United States

Wharf Mine

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Overview

Mine TypeOpen Pit
Commodities
  • Gold
  • Silver
Mining Method
  • Truck & Shovel / Loader
Production Start... Lock
Mine Life2029
ShapshotThe Wharf mine property consists of several areas of adjoining gold mineralization, which have been mined as a series of open pits.

In January 2022, the Lawrence County Commission approved Coeur Wharf's Conditional Use Permit application, also known as the Boston Expansion. This approval, which is one of the two needed, the other being the State Mine Permit approval, allows for an expansion of our mining operations by 48.7 acres and potentially extends the mine life for one to three years. In August 2023, following two years of environmental baseline studies and regulator review, the South Dakota State Board of Minerals and Environment approved a new State Mine Permit for the Wharf mine incorporating the Boston Expansion area. Simultaneously, an increased bond amount was also approved to include additional land disturbance associated with the Boston Expansion.

Owners

SourceSource
CompanyInterestOwnership
Coeur Mining, Inc. 100 % Indirect
Wharf Resources U.S.A. Inc. (operator) 100 % Indirect
The Wharf mine is operated by wholly-owned subsidiaries of Coeur Mining, Inc., Wharf Resources (U.S.A.) Inc. and Golden Reward Mining Limited Partnership (wholly-owned subsidiary of Wharf Resources).

Contractors

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Deposit type

  • Epithermal
  • Porphyry

Summary:

The deposits in the Wharf Operations area are considered to be examples of structurally controlled and disseminated gold mineralization. The Wharf deposit has been described as a hydrothermal replacement deposit, (Lessard and Loomis, 1990) a Carlin-type deposit (Paterson, 1990), and more recently as a low- to intermediate-sulfidation epithermal deposit. (Pedraza Rojas, 2017).

Host rocks to epithermal deposits are dominantly silty carbonates, but mineralization can also be present in siliceous and silicified rocks as well as intrusive rocks. Low- to intermediate-sulfidation epithermal deposits commonly exhibit significant structural (faults) and stratigraphic (composition/permeability) controls. Mineralization often consists of extremely fine-grained disseminated gold, hosted primarily by arsenian pyrite.

Wharf differs from this standard model in that host rocks are dominantly sandstone with varying carbonate content and trachytic porphyry, and mineralization consists of native gold and electrum and remobilized gold in addition to early-stage gold-bearing sulfides.

Deposit Dimensions
The Wharf deposit dimensions range from 8,000–9,000 ft long in the east–northeast direction, 2,100–5,000 ft wide, 150 ft thick in historically mined areas to 500 ft in active pits. Mineralization has been drill tested to varying depths to the Precambrian surface, which ranges from 5,400–6,200 ft in elevation across the deposit.

Lithologies
Trachytic sills are the bulk of the mineralized lithology within the mine plan. Composition varies and includes trachytic, quartz trachytic, and quartz alkali feldspar trachytic (Pedraza, 2017). Phonolite is present as a large capping sill and as dikes and smaller sills and is post-mineral.

The entire Deadwood sequence is present in the current mine area, as well as some overlying Icebox Shale. Manto-like mineralization occurs in the sandstone and dolomitic zones of the lower member of the Deadwood Formation, and narrower, higher-grade zones occur in the upper sandstone and glauconitic sandstone units.

Precambrian metamorphic rocks including phyllites and quartzites underlie the property and but not intercepted by any of the pits.

A trachyte sill is a main host for mineralization, with low-grade disseminated mineralization throughout the body. Igneous bodies at Wharf are predominantly sills. Dikes are less volumetrically important but occur in most mined areas.

The best mineralized intrusion, the lower trachyte sill, occurs in several pits at Wharf. This trachyte sill was intruded both above and below the base of the Deadwood Formation.

Structure
Sills geometries in the pits vary. Sill thickness is highly varied; almost the entire depth of the Foley and American Eagle pits were porphyry sills, but other pits intersected the sills where they were 20–30 ft thick. Sills can be discordant across thick sequences of stratigraphy, moving upsection gradually, possibly along pre-existing structures.

