Carrizo Sand aquifer (Medina, Frio and Atascosa counties)
Texas, south of San Antonio, United States
Groundwater
- Type
- Groundwater
Sandstone aquifer dipping south-east from its outcrop. Three regimes from Fig. 2: outcrop and near-outcrop (high U, activity ratio 0.5 to 1.2), transition zone (U down by at least an order of magnitude, low ratio in the west) then downdip regime (low U, ratio up to 9); the abrupt U drop along a band parallel to the outcrop betrays a redox barrier, and the downdip 234U excess, injected by alpha recoil into U-poor water, points to an updip uranium accumulation (the authors' type I). Eastern samples lack high ratios. No known deposit: accumulation only inferred (Cowart and Osmond, 1977). Indicative coordinates (centre of the map).
(234U/238U) isotope ratio, no unit Values of the same system
Standard : équilibre séculaire
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 0.82 ± 0.18 | 0.52 / 1.16 | 19 | outcrop-regime water (solid circles of Fig. 2) Mean and standard deviation recalculated from 19 analyses (sites 582, 609, 588, 469, 599, 580, 579, 425, 610, 563, 561, 414, 471, 475, 474, 551, 565, 473, 572), 0.52 to 1.16, median 0.81; U 0.2 to 3.53 µg/L; oxidising U-rich water, generally depleted in 234U (ratio below 1). | Cowart et Osmond (1977), Uranium isotopes in groundwater: Their use in prospecting for sa… |
| 1.14 ± 0.29 | 0.69 / 1.75 | 14 | transition-zone water (triangles of Fig. 2) Mean and standard deviation recalculated from 14 analyses (sites 598, 583, 581, 467, 423, 578, 558, 562, 478, 555, 552, 554, 560, 573), 0.69 to 1.75, median 1.08; U 0.003 to 0.2 µg/L; in the west, low ratios (0.69 to 1.12) below the redox barrier; in the east (552, 558, 478, 573), ratios of 1.29 to 1.75 with no sharp boundary with the downdip zone. | Cowart et Osmond (1977), Uranium isotopes in groundwater: Their use in prospecting for sa… |
| 4.9 ± 2.38 | 1.41 / 9.02 | 14 | downdip-regime water (open circles of Fig. 2) Mean and standard deviation recalculated from 14 analyses (sites 584, 585, 586, 468, 465, 587, 466, 424, 597, 472, 568, 413, 577, 567), 1.41 to 9.02, median 5.16; U 0.003 to 0.05 µg/L; highest ratios (4.4 to 9.0) in the west, including 567 and 577 given the flow direction; lower in the east (413, 472, 568: 1.41 to 1.77). | Cowart et Osmond (1977), Uranium isotopes in groundwater: Their use in prospecting for sa… |
Deposits of the same type
- Navajo Sandstone aquifer, Rocky Ridge (well PM2) United States
- Navajo Sandstone aquifer, Hotevilla (well SCH2) United States
- Navajo Sandstone aquifer, Peabody (wells NAV9 and NAV6) United States
- Navajo Sandstone aquifer, Shonto (wells PM4 and PM2) United States
- Tungsten Queen mine waters United States
- Vinto drinking water (DW1 to DW3) Bolivia
- Rosario River fan hot springs Argentina
- Archibarca alluvial fan groundwater Argentina
Cite this page
IsoFind Atlas (2026). Carrizo Sand aquifer (Medina, Frio and Atascosa counties), isotope signatures. https://www.isofind.tech/isotopes/en/sites/aquifere-des-sables-de-carrizo-comtes-de-medina-frio-et-atascosa/ (accessed 2026-10-16).
@misc{isofind2026carrizosandaquifermedinafrioa,
title = {Carrizo Sand aquifer (Medina, Frio and Atascosa counties), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/sites/aquifere-des-sables-de-carrizo-comtes-de-medina-frio-et-atascosa/},
note = {Accessed 2026-10-16}
}Updated : 2026-10-16