. Workers in the early 1970s considered some of the mineralization to be similar in style to deposits in the Yellow Jacket Co-Cu-Au belt farther east and attributed the precious metal mineralization to iron formations associated with what were interpreted as metavolcanics rocks (Jayne, 1977). Cookro (1985) attributed the tungsten to Cretaceous skarns. Cookro et al. (1987) noted isotopic signatures that suggested an igneous or metamorphic origin likely of Late Cretaceous age but also noted the potential for overprinting Tertiary mineralization. Criss et al. (1983; 1991) noted associations between Tertiary intrusions and meteoric dominated epithermal systems including Yellow Pine. Bookstrom et al. (1998) attributed the various metals in the District to a variety of deposit types including distal disseminated gold, Au-Ag and mixed metal veins, simple antimony veins, disseminated antimony, quartz-scheelite veins and breccia deposits, mixed metal skarns and hot springs mercury. Konyshev (2020) noted similarities to the reduced intrusive systems in the Tintina Belt, specially Donlin Creek. Others have noted similarities to Carlin-type systems and reduced intrusion gold deposits (Dail et al., 2015; Dail, 2016; Hofstra et al., 2016) and orogenic gold to antimony-gold bearing Carlin-like systems in China (Dail, 2014; Gillerman et al., 2019b). The complicated paragenesis and prolonged extent of mineralizing events in the area spanning tens of millions of years preclude application of a single genetic model.

Within the Project area, the focus of past exploration for, and development of, Au-Ag-Sb-W-Hg deposits has been from both disseminated deposits extracted using conventional open pit methods and higher grade structurally controlled AuSb, W-Sb, Hg and Au-only deposits extracted using various underground mining methods. Mineralization occurs in numerous locations throughout the District in medium- to coarse-grained, felsic to intermediate intrusive host rocks and typically occurs as disseminated replacement mineralization within structurally prepared dilatant zones or adjacent to district- and regional-scale fault zones. Mineralization also occurs in association with sheeted veins, stockworks, endoskarns, and complex polymictic breccias. In the metamorphosed sedimentary rocks, mineralization occurs in association with dense fracture zones in structurally prepared sites and as stratiform manto-style replacements in reactive carbonate and calcareous siltite and schist units, as well as in cross-cutting breccia veins and dikes and jasperoids (quartz-replaced carbonates).

Intrusive hosted precious metals mineralization typically occurs in structurally prepared zones in association with very fine-grained disseminated arsenical pyrite (FeS2) and, to a lesser extent, arsenopyrite (FeAsS). Base metal sulfides are uncommon. Arsenical pyrite is the primary host for gold mineralization and the vast majority of the gold occurs in solid solution within the sulfide crystal lattice. Arsenopyrite is the only other significant gold-bearing sulfide mineral in the intrusive hosted deposits. Gold rarely occurs as discrete sub-micron particles in pyrite and other sulfides. Base metals are rare and occur at very low concentrations, at or below typical crustal abundance levels. Various oxidized products of the weathering of the primary sulfides are found in the intrusives including goethite, hematite, jarosite, and scorodite, and host precious metal mineralization in the oxidized portions of the deposits.

Antimony mineralization occurs primarily in the form of the mineral stibnite (Sb2S3). Other antimony-bearing phases include miargyrite (AgSbS2), gudmundite (FeSbS), chalcostibite (CuSbS2), tetrahedrite [(Cu, Fe)12Sb4S13], and owyheeite [(Pb)10(Ag)3-8(Sb)11-16(S)28]. There is a weak, but persistent association of volumetrically small base metal mineralization, typically <0.25%, associated with the antimony mineralization and includes rare occurrences of chalcopyrite (CuFeS2), galena (PbS), sphalerite (ZnS) and molybdenite (MoS2). Zones of high-grade, silver-rich mineralization locally occur with antimony and are related to the presence of pyrargyrite (Ag3SbS3), hessite (Ag2Te), and acanthite (Ag2S).

Tungsten mineralization is associated with the mineral scheelite (CaWO4). Observations indicate that some of the tungsten is associated with the stibnite mineralization but may also precede it since stibnite has been found in numerous past studies cementing veins and brecciated scheelite fragments.

