| Basis for focus area |
Includes the Mill City, Nightingale, and Potosi mining districts and others areas designated as high prospectivity for W skarns form Lederer and others (2021). |
| Identified resources |
Identified resources and historical production of tungsten. |
| Production |
Mill City district mines: Total recorded production for the productive year between 1925 and 1958 was 3,100,000 tons of ore, grade 0.57% WO3, 1,786,138 short ton units WO3 (McCandlish and Odell, 2013). Nightingale district mines: Total production was 108,000 metric tons, grade 0.61% WO3, 660 metric tons WO3 (Lederer and others, 2021). Nightingale mine (1918-1971): 40,044 short ton units WO3; M.G.L. mine (1917-1964): 32,200 short tons units WO3 (Stager and Tingley, 1988). Riley mine (1943-1957): 337,000 short ton units WO3; Riley Extension mine (1951-1957): 70,000 short ton units WO3; Pacific mine (1951-1956); 150,000 short ton units WO3; Granite Creek mine (1942-1957): 149,100 short ton units WO3; Valley View mine (1942-1956): 37,680 short ton units WO3; Markus mine (1955-1956): 100,000 short ton units WO3 (Stager and Tingley, 1988). |
| Status |
Past mining. |
| Estimated resources |
Estimated resources for the Mill City district: Measured 12,225 units WO3, Indicted 30,575 units WO3, Inferred 30,600 units WO3 (McCandlish and Odell, 2013). Riley Lease: Unclassified 10,000-20,000 standard tons with grade between 0.4 and 0.6% WO3 for calculated 65 metric tons W; Pacific deposit: 36,000 metric tons with grade of 0.5% WO3 for calculated contained 140 metric tons W; Granite Creek mine ore body: 91,000 metric tons with grade of 0.4% WO3 for calculated contained of 290 metric tons W (Karl and others, 2020). |
| Geologic maps |
Kerr (1934), scale 1:4,800; Kerr (1946), scale 1:8,800; Smith (1975), scale 1:4,800; Fanning (1982), scale 1:12,000; Smith and Guild (1942), scale 1:16,000; Hotz and Willden (1964), scale 1:62,500. |
| Geophysical data |
Partly adequate aeromagnetic coverage in some areas. Most of focus area has inadequate aeromagnetic and aeroradiometric coverage. |
| Favorable rocks and structures |
Mill City district: Triassic shale and limestone intruded by small bodies of granodiorite and hornblende andesite. Sedimentary rocks were metamorphosed to hornfels, slate, marble, and tactite. Scheelite ore deposits are in limestone beds metamorphosed to tactite (Klepper, 1943). Nightingale district: Metamorphosed limestone and slate intruded by a large granodiorite pluton and small dikes and bodies of quartz monzonite. Scheelite is in tactite (Smith and Guild, 1942). Potosi district: Tactites formed by metamorphism of limestone are the main host rock for scheelite. Tactites are along the contact of a granodiorite stock where it intruded limestone beds of the Preble Formation (Hotz and Willden, 1964). |
| Deposits |
Humboldt-Springer (MRDS dep_id: 10111438), Stank mine (MRDS dep_id: 10222344), Alpine mine (MRDS dep_id: 10045075), M.G.L. mine (MRDS dep_id: 10042417; USMIN Site_ID: NV00139), Nightingale mine (MRDS dep_id: 10042419; USMIN Site_ID: NV00141), Jaybird mine (MRDS dep_id: 10149744); Riley mine (MRDS dep_id: 10222483; USMIN Site_ID: NV00124), Riley Extension mine (MRDS dep_id: 10149720), Pacific mine (MRDS dep_id: 10045087; USMIN Site_ID: NV00131), Granite Creek mine (MRDS dep _id: 10045079; USMIN Site_ID: NV00132), Valley View mine (MRDS dep_id: 10045097; USMIN Site_ID: NV00133), Markus mine (MRDS dep_id: 10295153). |
| Evidence from mineral occurrences |
MRDS; USMIN. |
| Geochemical evidence |
Mill City: Ore minerals are scheelite and powellite; gangue minerals are epidote, garnet, quartz, pyrite, wollastonite, tremolite, calcite, and diopside. Nightingale district: Tactite contains abundant calcite and pyroxene, more or less scheelite, some tremolite, a little pyrrhotite, molybdenite, chalcopyrite, arsenopyrite, and pyrite, and trace titanite and apatite (Smith and Guild, 1942). Potosi district: Scheelite is the only tungsten mineral in tactite; associated minerals are quartz, epidote, garnet, and pyroxene, along with minor retrograde tremolite. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Comments |
Ore formation was controlled primarily by proximity of limestone beds to igneous intrusive bodies, and secondarily by faulting. In the Potosi district, minor amounts of scheelite were produced from alteration zones and bodies of quartz in granodiorite; but such occurrences, though interesting, are of little past or future importance as sources of W ore (Hotz and Willden, 1964). |
| Cover thickness and description |
Exposed at the surface. |
| Authors |
John L. Muntean. |
| New data needs |
Geologic mapping, geophysics. |
| Geologic mapping and modeling needs |
Updated geologic mapping. |
| Geophysical survey and modeling needs |
High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys. |
| Digital elevation data needs |
Lidar in progress (in part GeoDAWN). |
