| Basis for focus area |
Multi-part focus area composed of graphite mineral sites in MRDS that report graphite as the primary commodity and development status as historical producer surrounded by a 1 km buffer. In Robinson and others (2017), deposits in this focus area are listed as flake graphite. |
| Identified resources |
Historical production of graphite. |
| Production |
Eureka Plumbago mine: 500 tons graphite shipped prior to 1867 (Browne, 1869). |
| Status |
Past mining; no current mining. |
| Estimated resources |
Unknown. |
| Geologic maps |
Jennings and others (2010), scale 1:750,000. |
| Geophysical data |
Inadequate aeromagnetic and radiometric coverage. Numerous areas, only one of which has adequate aeromagnetic coverage. Aeromagnetic coverage generally of Rank 4. Fair gravity data coverage. Poor aeroradiometric coverage of Rank 5. |
| Favorable rocks and structures |
Metamorphic rocks in Horton and others (2017). |
| Deposits |
Eureka Plumbago (MRDS dep_id: 10111236), Morgan (MRDS dep_id: 10111233), Black Lady Nos 1 and 2 (MRDS dep_id: 10236245), Wedge (MRDS dep_id: 10099419). |
| Evidence from mineral occurrences |
MRDS; Robinson and others (2017). |
| Geochemical evidence |
Unknown. |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
Unknown. |
| Comments |
The Eureka Plumbago mine is located between Columbia and Sonora. Other graphite prospects have been noted 2.4 km (4 mi) north of the Eureka-Plumbago mine at the north end of Sonora near Gold Springs. Of these, some work was done on the Morgan Claim about 1.8 km (3 mi) west of Columbia. See Logan (1928). |
| Cover thickness and description |
On or near limestone of Paleozoic or Mesozoic age, undivided Paleozoic sedimentary rocks that includes schist (ls, Pz; Jennings and others, 1977), Carboniferous and Silurian-Ordovician rocks (C, CO; Jennings and others, 1977), and Precambrian igneous and metamorphic rocks (Pc; Jennings and others, 1977). |
| Authors |
David A. Ponce. |
| New data needs |
Geophysics, geologic mapping. |
| Geologic mapping and modeling needs |
Detailed geologic mapping. |
| Geophysical survey and modeling needs |
Aeromagnetic, gravity, and radiometric data. Graphite is unusually highly conductive and magnetotelluric surveys may be useful. |
| Digital elevation data needs |
Lidar variable over scattered focus area; some complete, some in progress, some inadequate. |
