Pioche Mining District, Lincoln County, Nevada, USAi

Regional Level Types
Pioche Mining District	Mining District
Lincoln County	County
Nevada	State
USA	Country

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Location & History: The Pioche District is a former Pb-Ag-Au-Mn-Fe-Cu-Zn-As mining area located in secs. 14, 17, 22, 23, 26, 32, 33 & 4, T1N, R67E, MDM, in the Pioche Hills southwest of Pioche, about 19 miles W of the Utah-Nevada border, on mixed ownership land including private land and Bureau of Land Management administered land (Bureau of Land Management Las Vegas administrative district). Owned & operated by Kerr-McGee.

The initial mineral discovery in Pioche occurred in 1863 and mining production began in 1869. The original ore consisted of oxidized silver chlorides occurring in fissures in Cambrian quartzites. The Raymond and Ely vein system contained high-grade lead-silver ore that was mined in the 1870s At one time Pioche was one of largest silver districts in the United States. Total mineral production exceeded $130,000,000. The primary metal values were for gold, silver, lead, zinc and copper. Low-grade argentiferous manganese oxides were also found in the region. Major periods of production were: 1895-1901; 1912-1920; 1934-1953; and 1958-1959. Minimal activity has occurred from 1959 to the present time. Early milling occurred in Pioche, but a shortage of water forced the mills to be relocated to Bullionville (near Panaca) around 1871. In 1924 Combined Metals Reduction Company developed a selective flotation process to treat the massive lead-zinc sulfide ores. Combined Metals Reduction Company processed ore at a mill in Bauer, Utah from 1923-1941, until the Caselton Mill was built in 1941. Mountain Mines, Inc. acquired the Caselton Tailings after the bankruptcy of Combined Metals Reduction Company in 1976. Mountain Mines, Inc. claims to have produced precious metals from the tailings with a small chemical processing facility located in the vicinity of the tailings. Numerous mining companies have had operators or exploration activity at site, including: Meadow Valley Mining Company (1864-1876); Consolidated Mining Company (1880's); White Pine Minerals Company (?); Combined Metals Reduction Company (1924-present); Pioche Manganese Company (WWII); Comet Coalition Mining Company (1964-1978); St. Patrick Mining Company (1975); Bunker Hill Mining Company (1976-77); Kerr-McGee Chemical Company (1980); Mountain Mines, Inc. (1976-present). Homestake Mining Company, Prince Consolidated Mining Company and Anaconda Company also have been active in the area. Midway Gold Company has recently (2004) been exploring for a faulted offset of the high-grade silver-gold Salt Lake Pioche vein under post- mineral volcanic rock. The property consists of five patented and 36 unpatented claims lying south of the town of Pioche on a combination of private patented mining claims and BLM administered lands. Midway began a 3500 foot reverse circulation drill program on the Pioche Project in October 2004.

Mineralogy/Geology:

Mineralization: Mineralization is replacement deposits (Mineral occurrence model information: Model code: 72; USGS model code 19a; Deposit model name: polymetallic replacement; Mark3 model number: 47), hosted in Early Cambrian/Neoproterozoic quartzite [Prospect Mountain Quartzite]; Early Cambrian limestone [Combined Metals Member of the Pioche Shale]; Middle Cambrian limestone [Lyndon Limestone]; Early Ordovician/Late Cambrian limestone [Mendha Limestone]; Middle Cambrian limestone [Highland Peak Limestone]; and, Tertiary granite porphyry dikes. Associated rocks include Middle Cambrian shale [Chisholm Shale]; Early Ordovician limestone [Yellow Hill Limestone]; Early Ordovician limestone [Tank Hill Limestone]; Late Ordovician/Middle Ordovician quartzite [Eureka Quartzite]; Late Ordovician dolomite [Ely Springs Dolomite]; Middle Devonian dolomite [Silverhorn Dolomite]; Late Devonian dolomite [West Range Dolomite]; dacite; andesite; rhyolite; Early Mississippian limestone [Bristol Pass Limestone]; Late Mississippian siltstone [Peers Spring Formation]; Late Mississippian quartzite [Scotty Wash Quartzite]; quartz monzonite intrusives; tuff; and, Pennsylvanian/Mississippian limestone [Bailey Spring Limestone]. Local alteration includes oxidation and hydrothermal activity. Local rocks include alluvial deposits.

