West Fork East Adit

Occurrence in Sweet Grass county in Montana, United States with commodities Platinum, Palladium, Rhodium, Gold, Copper, Nickel

Geologic information

Identification information

Deposit ID 10048513
MRDS ID MP00102
Record type Site
Current site name West Fork East Adit
Alternate or previous names J-M Reef

Geographic coordinates

Geographic coordinates: -109.96885, 45.39881 (WGS84)
Elevation 2027
Location accuracy 100(meters)
Relative position ABOUT 3.4 MI WEST-NORTHWEST OF MOUNTAIN VIEW LAKE, Acc West Fork Adit
(click for info)

Geographic areas

Country State County
United States Montana Sweet Grass

Comments on the location information

  • UNSURVEYED. IN CUSTER NATIONAL FOREST. ADIT SHOWN ON SEGERSTROM AND CARLSON

Commodities

Commodity Importance
Platinum Primary
Palladium Primary
Rhodium Primary
Gold Secondary
Copper Tertiary
Nickel Tertiary

Materials information

Materials Type of material
Chalcopyrite Ore
Pentlandite Ore
Pyrite Ore
Pyrrhotite Ore
Apatite Gangue
Chlorite Gangue
Hornblende Gangue
Magnetite Gangue
Olivine Gangue
Phlogopite Gangue
Plagioclase Gangue
Pyroxene Gangue
Serpentine Gangue
Talc Gangue
Tremolite Gangue

Analytical data

Result AVERAGE GRADE OF 14.7 PPM PT+PD, 0.15% CU+NI ACROSS 1.9 M OVER A STRIKE LENGTH OF 657 M. PT:PD=3.5

Mineral occurrence model information

Model code 4
USGS model code 2b
Deposit model name Merensky Reef PGE

Host and associated rocks

  • Host or associated Host
    Rock type Plutonic Rock > Mafic Intrusive Rock > Gabbro > Norite
    Stratigraphic age (youngest) Neoarchean
    Stratigraphic age (youngest) Early Cretaceous
  • Host or associated Host
    Rock type Plutonic Rock > Mafic Intrusive Rock > Gabbro > Troctolite
  • Host or associated Host
    Rock type Plutonic Rock > Mafic Intrusive Rock > Anorthosite
  • Host or associated Host
    Rock type Plutonic Rock > Ultramafic Intrusive Rock > Peridotite > Harzburgite

Nearby scientific data

(1) -109.96885, 45.39881

Geologic structures

Type of structure Regional
Structure 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)

Ore body information

  • General form STRATIFORM, DISSEMINATED

Controls for ore emplacement

  • Magma Mixing

Comments on the geologic information

  • J-M REEF IS 1-3 M THICK AND CAN BE TRACED FOR 40 KM. AGE OF STILLWATER COMPLEX IS 2,705 +/- 4 MA BASED ON U-PB SYSTEMATICS ON ZIRCON-BADDELEYITE (PREMO AND OTHERS, 1990)

Economic information

Economic information about the deposit and operations

Development status Occurrence
Commodity type Metallic
Deposit size Small
Significant No
Discovery year 1967
Discoverer Johns-Manville

Mining district

District name In Stillwater Complex

Land status

Ownership category National Forest

Ownership information

  • Type Operator
    Owner Johns-Manville Products Corp.
    First year 1977

Comments on the workings information

  • ADIT

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Mineral Resources Data System MRDS MP00102

Bibliographic references

  • Analytical Data

    CONN, 1979

  • Deposit

    SEGERSTROM, KENNETH, AND CARLSON, R.R., 1982, GEOLOGIC MAP OF THE BANDED UPPER ZONE OF THE STILLWATER COMPLEX AND ADJACENT ROCKS, STILLWATER, SWEET GRASS, AND PARK COUNTIES, MONTANA: U.S. GEOLOGICAL SURVEY MISCELLANEOUS GEOLOGIC INVESTIGATIONS MAP I-1383, SCALE 1:24,000.

  • 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

    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

    CONN, H.K., 1979, THE JOHNS-MANVILLE PLATINUM-PALLADIUM PROSPECT, STILLWATER COMPLEX, MONTANA, U.S.A.: CANADIAN MINERALOGIST, V. 17, P. 463-468.

General comments

Subject category Comment text
Deposit THE J-M REEF IS 400-450 M ABOVE THE BASE OF THE BANDED SERIES IN BASAL PART OF ANORTHOSITE I SUBZONE OF TROCTOLITE-ANORTHOSITE ZONE I. THIS COINCIDES WITH THE REAPPEARANCE OF OLIVINE IN THE CRYSTALLIZATION SEQUENCE.

Reporter information

Type Date Name Affiliation Comment
Reporter 01-OCT-91 Peterson, Jocelyn A. U.S. Geological Survey