Benbow Mine

The Benbow Mine is a chromium mine located in Stillwater county, Montana at an elevation of 8,451 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: Benbow Mine

Commodity

Primary: Chromium
Tertiary: Platinum
Tertiary: Palladium
Tertiary: Rhodium

Location

State: Montana
County: Stillwater
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

Type: Underground

Ownership

Owner Name: Anaconda Co.
Years: 1985 -

Production

Not available

Deposit

Record Type: Site
Operation Category: Past Producer
Operation Type: Unknown
Year First Production: 1941
Discovery Year: 1905
Discovery Method: Ore-Mineral In Place
Years of Production:
Organization:
Significant: N
Deposit Size: M

Physiography

General Physiographic Area: Rocky Mountain System
Physiographic Province: Middle Rocky Mountains
Physiographic Detail: East Flank Of Beartooth Mountains

Mineral Deposit Model

Model Name: Bushveld Cr

Orebody

Form: MASSIVE BANDS AND 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) ; Reg.Trends: Strike Of Ultramafic Zone: N60 Deg. W-N 80 Deg.W

Type: L
Description: Numerous Small Faults Striking Northward

Alterations

Alteration Type: L
Alteration Text: Some Serpentinization Of Harzburgite

Rocks

Name: Quartz Monzonite
Role: Associated
Age Type: Associated Rock
Age Young: Early Cretaceous

Name: Quartz Monzonite
Role: Associated
Age Type: Associated Rock Unit
Age Young: Neoarchean

Name: Quartz Monzonite
Role: Associated
Age Type: Host Rock
Age Young: Early Cretaceous

Analytical Data

Analytical Data: AVERAGE CR2O3 CONTENT: 24.5%. DIAMOND DRILL HOLE DATA (17 HOLES) YIELDED 21.6-36% CR203 OVER 4-9 FT WIDTHS. AVERAGE OF CHROMITITES: 89.9 PPB PT, 81.8 PPB PD, 52.1 PPB RH (MAX.: 330 PPB PT, 270 PPB PD, 190 PPB RH). ANALYSIS OF CLEANED SAMPLE: 24.05% FEO, 46.09% CR2O3, 23.81% AL2O3, 5.43% MGO, 1.02% SIO2. AVERAGE CR:FE=1.46 IN MASSIVE ORE

Materials

Ore: Chromite
Gangue: Olivine
Gangue: Serpentine

Comments

Comment (Location): UNSURVEYED. LOCATION GIVEN IS FOR SHAFT SYMBOL ON MAP. DEPOSIT EXTENDS ACROSS LITTLE ROCKY CREEK. LOCATED NEAR EAST END OF STILLWATER COMPLEX. IN CUSTER NATIONAL FOREST

Comment (Production): PRODUCTION DURING WWII FROM BENBOW+MOUAT-SAMPSON WAS 364,196 LT MINED, 237,771 LT MILLED, 91,164 LT CONCENTRATES

Comment (Geology): AGE OF STILLWATER COMPLEX IS 2,705 +/- 4 MA BASED ON U-PB SYSTEMATICS ON ZIRCON-BADDELEYITE (PREMO AND OTHERS, 1990) ; GEOL.DESC: AGE OF HOST ROCKS:PRE-CAMBRIAN; MAJOR.UNITS: STILLWATER COMPLEX.

Comment (Deposit): THE LARGEST POTENTIAL RESOURCES OF CHROMIUM AND PGE IN THE U.S. ARE IN THE STILLWATER COMPLEX. ; INFO.SRC : 1 PUB LIT

Comment (Deposit): RECORD W026522 HAS BEEN MERGED AND DELETED.

Comment (Workings): ADITS, MORE THAN 100 TRENCHES, 2,638 FT DIAMOND DRILL HOLES

Comment (Development): PROPERTY WAS WORKED DURING WWI BUT NO SHIPMENTS WERE MADE ; TOTAL$: 4 ; DEV$: 0.701 ; ECON.YEAR: 1943 ; ECON.COM: 1941-1943 FINANCED BY RECONSTRUCTION FINANCE CORP. ; MILL.CAP : 182 ST

Comment (Reserve-Resource): RESOURCE POTENTIAL IS FOR AREA BETWEEN BENBOW AND MOUAT-SAMPSON AT A DEPTH OF LESS THAN 2,000 FT. IDENTIFIED RESOURCES OF MOUAT-SAMPSON+BENBOW ARE 15 MILLION TONS AT 20-22% CR2O3

Comment (Deposit): THE AVERAGE THICKNESS OF THE DEPOSIT IS 4.9 FT AT 24.5% CR2O3. G CHROMITITE ZONE HAS BEEN MINED. OVERLAPPING LENSES WITH DISSEMINATED ORE BETWEEN. THERE ARE MANY SMALL RIGHT-LATERAL OFFSETS IN THE MAIN CHROMITITE BAND ALONG NORTH TRENDING FAULTS. DEPOSIT IS CUT BY SEVERAL LARGE DIABASE DIKES. MASSIVE+DISSEMINATED ORE IS 50 FT WIDE MAX.

Comment (Reserve-Resource): JACKSON ESTIMATED TOTAL CHROMITE RESERVES OF STILLWATER COMPLEX TO BE 2,520,000 LONG TONS CR2O3

References

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): PAGE, N.J, AND DOHRENWEND, J.C., 1973, MINERAL RESOURCE POTENTIAL OF THE STILLWATER COMPLEX AND ADJACENT ROCKS IN THE NORTHERN PART OF THE MOUNT WOOD AND MOUNT DOUGLAS QUADRANGLES, SOUTHWESTERN MONTANA: U.S. GEOLOGICAL SURVY CIRCULAR 684, 9 P.

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): 1939 DIREXPL USB

Reference (Reserve-Resource): PAGE AND OTHERS, 1972

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, NMONTANA: U.S. GEOLOGICAL SURVEY CIRCULAR 624, 12 P.

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. 918.

Reference (Deposit): WIMMLER, N.L., 1948, INVESTIGATION OF CHROMITE DEPOSITS OF THE STILLWATER COMPLEX, STILLWATER AND SWEETGRASS COUNTIES, MONT.: U.S. BUREAU OF MINES REPORT OF INVESTIGATIONS 4368, P. 16-19.

Reference (Deposit): PEOPLES, J.W., AND HOWLAND, A.L., 1940, CHROMITE DEPOSITS OF THE EASTERN PART OF THE STILLWATER COMPLEX, STILLWATER COUNTY, MONTANA: U.S. GEOLOGICAL SURVEY BULLETIN 922-N, P. 371-411.

Reference (Deposit): JACKSON, E.D., 1968, THE CHROMITE DEPOSITS OF THE STILLWATER COMPLEX, MONTANA, IN RIDGE, J.D., ED., ORE DEPOSITS OF THE UNITED STATES,1933/1967, GRATON-SALES VOLUME: NEW YORK, AMERICAN INSTITUTE OF MINING, METALLURGICAL, AND PETROLEUM ENGINEERS, P. 1495-1510.

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.