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  7. Deposit #USGS10042346

Benbow Chromium Mine

Nye, Montana

45.3643°N 109.8069°W

Mine Overview

The Benbow Chromium Mine is near Nye, Montana. Historically the site has been associated with the Stillwater Mining District which is now part of the Custer National Forest. The site was first discovered before 1905. The Benbow Chromium Mine was closed at the time of data entry with no known plans to re-open. Production size when active was considered to be small. Mine operations consist of underground workings. There is one known shaft. Subsurface depth reaches a maximum of 183 meters (600 feet) and extends 14,261 meters (46,787 feet) in length. The ore mined is composed of chromite with waste material consisting primarily of olivine and serpentine. The ore body is massive and disseminated in form reaching 2,743 meters (9,000 feet) long and 2 meters (8 feet) thick. Associated rock in this area is quartz monzonite from the Neoarchean era (2.80 to 2.50 billion years ago) to the Lower Cretaceous epoch (145.00 to 100.50 million years ago). The Middle Rocky Mountains physiographic province of the Rocky Mountain System characterize the geomorphology of the surrounding area.

Site identification and general characteristics. Learn about USGS mines.

  • Chromium Primary Commodity
  • Palladium, Platinum, and Rhodium Secondary Commodity
  • Site Record Type?
  • Mine Development Status?
  • Before 1905 Year Discovered?
  • Ore Mineral In Place Discovery Method?
  • 1941 First Year Of Production?
  • Small Production Size?
  • Metallic Site Commodity Type?
  • Medium Mine Size?

Mine Names

  1. Name? Status?
  2. Benbow Mine Current

Owner Name and Address

Anaconda Company

Type
Owner-Operator

Commodities

Additional textual information about a site or mine.

  1. Commodity Type Importance
  2. Chromium Metallic Primary
  3. Palladium Metallic Tertiary
  4. Platinum Metallic Tertiary
  5. Rhodium Metallic Tertiary

Deposit

THE AVERAGE THICKNESS OF THE DEPOSIT IS 4. 9 FEET 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 FEET WIDE MAX.

THE LARGEST POTENTIAL RESOURCES OF CHROMIUM AND PGE IN THE U. S. ARE IN THE STILLWATER COMPLEX.; INFORMATION SOURCE: 1 PUB LIT.

RECORD W026522 HAS BEEN MERGED AND DELETED.

Location Info

  1. Continent Country State County
  2. North America The United States Montana Stillwater

Notes

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.

Meridian / Township / Range Description

  1. Meridian? Township? Section? Aliquot?
  2. Montana Principle Meridian T.5S R.16E Sec. 30 SW
  3. Montana Principle Meridian T.5S R.16E Sec. 25 -
  4. Montana Principle Meridian T.5S R.16E Sec. 28 -
  5. Montana Principle Meridian T.5S R.16E Sec. 29 -
  6. Montana Principle Meridian T.5S R.16E Sec. 31 -

Land Status

Land status information.

  1. Land Status? Admin Area?
  2. National Forest -

Mining Districts

Formal or informal mining district names.

  1. District
  2. Stillwater Mining District

Development

PROPERTY WAS WORKED DURING WWI BUT NO SHIPMENTS WERE MADE; TOTAL$: 4; DEV$: 0. 701; ECON. YEAR: 1943; 1941-1943 FINANCED BY RECONSTRUCTION FINANCE CORP.; MILL. CAP : 182 ST.

Workings

Workings at the site.

Underground Workings #1

  • Type: Underground
  • Sub Surface Length: 14260.68 Meters
  • Sub Surface Depth: 182.88 Meters

Workings

ADITS, MORE THAN 100 TRENCHES, 2, 638 FEET DIAMOND DRILL HOLES.

Concentration Process

Processes that concentrated or enriched the mineralization of the mine.

  1. Concentration Process
  2. Magmatic Segregation, Crystal Settling

Geology

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

Materials

Minerals or other materials present in the mine.

  1. Role? Material?
  2. Gangue/Waste Olivine
  3. Gangue/Waste Serpentine
  4. Ore Chromite

Orebody

Characteristics of the ore body.

  • Length:
  • Thickness: 2.44 meters (8.01 feet)
  • Strike: approx n65 west
  • Dip: approx 80 - vert

Rocks

Geological materials at the site.