The ore bodies are tabular to lenticular replacement bodies, tapering away from fissures. Controls for ore emplacement include the intersections of steep fissures and limestone beds in the Pioche Shale.

Deposits are of 3 types: (1) silver-bearing fissure veins in quartzite; (2) silver-bearing mineralized granite porphyry; (3) replacement deposits in limestone and dolomite. All of them appear to have been formed at about the same time, in the epoch of mineralization that occurred shortly after the intrusion of the granitic rocks and their allied dikes of granite porphyry and lamprophyre.

The main orebody at the Caselton, Raymond & Ely/Combined Metals Reduction #1 mines is the result of selected replacement of the Combined Metals Limestone bed where it intersects the steeply-dipping Greenwood Fissure, which is a fault of slight displacement, usually expressed as a thin gouge seam but which may be up to 5 feet thick. It trends N70E, and dips 65-70N, nearly paralleling the Raymond and Ely vein, which dips 75S. The ore has been offset by many cross-faults the main orebody is a tabular massive sulfide bed extending laterally into the limestone layer, thickest (30-40 feet) adjacent to the Greenwood Fissure, and tapering down away from it. Bedded ore occurs up to 200 feet on either side of the Greenwood Fissure. The ore of the upper bed preserves the nodular character of the limestone host. Ore consists of about 60% pyrite, 22% sphalerite, 8% galena, minor chalcopyrite and practically no gangue minerals. The lower bed ore is massive with an irregular bottom contact, as the underlying quartzite has been irregularly replaced by pyrite and sphalerite. The ore is unoxidized. The Raymond and Ely vein in the Prospect Mountain Quartzite strikes parallel to the Greenwood Fissure. The Greenwood ore occurs chiefly in Pioche Shale. The Black Ledge vein of quartz and sphalerite was also mined yielding 12-20% zinc and 5-21 ounces of silver per ton. The Raymond and Ely vein system splits eastward into two branches: the Meadow Valley vein and the Burke Vein. The largest and richest ore shoot in the vein occurred just below the Pioche Shale within about 400 feet of the Yuba Dike. The complex sulfide ore was of no value until selective flotation was invented. The ore bed was mined for more than 10,000 feet along an east west channel 100 to 1800 feet wide. Ore body terminates against the frontal fault. The hanging wall was unsuccessfully explored to a depth of 2500 feet. Most gold came from the Combined Metals Mine. On Treasure Hill, the workings explore a series of faults and shears and the north end of the Yuba dike, a principal contributor to the mineralization of the area. Much of the fault breccia shows milling texture with jarosite and iron-manganese oxides coating most exposed surfaces. The quartzite ranges from white to grey-rose colored with prominent banding. Pods of very fine-grained argentiferous minerals along with galena and other sulfides are disseminated throughout the breccia. Yellow oxides are also common on exposed surfaces. Abundant sericite is present. Locally the breccia zones are silicified and abundant gossan occurs where ore minerals have weathered out. Late opaline silica is deposited on fracture surfaces and iron sulfides have altered to specular hematite. Euhedral quartz crystals line cavities. Quartz vein material which fills fault fissures exhibits brecciation and is recemented with silica, and contains bands of finely disseminated grey sulfides. The Raymond and Ely, Meadow Valley, and Burke veins strike roughly east-west and dip 50 degrees south. Oxidized silver ore in the quartzite decreased in grade eastward and downward. The Meadow Valley vein was mined continuously for 2000 feet to a depth of 1,200 feet. Average ore thickness was 2-3 feet. Galena and sphalerite are increasingly abundant in the lower levels. Rich silver-lead ore was mined from the Yuba Dike. Three or more cross veins strike northeast at 45 degrees to the principal veins. The "quartzite fissures" are veins with filling of loose rubble of angular quartzite fragments to breccia cemented by lead carbonate, limonite, and jarosite. The quartzite fissures strie N15-20W.

Geologic structures: Local structures include steeply dipping fissures - N50-70E mineralized zone. Regional structures include E-W and N-S normal faulting before thrusting; N60 degree S faults mineralized; N-S, NW-trending post mineralization. The Pioche Hills appear to be a window in a regional thrust of upper Cambrian rocks over lower Cambrian and Tertiary volcanics. The Pioche Shale bed was dropped by closely spaced parallel normal faults. mineralization principally occur in the Combined Metals bed of the Pioche Shale. Highland Peak overthrust.

