Graduate Thesis Or Dissertation
 

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0r967719n

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  • The Greenstone Mountain area, which includes the Utopia mining district, is located in the foothills of the Pioneer Range, Beaverhead County, Montana. Approximately 12, 600 feet of Paleozoic and Mesozoic sedimentary rocks and an undetermined thickness of Precambrian sediments and Late Cretaceous igneous rocks are exposed within the area of investigation. Most of the sedimentary rocks were deposited along the margin of the Cordilleran miogeosyncline. Precambrian Beltian sediments are the oldest exposed rocks in the map area. Pre-Mississippian Paleozoic rocks have not been differentiated in this study but probably represent the Cambrian and Devonian Systems. Other Paleozoic rock units include the Lodgepole and Mission Canyon Formations of Mississippian age, the Amsden Formation of Mississippian to Pennsylvanian age, the Quadrant Formation of Pennsylvanian age, and the Phosphoria Formation of Permian age. Mesozoic sediments include the Dinwoody and Woodside Formations of Triassic age and the Kootenai Formation and Colorado Group of Cretaceous age. The Jurassic System is not represented. During the Late Cretaceous Laramide orogeny the sedimentary rocks of the area were folded and faulted. The dominant structures produced during this period of deformation are northeast- to north-trending anticlines and synclines that are locally overturned to the east. Steep faults of small to moderate displacement disrupt the folds. Quartz monzonite intrusive rocks were emplaced following the Laramide orogeny and are probably genetically related to the Boulder Batholith. The intrusion gave rise to mineralization and thermal metamorphism of the surrounding country rocks. Quaternary glacial and fluvial deposits mantle parts of the area. At least three valley glaciers advanced into the northwestern corner of the area in Late Pleistocene time and left lateral and terminal moraines. Pleistocene terrace gravels are situated along Birch Creek and on lowlands in the west, and Recent alluvium is being deposited along existing streams.
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