A weakly mineralized dike up to 100 ft wide was present in the easternmost Bald Mountain area. Narrow, late phonolite dikes cross-cut trachyte sills in several places in the pits.

A fault zone exposes Precambrian rocks at Bald Mountain, east of the haul road tunnels connecting Wharf to Golden Reward. Zones of intense silicification, clay alteration, and brecciation parallel the fault. This fault continues south to Golden Reward, and parallels northtrending Precambrian structures and is probably a reactivated older structure. Other faults with minor offset are present throughout the site and have been viewed in-pit.

The main trends of mineralization at Wharf parallel the strike of major joint sets measured in upper and lower Deadwood Formation outcrops (Shapiro and Gries, 1970).

Alteration
Silicic alteration within the Golden Reward portion of the property was common in mineralized areas and was expressed as quartz veins, stockworks, and as disseminated quartz with sulfides (Emanuel et al., 1990). Silicification in the Annie Creek portion of the property was typically focused around fractures (Loomis and Alexander, 1990). Silicification included destruction of glauconite in sandstone and porphyritic texture in the intrusions, replacement of dolomite crystals, and preservation of primary sedimentary structures (Paterson and Giebink, 1989; Loomis and Alexander, 1990). In the Foley sill at Wharf, zones of silicification were observed to be enclosed by decalcified zones, with metal grade decreasing from the zone interior outward (Loomis and Alexander, 1990). Silicification also occurred along structures, such as the Bald Mountain fault zone, at contacts with the igneous intrusions, and along bedding planes and lithologic contacts.

Outside of these silicified zones, carbonate replacement and veinlets formed by remobilization of carbonate from the mineralized zone (Loomis and Alexander, 1990). Locally, rather than decalcification, original calcareous horizons were replaced with dolomite (Shapiro and Gries, 1970). In the mine area, phenocrysts in trachytic porphyry sills are partially replaced by carbonate, and carbonate veinlets occur within the sills.

Argillization occurs in porphyritic intrusive rocks. Prominent clay-altered structures were visible in the pits, but these structures were barren and typically contained an extremely altered phonolite dike core. A late-stage barren phonolite cap at Green Mountain and along Foley Ridge had similar strong argillic alteration along fractures.

Mineralization
Most of the mineralized intrusive rocks at Wharf are trachytic in composition. Trachyte porphyry forms sills that exhibit fracture-controlled mineralization. Locally, gold is disseminated strongly fractured zones contain higher grades and more continuous mineralization.

Quartz trachytic and quartz alkali feldspar trachytic rocks are varyingly mineralized, with a barren sill in the western portion of the mine area, and a more mineralized sill has been mined in the eastern portion of the pit. A thin biotite-rich sill similar in texture and composition to the barren cap phonolite is also mineralized.

The upper and lower Deadwood Formation are host to higher-grade mineralization. The upper unit has narrower, higher-grade, more structurally controlled mineralization, with the lower Deadwood exhibiting more pervasive mineralization. More impermeable units such as the interbedded shale units of the Deadwood Formation are less mineralized, but in places host structurally controlled mineralization.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityUnits2024202320222021202020192018
Gold oz 0000000000000000000000000000000000076,840
Silver oz 00000000000000000000000000050,576
Gold Equivalent oz 77,683
^ Guidance / Forecast.

Operational metrics

Metrics202320222021202020192018
Ore tonnes mined 00000000000000000000000000000000000
Tonnes milled 000000000000000000000000000000000004,923,774 tons
Waste 000000000000000

Production Costs

CommodityUnits2024202320222021202020192018
Total cash costs (sold) Gold Equivalent USD 880 / oz  
Total cash costs (sold) Gold USD 00000000 00000000 00000000 0000000 0000000 937 / oz   879 / oz  
^ Guidance / Forecast.
Net of By-Product.

Financials

Units2024202320222021202020192018
Capital expenditures (planned) M USD  ....  Subscribe
Capital expenditures M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 3.4  
Sustaining costs M USD
Revenue M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 96.5  
After-tax Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 13.5  
Operating Cash Flow M USD  ....  Subscribe

Heavy Mobile Equipment

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Personnel

Mine Management

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EmployeesYear
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Aerial view:

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