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United States
East Boulder Mine (Stillwater Operation)

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 Location:
126 km W from Billings, Montana, United States

  Regional Office:
26 West Dry Creek Circle Suite 400
Littleton
Colorado, United States
80120
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WebsiteWeb
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Overview

StageProduction
Mine TypeUnderground
Commodities
  • Palladium
  • Platinum
Mining Method
  • Ramp & Fill
  • Overhand Cut & Fill
  • Sub-level stoping
  • Alimak
  • Longhole open stoping
  • Transverse stoping
  • Longitudinal stoping
  • Cemented backfill
  • Hydraulic backfill
Production Start...
Mine Life2065
Key infrastructure East Boulder mine includes the mining operations and ancillary buildings that contain the concentrator, workshop, warehouse, twin tunnels to access mine, sand plant.

The underground mining fleet ranges in age from 22 years to one year, with an average age of 16 years, and represents 4% of the property’s book value. An aggressive underground equipment replacement program is slated for the next few years.


Owners

Source: p. 11,61,62
CompanyInterestOwnership
Stillwater Mining Company Inc. (operator) 100 % Direct
Sibanye-Stillwater Ltd. 100 % Indirect
Sibanye-Stillwater wholly owns and operates PGM mining and processing operations and mining claims (together known as the US PGM operations). These wholly-owned assets include the Stillwater mine (inclusive of the Stillwater East expansion project, which is under development), the East Boulder mine, two concentrator plants, and the surrounding PGM mining claims located near the town of Nye. In addition, the Group owns and operates a metallurgical smelter and base metals refinery complex situated in the town of Columbus, Montana.

Contractors

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Deposit Type

  • Magmatic


Summary:

The Stillwater Complex is a large layered igneous complex resulting from magma intrusion through regional transverse faults into highly deformed Archaean sedimentary rocks. However, the flat-lying part of the Stillwater Complex occurs at significant depth below surface, which makes the exploitation of the J-M Reef in this part of the complex uneconomic.

The magma intrusion and emplacement relating to the Stillwater Complex were accompanied by fractionation and accumulation of magmatic crystals that gave rise to the conspicuous magmatic layering observed in the complex. The magmatic layering is reflected by the changes in mineralogy, mode, grain size and texture across the stratigraphic profile of the complex. However, the overall texture of the lithological units in the Stillwater Complex is typified by subhedral to euhedral cumulate grains in a framework of post- cumulus interstitial material including oikocrysts. The mineralogical, modal, grain size and textural variations formed the basis for subdividing the Stillwater Complex into five major series (from bottom upwards) as follows: the Basal Series, Ultramafic Series, Lower Banded Series, Middle Banded Series and Upper Banded Series. The Ultramafic Series (UMS) is further subdivided into the Bronzitite Zone and Peridotite Zone. The Lower Banded Series hosts the J-M Reef targeted at Stillwater and East Boulder Mines.

The steep dipping nature of the lithological layers in the exposed part of the Stillw ........


Mining Methods

  • Ramp & Fill
  • Overhand Cut & Fill
  • Sub-level stoping
  • Alimak
  • Longhole open stoping
  • Transverse stoping
  • Longitudinal stoping
  • Cemented backfill
  • Hydraulic backfill


Summary:

The J-M Reef outcrops over a 28-mile strike length on the Sibanye-Stillwater Mining Claims but the topography, altitude and thickness of the reef preclude economic exploitation of the reef through open pit mining methods. Accordingly, waste stripping which would be applicable to an open pit mining is not required. The J-M Reef at East Boulder Mine dips 35° to 55° (averaging 50°) to the north. The shallowest dip (35°) is observed in the far west area accessed by the 6500 Level Footwall Lateral.

Both Stillwater and East Boulder Mines employ the following underground mining methods, whic suited for the variable steep dips and narrow widths of the J-M Reef:
- Captive Cut and Fill stoping, utilising either conventional, AlimakTM or raise boring to create accesses, and the resulting stopes are also known as captive stopes - this method is being phased out;
- Ramp and Fill using overhand or underhand approaches; and
- Sub-level extraction by long hole open stoping with subsequent backfill. Longitudinal and transverse stoping methods are variations of the long hole stoping method in use at the mines.

The mining method mix is adjustable and largely driven by mineralisation grade, ground conditions encountered and the requirement to minimise dilution. The percentage distribution (frequency of use) of the three mining methods within each of the mines since FY2016 indicating the predominance of the mechanised Ramp and Fill method. Ramp and Fill stopi ........


