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U-Pb isochron age and Pb isotope systematics of the Golden Fleece vein; implications for the relationship of mineralization to the Lake City caldera, western San Juan Mountains, Colorado

Economic Geology
By: , , , , and 
https://doi.org/10.2113/gsecongeo.80.2.410

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Abstract

A U-Pb isochron age of 27.5 + or - 0.5 m.y. has been determined for the Golden Fleece vein, southwestern Colorado, which contains an assemblage of pitchblende and gold-silver tellurides unique within the Lake City area. Initial Pb isotope ratios of ore samples from the vein ( 206 Pb/ 204 Pb = 19.08-19.58; 207 Pb/ 204 Pb = 15.643-15.682; 208 Pb/ 204 Pb = 38.533-38.84) are among the most radiogenic values reported from the San Juan Mountains and suggest that a significant component of common Pb, and possibly other metals, was derived from upper crustal Precambrian rocks by deeply circulating hydrothermal fluids. The 27.5-m.y. age of the Golden Fleece vein is identical, within analytical uncertainty, to the age of the quartz latite lavas that it cuts. This clearly documents the relationship of the vein to the waning stages of activity associated with the Uncompahgre caldera (27-29 m.y.) rather than to early activity related to the 23.1-m.y.-old Lake City caldera. Other veins in the Lake City area have Pb isotope ratios and mineral assemblages that are distinctly different from the Golden Fleece, and most of these veins are thought to be genetically related to the younger Lake City caldera.

Publication type Article
Publication Subtype Journal Article
Title U-Pb isochron age and Pb isotope systematics of the Golden Fleece vein; implications for the relationship of mineralization to the Lake City caldera, western San Juan Mountains, Colorado
Series title Economic Geology
DOI 10.2113/gsecongeo.80.2.410
Volume 80
Issue 2
Year Published 1985
Language English
Publisher Society of Economic Geologists
Description 8 p.
First page 410
Last page 417
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