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United States
Stillwater Operation (East Boulder Mine, Stillwater Mine)

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 Location:
115 km SW from Billings, Montana, United States

  Regional Office:
26 West Dry Creek Circle Suite 400
Littleton
Colorado, United States
80120
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  • Overview
  • Owners
  • Geology
  • Mining
  • Processing
  • Production
  • Reserves
  • Costs & Financials
  • Personnel
  • Filings & News

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Overview

StageProduction
Mine TypeUnderground
Commodities
  • Platinum
  • Palladium
Mining Method
  • Ramp & Fill
  • Overhand Cut & Fill
  • Raiseboring
  • Sub-level stoping
  • Alimak
  • Hydraulic backfill
Processing
  • Crush & Screen plant
  • Dewatering
  • Filter press plant
  • Flotation
Mine Life2061
In 2020 the Blitz (Stillwater East) expansion project at the Stillwater mine realised 99koz. In 2020, the project schedule was revisited after substantial delays due to water inflow encountered in the Benbow decline. The current plan puts targeted production of 300koz in 2024. This addition will bring the Stillwater Mine Complex to 625koz annually.

The East Boulder “Fill the Mill” project was completed in the fourth quarter of 2020 with the addition of a seventh production mining block to the previous six. This will allow East Boulder to fill its mill to capacity, which will move East Boulder ounce production from 230koz to 275koz annually in 2021. Mine production began in November 2020.


Owners

Source: p. 57,58
CompanyInterestOwnership
Stillwater Mining Company Inc. (operator) 100 % Direct
Sibanye-Stillwater Ltd. 100 % Indirect
Ownership Tree

Deposit Type

  • Magmatic
  • Footwall hosted


Summary:

The J-M Reef is a magmatic reef type PGM deposit defined as the palladium-platinum rich stratigraphic interval, mainly occurring within a troctolite (OB-I zone) of the Lower Banded Series. The J-M Reef shows a high degree of variability in grades and thickness at a local level and the J-M Reef has PGM grades that are significantly higher than the Merensky Reef. The J-M Reef pinches and swells typically ranging from 0.9m to 2.7m and averaging 1.8m in thickness but can locally form keel-shaped zones which transgress the footwall mafic rocks, commonly reaching thicknesses of 6m and greater. These wider areas are locally referred to as “ballrooms”. There is no correlation of thickness to grade, so as these sulphide zones thicken, they can maintain grade and become an important source of metal. The J-M Reef shows a high degree of variability in grades and thickness at a local level and the J-M Reef has PGM grades that are significantly higher than the Merensky Reef. The J-M Reef pinches and swells typically ranging from 0.9m to 2.7m and averaging 1.8m in thickness but can locally form keel-shaped zones which transgress the footwall mafic rocks, commonly reaching thicknesses of 6m and greater. These wider areas are locally referred to as “ballrooms”. There is no correlation of thickness to grade, so as these sulphide zones thicken, they can maintain grade and become an important source of metal.

Palladium and platinum are the main PGMs, both constituting between 7g/t to 40g/t over a variable thickness with economic mineralised thickness ranging from 0.9m – 2.7m and averaging 1.8m. In situ palladium:platinum ratio of 3.4:1 to 3.6:1. Other associated PGMs, such as rhodium, iridium, ruthenium, osmium and gold occur in low concentrations.

The J-M Reef contains approximately 0.25% to 3% visible disseminated coppernickel sulphide minerals, predominantly chalcopyrite, pyrrhotite, and pentlandite, with microscopic PGM minerals and platinum-iron alloys. Copper, nickel, gold and rhodium are by-products of J-M Reef production. These sulphides are interstitial and will often mimic the host rock in texture. The sulphide can occur as coarse-grained networks in pegmatoidal olivine-bearing rock or as fine-grained disseminations in fine-grained anorthosites. As they transgress into footwall rocks, the hosts can often be medium-grained gabbro and gabbro-norites. A common hangingwall lithology is typically slightly finer-grained and anorthosite-rich. Economic mineralisation is rarely seen above this rock type.

Most of the regional faults affecting the Stillwater Complex have been grouped as west-northwest trending thrust and reverse faults and north-northeast trending steeply dipping transverse faults. Local and regional structure, as well as local mafic intrusive dykes, create disturbances to mining.


Mining Methods

  • Ramp & Fill
  • Overhand Cut & Fill
  • Raiseboring
  • Sub-level stoping
  • Alimak
  • Hydraulic backfill


Summary:

The Stillwater (including the Blitz expansion project) and East Boulder operations are located near the towns of Nye and McLeod in Montana, USA. Both are underground PGM operations. PGM production commenced in 1986 and has largely been uninterrupted.

The operations both target the J-M Reef zone, predominantly via mechanised ramp and fill mining method (+80%). All surface infrastructure and tailings management facilities are located within Stillwater and East Boulder operation operating permits, which cover an area measuring 1,396ha.

The Stillwater operation has two principal mining sections. The current section, which has been in operation since 1986, produces approximately 380koz per annum of platinum and palladium in concentrate. The Blitz section, a major expansion project currently under development, started ore production in 2017 and is currently producing 75koz per annum. The current section of the operation is accessed by a 580m deep shaft and five portals. The Blitz section is accessed by two portals.