Metasediment-hosted mineralization has a similar sulfide suite and geochemistry, but with higher carbonate content in the gangue and a much more diverse suite of late stage minerals. As in the intrusive-hosted mineralization, gold is associated with very fine-grained arsenical pyrite and is tied up in the pyrite lattice.

Yellow Pine Deposit
In the central region of the deposit, between 1,188,200N and 1,189,600N, mineralization is broadly disseminated over a width of 500 feet east of the Hanging Wall fault and west of the post-mineralization Hennessey fault, except where Hennessey fault has offset the western part of the mineralization to the north. Gold and antimony mineralization in the central region of the deposit are bounded to the south by a complex fault network consisting of the C-structure, the Granite fault, and the northwesterly striking Midnight fault. The width of mineralization in Central Yellow Pine ranges from 165 ft to over 650 ft wide, over 1,400 feet of strike length and extends down dip over 1,200 ft.

Mineralization in the northern Homestake area of the Yellow Pine deposit ranges from 80 to 150 ft thick and extends for over 800 ft along strike and down dip. Here, mineralization occurs as a tabular body in the hanging wall of the Hidden fault/Clark Tunnel structure. Gold mineralization also occurs within the metasediments at Homestake, where both disseminated and vein-hosted gold occurs within the upper Calc-Silicate and Middle Marble formations.

Hangar Flats Deposit
Mineralization in the Hangar Flats Deposit is entirely intrusive hosted and is localized in and along the flanks of the MCFZ. The highest grades of gold, silver, and antimony, defined on the basis of drilling and legacy production, occur within sub-vertical, north-plunging, tabular to pipe-like breccia bodies formed at the intersection of the main north-south structural features and shallowly northwest-dipping dilatant splay structures. These mineralized breccia zones range from 16 ft to over 330 ft in true thickness and can be traced several hundred feet down dip. Disseminated replacement style gold mineralization occurs throughout the MCFZ and eastern footwall encompassing the higher-grade tabular breccia zones. Disseminated gold mineralization also occurs as shallowly dipping tabular bodies along the northwest dipping splay structures which pinch out to the east away from the main MCFZ.

West End Deposit
Mineralization in the West End Deposit is structurally and stratigraphically controlled. Within the WEFZ, gold mineralization occurs within silicified breccia zones and as replacement style mineralization where the northeast-dipping calc-silicate and schistose units are sheared and offset by the structure. Outside of the WEFZ, mineralized zones occur as stacked ellipsoidal bodies plunging along the intersection of favorable lithologic units and structural zones and as tabular bodies extending along bedding. Mineralization also occurs as fracture filling within siliciclastic sequences and other less favorable lithologic units. True widths of these bodies range from 50 ft to over


Mining Methods

  • Truck & Shovel / Loader

Source: p.402,405-407

Summary:

Mining at the Stibnite Gold Project would be accomplished using conventional open pit hard rock mining methods. Mining is planned to deliver 8.05 Mst of ore to the crusher per year (22,050 st/d), with stockpiling by ore type (low antimony sulfide, high antimony sulfide and oxide).

The mine plan developed for the Project incorporates the mining of three primary mineral deposits – Yellow Pine, Hangar Flats, and West End – and re-mining and re-processing of the Historic Tailings.

The Historical Tailings will be trucked to a re-pulping facility adjacent to the tailings eposit and hydraulically transferred to the process plant grinding circuit via a re-pulping facility.

Most of the development rock from the three open pits will be sent to one of five destinations: the TSF embankment, the TSF Buttress, the Yellow Pine open pit backfill, the Hangar Flats open pit backfill, and the West End open pit backfill.

YELLOW PIT PHASE DESIGN
In addition to the nested pit shells produced in the Ultimate Pit Limit Analysis, a suite of directional pit shells was generated for the Yellow Pine deposit to identify potential for mining the main portion of Yellow Pine first and the northern Homestake area last. This phasing sequence allows for accelerated access to high-value ore deep in the central Yellow Pine deposit and provides for a short development rock haul from the Homestake area to the Yellow Pine pit backfill to reduce haulage cost.

