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United States
Kensington Mine

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 Location:
7 km N from Juneau, Alaska, United States

  Address:
3031 Clinton Dr., Ste. 202
Juneau
Alaska, United States
99801
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  • Mining
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  • Reserves
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  • Fleet
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  • Filings & News

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Overview

StageProduction
Mine TypeUnderground
Commodities
  • Gold
Mining Method
  • Drift & Fill
  • Transverse stoping
  • Longitudinal stoping
  • Paste backfill
Processing
  • Filter press plant
  • Dewatering
  • Flotation
Mine Life3 years (as of Jan 1, 2021)
Latest NewsCoeur Reports Fourth Quarter and Full-Year 2021 Results     February 16, 2022


Owners

Source: p. 22
CompanyInterestOwnership
Coeur Mining, Inc. 100 % Indirect
Coeur Alaska, Inc. (operator) 100 % Direct
Coeur owns 100% of Coeur Alaska, Inc. ("Coeur Alaska"), which operates the Kensington mine, an underground gold mine located north of Juneau, Alaska.

Deposit Type

  • Vein / narrow vein
  • Mesothermal
  • Orogenic


Summary:

The Kensington and Jualin deposits are located in the Berners Bay mining district which lies on the northern end of the Juneau Gold Belt, a 120 mile long, 10 mile wide structural zone containing numerous mesothermal gold deposits. The district is flanked by Triassic aged mafic metavolcanic rocks to the east-northeast and Cretaceous aged pelitic sediments to the west-southwest. The contact between these two units has been intruded by the northwest-trending, Cretaceous aged Jualin Diorite stock measuring approximately five miles long by three miles wide. Regional deformation and shearing within and adjacent to the Jualin Diorite has resulted in emplacement of numerous goldbearing, mesothermal quartz-carbonate vein deposits.

The Kensington deposit is a mesothermal orogenic deposit of gold-bearing quartz veins.

The Project area retains additional exploration potential, as many of the areas along the three district-scale structural trends (Comet, Orval, and Lion’s Head shear zones) that host numerous gold occurrences have received only limited modern exploration attention.

The deposits with economic significance exhibit two distinct habits:

1. High-grade shear-hosted veins of limited strike and dip length within a narrow halo of locally auriferous quartz-veined diorite, and

2. Vein packages comprised of extensional vein arrays, sheeted extensional veins, and stacked en-echelon shear veins.

Vein mineralization is characterized by gold and gold-silver telluride minerals with minor associated native gold. Most of the gold is contained in Calaverite (AuTe2) which occurs in association with native gold as inclusions in and interstitial to pyrite grains and in microfractures in pyrite. Trace amounts of petzite (Ag3AuTe2), coloradoite (HgTe) and altaite (PbTe) have also been noted. Minor amounts of chalcopyrite are also present along with trace amounts of bornite, molybdenite, sphalerite, galena, and pyrrhotite. The auriferous pyrite typically occurs in small to large blebs or clots within the quartz and quartz-carbonate veins.


Mining Methods

  • Drift & Fill
  • Transverse stoping
  • Longitudinal stoping
  • Paste backfill


Summary:

The mine property consists of two contiguous mineral claim groups controlled by Coeur Alaska: the Kensington Group and Jualin Group. The Kensington Group hosts the Raven, Kensington, Eureka, Johnson, and Elmira deposits. The Jualin Group hosts the Jualin and the Empire deposits.

The primary access to the Kensington and Raven underground mine areas is via the Kensington Portal at the 964-foot elevation. The Kensington Portal (previously known as the Jualin Portal) is in the same general area as the mill and ore stockpile. The Kensington Portal is the primary equipment and personnel travel way. The Comet Portal (792-foot elevation), on the eastern shore of Lynn Canal, serves as the secondary escapeway for the underground mine.

The primary mining method is transverse longhole stoping with paste backfill and mainly used in the center area at Kensington. Drilling shows that the Kensington orebody narrows to the north and south (4 to 20 feet thick), thus longitudinal longhole stoping is used. In Raven longitudinal longhole stoping is the predominate mining method as the orebody is mainly narrow, between 5 to 20 feet thick, with most of mining in material 5 feet or less in thickness.

A minor amount of drift and fill mining has been done in Kensington Block E (Zone 41). Where a drift is driven (15 × 15 feet) parallel to the ore boundary, and driven within the structure until the vein is too narrow to economically drive on, then the remaining ore is either slabbed out of the drift walls, or in the case of a wider portion of the ore on a given elevation, short headings are driven (15 × 15 feet) and filled with paste or Cemented Rock Fill (CRF). There is no drift and fill in the current Mineral Reserves as most has been converted to narrow longitudinal stopes to limit the amount of lateral development, and improve extraction ratios. Options remain open to employ a drift and fill or cut and fill mining method again in the future depending on circumstances and morphologies.

