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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
  • Owners
  • Geology
  • Mining
  • Processing
  • Production
  • Reserves
  • Costs & Financials
  • Personnel
  • Filings & News

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Overview

StageProduction
Mine TypeUnderground
Commodities
  • Palladium
  • Platinum
Mining Method
  • Ramp & Fill
  • Overhand Cut & Fill
  • Raiseboring
  • Sub-level stoping
  • Alimak
  • Hydraulic backfill
Processing
  • Flotation
Mine Life2059
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


Summary:

The Stillwater Complex is a layered ultramafic to mafic igneous complex formed by the gradual cooling of an enormous subterranean intrusion. In such intrusions, the gradual cooling leads to the formation of layers of crystals with similar geochemical properties. Some of these layers are essentially monomineralic (anorthosites composed of high-calcium plagioclase), while others have additional minerals such as troctolites, which contain both high-calcium plagioclase and olivine. The layering is very distinct and resembles the layering of sedimentary rocks even though the rocks of the complex are igneous. These layers form over extremely large areas. The fact of this layering is critically important to understanding the deposition of the palladium- and platinum- bearing minerals in the J-M Reef.

The J-M Reef is recognized by the presence of chalcopyrite, pyrrhotite, pentlandite, and, rarely, pyrite within the reef package. Other base-metal sulfides have been identified, but their presence is subordinate. The platinum group minerals can rarely be recognized with a hand lens. SMC (2001) reported that platinum occurs primarily (67%) as sulfide, 25% as the metal alloy, isoferroplatinum, and 8% as the telluride, moncheite. Palladium occurs primarily (80%) as a solid-solution in pentlandite, 15% as sulfides, and 5% in the telluride, moncheite. The platinum:palladium ratio averages 1:3.5 in-situ at the Stillwater Mine, except for the Dow (Upper West) area of the mine, where the platinum:palladium ratio increases to 1:3.9 in- situ, and averages 1:3.6 to 3.7 in-situ at the East Boulder Mine. The currently delineated proven reserves at the East Boulder Mine have a lower PGM grade and higher copper plus nickel content than the Stillwater Mine. At the west end of the Stillwater Mine in the Dow sector, an area of higher copper plus nickel content has been identified that is similar to the East Boulder Mine mineralization.


Mining Methods

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


Summary:

The East Boulder operation is accessed via twin 5,800m long decline tunnels.

Key infrastructure includes the mining operations and ancillary buildings that contain the concentrator, workshop, warehouse, changing facilities, twin tunnels to access mine, sand plant, water treatment, storage facilities and offices.

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

  • Flotation

Source: Subscription required

Summary:

East Boulder has been in operation since 2002, and currently produces approximately 230Koz per annum of platinum and palladium in concentrate.

Currently 48% of all concentrator tailings are returned underground for backfill, with the remaining 52% sent via pipeline to a TSF adjacent to the mine site.

Recoveries & Grades:

CommodityParameter2020201620152014
2E (Pt, Pd) Recovery Rate, %  ......  Subscription required909190
Palladium Recovery Rate, %  ......  Subscription required909190
Palladium Concentrate Grade, oz/ton  ......  Subscription required11.310.711
Platinum Recovery Rate, %  ......  Subscription required909190
Platinum Concentrate Grade, oz/ton  ......  Subscription required3.223.053.19
2E (Pt, Pd) Head Grade, oz/ton  ......  Subscription required0.370.380.38

Production:

CommodityProductUnits2020201920182017201620152014
2E (Pt, Pd) Metal in concentrate koz  ......  Subscription required  ......  Subscription required228148218201177
Palladium Metal in concentrate koz  ......  Subscription required  ......  Subscription required  ......  Subscription required
Platinum Metal in concentrate koz  ......  Subscription required  ......  Subscription required  ......  Subscription required
2E (Pt, Pd) Concentrate kt 13,78213,34711,691
Subscription required - Subscription is required.

Operational Metrics:

Metrics202020192018201720162015
Daily milling rate  ......  Subscription required
Daily milling capacity  ......  Subscription required1,800 t1,800 t1,600 t2,000 tons2,000 tons
Annual milling rate  ......  Subscription required608 kt
Tonnes milled  ......  Subscription required656 k tons583 k tons
Daily mining rate  ......  Subscription required1,755 tons1,589 tons
Subscription required - Subscription is required.

Reserves at December 31, 2020:
Mineral Reserve cut-off grade is 1.7 g/t 2E.

CategoryTonnage CommodityGradeContained Metal
Proven 3.5 Mt 2E (Pt, Pd) 12.6 g/t 1.437 M oz
Probable 23.7 Mt 2E (Pt, Pd) 12.6 g/t 9.612 M oz
Proven & Probable 27.2 Mt 2E (Pt, Pd) 12.6 g/t 11.049 M oz
Measured 5.7 Mt 2E (Pt, Pd) 12.8 g/t 2.361 M oz
Indicated 38.6 Mt 2E (Pt, Pd) 12.2 g/t 15.116 M oz
Inferred 47.9 Mt 2E (Pt, Pd) 13.7 g/t 21.168 M oz
Total Resource 92.2 Mt 2E (Pt, Pd) 13 g/t 38.645 M oz

Commodity Production Costs:

CommodityUnits201620152014
Total cash costs 2E (Pt, Pd) USD 441 / oz† 508 / oz† 547 / oz†
† Net of By-Product.

Operating Costs:

Units201620152014
Total operating costs ($/ton milled) USD 147175187

Financials:

Units20162015
Sustaining costs M USD 16.7   15.1  


Heavy Mobile Equipment:

Mine Management:

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
....................... Subscription required ....................... Subscription required Subscription required Jun 8, 2021
Subscription required - Subscription is required.

Staff:

EmployeesContractorsTotal WorkforceYear
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 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
Subscription required - Subscription is required.

Aerial view:

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