HANGAR PLATES PHASE DESIGN
The Hangar Flats pit design consists of a single phase due to its small size and steep topography which requires a topdown mining approach. An internal phase within Hangar Flats would likely result in very narrow bench widths in the northwest highwall causing significantly reduced mining production rates.

WEST END PIT PHASE DESIGN
Four pit phases were designed for the West End pit: (1) Middle Marble limestone mining, (2) Midnight area pit production, (3) South West End pit production, and (4) Main West End pit production. Mining limestone from the Middle Marble geologic unit located in the northeast portion of the West End open pit is required for the lime kiln to produce lime used in ore processing. The Midnight Area phase sequence is primarily driven by when access is available for backfilling this area using development rock produced in the Main West End phase. The South West End phase is accessible via the ROM-to-West End Haul Road and can be mined independent of the Main West End phase. The Main West End phase does not benefit significantly from additional phasing due to the homogeneous nature of the ore body.

HISTORICAL TAILINGS PIT PHASE DESIGN
The 2,687 kt of Historical Tailings will be excavated and hauled by truck to a nearby handling facility where it would be screened, re-pulped, and pumped to the grinding circuit. For mine planning purposes, the Historical Tailings resource is modeled with constant grade and value throughout the deposit. Therefore, phasing the Historical Tailings is not influenced by advancing access to higher value ore but instead by the need to accommodate construction of adjacent facilities and avoid costs associated with double handling of the material. The Historical Tailings are planned to be excavated and processed during the first 4 years of mill operation.


Crushing and Grinding
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Processing

  • Carbon re-activation kiln
  • In-situ acid neutralization (ISAN)
  • Flotation
  • Agitated tank (VAT) leaching
  • Counter current decantation (CCD)
  • Pressure oxidation
  • Carbon in pulp (CIP)
  • Carbon adsorption-desorption-recovery (ADR)
  • Elution
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Flow Sheet: Source
Source: Source

Summary:

The Stibnite Gold Project process plant has been designed to process both sulfide and oxide mineralized material from three deposits (Hangar Flats, Yellow Pine, and West End) as well as Historic Tailings from former milling operations. The design of the processing facility was developed based on the laboratory testing, to treat an average of 22,046 st/d, 365 days per year for a total of 8.05 million tons per year.

ROM material would be crushed and milled, then flotation and hydrometallurgical operations would be used to recover antimony as a stibnite flotation concentrate (with some silver and minor gold), doré bars containing gold and silver, and small quantities of elemental mercury, collected in flasks, to prevent its potential release into the environment. Historic Tailings would be introduced into the ball mill during the first 3 - 4 years of operation.

The process operations include the following components:

• Crushing Circuit – ROM material would be dumped onto a grizzly screen and into the crusher dump hopper feeding a jaw crusher operating at an average utilization of 75% yielding an instantaneous design-throughput of 1,111 tonnes per hour (t/h).

• Grinding Circuit – The grinding circuit incorporates a single semi-autogenous (SAG) mill, single ball mill design with an average utilization of 90%, yielding an instantaneous design- throughput of 926 t/h. When Historical Tailings are processed during early years of the operation, the slurry from the plant would also flow to the cyclone feed pump box. Cyclone underflow flows by gravity to the ball mill; cyclone overflow, at 33% solids with a target size of 80% passing (P80) 85 microns, would be screened to remove tramp oversize and flow through a feed sample system and on to the antimony or gold rougher flotation circuit, depending on the antimony concentration of the material.

• Flotation Circuit (Antimony and Gold) – The flotation circuit consists of up to two sequential flotation stages to produce two different concentrates; the first stage of the circuit was designed to produce an antimony concentrate when the antimony grade is high enough, or bypassed if not, and the second stage was designed to produce a gold-rich sulfide concentrate. The antimony concentrate will be packaged and sold. The goldrich sulfide concentrate will be stored in three surge tanks.

• Pressure Oxidation Circuit – Concentrate from the surge tanks would be pumped to the autoclave feed tank, which would feed the autoclave. The autoclave is designed to provide 75 minutes of retention time at 220 degrees Celsius (428 degrees Fahrenheit) to oxidize the sulfides and liberate the precious metals. Autoclave discharge would be processed through flash vessels and gas discharge would be condensed and the remaining gas cleaned through a scrubber.

