Tuesday, May 18, 2010

The Copper King Mine, Wyoming - two million ounce deposit

Photo of Hecla Mill, JE Stimson Collection
The Copper King mine (NW section 36, T14N, R70W) was mapped and sampled by the author and others in the past. The Copper King (Arizona) mine was located in 1881 and developed by the Adams Copper Mining and Reduction Company. The property was later worked by the Hecla Mining Company.

All that remains of the old Hecla mill is a rock foundation on the side of the
This property has a 2 million ounce gold equivalent of gold-and copper associated with shears, faults, veins, veinlets and stockworks in granodiorite and quartz monzonite that have distinct propylitic and potassic hydrothermal alteration mineral assemblages similar to younger copper-gold porphyry deposits. The geology also suggests that the ore deposit could be expanded. That's right, the eastern flank of the Copper King was down-faulted. So what lies under the Tertiary cover in that area?  Hopefully, drilling and geophysics will resolve that question in 2013 or 2014.

The Copper King is considered one of the five best gold deposits in Wyoming and is likely the root zone of a deeply dissected Proterozoic age porphyry gold-copper deposit.

A shaft was sunk 157 feet with 102 feet of crosscuts on the 80-foot level, and 260-feet of drifts and crosscuts and three large rooms on the 130-foot level. A 100-foot adit was driven near the shaft but stopped short of intersecting the shaft. Some ore was shipped, although the total amount of production is unknown (Ferguson, 1965).

Photo of Hecla smelter located across the road
from the Silver Crown Mill, Ferguson Archives.
The Copper King is a deeply dissected Proterozoic age copper-gold porphyry deposit with disseminated sulfides and stockworks surrounded by propylitic and potassic alteration zones. Fourteen samples collected by Jamison (1912b) varied from 0.22% to 2.43% Cu, 0.06 to 0.42 opt Au, and 0.4 to 0.8 opt Ag. Mineralization at the surface occurs as malachite and chrysocolla: at depth as chalcopyrite, pyrite, minor bornite, pyrrhotite and native copper (McGraw, 1954; Soule, 1955).

Potassic alteration of granodiorite at the Copper King.
Primary hypogene mineralization was intersected during drilling to a depth of 150 to 180 feet by the Bureau of Mines. The primary ore is overlain by an oxidized and leached cap extending from the surface down to depths of 30 to 150 feet (Soule, 1955). Near the Copper King shaft, a zone of intense silicification consists of intersecting quartz veins and veinlets. Extending out from the shaft is a zone of potassium silicate alteration expressed by secondary enrichment of biotite and microcline-quartz intergrowths with some muscovite, sericite, epidote, and sulfides. This potassic altered zone is enclosed by a propylitic altered zone consisting of secondary chlorite and epidote with sulfides (Hausel and Jones, 1982b).

The available drilling data indicate that the maximum metal concentrations were on the order of 1.5% Cu and 0.2 opt Au (Klein, 1974). Drilling by the U.S. Bureau of Mines showed mineralization continued to a depth of at least 1,024 feet. Spectrographic analyses showed traces of lead, zinc, tungsten, and 0.5 to 3.0% TiO2 (Soule, 1955). An estimate of the in situ ore reserves were made by Nevin (1973) based on drilling:
Tons                  Cu                           Au                                  Stripping ratio
(millions)          (%)                         (opt)                                    (waste/ore)

2.8                   0.36                         0.044                                          0.5
6.0                   0.32                         0.038                                          1.2
13.5                 0.26                         0.028                                          1.8
35.0                 0.21                         0.022                                          2.0

In 1987, Caledonia Resources leased the mine to test as a large-tonnage, low-grade, disseminated gold deposit. The company reported preliminary gold estimates on the order of 4.5 million tons of ore averaging 0.044 opt Au (or about 200,000 ounces of contained gold). Sampling suggests the deposit has a minimum strike length of 600 to 700 feet with a 300 foot width that is open at depth (Stockwatch, 1987). More recent data by Compass Minerals expanded the gold-copper resource. The company reported a gold resource of 23 million tons of ore grading at 0.82 grams or essentially 770,000 ounces of contained gold, while Paso Rico Resources indicated the deposit to contain a million ounce equivalent gold-copper resource (Hausel, 2008a). More recent work by Saratoga Gold Mining Company outlined a 2 million ounce equivalent ore deposit containing 1.2 million ounces of gold and considerable copper. And based on mapping by the author, it is likely that this resource will be expanded.

Photo of the interior of the Hecla mill near Cheyenne
Wyoming. JE Stimson Collection, University of Wyoming.
Geochemical and geophysical anomalies suggest the known resource could be increased. For example, a large magnetic anomaly (1,000 ft wide x 2,000 ft long, 450 gamma magnitude), almost identical to that reflected by the Copper King deposit (800 ft wide x 1,500 ft long, 500 ft gamma magnitude) was identified in a gravel covered area 4,500 feet to the southeast. Soil samples over this anomaly returned anomalous values for the pathfinder elements mercury, zinc, and arsenic supporting the presence of hidden mineralization. Geological and geophysical evidence also suggests the presence of sulfides down plunge to the southwest and to the east of the Copper King. An IP (induced polarization) survey identified a moderate to shallow metal factor anomaly trending east-northeast of the principal mineralized area (Klein, 1974).

Mineralized terrains showing location of Silver
Crown district in southeastern Wyoming.

Aerial photo showing location of the Copper King mine

  Will the Copper King ever be mined? If a reasonable mining plan and royalty can be negotiated with the State of Wyoming, the answer is 'yes'. The deposit is mostly on State land which is beneficial. If it were on public lands, the Federal Government would tie this property up in their bureaucratic network until any mining company would give up due to the mountains of paperwork.

The author (Gem Hunter) back at the Copper King
mine in 2012.
Over 30 years, I explored Wyoming and mapped most of the hardrock mining districts and found a few deposits with very favorable geology that needed to be explored further. Besides the Carissa Mine and the Rattlesnake Hills gold deposits, the Copper King was one of the top gold deposits in the state that I felt would be mined with higher gold prices. Today, we have those high gold and copper deposits and with further exploration, I would not be surprised to see this deposit surpass the 2.5 to 3 million ounce equivalent.

What really surprises me is there are other mineral deposits (including gold) sitting at a number of locations in Wyoming - some with surprising size that are being ignored by industry and the State. Some are worth $millions, others $billions and at least one might be worth $hundreds of billions.

Maybe its time to go Gold Prospecting, Diamond Prospecting or Gemstone Prospecting in Wyoming.

Geological map of the Silver Crown district

I found it!!!  Yes, the two-million ounce gold deposit at Copper King has even more ore. I
was able to follow and map a fault that offsets the eastern edge of the ore deposit by dropping
it down to the east. This means, there is more ore to be found under a blanket of gravel. How
much more? Need to drill to find out.