Stillwater Complex (J-M Reef)
Montana (southwest, Beartooth Mountains), United States
Magmatic (Ni-Cu-PGE, carbonatites)PGE (Pt, Pd) - Cr
- Type
- PGE in a layered mafic-ultramafic intrusion (2.7 Ga)
The largest platinum-group element deposit in the United States, mined by Sibanye-Stillwater. The J-M Reef and the Picket Pin deposit carry Pt-Pd mineralisation in an Archaean layered intrusion (2.7 Ga). The J-M Reef is the stratigraphic equivalent of the Merensky Reef, but palladium dominates (Pd above Pt, the reverse of the Bushveld).
δ34S in ‰ (per mil) Values of the same system
Standard : V-CDT
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| 0.4 ± 1.7 ‰ | −3.8 / 7.8 ‰ | 233 | bulk samples (metasediments, sills, basal sulfides and J-M Reef) Mean 0.4 ‰, standard deviation 1.7 ‰. Three groups are statistically distinct: the host metagreywackes and metashales (mean 2.8 ‰); BIF, associated sills and basal sulfides of the complex (mean -0.7 ‰); disseminated sulfides above the basal accumulations, including the J-M Reef (mean 1.2 ‰). These groups make it possible to model crustal contamination of the complex. | Zientek et al. (USGS), Sulfur isotope studies of the Stillwater Complex and associated ro… (2000) |
| −0.4 ‰ | 1 | J-M Reef sulfides (sample ST9) Single analysis. | Malitch et al. (2014), Insights into ore genesis of Ni-Cu-PGE sulfide deposits of the Nor… |
δ65Cu in ‰ (per mil) Values of the same system
Standard : NIST SRM 976
| Value | Range | n | Mineral or matrix | Source |
|---|---|---|---|---|
| −0.1 ‰ | 1 | J-M Reef sulfides (sample ST9) Single analysis. | Malitch et al. (2014), Insights into ore genesis of Ni-Cu-PGE sulfide deposits of the Nor… |
Deposits of the same type
- Sudbury Canada
- Hart deposit (Abitibi) Canada
- Voisey's Bay Canada
- Rössing Namibia
- Pechenga Russia
- Great Dyke (Main Sulfide Zone) Zimbabwe
- Bushveld, Merensky Reef South Africa
- Bushveld, UG2 chromitite South Africa
Cite this page
IsoFind Atlas (2026). Stillwater Complex (J-M Reef), isotope signatures. https://www.isofind.tech/isotopes/en/deposits/complexe-de-stillwater-j-m-reef/ (accessed 2026-10-06).
@misc{isofind2026stillwatercomplexjmreefisotop,
title = {Stillwater Complex (J-M Reef), isotope signatures},
author = {{IsoFind Atlas}},
year = {2026},
url = {https://www.isofind.tech/isotopes/en/deposits/complexe-de-stillwater-j-m-reef/},
note = {Accessed 2026-10-06}
}Updated : 2026-10-06