The Combined Metals member of the Pioche Shale is the host rock for the replacement ore bodies. It consists of 3 parts: (1): a lower 3 foot of massive limestone; (2): a middle 3-foot thick calcareous sandstone (which in the ore body is unreplaced) and, (3): an upper 30-foot layer of thin-bedded nodular limestones, usually only 2-3 inches thick, and so nodular that they look like "beds of flattened potatoes." The nodules are coated with a thin black carbonaceous skin. The Pioche Shale belt trends NW between 2 faults.

Workings: The veins were developed by extensive underground workings, including shafts, adits, trenches, cuts, and prospect pits. Most of the old underground workings were caved by the 1980's. There was a small open pit and heap-leach operation working in the 1980's. Water was in the old workings at the 1,200 foot level.

Production Information: From 1905 to 1958 the total production from the Pioche district mines was 810,366 ounces of Au, 17,956,492 ounces of Ag, 6,254,900 pounds of Cu, 317,007,800 pounds of Pb, 640,224,100 pounds of Zn, and 711,400 tons of Mn ore. 1869 to 1904 production was not broken down. Reserves: 1958: Caselton type ore: 2,642,830 metric tons (includes production) 0.046% Au, 5.32% Ag, 4.81% Pb, 11.82% Zn; Pan American type ore: 149,629 metric tons, 0.028% Au, 1.64% Ag, 1.39% Pb, 2.66% Zn, 9.7% Mn; 1952: Caselton type ore: 674,300 metric tons (includes production) 0.013% Au, 0.65% Ag, 0.6% Pb, 9.5% Zn, 0.4% Cu; 1949: Caselton type ore: 197,921 metric tons (includes production) 0.035% Au, 3.21% Ag, 1.24% Pb, 9.7% Zn, 0.14% Cu; 12.32% Mn (oxidized ore); 31.5% Fe (oxidized ore).



Structure: E-W and N-S normal faulting before thrusting; N60 degree S faults mineralized; N-S, NW-trending post mineral. The Pioche Hills appear to be a window in a regional thrust of upper Cambrian rocks over lower Cambrian and Tertiary volcanics. Pioche Shale bed dropped by closely spaced parallel normal faults mineralization principally in Combined Metals bed of the Pioche Shale. Highland Peak overthrust steeply dipping fissures: N50-70E mineralized zone

Alteration: oxidation; hydrothermal

Commodity: Ore Materials: argentite, cerargyrite, cerussite, galena, pyrite, sphalerite, chalcopyrite, gold Gangue Materials: quartz, calcite, siderite, jarosite, limonite

Deposit: The main orebody at the Caselton, Raymond & Ely/Combined Metals Reduction #1 mines is the result of selected replacement of the Combined Metals Limestone bed where it intersects the steeply-dipping Greenwood Fissure, which is a fault of slight displacement, usually expressed as a thin gouge seam but which may be up to 5 feet thick. It trends N70E, and dips 65-70N, nearly paralleling the Raymond and Ely vein, which dips 75S. The ore has been offset by many cross-faults the main orebody is a tabular massive sulfide bed extending laterally into the limestone layer, thickest (30-40 feet) adjacent to the Greenwood Fissure, and tapering down away from it. Bedded ore occurs up to 200 feet on either side of the Greenwood Fissure. The ore of the upper bed preserves the nodular character of the limestone host. Ore consists of about 60% pyrite, 22% sphalerite, 8% galena, minor chalcopyrite and practically no gangue minerals. The lower bed ore is massive with an irregular bottom contact, as the underlying quartzite has been irregularly replaced by pyrite and sphalerite. The ore is unoxidized. The Raymond and Ely vein in the Prospect Mountain Quartzite strikes parallel to the Greenwood Fissure. The Greenwood ore occurs chiefly in Pioche Shale. The Black Ledge vein of quartz and sphalerite was also mined yielding 12-20% zinc and 5-21 ounces of silver per ton. The Raymond and Ely vein system splits eastward into two branches: the Meadow Valley vein and the Burke Vein. The largest and richest ore shoot in the vein occurred just below the Pioche Shale within about 400 feet of the Yuba Dike. The complex sulfide ore was of no value until selective flotation was invented. The ore bed was mined for more than 10,000 feet along an east west channel 100 to 1800 feet wide. Ore body terminates against the frontal fault. The hanging wall was unsuccessfully explored to a depth of 2500 feet. Most gold came from the Combined Metals Mine. On Treasure Hill, the workings explore a series of faults and shears and the north end of the Yuba dike, a principal contributor to the mineralization of the area. Much of the fault breccia shows milling texture with jarosite and iron-manganese oxides coating most exposed surfaces. The quartzite ranges from white to grey-rose colored with prominent banding. Pods of very fine-grained argentiferous minerals along with galena and other sulfides are disseminated throughout the breccia. Yellow oxides are also common on exposed surfaces. Abundant sericite is present. Locally the breccia zones are silicified and abundant gossan occurs where ore minerals have weathered out. Late opaline silica is deposited on fracture surfaces and iron sulfides have altered to specular hematite. Euhedral quartz crystals line cavities. Quartz vein material which fills fault fissures exhibits brecciation and is recemented with silica, and contains bands of finely disseminated grey sulfides. The Raymond and Ely, Meadow Valley, and Burke veins strike roughly east-west and dip 50 degrees south. Oxidized silver ore in the quartzite decreased in grade eastward and downward. The Meadow Valley vein was mined continuously for 2000 feet to a depth of 1,200 feet. Average ore thickness was 2-3 feet. Galena and sphalerite are increasingly abundant in the lower levels. Rich silver-lead ore was mined from the Yuba Dike. Three or more cross veins strike northeast at 45 degrees to the principal veins. The "quartzite fissures" are veins with filling of loose rubble of angular quartzite fragments to breccia cemented by lead carbonate, limonite, and jarosite. The quartzite fissures strie N15-20W.

