Dunka Road (Duluth Complex)
Minnesota, Duluth Complex (Partridge River troctolite), United States
Magmatic (Ni-Cu-PGE, carbonatites)Cu-Ni (EGP)
- Type
- Magmatic Ni-Cu sulphides (country-rock contamination)
Duluth Complex (Midcontinent Rift, about 1.1 Ga), Partridge River troctolite (Troctolitic Series: troctolite, peridotite, norite, olivine gabbro) intrusive into the Anorthositic Series; host rocks are graphitic, locally sulphidic pelitic metasediments of the Virginia Formation, above the Biwabik Iron Formation and the Giant's Range batholith. Mostly disseminated ore (2 to 3 % sulphides) with pyrrhotite, chalcopyrite, cubanite and minor pentlandite, Cu:Ni about 4-5:1, near the basal contact and Virginia Formation xenoliths. Sulphur derived mainly from Virginia Formation pyrite through in situ devolatilisation (FeS2 + 3 H2O + 5/2 C = FeS + 3/2 CO2 + CH4 + H2S), late sulphide saturation and no isotopic homogenisation; δ18O anomalies restricted to about 3 m from xenoliths (local partial melting) according to Ripley (1986). Coordinates not given.
δ34S in ‰ (per mil) Values of the same system
Standard : V-CDT
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 7.5 ‰ | 0.2 / 15.3 ‰ | sulphides of mineralised troctolites Range from the text, mean and mode close to +7.5 ‰ (Ripley, 1981); no trend, erratic values; pyrrhotite and pyrite of the underlying Virginia Formation in the same range. | Ripley (1986), Application of Stable Isotopic Studies to Problems of Magmatic Sulfide Ore… |
δ18O in ‰ (per mil) Values of the same system
Standard : V-SMOW
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 5.8 / 9.6 ‰ | troctolites and norites (whole rock) Range from the text; anomalous values (> 8 ‰) only near xenoliths, where orthopyroxene replaces olivine. | Ripley (1986), Application of Stable Isotopic Studies to Problems of Magmatic Sulfide Ore… | ||
| 8.8 / 11.1 ‰ | Virginia Formation hornfels (host rock and xenoliths) Range from the text. | Ripley (1986), Application of Stable Isotopic Studies to Problems of Magmatic Sulfide Ore… |
Deposits of the same type
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- Bushveld, UG2 chromitite South Africa
- Bushveld, Platreef South Africa
- Sudbury Canada
- Voisey's Bay Canada
- Rössing Namibia
Cite this page
IsoFind Atlas (2026). Dunka Road (Duluth Complex), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/dunka-road-complexe-de-duluth/ (accessed 2026-10-14).
@misc{isofind2026dunkaroadduluthcomplexisotope,
title = {Dunka Road (Duluth Complex), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/dunka-road-complexe-de-duluth/},
note = {Accessed 2026-10-14}
}Updated : 2026-10-14