Guarda district (Belmonte, Torrinhas, Fonte do Seixo)
Guarda district, Portugal
Other hydrothermalSn (W)
- Type
- Granite-related cassiterite veins and greisens
Tin mines and pegmatites of the Guarda district (Gonçalo and Belmonte, Torrinhas, Fonte do Seixo, Quinta do Beja, Freixo de Numão). Cassiterite studied by Marahrens (2021) for Bronze Age tin provenance. Approximate position of the administrative district; mines are listed in the notes. Indicative coordinates.
δ124Sn in ‰ (per mil) Values of the same system
Standard : NIST SRM 3161a
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 0.33 ± 0.23 ‰ | 0 / 0.65 ‰ | 6 | primary cassiterite Mean and standard deviation recalculated from 6 samples, Appendix A3. Mean δ124/120Sn of 0.04 ‰ (Puratronic). Replicates of a sample averaged. Breakdown (δ124Sn): Mina da Fonte do Seixo 0.65; Quinta do Beja 0.48; Gonçalo, Belmonte 0.27; Mina da Vela, Gonçalo 0.19; Mina das Torrinhas 0.00; Freixo de Numão 0.38. | Marahrens (2021), Tin isotope analysis of tin ore deposits in Europe and Central Asia in … |
206Pb/204Pb isotope ratio, no unit Values of the same system
Standard : NIST SRM 981
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 21.4589 / 31.7754 | 2 | cassiterite concentrate (bulk lead) Range of 2 ores, "Lead isotopes - tin ores" sheet of OSM2 (placer). The source places the Fonte do Seixo mine at Castelo Branco; Baldio do Conde has a 208Pb/204Pb of 189.6, thorium-derived lead. Cassiterite lead is partly radiogenic and spreads along an isochron: no representative central value. Sites: Baldio do Conde (Santa Eulália mining field?), Da Fonte do Seixo Mine. | Williams et al. (2025), From Land's End to the Levant: did Britain's tin sources transfor… |
207Pb/204Pb isotope ratio, no unit Values of the same system
Standard : NIST SRM 981
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 15.8056 / 16.366 | 2 | cassiterite concentrate (bulk lead) Range of 2 ores, "Lead isotopes - tin ores" sheet of OSM2 (placer). The source places the Fonte do Seixo mine at Castelo Branco; Baldio do Conde has a 208Pb/204Pb of 189.6, thorium-derived lead. Cassiterite lead is partly radiogenic and spreads along an isochron: no representative central value. Sites: Baldio do Conde (Santa Eulália mining field?), Da Fonte do Seixo Mine. | Williams et al. (2025), From Land's End to the Levant: did Britain's tin sources transfor… |
208Pb/204Pb isotope ratio, no unit Values of the same system
Standard : NIST SRM 981
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 38.537 / 189.631 | 2 | cassiterite concentrate (bulk lead) Range of 2 ores, "Lead isotopes - tin ores" sheet of OSM2 (placer). The source places the Fonte do Seixo mine at Castelo Branco; Baldio do Conde has a 208Pb/204Pb of 189.6, thorium-derived lead. Cassiterite lead is partly radiogenic and spreads along an isochron: no representative central value. Sites: Baldio do Conde (Santa Eulália mining field?), Da Fonte do Seixo Mine. | Williams et al. (2025), From Land's End to the Levant: did Britain's tin sources transfor… |
Deposits of the same type
- Castelo Branco district (Fonte das Galoas, Gaia) Portugal
- Panasqueira Portugal
- Viseu district (tin fields) Portugal
- Torrecilla de los Ángeles Spain
- Aveiro district (Regoufe, Bustelo) Portugal
- Cáceres Province (unspecified origin) Spain
- Vila Real district (including Borralha) Portugal
- Porto district (Rebordosa, Friande) Portugal
Cite this page
IsoFind Atlas (2026). Guarda district (Belmonte, Torrinhas, Fonte do Seixo), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/district-de-guarda-belmonte-torrinhas-fonte-do-seixo/ (accessed 2026-10-13).
@misc{isofind2026guardadistrictbelmontetorrinh,
title = {Guarda district (Belmonte, Torrinhas, Fonte do Seixo), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/district-de-guarda-belmonte-torrinhas-fonte-do-seixo/},
note = {Accessed 2026-10-13}
}Updated : 2026-10-13