  1. Class? 1st Order Name? 2nd Order Name? 3rd Order Name? 4th Order Name? Most Specific Name? Begin Time End Time Description?
  2. Associated Rock Plutonic Rock Granitoid Quartz Monzonite - Quartz Monzonite Neoarchean Lower Cretaceous -
  3. Associated Rock Stillwater Complex, Ultramafic Series Plutonic Rock Mafic Intrusive Rock - Mafic Intrusive Rock - - -
  4. Host Rock Plutonic Rock Ultramafic Intrusive Rock Peridotite - Harzburgite - - -
  5. Mineralization - - - - - Neoarchean Neoarchean -

Structure

Geologic structural features affecting or characterizing the site or mine.

  1. Scale Description
  2. Local Numerous Small Faults Striking Northward
  3. Regional Reg-Trends: Strike Of Ultramafic Zone: N60 Degree West-North 80 Deg-W; 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)

Tectonic

Tectonic setting in which the site or deposit is situated.

  1. Setting?
  2. Tectonic Setting At Time Of Emplacement Of The Stillwater Complex Is Unknown- The Complex Was Emplaced Shortly After A Major Regional, Subduction-Related Magmatic Event That Culminated In Emplacement Of The 2-73-2-79 Ga Granitoid Suite In The Batholith Exposed In The Beartooth Uplift (wooden And Others, 1991)- However, There Is No Evidence That The Magmatism That Formed The Stillwater Complex Is Related To Convergent Margin Tectonics And Magmatism

Physiography

Physiographic area where the resource is found.

  1. Division Province? Section
  2. Rocky Mountain System Middle Rocky Mountains -

Alteration

Mineralogical and chemical alteration at or near the site, which may help to indicate the geographic extent of the geological processes producing the mine.

  1. Type? Alterations
  2. Local Some Serpentinization Of Harzburgite

Analytical Data

Results of chemical or mineralogical analysis on materials at or near the site

  1. Line? Analysis Data?
  2. 1 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

Model

Mineral deposit model of the site.

  1. Name? USGS Model Code? BC Model Code? Mark 3 model code?
  2. BUSHVELD CHROMIUM 2A - -

Ore Control

Controls on emplacement of ore such as faults or other structural features.

  1. Text?
  2. Crystal Settling In Large Magma Chamber

Reserve-resource

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 FEET IDENTIFIED RESOURCES OF MOUAT-SAMPSON+BENBOW ARE 15 MILLION TONS AT 20-22% CR2O3.

Nearby Deposits

Other deposits in the same region.

  1. Benbow Chromium Mine

    • Chromium commodity Site type Mine status
    • Stillwater, Montana
    • Underground
    • 0.04 miles
    Read More

  2. Benbow Nickel-Copper Nickel Prospect

    • Nickel commodity Site type Prospect status
    • Stillwater, Montana
    • Surface And Underground
    • 0.45 miles
    Read More

  3. Benbow Nickel-Copper Nickel Occurrence

    • Copper commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.46 miles
    Read More

  4. Little Rocky Creek Nickel-Copper Copper Occurrence

    • Copper commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.50 miles
    Read More

  5. Benbow Cr-Pt Chromium Occurrence

    • Chromium commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.51 miles
    Read More

  6. Nye Basin Cr-Pt Platinum Occurrence

    • Chromium commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.86 miles
    Read More

  7. Nye Basin Big Seven Prospect

    • Chromium commodity Site type Prospect status
    • Stillwater, Montana
    • 0.86 miles
    Read More

  8. Blitz Platinum Occurrence

    • Palladium commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.87 miles
    Read More

  9. Chrome Lake Cr-Pt Chromium Occurrence

    • Chromium commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.97 miles
    Read More

  10. Chrome Lake Nickel-Copper Copper Occurrence

    • Copper commodity Site type Occurrence status
    • Stillwater, Montana
    • 0.99 miles
    Read More

Nearby Places

Nearby Mining Districts

Nearby Lands

Footnotes

* Mine bounds on map indicate the general area that a mine occupies. For an detailed map, refer to the overseeing BLM field office.

** The mine central point is based on an average of the mine's bounding box(es) and does not necessarily fall on the claim itself.

1 World-class significance is determined by total endowment of the contained commodity. This includes all past production and remaining reserves. Each commodity is considered separately and commodities cannot be combined to arrive at a significant size. The tonnage thresholds are from the mine model grade-tonnage studies. As of June 2008, many entries were classified as significant under less strict rules.

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