Weathering of the meade peak phosphatic shale member, phosphoria formation: Observations based on uranium and its decay products
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Abstract
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.
Suggested Citation
Zielinski, R.A., Budahn, J.R., Grauch, R.I., Paces, J., Simmons, K.R., 2004, Weathering of the meade peak phosphatic shale member, phosphoria formation: Observations based on uranium and its decay products, chap. 9 of Handbook of exploration and environmental geochemistry, v. 8, p. 227-250, https://doi.org/10.1016/S1874-2734(04)80011-1.
| Publication type | Book chapter |
|---|---|
| Publication Subtype | Book Chapter |
| Title | Weathering of the meade peak phosphatic shale member, phosphoria formation: Observations based on uranium and its decay products |
| Chapter | 9 |
| DOI | 10.1016/S1874-2734(04)80011-1 |
| Volume | 8 |
| Year Published | 2004 |
| Language | English |
| Publisher | Elsevier |
| Contributing office(s) | Central Energy Resources Science Center, Central Mineral and Environmental Resources Science Center |
| Description | 24 p. |
| Larger Work Type | Book |
| Larger Work Subtype | Monograph |
| Larger Work Title | Handbook of exploration and environmental geochemistry |
| First page | 227 |
| Last page | 250 |