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Benbow Mine

Past Producer in Stillwater county in Montana, United States with commodities Chromium, Platinum, Palladium, Rhodium
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Geologic information

Identification information

Deposit ID 10042346
MRDS ID M060101
Record type Site
Current site name Benbow Mine

Geographic coordinates

Geographic coordinates: -109.8069, 45.36436 (WGS84)
Elevation 2576
Relative position 42 MI FROM COLUMBUS; 9 MI FROM DEAN; 34 MI SOUTHEAST OF BIG TIMBER
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Geographic areas

Country State County
United States Montana Stillwater

Public Land Survey System information

Meridian Township Range Section Fraction State
Montana Principal 005S;005S 015E;016E 25;28,29,30,31 Montana

Comments on the location information

  • 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

Commodities

Commodity Importance
Chromium Primary
Platinum Tertiary
Palladium Tertiary
Rhodium Tertiary

Materials information

Materials Type of material
Chromite Ore
Olivine Gangue
Serpentine Gangue

Alteration

  • (Local) Some Serpentinization Of Harzburgite

Analytical data

Result 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

Mineral occurrence model information

Model code 2
USGS model code 2a
Deposit model name Bushveld Cr

Host and associated rocks

  • Host or associated Associated
    Rock type Plutonic Rock > Granitoid > Quartz Monzonite
    Stratigraphic age (youngest) Early Cretaceous
    Stratigraphic age (youngest) Neoarchean
    Stratigraphic age (youngest) Early Cretaceous
  • Host or associated Associated
    Rock type Plutonic Rock > Mafic Intrusive Rock
    Rock unit name Stillwater Complex, Ultramafic Series
    Rock description Stillwater Complex, Ultramafic Series
  • Host or associated Host
    Rock type Plutonic Rock > Ultramafic Intrusive Rock > Peridotite > Harzburgite

Nearby scientific data

(1) -109.8069, 45.36436
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Geologic structures

Type Description Terms
Regional 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
Local Numerous Small Faults Striking Northward

Ore body information

  • General form MASSIVE BANDS AND DISSEMINATED
    Strike APPROX N65W
    Dip APPROX 80-VERT
    Thickness 2.44M
    Depth to top 0M
    Length 2743.2M

Controls for ore emplacement

  • Crystal Settling In Large Magma Chamber

Comments on the geologic information

  • 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.

Economic information

Economic information about the deposit and operations

Development status Past Producer
Commodity type Metallic
Deposit size Medium
Significant No
Discovery year <1905
Discovery method Ore-Mineral In Place
Year of first production 1941

Mining district

District name In Stillwater Complex

Land status

Ownership category National Forest

Ownership information

  • Type Owner-Operator
    Owner Anaconda Co.
    First year 1985

Comments on the production information

  • PRODUCTION DURING WWII FROM BENBOW+MOUAT-SAMPSON WAS 364,196 LT MINED, 237,771 LT MILLED, 91,164 LT CONCENTRATES

Comments on the reserve resource information

  • JACKSON ESTIMATED TOTAL CHROMITE RESERVES OF STILLWATER COMPLEX TO BE 2,520,000 LONG TONS CR2O3
  • 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

Workings at the site

  • Type of workings Underground
    Length 14260.68M
    Overall depth 182.88M

Comments on the workings information

  • ADITS, MORE THAN 100 TRENCHES, 2,638 FT DIAMOND DRILL HOLES

Comments on 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

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS M060101
USGS International Strategic Minerals Inventory ISMI CR056
U.S. Bureau of Mines Minerals Availability System MAS 0300950004

Bibliographic references

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • Deposit

    1939 DIREXPL USB

  • Reserve-Resource

    PAGE AND OTHERS, 1972

General comments

Subject category Comment text
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.
Deposit THE LARGEST POTENTIAL RESOURCES OF CHROMIUM AND PGE IN THE U.S. ARE IN THE STILLWATER COMPLEX. ; INFO.SRC : 1 PUB LIT
Deposit RECORD W026522 HAS BEEN MERGED AND DELETED.

Reporter information

Type Date Name Affiliation Comment
Reporter 01-JAN-1973 Dohrenwend, John C. U.S. Geological Survey
Updater 01-JUN-1977 Berg, Richard B. (Krohn, D. H.) U.S. Geological Survey
Updater 01-AUG-1991 Peterson, Jocelyn A. U.S. Geological Survey