• Oxygen Plant – An oxygen plant producing 607 t/d of gas at 95 percent oxygen and a gauge pressure of 40 bars is planned. The oxygen would be from a vendor-owned oxygen plant located near the autoclave building providing the autoclave with an “over the fence” supply.

• Lime Plant – Limestone quarried from the West End pit would be hauled to an area south of the primary crusher pad. The material would be crushed and screened to feed the limestone grinding mill and the lime kiln. Ground limestone slurry and milk of lime are used to control acid in the autoclave, neutralize solutions and slurries coming out of the POX process, and control pH for leaching.

• Oxidized Sulfide Processing – After pressure oxidation, slurry discharge from the flash vessels would be neutralized and cooled prior leaching. The slurry would then be leached in cyanide solution, followed by a seven-stage pump-cell carbon-in-pulp (CIP) circuit for precious metal recovery from this high-grade stream. The sulfide CIP tailings would be detoxified and discharged to the flotation tailings thickener. Alternatively, the sulfide leach tailings would be combined with flotation tailings when the latter undergoes cyanide leaching, as described in the next bullet point.

• Oxide Carbon-in-Leach and Tailings Detoxification – A future oxide leach circuit is included in the design of the process plant to be running in Year 7 of mill operations. This circuit would recover gold from nonrefractory material in the flotation tailings when the mill is processing transition ore from the West End deposit. This circuit would also directly process oxide material from the West End deposit as a whole-ore leach process, that is, without undergoing flotation.

• Carbon Handling – Loaded carbon from the CIP circuit would be processed through a conventional carbon handling circuit, using the hot pressure-stripping of loaded carbon.

• Gold Room – Precious metals would be recovered from the strip solution by electrowinning.

• Tailings – Neutralized and thickened tailings would be pumped from the process plant to the TSF in a HDPElined carbon steel pipe.

• Process Control Systems – The process plant design includes an integrated process control system.

Recoveries & Grades:

CommodityParameterAvg. LOM
Gold Head Grade, g/t 1.17
Silver Head Grade, g/t 1.54
Antimony Head Grade, % 0.06

Projected Production:

CommodityProductUnitsAvg. AnnualLOM
Gold Metal in concentrate koz 21
Gold Payable metal koz 2974,200
Gold Metal in doré koz 4,217
Silver Metal in doré koz 852
Silver Metal in concentrate koz 858
Silver Payable metal koz 968
Antimony Concentrate kt 93
Antimony Payable metal k lbs 78,433
Antimony Metal in concentrate k lbs 115,342

Operational Metrics:

Metrics
Stripping / waste ratio 2.49 *
Daily ore mining rate 22,050 tons *
Waste tonnes, LOM 258.98 M tons *
Ore tonnes mined, LOM 104.62 M tons *
Total tonnes mined, LOM 363.6 M tons *
Daily processing capacity 22,046 tons *
Tonnes processed, LOM 104.6 Mt *
Annual processing capacity 8.05 M tons *
Annual mining rate 34 M tons *
Annual ore mining rate 8.05 M tons *
* According to 2020 study.

Reserves at December 22, 2020:
Open pit sulfide Mineral Resources are reported at a cutoff grade of 0.75 g/t Au and open pit oxide Mineral Resources are reported at a cutoff grade of 0.45 g/t Au.

CategoryTonnage CommodityGradeContained Metal
Proven & Probable 104,625 kt Gold 1.43 g/t 4,819 koz
Proven & Probable 104,625 kt Silver 1.91 g/t 6,431 koz
Proven & Probable 104,625 kt Antimony 0.064 % 148,686 k lbs
Measured & Indicated 132,269 kt Gold 1.42 g/t 6,034 koz
Measured & Indicated 132,269 kt Silver 2.07 g/t 8,814 koz
Measured & Indicated 132,269 kt Antimony 0.07 % 205,885 k lbs
Inferred 36,168 kt Gold 1.07 g/t 1,246 koz
Inferred 36,168 kt Silver 1.59 g/t 1,849 koz
Inferred 36,168 kt Antimony 0.04 % 29,272 k lbs

Commodity Production Costs:

CommodityUnitsAverage
Credits (by-product) Gold USD -70 / oz *  
Cash costs Gold USD 608 / oz *  
Cash costs Gold USD 538 / oz *†  
Total cash costs Gold USD 571 / oz *†  
All-in sustaining costs (AISC) Gold USD 636 / oz *†  
All-in costs Gold USD 950 / oz *†  
Assumed price Antimony USD 3.5 / lb *  
Assumed price Silver USD 20 / oz *  
Assumed price Gold USD 1,600 / oz *  
* According to 2020 study / presentation.
† Net of By-Product.

