East Boulder Plateau

The East Boulder Plateau is a chromium mine located in Sweet Grass county, Montana at an elevation of 9,449 feet.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

Satelite View

MRDS mine locations are often very general, and in some cases are incorrect. Some mine remains have been covered or removed by modern industrial activity or by development of things like housing. The satellite view offers a quick glimpse as to whether the MRDS location corresponds to visible mine remains.

Site Name

Primary: East Boulder Plateau
Secondary: Champion Group
Secondary: Chrome Mountain

Commodity

Primary: Chromium
Secondary: Platinum
Secondary: Palladium
Secondary: Rhodium

Location

State: Montana
County: Sweet Grass
District: In Stillwater Complex

Land Status

Land ownership: National Forest
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

Record Type: Site
Operation Category: Occurrence
Operation Type: Unknown
Discovery Year: 1940
Discovery Method: Unknown
Years of Production:
Organization:
Significant: N
Deposit Size: S

Physiography

General Physiographic Area: Rocky Mountain System
Physiographic Province: Middle Rocky Mountains
Physiographic Detail: Absaroka Mountains

Mineral Deposit Model

Model Name: Bushveld Cr

Orebody

Form: MASSIVE BAND, DISSEMINATED

Structure

Type: R
Description: The Stillwater Complex Is Exposed Along The Northern Margin Of The Beartooth Uplift, One Of Several Laramide Basement-Cored Ranges That Make Up The Rocky Mountain Foreland Of South-Central Montana (Foose And Others, 1961: Kulik And Schmidt, 1988)

Type: L
Description: Strike-Slip Fault And Cross-Faults

Alterations

Not available

Rocks

Name: Harzburgite
Role: Host
Age Type: Associated Rock Unit
Age Young: Neoarchean

Name: Harzburgite
Role: Host
Age Type: Host Rock
Age Young: Early Cretaceous

Analytical Data

Analytical Data: 7 TRENCH SAMPLES AT 0.9-2.5 FT: 1.65-34.7% CR2O3, AVERAGE 2.8 FT AT 16.8% CR2O3. MAX. OF 2 ANALYSES: 2.7 PPM PT, 5.76 PPM PD, 0.3 PPM RH. AVERAGE CHROMITITE: 74.2 PPB PT, 103.8 PPB PD, 63.4 PPB RH.

Materials

Ore: Chromite
Gangue: Olivine

Comments

Comment (Location): UNSURVEYED. LOCATED ON SLOPE AROUND CHROME MOUNTAIN. IN GALLATIN NATIONAL FOREST

Comment (Workings): A FEW SHALLOW PITS

Comment (Geology): AGE OF STILLWATER COMPLEX IS 2,705 +/- 4 MA BASED ON U-PB SYSTEMATICS ON ZIRCON-BADDELEYITE (PREMO AND OTHERS, 1990)

Comment (Deposit): MAIN LAYER IS G CHROMITITE. MASSIVE ORE AVERAGES 1 FT THICK; DISSEMINATED ORE AVERAGES 1 FT THICK. THERE ARE SEVERAL BANDS AND STRINGERS LESS THAN 1 FT THICK. BANDS ARE OFFSET BY FAULTS. CHROMITE IS INTERMITTENTLY EXPOSED IN OUTCROP

References

Reference (Deposit): PAGE, N.J, RILEY, L.B., AND HAFFTY, JOSEPH, 1969, PLATINUM, PALLADIUM, AND RHODIUM ANALYSES OF ULTRAMAFIC AND MAFIC ROCKS FROM THE STILLWATER COMPLEX, MONTANA: U.S. GEOLOGICAL SURVEY CIRCULAR 624, P. 10.

Reference (Deposit): PAGE, N.J, RILEY, L.B., AND HAFFTY, JOSEPH, 1972, VERTICAL AND LATERAL VARIATION OF PLATINUM, PALLADIUM, AND RHODIUM IN THE STILLWATER COMPLEX, MONTANA: ECONOMIC GEOLOGY, V. 67, P. 1356.

Reference (Deposit): ZIENTEK, M.L., 1993, MINERAL RESOURCE APPRAISAL FOR LOCATABLE MINERALS: THE STILLWATER COMPLEX, IN HAMMARSTROM, J.M., ZIENTEK, M.L., AND ELLIOTT, J.E., EDS., MINERAL RESOURCE ASSESSMENT OF THE ABSAROKA-BEARTOOTH STUDY AREA, CUSTER AND GALLATIN NATIONAL FORESTS, MONTANA: U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 93-207, P. F1-F83.

Reference (Deposit): PREMO, W.R., HELZ, R.T., ZIENTEK, M.L., AND LANGSTON, R.B., 1990, U-PB AND SM-ND AGES FOR THE STILLWATER COMPLEX AND ITS ASSOCIATED SILLS AND DIKES, BEARTOOTH MOUNTAINS, MONTANA: IDENTIFICATION OF A PARENT MAGMA?: GEOLOGY, V. 18, P. 1065-1068.

Reference (Deposit): 1955 GEOLMAP HOWLAND, BULL 1015-D, P. 110

Reference (Deposit): WIMMLER, N.L., 1948, INVESTIGATION OF CHROMITE DEPOSITS OF THE STILLWATER COMPLEX, STILLWATER AND SWEETGRASS COUNTIES, MONTANA: U.S. BUREAU OF MINES REPORT OF IVESTIGATIONS 4368, P. 40-41.

Reference (Deposit): HOWLAND, A.L., 1955, CHROMITE DEPOSITS IN THE CENTRAL PART OF THE STILLWATER COMPLEX, SWEET GRASS COUNTY, MONTANA: U.S. GEOLOGICAL SURVEY BULLETIN 1015-D, P. 110-112.

Reference (Deposit): HOWLAND, A.L., GARRELS, E.M., AND JONES, W.R., 1949, CHROMITE DEPOSITS OF BOULDER RIVER AREA, SWEETGRASS COUNTY, MONTANA: U.S. GEOLOGICAL SURVEY BULLETIN 948-C, P. 74.

Principal Gold Districts of Montana

In Montana, 54 mining districts have each have produced more than 10,000 ounces of gold. The largest producers are Butte, Helena, Marysville, and Virginia City, each having produced more than one million ounces. Twenty seven other districts are each credited with between 100,000 and one million ounces of gold production. Read more: Principal Gold Districts of Montana.