United States

Isabella Pearl Mine

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Overview

Mine TypeOpen Pit
StatusActive
Commodities
  • Gold
  • Silver
Mining Method
  • Truck & Shovel / Loader
Production Start... Lock
Mine Life... Lock
SnapshotMine operations at Isabella Pearl are projected to conclude in 2024 depending on the final mine sequencing of the next four benches planned in the Pearl zone after the Fortitude receives regulatory approval to mine deeper.

A near-term decision from the Bureau of Land Management (BLM) is expected for the Pearl deep portion of the Isabella Pearl mine, which would allow for final mine sequencing in the higher-grade Pearl portion of the deposit’s oxide and transitional oxide gold ore areas.

Final mine operation timing could be impacted by BLM permit timing as well as any additional mineralization that may be encountered outside of the current mine plan.

Owners

SourceSource
CompanyInterestOwnership
Fortitude Gold Corp. 100 % Indirect
The Isabella Pearl mine is 100% owned by Fortitude Gold, through subsidiary Walker Lake Minerals Corp.

Contractors

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Deposit type

  • Epithermal

Summary:

Alteration and mineral assemblages throughout the deposit are represented by widespread argillic alteration, generally abundant alunite, and the presence of minor amounts of base metals, all of which indicate the ore deposits to belong to the high sulfidation (acid sulfate) class of epithermal mineral deposits. Fluid inclusion data indicates the solutions that deposited the coarse-grained quartz were dilute, with a salinity of 1-2 weight percent NaCl and temperatures ranging 200 to 300° C. Temporal relationships and the thickness of the tuff units suggest that the depth of formation was more than 900m. The geometry of the deposit is controlled by two dominant geologic features; favorable stratigraphic horizon, and structural connectivity to mineralizing fluids. In high sulfidation environments the fluids ascend via structural feeders and under acid attack particularly replaces more favorable units; in the case of Isabella Pearl the Guild Mine member of the Mickey pass Tuff was this unit.

The gold-silver mineralized zones include the Isabella, Pearl, and Civit Cat oxide deposits and the Pearl and Civit Cat sulfide deposits, collectively referred to in this report as the Isabella Pearl deposit. Alteration and mineral assemblages at Isabella Pearl, including widespread argillic alteration and generally abundant alunite, indicate the deposits belong to the high-sulfidation class of epithermal mineral deposits. K-Ar age determinations indicate the mineralization is about 19 Ma, some 7 to 10 million years younger than the age of the host rocks. This early Miocene age conforms to the age of other highsulfidation epithermal precious-metal deposits in the Walker Lane (e.g., Goldfield and Paradise Peak).

Silicification generally grades outward into argillization, which then grades into propylitically altered rocks. Silicification is localized by faults and shears, and in many areas, silica has replaced large masses of both the volcanic and granitic rocks. Gold is associated with this silicification, occurring primarily within the Guild Mine Member in the lower part of the Mickey Pass Tuff. This alteration assemblage is also present in the lower, more densely welded tuff characteristic of the Pearl deposit, but it is tightly confined around the mineralized core the deposit.

The Isabella mineralization is moderately argillized to highly siliceous, contains numerous vugs in former feldspar and pumice sites (vuggy-silica textures), and typically lacks any evidence of cross-cutting veinlets. Narrow, structurally controlled zones of silica-pyrite, as well as the more pervasive silica replacement bodies, generally grade outward into silica-kaolinite with local alunite envelopes, which in turn grade into pervasive illite-montmorillonite zones. The iron oxide minerals goethite, jarosite, and hematite are present in the siliceous groundmass. Gold occurs as very small (<10 microns) liberated particles in cavities and along fracture surfaces. Rare secondary minerals include barite, cinnabar, and scorodite. A nearhorizontal zone of pervasive argillic and advanced-argillic alteration occurs above the Isabella deposit in the upper, poorly to moderately welded rhyolitic ash-flow tuff of the Guild Mine Member. Within this altered zone, alunite occurs as pseudomorphs after potassium feldspar phenocrysts and as replacements of pumice fragments.

The Pearl deposit is hosted by the lower, densely welded portion of the Guild Mine Member and, to a lesser extent, by Cretaceous granite. Mineralization is largely controlled by the northwest- striking, northeast-dipping contact zone between the granitic basement and the overlying Tertiary volcanic units. This contact may be partially or entirely faulted; this report assumes the contact is marked by the fault. Strong silicification accompanies gold mineralization and is associated with fracture fillings and replacement of the welded tuff. The mineralization is usually associated with strong brecciation. Multiple stages of fracturing and brecciation with associated silicification have been observed in drill core.

Sulfide minerals at Pearl commonly exceed ten percent (by volume) and are composed primarily of crystalline grains and aggregates of pyrite, colloform banded “melnikovite”-type pyrite, and bladed marcasite (or pyrite after marcasite) in dark microcrystalline quartz. This quartz has replaced both the volcanic and intrusive host rocks. In the granite, alteration has resulted in the complete leaching of feldspars and ferromagnesian silicates, and pyrite and marcasite have filled the voids left by the silicate dissolution. Rare sulfide minerals observed in thin and polished sections include arsenopyrite, pyrrhotite, galena, sphalerite, chalcocite, chalcopyrite, polybasite, and pyrargyrite. Other minerals include very minor magnetite, zircon, monazite, and rutile. Native gold has not been observed in the sulfide mineralization.

The oxidation boundary is depressed over and immediately around the Pearl deposit, with oxide mineralization extending to more than 150 m (500 ft) below the surface. Goethite, jarosite, and manganese oxide are common, and barite and chlorargyrite occur rarely in the siliceous groundmass. Gold within the oxide mineralization occurs both as locked and liberated particles, as well as electrum. Particles range in size from 2 to 34 microns, averaging 14 microns. The liberated particles occur as small wire-like grains in cavities, while the locked gold is encapsulated by silica or goethite.

The Civit Cat mineralization, which is relatively minor and poorly defined by drilling, lies to the northeast of Pearl and is associated with the northwest-striking, southwest-dipping Civit Cat fault. The control on mineralization by the Pearl and Civit Cat faults, which have similar strikes but opposing dips, results in northwest-trending, roughly lens-shaped zones of mineralization that flank both sides of a graben-like structural trough.

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

CommodityUnits20232022202120202019
Gold oz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe10,883
Silver oz  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe9,752
All production numbers are expressed as metal in doré.

Operational metrics

Metrics20232022202120202019
Ore tonnes mined  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe1,464,682 t
Waste  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe4,504,360 t
Hourly processing capacity  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
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Production Costs

CommodityUnits20232022202120202019
Credits (by-product) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe -14 / oz  
Total cash costs (sold) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 1,054 / oz  
Total cash costs (sold) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 1,040 / oz **  
All-in sustaining costs (sold) Gold USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 1,049 / oz **  
** Net of By-Product.

Financials

Units20232022202120202019
Sustaining costs M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 0.09  
Revenue M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 15.1  
Gross profit M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Pre-tax Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
After-tax Income M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe 0.3  
Operating Cash Flow M USD  ....  Subscribe  ....  Subscribe  ....  Subscribe  ....  Subscribe
Book Value M USD  ....  Subscribe  ....  Subscribe

Heavy Mobile Equipment

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Personnel

Mine Management

Job TitleNamePhoneEmailProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Mar 1, 2024
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....................... Subscription required ....................... Subscription required ........... Subscription required ........... Subscription required Feb 5, 2024

Total WorkforceYear
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