U-Pb ages of uraniferous opals and implications for the history of beryllium, fluorine, and uranium mineralization at Spor Mountain, Utah
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Abstract
The U-Pb isotope systematics of uraniferous opals from Spor Mountain, Utah, were investigated to determine the suitability of such material for geochronologic purposes, and to estimate the timing of uranium and associated beryllium and fluorine mineralization. The results indicate that uraniferous opals can approximate a closed system for uranium and uranium daughters, so that dating samples as young as ∼1 m.y. should be possible. In addition, the expected lack of initial230Th and231Pa in opals permits valuable information on the initial234U/238U to be obtained on suitable samples of ≲10 m.y. age. The oldest207Pb/235U apparent age observed, 20.8 ± 1m.y., was that of the opal-fluorite core of a nodule from a beryllium deposit in the Spor Mountain Formation. This age is indistinguishable from that of fission-track and K-Ar ages from the host rhyolite, and links the mineralization to the first episode of alkali rhyolite magmatism and related hydrothermal activity at Spor Mountain. Successively younger ages of 13 m.y. and 8–9 m.y. on concentric outer zones of the same nodule indicate that opal formed either episodically or continuously for over 10 m.y. Several samples of both fracture-filling and massive-nodule opal associated with beryllium deposits gave207Pb/235U apparent ages of 13–16 m.y., which may reflect a restricted period of mineralization or perhaps an averaging of 21−and<13−m.y. periods of opal growth. Several samples of fracture-filling opal in volcanic rocks as young as 6 m.y. gave207Pb/235U ages of 3.4–4.8 m.y. These ages may reflect hot-spring activity after the last major eruption of alkali rhyolite.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | U-Pb ages of uraniferous opals and implications for the history of beryllium, fluorine, and uranium mineralization at Spor Mountain, Utah |
Series title | Earth and Planetary Science Letters |
DOI | 10.1016/0012-821X(80)90008-4 |
Volume | 46 |
Issue | 2 |
Year Published | 1980 |
Language | English |
Publisher | Elsevier |
Description | 12 p. |
First page | 221 |
Last page | 232 |
Country | United States |
State | Utah |
Other Geospatial | Spor Mountain |
Google Analytic Metrics | Metrics page |