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Thomas Round Mountain

Producer in Mendocino county in California, United States with commodity Manganese
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Host and associated rocks
  9. Nearby scientific data
  10. Ore body information
  11. Economic information about the deposit and operations
  12. Links to other databases
  13. Bibliographic references
  14. General comments
  15. Reporter information

Geologic information

Identification information

Deposit ID 10031341
MRDS ID M010040
Record type Site
Current site name Thomas Round Mountain

Geographic coordinates

Geographic coordinates: -123.1722, 39.30126 (WGS84)
Relative position MINE IS IN THE N1/2 SEC. 22 (DIV. MINES V. 49, NO. 4, P. 364). TUNNEL IN NE1/4 MINE IN SE1/4. POTTER VALLEY QUAD. E. SIDE OF RIDGE BETWEEN POTTER VALLEY AND REDWOOD VALLEY.

Site location context

Political divisions (FIPS codes)

Mendocino(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Redwood Valley(quadrangle 1:24,000 scale)

Ukiah(quadrangle 1:100,000 scale)

Ukiah(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Russian(hydrologic unit)

Northern California Coastal(hydrologic accounting unit)

Klamath-Northern California Coastal(hydrologic subregion)

California(hydrologic region)

Geographic areas

Country State County
United States California Mendocino

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 017N 012W 22,27,34,35 California

Commodities

Commodity Importance
Manganese Critical Primary

Materials information

Materials Type of material
Rhodochrosite Ore

Host and associated rocks

  • Host or associated Host
    Rock type Sedimentary Rock > Chemical Sediment > Chert
    Rock unit name Franciscan Complex
    Rock description Franciscan Complex
    Stratigraphic age (youngest) Late Cretaceous
    Stratigraphic age (youngest) Late Cretaceous

Nearby scientific data

(1) -123.1722, 39.30126
ListMap

Economic information

Ore body information

  • Strike N 45 W
    Dip 65 NE TO VERTICAL

Comments on the geologic information

  • ORE HOSTED IN FRANCISCAN COMPLEX--L. TO L. ; GEOL.DESC: ORE BODY NEAR TOP OF WELL-BEDDED RED CHERT AND POORLY BEDDED WHITE CHERT. CHERT IS OVERLAIN AND UNDERLAIN BY SANDSTONE. CHERT HAS A GENERAL STRIKE OF N 45 W, AND DIPS 45 TO 80 N. E. AN E. - W. TRANSVERSE FAULT CUTS THE SEQUENCE. MAIN ORE BODY HAS SAME ATTITUDE AS CHERT. SILICEOUS ORE TOWARDS THE BOTTOM OF THE BODY CONTAINS BLACK MANGANESE OXIDES, WITH ABUNDANT CHERT IN CORES AND PATCHES. HIGH GRADE ORE IS NEOTOCITE CUT BY VEINLETS OF RHODOCHROSITE.

Economic information about the deposit and operations

Development status Producer
Commodity type Metallic
Deposit size Large
Significant No

Comments on the production information

  • MINE IS CREDITED WITH PRODUCTION OF 6,230 TONS OF ORE FROM 1914 TO 1918, AVERAGING 50% MANGANESE AND 7 TO 10% SILICA (1,500 TONS MAY HAVE BEEN FROM SOUTH THOMAS MINE). NO PRODUCTION SINCE 1918; MOST ADITS ARE CAVED. IDLE.

Comments on the workings information

  • OPEN CUTS, ADITS.

Reference information

Bibliographic references

  • Deposit

    CALIF. JOUR. MINES & GEOLOGY, V. 49, NO. 4, OCT. 1953, PP. 364, 391

  • Deposit

    D.O.M. BULL. 152, PP. 152-145

  • Deposit

    USBM R.I. 4849, P. 11-14.

General comments

Subject category Comment text
Deposit MOST OF BLACK OXIDE ORE HAS PROBABLY BEEN MINED BUT FAVORABLE AREAS REMAIN TO BE EXPLORED AND THERE SHOULD BE GOOD CHANCES FOR DEVELOPING LARGE RESERVES OF PRIMARY ORES, PROBABLY NEOTOCITE AND RHODOCHROSITE.

Reporter information

Type Date Name Affiliation Comment
Reporter 01-JUN-1973 Gere, W. U.S. Geological Survey
Updater 01-DEC-1977 Killman, K.; Albers, J. U.S. Geological Survey

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

Maps centered on this site

Authoritative California resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.