After being mucked clean, open stopes were filled with waste rock prior to 2013 and paste fill after 2013 when the paste plant was commissioned.

In Kensington transverse stoping, the dimension is primarily 40 feet in width, nominal height of 75 feet, and variable lengths, from 25 to 150 feet along strike. Access ramps (16 × 16 feet) and level development (15 × 15 feet) are driven in the footwall (above 910 level) or hanging wall (below 850 Level) of the orebody with twin boom jumbos, Load/Haul/Dump (LHD) loaders, and teledump low profile mine haul trucks. Ore is extracted by driving across the orebody on two levels, drilling and blasting with 60 to 80 feet vertical rings of blast holes between the two levels at a width of 40 to 50 feet and creating an open stope near perpendicular to the strike of the ore using Cubex and Simba longhole drills. Vertical raising within and outside of the orebody is done with the Cubex longhole drill in most instances. Where greater ground control and dimension control is desired, a raisebore of the appropriate size is selected to pilot a hole between existing excavations and then backreamed to the desired dimension.

In longitudinal stoping, ore is extracted by driving along the orebody on two levels, drilling and blasting with 60 to 90 feet rings of blast holes drilled down dip creating an open stope parallel to the strike and dip of the ore. Longitudinal stoping is used in ore up to 25 feet wide. Strike lengths will predominantly be constrained to less than 100 feet, with 80 feet as the optimum length open, to prevent hanging wall failures.


Crushing and Grinding
Flow Sheet: Source
Crusher / Mill TypeModelSizePowerQuantity
Jaw crusher 1
Cone crusher 1
Ball mill 11'1" x 19'8" 1250 HP 1

Summary:

Crushing and milling facilities are located directly south of the Jualin Portal. On the portal bench, the ore is segregated by grade and blended before being fed to the crushing plant. The crushing plant is a two stage, closed-circuit system.

Crushing
After blending based on grade, ore is fed to the crushing plant using a vibratory feeder. First stage crushing is achieved by using a jaw crusher to reduce the ore size to minus 4 inches. The primary crusher product is fed to a vibrating double deck screen. Until mid- 2012, the lower screen deck separated the material at minus 0.375 inch. In mid2012, the lower screen deck was changed to 0.75-inch opening, and then a mixture of 1 inch and 1.5-inch openings since 2014. This allows higher throughput by reducing circulating load in the crushing circuit. The oversize screen product is conveyed to a cone crusher, set at 0.75 inch. The secondary crusher product returns to the screen deck. The undersize screen product is fed to the mill. Mill feed is stored in a 1,100-ton capacity fine ore bin.

Grinding
Ore from the fine ore bin is fed to the primary ball mill by a conveyor belt. Grinding is accomplished using a 19.8-feet-long × 11.1-feet diameter ball mill equipped with a 1,250 HP motor. The ball mill discharge is fed to one of two 20-inch cyclones. The cyclone overflow, P80 of 210 µm, is fed to the flotation circuit, while the underflow is returned to the ball mill.


Processing

  • Filter press plant
  • Dewatering
  • Flotation

Flow Sheet: Subscription required

Summary:

Coeur Alaska’s Kensington Mine uses a flotation mill to recover gold from sulphide bearing rock. Once crushed, the ore is fed to the ball mill and then to the flotation circuit. The initial design for the recovery process was a standard rougher/scavenger, cleaner re-cleaner configuration. The flotation circuit was modified in 2012 to maximize recovery. The end product of this facility is a gold concentrate consisting primarily of pyrite.

Primary flotation is affected in a circuit comprised of two rougher cells and four scavenger cells. Until late 2011, all of the concentrate produced in the primary circuit was sent to an 11 ft. 5 inch long by 7 ft. 2 inch diameter regrind mill, targeting a grind size p80 of 38µm, before being introduced to the cleaning circuit. This secondary grinding step was eliminated to prevent loss of mineral slimes. Rougher flotation product is either sent directly to the concentrate thickener or to the cleaner circuit. Scavenger product is sent to the ........

Recoveries & Grades:

CommodityParameter2021202020192018201720162015
Gold Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required9393.594.794.9
Gold Head Grade, oz/ton  ......  Subscription required  ......  Subscription required  ......  Subscription required0.190.180.210.2

Production:

CommodityUnits2022202120202019201820172016
Gold oz  ......  Subscription required ^  ......  Subscription required  ......  Subscription required  ......  Subscription required113,778115,094124,331
All production numbers are expressed as metal in concentrate. ^ Guidance / Forecast.
Subscription required - Subscription is required.

