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PRE-ORE POTASSIUM METASOMATISM, CREEDE MINING DISTRICT, COLORADO.

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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.

Additional Publication Details

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