Operating Costs:

Units2020
OP mining costs ($/ton mined) USD 2.24 *
OP mining costs ($/ton milled) USD 8.22 *
Processing costs ($/ton milled) USD 12.8 *
G&A ($/ton milled) USD 3.43 *
Total operating costs ($/ton milled) USD 24.4 *
* According to 2020 study.

2020 Study Costs and Valuation Metrics :

MetricsUnitsLOM Total
Initial CapEx $M USD 1,219
Equipment leasing costs $M USD 149.4
Sustaining CapEx $M USD 289.6
Closure costs $M USD 99.3
Total CapEx $M USD 1,658
OP OpEx $M USD 860.2
Processing OpEx $M USD 1,332
G&A costs $M USD 358,607
Total OpEx $M USD 2,554
Mining Taxes $M USD 27.3
Income Taxes $M USD 407.5
Total Taxes $M USD 434.7
Royalty payments $M USD 114.1
Gross revenue (LOM) $M USD 6,988
EBITDA (LOM) $M USD 4,343
Net Operating Income (LOM) $M USD 4,325
Pre-tax Cash Flow (LOM) $M USD 2,667
After-tax Cash Flow (LOM) $M USD 2,232
Pre-tax NPV @ 5% $M USD 1,599
Pre-tax NPV @ 10% $M USD 919.1
Pre-tax NPV @ 7% $M USD 1,290
After-tax NPV @ 5% $M USD 1,320
After-tax NPV @ 10% $M USD 733.2
After-tax NPV @ 7% $M USD 1,054
Pre-tax IRR, % 24.3
After-tax IRR, % 22.3
Pre-tax payback period, years 2.9
After-tax payback period, years 2.9


Proposed Heavy Mobile Equipment as of December 22, 2020:
Source: Source p.414
HME TypeSizeQuantityLeased or
Contractor
ANFO Loader 8 tons 1 Leased
Dozer 215 HP 2 Leased
Dozer 600 HP 5 Leased
Drill 5 inch 2 Leased
Drill (blasthole) 50 ft 5 Leased
Excavator 5 cu. yd 3 Leased
Forklift 3 tons 1 Leased
Grader 300 HP 2 Leased
Grader 240 HP 1 Leased
Loader 8 cu. yd 3 Leased
Loader 28 cu. yd 1 Leased
Shovel 28 cu. yd 2 Leased
Tire manipulator 1 Leased
Truck (dump) 45 tons 8 Leased
Truck (fuel / lube) 45 tons 2 Leased
Truck (haul) 150 tons 16 Leased
Truck (rock spreader) 100 tons 1 Leased
Truck (service) 17.5 tons 2 Leased
Truck (stemming) 15 cu. yd 1 Leased
Truck (water) 9000 gallons 2 Leased

Mine Management:

Job TitleNameProfileRef. Date
Consultant - Costs Chris Roos LinkedIn Dec 22, 2020
Consultant - Infrastructure Richard Zimmerman LinkedIn Dec 22, 2020
Consultant - Recovery Methods Art Ibrado LinkedIn Dec 22, 2020
VP Permitting Alan Haslam LinkedIn Apr 6, 2022

Staff:

Total WorkforceYear
554 2020

Corporate Filings & Presentations:

DocumentYear
Corporate Presentation 2021
Corporate Presentation 2020
Feasibility Study Report 2020
Press Release 2018
Pre-Feasibility Study Report 2014

News:

NewsDate
Perpetua Resources Corp. : U.S. Forest Service Comment Period Closes for Proposed Stibnite Gold Project with Strong Public Support January 11, 2023
Perpetua Resources Receives Critical Minerals Award of up to $24.8 million under the Defense Production Act December 19, 2022

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