Weathering of the meade peak phosphatic shale member, phosphoria formation: Observations based on uranium and its decay products
Variably weathered outcrop samples of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation have 5-10% of the contained uranium (U) in a form readily extractable by 0.1 M sodium bicarbonate. Fission track radiography of outcrop samples and other less-weathered channel and core samples indicate that this mobile fraction of U is likely hosted by organic matter, secondary iron oxides and clay minerals, trace uraninite, and very fine-grained apatite cement. During weathering, this extractable U fraction is especially susceptible to redistribution, which produces small but measurable departures (1-15%) from radioactive (secular) equilibrium in the 238U decay-series. The most weath- ered samples show the strongest isotopic evidence for redistribution of U during the last 350 ka, but sequestration of U by alteration products limits open-system losses of U at the whole-rock scale. In less-weathered samples, isotopic evidence for minor U loss (or gain) over longer time periods (1 Ma) is consistent with relatively non-aggressive attack of phosphatic rock during weathering. Comparative extractability of selenium (Se) suggests that a larger fraction of Se (19%) is readily available for mobilization during the earliest stages of weathering.
Citation Information
| Publication Year | 2004 |
|---|---|
| Title | Weathering of the meade peak phosphatic shale member, phosphoria formation: Observations based on uranium and its decay products |
| DOI | 10.1016/S1874-2734(04)80011-1 |
| Authors | Robert A. Zielinski, James R. Budahn, Richard I. Grauch, J. B. Paces, K. R. Simmons |
| Publication Type | Book Chapter |
| Publication Subtype | Book Chapter |
| Index ID | 70207566 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | Central Energy Resources Science Center; Central Mineral and Environmental Resources Science Center |
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Robert Zielinski
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Jim Budahn
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Richard I Grauch
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Robert Zielinski
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