Crushing and Grinding
Source: Subscription required


Processing

Flow Sheet: Subscription required

Summary:

- subscription is required.


Production:

CommodityProductUnits2022202120202019201820172016
2E (Pt, Pd) Metal in concentrate koz  ......  Subscription required  ......  Subscription required  ......  Subscription required  ......  Subscription required228148218
Palladium Metal in concentrate koz  ......  Subscription required
Platinum Metal in concentrate koz  ......  Subscription required
2E (Pt, Pd) Concentrate kt 13,782
Subscription required - Subscription is required.

Operational Metrics:

Metrics202220212020201920182017
Daily milling rate  ......  Subscription required  ......  Subscription required1,600 t1,600 t
Daily milling capacity  ......  Subscription required  ......  Subscription required1,800 t1,800 t1,800 t1,600 t
Annual milling capacity  ......  Subscription required  ......  Subscription required
Ore tonnes mined  ......  Subscription required  ......  Subscription required679,270 tons669,169 tons
Tonnes milled  ......  Subscription required  ......  Subscription required722,200 tons669,169 tons
Annual milling rate  ......  Subscription required  ......  Subscription required608 kt
Daily mining rate  ......  Subscription required  ......  Subscription required
Subscription required - Subscription is required.

Reserves at December 31, 2022:
Mineral Reserve cut-off grade is 1.7 g/t 2E.
Mineral Resource cut-off grade 1.7g/t 2E (Pt, Pd).

CategoryTonnage CommodityGradeContained Metal
Proven 4 Mt 2E (Pt, Pd) 11.9 g/t 1.5 M oz
Probable 24.2 Mt 2E (Pt, Pd) 12.2 g/t 9.5 M oz
Proven & Probable 28.2 Mt 2E (Pt, Pd) 12.2 g/t 11 M oz
Measured 16.7 Mt 2E (Pt, Pd) 11.6 g/t 6.2 M oz
Indicated 26.4 Mt 2E (Pt, Pd) 11.1 g/t 9.5 M oz
Measured & Indicated 43.1 Mt 2E (Pt, Pd) 11.3 g/t 15.7 M oz
Inferred 56.1 Mt 2E (Pt, Pd) 12.1 g/t 21.9 M oz

Commodity Production Costs:

CommodityUnits2016
Total cash costs 2E (Pt, Pd) USD 441 / oz†  
† Net of By-Product.

Operating Costs:

Units20212020201920162015
Total operating costs ($/ton milled) USD 166.95  144.54  137.08  133.36  158.76  

Financials:

Units20222021202020192016
Capital expenditures M USD  ......  Subscription required  ......  Subscription required  ......  Subscription required
Sustaining costs M USD 16.7  
Book Value M USD  ......  Subscription required  ......  Subscription required
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Water Supply
Source: Subscription required

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Heavy Mobile Equipment as of December 31, 2021:
HME TypeQuantity
Continuous Miner ....................... Subscription required
Drill ....................... Subscription required
Forklift ....................... Subscription required
Loader ....................... Subscription required
Loader (mini) ....................... Subscription required
Load-Haul-Dump (LHD) ....................... Subscription required
Locomotive ....................... Subscription required
Tractor trailer ....................... Subscription required
Truck (dump) ....................... Subscription required
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Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
....................... Subscription required ....................... Subscription required Subscription required Sep 15, 2023
Subscription required - Subscription is required.

Staff:

EmployeesContractorsTotal WorkforceYear
Subscription required Subscription required Subscription required 2022
Subscription required Subscription required Subscription required 2021
Subscription required Subscription required Subscription required 2020
Subscription required Subscription required Subscription required 2019
Subscription required Subscription required Subscription required 2018
Subscription required Subscription required Subscription required 2017
Subscription required 2016
Subscription required 2015

Corporate Filings & Presentations:

DocumentYear
Corporate Presentation 2023
Corporate Presentation 2022
Financial Review 2022
Integrated Report 2022
Year-end Mineral Reserves 2022
................................... Subscription required 2021
................................... Subscription required 2021
................................... Subscription required 2020
................................... Subscription required 2020
................................... Subscription required 2019
................................... Subscription required 2019
................................... Subscription required 2019
Form 20-F 2018
Integrated Report 2018
Year-end Mineral Reserves 2018
Form 20-F 2017
Year-end Mineral Reserves 2017
Form 10-K 2016
Form 10-K 2015
Technical Report 2011
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