Guide to the Stillwater Complex Exposed in the West Fork Area
Route
Start point
Carter's Camp at the intersection of Montana Highways 419 and 420.
End point
Roads (and Trails)
Montana 419, U.S. Forest Service Road 846, West Fork Trail
Total distance
Geology
Summary
The parts of the Stillwater Complex exposed along the West Fork of the Stillwater River were the site of early chromite exploration, followed by Cu-Ni-sulfide exploration and, finally, platinum-group-element (PGE) exploration. The best exposures of Troctolite-Anorthosite zone I (TAZ I) anywhere in the complex and the discovery outcrops of the J-M Reef occur in cliffs on the west side of the river and are readily accessible. Parking for these outcrops is immediately beyond the bridge across the West Fork of the Stillwater River at the Absaroka-Beartooth Wilderness boundary. The lower chromite seams in the Peridotite-zone cumulates are well-exposed in the West Fork area but require nearly a full day to visit on foot. These exposures provide the opportunity to trace chromite seams and to study the changes in their internal stratigraphy and chemistry. The West Fork area illustrates quite well that not all members in Peridotite-zone cyclic units are continuous.
Key Lithologic Features
- olivine-plagioclase cumulates of Troctolite-Anorthosite Zone I
- J-M Reef (Pt-Pd deposit)
- West Fork adit rock dump
- A and B chromitites in the Peridotite zone of the Ultramafic Series
Structures
Landforms
Other Features
Reference
Mann, E.L., Lipin, B.R., Page, N.J., Foose, M.P., and Loferski, P.J., 1985, Guide to the Stillwater Complex exposed in the West Fork area,
in Czamanske, G.K., and Zientek, M.L., eds.,
The Stillwater Complex, Montana: Geology and Guide : Montana Bureau of Mines and Geology Special Publication 92, p. 231-246.
Availability
Order from the Montana Bureau of Mines and Geology. Search for
this publication's record at the MBMG for ordering information.
