PRE-ORE POTASSIUM METASOMATISM, CREEDE MINING DISTRICT, COLORADO.
By: P. M. Bethke, R. O. Rye, and P. B. Barton Jr.
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Abstract
Rhyolitic welded-tuff wallrocks of the epithermal base and precious metal veins of the Creede district were pervasively altered by the addition of more than two billion metric tons of potassium some 1. 5-2 million years before mineralization. Sodium, calcium and magnesium were strongly depleted, yielding a nearly binary quartz plus potassium feldspar assemblage containing as much as 13 weight percent K//2O. This large-scale metasomatism, originally noted by Steven and Rattle (1965), took place progressively by initial alteration of plagioclase phenocrysts to orthoclase or microcline followed by alteration of the groundmass feldspar to orthoclase and gradual change of the sanidine phenocrysts to more Or-rich compositions. Oxygen isotope and chemical studies show that the metasomatism resulted from the interaction of the tuffs with deeply circulating heated ground water and suggest that the potassium metasomatism of rhyolitic rocks is the facies equivalent of propylitization of volcanic rocks of more basic composition.
| Publication type | Conference Paper |
|---|---|
| Publication Subtype | Conference Paper |
| Title | PRE-ORE POTASSIUM METASOMATISM, CREEDE MINING DISTRICT, COLORADO. |
| ISBN | 0895204460 |
| Year Published | 1985 |
| Language | English |
| Publisher | Soc of Mining Engineers of AIME |
| Publisher location | New York, NY, USA |
| First page | 241 |
| Conference Title | Mineralogy - Applications to the Minerals Industry, Proceedings of the Paul F. Kerr Memorial Symposium. |
| Conference Location | New York, NY, USA |
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