Deposit type: Polymetallic replacement

Development: The initial mineral discovery in Pioche occurred in 1863 and mining production began in 1869. The original ore consisted of oxidized silver chlorides occurring in fissures in Cambrian quartzites. The Raymond and Ely vein system contained high-grade lead-silver ore that was mined in the 1870s At one time Pioche was one of largest silver districts in the United States. Total mineral production exceeded $130,000,000. The primary metal values were for gold, silver, lead, zinc and copper. Low-grade argentiferous manganese oxides were also found in the region. Major periods of production were: 1895-1901; 1912-1920; 1934-1953; and 1958-1959. Minimal activity has occurred from 1959 to the present time. Early milling occurred in Pioche, but a shortage of water forced the mills to be relocated to Bullionville (near Panaca) around 1871. In 1924 Combined Metals Reduction Company developed a selective flotation process to treat the massive lead-zinc sulfide ores. Combined Metals Reduction Company processed ore at a mill in Bauer, Utah from 1923-1941, until the Caselton Mill was built in 1941. Mountain Mines, Inc. acquired the Caselton Tailings after the bankruptcy of Combined Metals Reduction Company in 1976. Mountain Mines, Inc. claims to have produced precious metals from the tailings with a small chemical processing facility located in the vicinity of the tailings. Numerous mining companies have had operators or exploration activity at site, including: Meadow Valley Mining Company (1864-1876); Consolidated Mining Company (1880's); White Pine Minerals Company (?); Combined Metals Reduction Company (1924-present); Pioche Manganese Company (WWII); Comet Coalition Mining Company (1964-1978); St. Patrick Mining Company (1975); Bunker Hill Mining Company (1976-77); Kerr-McGee Chemical Company (1980); Mountain Mines, Inc. (1976-present). Homestake Mining Company, Prince Consolidated Mining Company and Anaconda Company also have been active in the area. Midway Gold Company has recently (2004) been exploring for a faulted offset of the high-grade silver-gold Salt Lake Pioche vein under post- mineral volcanic rock. The property consists of five patented and 36 unpatented claims lying south of the town of Pioche on a combination of private patented mining claims and BLM administered lands. Midway began a 3500 foot reverse circulation drill program on the Pioche Project in October 2004.

Geology: The Combined Metals Member of the Pioche Shale is the host rock for the replacement orebodies. It consists of 3 parts: (1) a lower 3 ft of massive limestone (2) a middle 3-ft thick calcareous sandstone (which in the orebody is unreplaced) and (3) an upper 30-ft layer of thin-bedded nodular limestones, usually only 2-3 inches thick and so nodular that they look like "beds of flattened potatoes". The nodules are coated with a thin black carbonaceous skin. The Pioche Shale belt trends NW between 2 faults.

Ore(s): Ore occurs in tabular replacement bodies, at the intersection of steep fissures and limestone beds in Pioche Shale.

Commodity List

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Mineral List

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75 valid minerals.

Rock Types Recorded

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