East Boulder has been in operation since 2002, and currently produces approximately 230Koz per annum of platinum and palladium in concentrate. The East Boulder operation is accessed via twin 5,800m long decline tunnels.

The three principal mining methods are:
• Mechanised ramp and fill (both overhand and underhand) (80 – 90%);
• Sub-level extraction by long hole, open stoping with hydraulic backfilling (10 – 15%);
• Overhand cut and fill (C&F) stoping, utilising either raisebore or Alimak for access (<5%).


Crushing and Grinding


Processing

  • Crush & Screen plant
  • Dewatering
  • Filter press plant
  • Flotation

Source: Subscription required

Summary:

Ore from the two operations is milled and treated at integrated concentrator complexes located at each operation. Concentrate smelting and refining takes place at the Columbus smelter complex, situated in the town of Columbus, Montana.

Mineral processing and capacity:
- Stillwater plant: Flotation with Design capacity of 3,100 tpd;
- East Boulder plant: Flotation with Design capacity of 1,800 tpd.

Recoveries & Grades:

CommodityParameter2021202020192018201720162015
2E (Pt, Pd) Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required91.3919292
2E (Pt, Pd) Head Grade, g/t  ......  Subscription required  ......  Subscription required  ......  Subscription required15150.440.43
Platinum Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required9292
Platinum Concentrate Grade, oz/ton  ......  Subscription required  ......  Subscription required  ......  Subscription required4.163.9
Palladium Recovery Rate, %  ......  Subscription required  ......  Subscription required  ......  Subscription required9292
Palladium Concentrate Grade, oz/ton  ......  Subscription required  ......  Subscription required  ......  Subscription required14.113

Production:

CommodityProductUnits2022202120202019201820172016
2E (Pt, Pd) Metal in concentrate koz  ......  Subscription required ^  ......  Subscription required  ......  Subscription required  ......  Subscription required593376545
Platinum Metal in concentrate koz  ......  Subscription required
Palladium Metal in concentrate koz  ......  Subscription required
2E (Pt, Pd) Concentrate kt 29,118
^ Guidance / Forecast.
Subscription required - Subscription is required.

Operational Metrics:

Metrics202120202019201820172016
Tonnes milled  ......  Subscription required  ......  Subscription required1,411 kt1,339 kt855 kt1,371 k tons
Subscription required - Subscription is required.

Reserves at December 31, 2021:

CategoryTonnage CommodityGradeContained Metal
Proven 8.2 Mt PGM 15.4 g/t 4.1 M oz
Probable 60.1 Mt PGM 12 g/t 23.2 M oz
Proven & Probable 68.3 Mt PGM 12.4 g/t 27.3 M oz
Measured 39.9 Mt PGM 14.7 g/t 18.9 M oz
Indicated 59.1 Mt PGM 13.8 g/t 26.1 M oz
Measured & Indicated 99 Mt PGM 14.1 g/t 45 M oz
Inferred 113.6 Mt PGM 12.2 g/t 44.6 M oz

Commodity Production Costs:

CommodityUnits2021202020192018201720162015
Total cash costs 2E (Pt, Pd) USD 438 / oz† 495 / oz†
All-in sustaining costs (AISC) 2E (Pt, Pd) USD  ......  Subscription required†  ......  Subscription required†  ......  Subscription required† 677 / oz† 651 / oz† 622 / oz† 709 / oz†
All-in costs 2E (Pt, Pd) USD  ......  Subscription required†  ......  Subscription required†  ......  Subscription required† 880 / oz† 821 / oz†
^ Guidance / Forecast.
† Net of By-Product.
Subscription required - Subscription is required.

Operating Costs:

Units20212020201620152014
Total operating costs ($/t milled) ZAR 5,1745,203174194220

Financials:

Units2022202120202019201820172016
Capital expenditures (planned) M USD  ......  Subscription required
Sustaining costs M  ......  Subscription required  ......  Subscription required  ......  Subscription required260.2  ZAR 226.9  ZAR 56.3  USD
Growth Capital M  ......  Subscription required  ......  Subscription required  ......  Subscription required1,574  ZAR
Capital expenditures M  ......  Subscription required  ......  Subscription required  ......  Subscription required2,833  ZAR 1,654  ZAR
Revenue M  ......  Subscription required  ......  Subscription required  ......  Subscription required15,873  ZAR 9,162  ZAR 711.3  USD
Operating Income M 24.1  USD
Pre-tax Income M  ......  Subscription required
After-tax Income M  ......  Subscription required  ......  Subscription required-1,531  ZAR 2,028  ZAR 9.5  USD
Subscription required - Subscription is required


Heavy Mobile Equipment:

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Jul 6, 2022
....................... Subscription required ....................... Subscription required Subscription required Jul 6, 2022
....................... Subscription required ....................... Subscription required Subscription required Jul 6, 2022
....................... Subscription required ....................... Subscription required Subscription required Jul 6, 2022
Subscription required - Subscription is required.

Staff:

EmployeesContractorsTotal WorkforceYear
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
................................... 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
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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Aerial view:

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