| Abstract: | Two types of uranium orebodies occur in continental sandstones of the Upper Jurassic Morrison formation: 1) ‘primary‘ tabular peneconcordant bodies rich in interstitial organic material (containing most of the U) and older than the overlying Cretaceous Dakota sandstone and 2) younger discordant ore-bodies associated with Tertiary faults, containing little organic material (coffinite is the U-carrier) and considered to be redistributed primary ore. U/Pb isotope ages of four of the younger ore-bodies from the Ambrosia Lake district are concordant at 3.3-12.5 m.y. U/Pb isotope ages of primary ores from the same district show pronounced normal discordance, explained by continuous loss of Pb and 238U daughters and, locally, by U-gain during Tertiary redistribution. The primary ores, without Tertiary U-gain, plot on the concordia diagram close to a calculated continuous diffusion curve for coupled loss of Pb and 238U daughters. The concordia intercept of this curve corresponds with an age of approx 130 m.y. Ore-bodies in the Smith Lake district have characteristics both of primary (co-extensive with organic material) and redistributed (discordant) types. They show less coherent U/Pb isotope systematics but give only pre-Tertiary apparent ages.-G.J.N. |
| Genre: | Article |
| ProdID: | 70014077 |
| Citation Author: | Ludwig, K. R.; Simmons, K. R.; Webster, J. D. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 337 |
| Citation Issue: | 2 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | Economic Geology |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 16 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | U-Pb isotope systematics and apparent ages of uranium ores, Ambrosia Lake and Smith Lake districts, Grants mineral belt, New Mexico.; 1984; Article; Journal; Economic Geology; Ludwig, K. R.; Simmons, K. R.; Webster, J. D. |
| Citation Start Page: | 322 |
| Citation Volume: | 79 |
| Citation Year: | 1984 |
| Type: | citation/reference |
| Text: | U-Pb isotope systematics and apparent ages of uranium ores, Ambrosia Lake and Smith Lake districts, Grants mineral belt, New Mexico.; 1984; Article; Journal; Economic Geology; Ludwig, K. R.; Simmons, K. R.; Webster, J. D. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Sun, 1 Jan 1984 00:00 -0600 |
| Publisher: | |
