Little Belt Mountains Field Trip
The Little Belt Mountains are one of the foreland uplifts known as Laramide uplifts. The Little
Belt anticline is a major foreland fold draped over an upthrust basement block. This is an
excellent example of "thick-skinned" tectonics. In contrast to the geology seen along U.S. 89,
this field trip is a tour of 10 laccoliths--igneous intrusions into the large fold structure. The
Central Montana Alkalic Igneous Province characterized by the high potassium content of the
igneous rocks. Large diameter diatreme. Barker-Hughesville Mining District (lead-zinc-silver
ores). Acid-mine drainage and environmental impact. Tri-lobed pattern of laccoliths with
central feeder stock. "Cookie-cutter" fault around a bysmalith. Glacial cirques. Sapphire mine.
Primary topics: structure, igneous rocks, and mining districts
Route: Monarch-Hughesville-Blankenship Divide-Dry Wolf-Elk Saddle-Lake Elva-Yogo
Gulch-sapphire mine-Utica
Reference:
Baker, D.W., McBride, G. and Dahy, J. (1991) Field guide to the Little Belt Mountains. In
Guidebook of the Central Montana Alkalic Province - Geology, Ore Deposits and Origin.
Montana Bureau of Mines and Geology Special Publication 100, p. 145-162.
Guidebook
Guidebook to the Igneous Rocks and Mineral Deposits in the Little Belt Mountains. The 120
page geology guidebook describes the geologic features, ore deposits, and igneous rocks seen on
the field trip and the geologic setting in which they occur.
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Last Updated October 31, 2000 by David Baker