Central City district (Gilpin County)
Colorado, Gilpin County, United States
UraniumAu, Ag, U (Pb, Zn, Cu)
- Type
- Polymetallic veins with uraninite and Fe-Zn-Cu sulphides (IAEA class 1.1, intrusive)
Uranium ore sample from the Queen's University collection analysed by Voinot et al. (2024) for U, Mo and Tl; ε205Tl and δ238U decrease together in metamorphic and unconformity deposits (U reduction and Tl redox change), whereas δ97Mo is strongly modified by late remobilisation. Uraninite with Fe-Zn-Cu sulphides (about 61-65 Ma), secondary metatorbernite in the Eureka Gulch area: both samples, very rich in S and Tl, have high ε205Tl (+3.7 to +4.6) that the authors relate to heavy Tl capture by sulphides. Indicative coordinates (Central City). Uvarova et al. (2014): δ238U (normalisation offset by about +0.60 ‰) and δ234U of samples from the Queen's University collection (Table 2).
δ238U in ‰ (per mil) Values of the same system
Standard : NBL CRM 112-A
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| −0.47 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Gilpin County) Single analysis; per-sample uncertainty not published; full-procedure duplicate at -0.46; sample M19032; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 65 Ma; 61.48 % U, 29.39 µg/g Tl, 319.98 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| −0.72 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Central City) Single analysis; per-sample uncertainty not published; sample M19033; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 61 Ma; 56.74 % U, 212.1 µg/g Tl, 40.06 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| −0.12 ± 0.1 ‰ | 1 | uraninite Single analysis; ± 0.10 ‰ (2 SD, reproducibility); sample M19033, Wood Lode, Central City, Colorado; bracketing-only δ238U at -0.12; 238U/235U of 137.82; about -0.72 ‰ after removing the 0.60 ‰ offset specific to this study; same sample as Voinot et al. (2024), published at -0.72 ‰. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… | |
| 0.13 ± 0.1 ‰ | 1 | uraninite Single analysis; ± 0.10 ‰ (2 SD, reproducibility); sample M19032, German mine, Gilpin County, Colorado; bracketing-only δ238U at +0.14; 238U/235U of 137.855; about -0.47 ‰ after removing the 0.60 ‰ offset specific to this study; same sample as Voinot et al. (2024), published at -0.47 ‰. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… | |
| 0.07 ± 0.1 ‰ | 1 | uraninite Single analysis; ± 0.10 ‰ (2 SD, reproducibility); sample M11336, Black Hawk, Gilpin County, Colorado; bracketing-only δ238U at +0.12; 238U/235U of 137.847; about -0.53 ‰ after removing the 0.60 ‰ offset specific to this study. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… |
δ234U in ‰ (per mil) Values of the same system
Standard : équilibre séculaire
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| −2 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Gilpin County) Single analysis; per-sample uncertainty not published; full-procedure duplicate at -4.0; sample M19032; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 65 Ma; 61.48 % U, 29.39 µg/g Tl, 319.98 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| 0 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Central City) Single analysis; per-sample uncertainty not published; sample M19033; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 61 Ma; 56.74 % U, 212.1 µg/g Tl, 40.06 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| 2 ‰ | 1 | uraninite Single analysis; per-sample uncertainty not published; sample M19033, Wood Lode, Central City, Colorado; Voinot et al. (2024) report 0 ‰ on the same sample. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… | |
| 0 ‰ | 1 | uraninite Single analysis; per-sample uncertainty not published; sample M19032, German mine, Gilpin County, Colorado; Voinot et al. (2024) report -2 ‰ on the same sample. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… | |
| −4 ‰ | 1 | uraninite Single analysis; per-sample uncertainty not published; sample M11336, Black Hawk, Gilpin County, Colorado. | Uvarova et al. (2014), Variations in the uranium isotopic compositions of uranium ores fr… |
ε205Tl in ε units (parts per 10,000) Values of the same system
Standard : NIST SRM 997
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 4.6 ± 0.8 ε | 1 | uraninite with Fe-Zn-Cu sulphides (Gilpin County) Single analysis; ± 0.8 (2 SD); full-procedure duplicate at +5.0 ± 0.9; sample M19032; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 65 Ma; 61.48 % U, 29.39 µg/g Tl, 319.98 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| 3.7 ± 0.5 ε | 1 | uraninite with Fe-Zn-Cu sulphides (Central City) Single analysis; ± 0.5 (2 SD); sample M19033; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 61 Ma; 56.74 % U, 212.1 µg/g Tl, 40.06 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … |
δ97Mo in ‰ (per mil) Values of the same system
Standard : NIST SRM 3134
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 2.3 ± 0.1 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Gilpin County) Single analysis; ± 0.1 (2 SD); full-procedure duplicate at +2.2 ± 0.1; sample M19032; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 65 Ma; 61.48 % U, 29.39 µg/g Tl, 319.98 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … | |
| 3.7 ± 0.1 ‰ | 1 | uraninite with Fe-Zn-Cu sulphides (Central City) Single analysis; ± 0.1 (2 SD); sample M19033; IAEA class 1.1. Anatectic: Pegmatite - alaskite (intrusive); average age used 61 Ma; 56.74 % U, 212.1 µg/g Tl, 40.06 µg/g Mo. | Voinot et al. (2024), Tl, Mo and U isotopes in U-ore deposits record Earth's fundamental … |
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Cite this page
IsoFind Atlas (2026). Central City district (Gilpin County), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/district-de-central-city-comte-de-gilpin/ (accessed 2026-10-16).
@misc{isofind2026centralcitydistrictgilpincoun,
title = {Central City district (Gilpin County), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/district-de-central-city-comte-de-gilpin/},
note = {Accessed 2026-10-16}
}Updated : 2026-10-16