Freetown Layered Complex (Guma Water eluvial nuggets)
Freetown Peninsula, Sierra Leone
Magmatic (Ni-Cu-PGE, carbonatites)PGE (Pt)
- Type
- Eluvial platinum-group minerals associated with a layered intrusion
Tholeiitic layered intrusion of 193 ± 3 Ma (over 6000 m, five zones), linked to the opening of the Atlantic, emplaced in the Kasila Group, in the core of a former Archean craton. Platinum-group mineral nuggets in laterites and stream gravels; samples from an eluvial deposit on the Guma Water hill slope, at No. 2 village, between zones 3 and 4. Hattori et al. (1991): early erlichmanite nuggets (187Os/186Os about 1.08, mantle), Pt-Fe alloys formed later in a residual melt contaminated by crustal Os.
187Os/188Os isotope ratio, no unit Values of the same system
Standard : Rapport absolu, sans standard de référence
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 0.1309 ± 0.0006 | 0.13 / 0.1319 | 15 | erlichmanite nuggets (two zoned nuggets) Mean and standard deviation recalculated from 15 analyses, 0.1300 to 0.1319 (L-L2 A 0.1311; L-L2 B 0.1319; L-L2 C 0.1305; L-L2 D 0.1317; L-L2 E 0.1311; L-L2 F 0.1308; L-L2 G 0.1305; SL-L1 1 0.1317; SL-L1 2 0.1301; SL-L1 3 0.1300; SL-L1 4 0.1305; SL-L1 5 0.1300; SL-L1 6 0.1311; SL-L1 7 0.1311; SL-L1 8 0.1311). Published 187Os/186Os 1.080 to 1.096, homogeneous within each nugget despite Os-Ru zoning. The table names the first nugget "L-L2", the Fig. 3 caption "SL-L2". | Hattori et al. (1991), Osmium isotope ratios of PGM grains associated with the Freetown L… |
| 0.17 ± 0.0019 | 0.1669 / 0.1721 | 5 | laurite and cuprorhodsite inclusions in a Pt-Fe alloy (nugget SL-UP3) Mean and standard deviation recalculated from 5 analyses, 0.1669 to 0.1721 (SL-UP3 cuprorhodsite 1 0.1699; SL-UP3 laurite 1 0.1707; SL-UP3 laurite 2 0.1702; SL-UP3 cuprorhodsite A 0.1669; SL-UP3 cuprorhodsite B 0.1721). Published 187Os/186Os 1.387 to 1.430. | Hattori et al. (1991), Osmium isotope ratios of PGM grains associated with the Freetown L… |
| 0.1903 ± 0.0346 | 0.1503 / 0.2477 | 16 | osmium lamellae and rods (Os-Ir-Ru alloys) in Pt-Fe alloys Mean and standard deviation recalculated from 16 analyses, 0.1503 to 0.2477 (SL-UP7 A 0.1508; SL-UP7 B 0.1503; SL-UP7 C 0.1506; L1088/21-5 1 0.2166; L1088/21-8 1 0.2098; L1088/21-8 2 0.2001; L1088/21-8 3 0.2011; L1088/21-8 4 0.1976; L1088/21-9 1 0.2290; L1088/21-9 2 0.2291; L1088/21-9 3 0.2287; L1088/21-18 1 0.2477; L1088/21-21 1 0.1599; L1088/21-21 2 0.1605; L1088/21-21 3 0.1580; L1088/21-21 4 0.1543). Published 187Os/186Os 1.249 to 2.058, homogeneous within each nugget but highly variable between nuggets: variable crustal contamination of the residual melt according to the authors. | Hattori et al. (1991), Osmium isotope ratios of PGM grains associated with the Freetown L… |
Deposits of the same type
- Bayan Obo China
- Norilsk-Talnakh Russia
- Bushveld, Merensky Reef South Africa
- Bushveld, UG2 chromitite South Africa
- Bushveld, Platreef South Africa
- Sudbury Canada
- Voisey's Bay Canada
- Rössing Namibia
Cite this page
IsoFind Atlas (2026). Freetown Layered Complex (Guma Water eluvial nuggets), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/complexe-stratifie-de-freetown-pepites-eluviales-de-guma-water/ (accessed 2026-10-20).
@misc{isofind2026freetownlayeredcomplexgumawat,
title = {Freetown Layered Complex (Guma Water eluvial nuggets), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/complexe-stratifie-de-freetown-pepites-eluviales-de-guma-water/},
note = {Accessed 2026-10-20}
}Updated : 2026-10-20