Operational Metrics:

Metrics202120202019201820172016
Ore tonnes mined  ......  Subscription required  ......  Subscription required
Tonnes milled  ......  Subscription required  ......  Subscription required658,378 tons661,731 tons668,727 tons620,209 tons
Subscription required - Subscription is required.

Reserves at December 31, 2021:
Mineral Reserve reported above a gold cut-off grade of 0.143-0.201 oz/st Au.
Mineral Resource reported above a variable gold cut-off grade that ranges from 0.116–0.164 oz/ton Au.

CategoryTonnage CommodityGradeContained Metal
Proven 656 k tons Gold 0.191 oz/ton 125 koz
Probable 690 k tons Gold 0.197 oz/ton 136 koz
Proven & Probable 1,346 k tons Gold 0.194 oz/ton 261 koz
Measured 2,860 k tons Gold 0.231 oz/ton 660 koz
Indicated 1,263 k tons Gold 0.256 oz/ton 323 koz
Measured & Indicated 4,123 k tons Gold 0.238 oz/ton 983 koz
Inferred 1,915 k tons Gold 0.238 oz/ton 455 koz

Commodity Production Costs:

CommodityUnits2021202020192018201720162015
Total cash costs (sold) Gold USD  ......  Subscription required  ......  Subscription required  ......  Subscription required 1,055 / oz 922 / oz 795 / oz 803 / oz
^ Guidance / Forecast.
Subscription required - Subscription is required.

Operating Costs:

Units20212020
UG mining costs ($/ton mined) USD 7068
Processing costs ($/ton milled) USD  ......  Subscription required  ......  Subscription required
G&A ($/ton milled) USD  ......  Subscription required  ......  Subscription required
Subscription required - Subscription is required.

Financials:

Units2022202120202019201820172016
Capital expenditures (planned) M USD  ......  Subscription required
Capital expenditures M USD  ......  Subscription required  ......  Subscription required  ......  Subscription required44.7   36.2   36.8  
Sustaining costs M USD 20.7   22.8  
Revenue M USD  ......  Subscription required  ......  Subscription required  ......  Subscription required132.9   154.5   146.6  
After-tax Income M USD  ......  Subscription required  ......  Subscription required  ......  Subscription required-14.7   -9   10.4  
Operating Cash Flow M USD 37.6   50.8  
Subscription required - Subscription is required


Heavy Mobile Equipment as of April 25, 2018:
HME TypeModelQuantity
Drill ....................... Subscription required ....................... Subscription required
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Drill (long hole) ....................... Subscription required ....................... Subscription required
Drill (long hole) ....................... Subscription required ....................... Subscription required
Drill (long hole) ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Loader ....................... Subscription required ....................... Subscription required
Truck (underground) ....................... Subscription required ....................... Subscription required
Truck (underground) ....................... Subscription required ....................... Subscription required
Truck (underground) ....................... Subscription required ....................... Subscription required
Truck (underground) ....................... Subscription required ....................... Subscription required
Truck (underground) ....................... Subscription required ....................... Subscription required
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Mine Management:

Job TitleNameEmailProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Feb 23, 2022
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Subscription required - Subscription is required.

Staff:

EmployeesYear
Subscription required 2021
Subscription required 2020
Subscription required 2019
Subscription required 2018
Subscription required 2017
Subscription required 2016
Subscription required 2015

Corporate Filings & Presentations:

DocumentYear
Corporate Presentation 2022
................................... Subscription required 2021
................................... Subscription required 2021
................................... Subscription required 2021
................................... Subscription required 2021
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
Form 10-K 2018
Press Release 2018
Technical Report 2018
Year-end Mineral Reserves 2018
Annual Report 2017
Year-end Mineral Reserves 2017
Annual Report 2016
Press Release 2016
Press Release 2016
Year-end Mineral Reserves 2016
Annual Report 2015
Technical Report 2015
Year-end Mineral Reserves 2015
Annual Report 2013
Subscription required - Subscription is required.

News:

NewsDate
Coeur Reports Fourth Quarter and Full-Year 2021 Results February 16, 2022
Coeur Reports Year-End 2021 Mineral Reserves and Resources February 16, 2022
Coeur Reports Year-End 2020 Mineral Reserves and Resources, and Provides Palmarejo, Kensington and Crown Exploration Update February 17, 2021

Aerial view:

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