Summary:
The Fire Creek deposit is considered to be a low-sulfidation, epithermal deposit.
Low-sulfidation epithermal systems are also referred to as quartz ± calcite ± adularia ± illite or adularia-sericite epithermal systems. These nomenclatures refer to the oxidation state of the ore fluid sulfur component, gangue mineralogy and hydrothermal fluid pH, respectively. Ore-fluids in a low-sulfidation hydrothermal system are reduced, have a near-neutral pH and are dominated by deeply-circulated meteoric water. These deposits form in the shallow crust, 0.5 to 1.5 miles at temperatures of greater than 300°C in subaerial volcanic settings. Steeply-dipping, open-space veins are common. Quartz is the principal gangue mineral and can be accompanied by chalcedony, adularia, illite, pyrite, calcite, and rhodochrosite. Boiling is the dominant metal deposition mechanism and commonly results in vein textures including crustiform-colloform bands and platy calcite and/or quartz-after-calcite pseudomorphs. Ore metals are usually Au-Ag, Ag-Au or Ag-Pb-Zn and, contrary to the ore-fluid source, metals in NNR-related epithermal deposits are sourced from mantle-derived basaltic magmas (Kamenov et al., 2007).
Zoned hydrothermal alteration comprises widespread and deep propylitization that grades upwards to clay, carbonate and zeolite formation. Proximal alteration comprises quartz, adularia, and pyrite. High-level advanced argillic alteration characterized by clay-carbonate-pyrite or kaolinite-alunite-opal ± pyrite alteration can be present above the ore-grade zone and is the result of steam-heated, acidic, ascending fluids generated during boiling.
Electrun is primarily present in its native state along discrete layers within veins. Native electrum can occur as large clots or bands, dendritic growths, and fine-grained disseminations. Other less common habits include encapsulations in quartz, pyrite replacements and coatings on pyrite or arsenopyrite (Thompson, 2014). Silver occurs encapsulated in quartz and locally in naumannite or ruby silver encapsulations in quartz (Thompson, 2014). Dark grey ginguro bands of an unidentified silver-bearing mineral are present along vein banding as well. The silver gold ratio is approximately one to one.
Commodity Production
Fire Creek mine was acquired by Hecla Mining in July 2018. Since that time, mine's production and financial results have been included into the Nevada Operations Segment.
| Commodity | Units | 2017 | 2016 | 2015 |
|
Gold
|
oz
| 107,143 | 101,286 | 77,055 |
|
Silver
|
oz
| 72,283 | 80,593 | 92,114 |
|
Gold Equivalent
|
oz
| 108,126 | 102,383 | 78,312 |
All production numbers are expressed as metal in doré.