The Mountain View Area of the Stillwater Complex as a Field Teaching Model:

I. S. McCallum, University of Washington

Intended Audience: Geology majors: I will assume that most students in this group who make the trip to the Stillwater Complex do so after a year of traditional geology classes, i.e., they will have been exposed to mineralogy, petrology, structural geology and stratigraphy, and that they will have knowledge of the basic sciences equivalent to a full year of mathematics, physics and chemistry.

Location:

Two sites at the Mountain View of the Stillwater Complex, Montana: (a) a section through the Ultramafic series in the vicinity of the old Mouat Chrome Mine and (b) a section through the Banded series exposed on the mine road 3/4 mile south of the junction with the West Fork USFS road.

Summary:

Context:

Two sections in the Mountain View of the Stillwater Complex are readily accessible for field-based teaching of petrologic and geochemical principles: (a) a section through the Ultramafic series in the vicinity of the old Mouat Chrome Mine and (b) a section through the Banded series exposed on the mine road ¾ mile south of the junction with the West Fork USFS road. Both sections provide ideal field settings to demonstrate a number of relatively simple concepts that we commonly discuss in abstract terms in the classroom. To this end, the Mountain View field site has many advantages: it is readily accessible to large numbers of students, the rocks are well exposed and unaltered, detailed maps are readily available, there is a very large petrologic and geochemical database, a number of seminal papers on this area have been published, the mineralogy is simple and the constituent minerals in all rock types are easily identified with a simple 10x hand lens. In addition, this area demonstrates the importance of the Stillwater Complex as a major economic resource.

Goals:

To some extent the learning objective will be different depending on the level of the student and the extent of background knowledge. The fundamental objective is to have the students realize that rocks are much more than collections of minerals and that the mineral assemblages and rock sequences conform to simple basic scientific principles. A major objective is to have students make semi-quantitative observations of the rocks with a view to understanding basic petrologic principles such as fractional crystallization, magma mixing, assimilation, compaction, and fluid migration. The exposed sequences examined by the students provide superb examples to which more advanced students can apply the principles of thermodynamics and phase equilibria to actual rocks. The Ultramafic sequence also allows the students to make an estimate of the total reserves of Cr ore associated with the main Cr seam in the complex.

Assessment and Evaluation:

The goals of the activity are met if students are engaged in the field trip and are able to come up with plausible, creative explanations for the geology of the Stillwater Complex based on field observations.

Materials and Handouts:

• The Mountain View Area of the Stillwater Complex as a Field Teaching Model - Activity description (Microsoft Word 53kB Nov19 03)

References:

• The Stillwater Complex: A Review of the Geology (Microsoft Word 1.4MB Nov19 03)
• Stratigraphic Column (Acrobat (PDF) 146kB Nov19 03)