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The AAPG/Datapages Combined Publications Database

Earth Science Bulletin (WGA)

Abstract


Earth Science Bulletin
Vol. 12 (1979), No. 2. (June), Pages 58-69

Precambrian Complex of Casper Mountain, Wyoming –A Preliminary Paper

Arthur E. Burford, Robert G. Corbett, Paul C. Franks, LaVerne M. Friberg, Richard C. Lorson, Frank A. Marsek, Richard F. Nanna, John C. Schumacher, Richard E. Wymer

Abstract

The Precambrian core of Casper Mountain illustrates a complex history of early sedimentation; periods of high-arid low-grade regional metamorphism; distinct ultramafic, mafic, and granitic intrusive episodes; and various stages and styles of structural deformation. The assemblage of igneous and metamorphic rocks includes, from generally oldest to youngest: Biotite-quartz-feldspar and quartz-feldspar gneisses of mixed parentages, amphibolites of varying ages and parentages, quartzite, intrusive granite and granodiorite, earlier pink and later white pegmatites, serpentinite and related metamorphosed ultramafic rocks, and late intrusive diabase.

Principal Precambrian events began with a long period of sediment accumulation and probable introduction of mafic dikes, sills, and possible flows. This culminated in a major period of amphibolite-grade regional metamorphism that formed the gneisses, amphibolites, and quartzite probably about 2700 or 2800 m.y. ago. A large mass of ultramafic magma subsequently intruded the highly deformed sequence followed, in turn, by minor porphyritic diabase injection. Between about 2600 and 2400 m.y. ago a granitic pluton was emplaced, accompanied and/or followed by at least two varieties of pegmatites and a late stage of low-grade metamorphism. Minor intrusion of diabase occurred from 2200 to 800 m.y. ago.

Mineralization includes the serpentinization (limited formation of chrysotile), limited chromite-bearing schist occurrence, feldspar and beryl-bearing pegmatites, shows of copper, and reputed occurrences of gold.


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