1. Sulfur Isotope Studies of PGE Enrichment in the J-M Reef, Stillwater Complex, Montana, USA
B. Wernette, E.M. Ripley, C. Li, J. Smith, B. Underwood, A. Ayre
October 30th, 2017
Today I will be talking to you about multiple sulfur isotope studies of PGE enrichment in the J-M Reef of the Stillwater Complex, Montana, USA. Before we begin I’d just like to acknowledge that this work is the result of effort from a lot of contributing lab members listed here. Id also like to thank the Stillwater Mining Company, Indiana University, and the National Science Foundation for providing the funds that made this project possible.
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2. Stillwater Complex: Overview
Modified from Zientek et al., 2002
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3. Stillwater Complex: Overview
Google Maps: maps.google.com
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4. Stillwater Complex: Overview
2.709 Ga (U-Pb, Wall and Scoates, 2016) Layered Mafic Intrusion
Globally, one of two active PGE mines
Stillwater Complex, USA, 42 km wide
Bushvled Complex, RSA, 250 km wide
Subdivided into five lithologic series
Upper Banded Series
Middle Banded Series
Lower Banded Series
Ultramafic Series
Basal Series
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5. Stillwater Complex: Overview
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Stillwater Mining, 2015 Annual Report

6. Layered Intrusions: A Recipe
Economic
Layered Intrusions: A Recipe
Restricted range of mantle melting
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Calculations after Naldrett, 2013

7. Layered Intrusions: A Recipe
Economic
Layered Intrusions: A Recipe
Sulfur Saturation
Main PGE, Cu, Ni, Fe ligand
Fractional Crystallization
Assimilation
Le Vaillant et al., 2016
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8. Sulfur Isotopes and Crustal Assimilation
% Abundance
32S
95.02
33S
0.75
34S
4.21
36S
0.02
δ34S = ((δ34S / δ32S)sample – (δ34S / δ32S)std)/(δ34S / δ32S)std * 103
Seal, 2006
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9. Sulfur Isotopes and Crustal Assimilation
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10. Sulfur Isotopes and Crustal Assimilation
Farquhar et al., 2010
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11. Evidence of Crustal Assimilation?
Modified from Zientek et al., 2002
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Photomicrographs provided by Josh Smith, Indiana University

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Modified from Ripley et al., 2017
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Modified from Ripley et al., 2017
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Conclusions
Crustal Sulfur involvement in the Stillwater Complex?
Yes! Clear in the Basal Series
Locally in the Banded Series
Evidence: both d34S and D33S values
The J-M Reef shows no D33S anomaly which may be the product of mixing?
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16. Stillwater …continued….
Polovina and Hudson, 2001
Godel and Barnes, 2008
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Wernette et al., 2017 (submitted)

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Wernette et al., 2017 (submitted)
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An Explanation…
Preferential alteration of more permeable lithologies
Rocks with anomalous δ34S average ≥ 90 % olivine
6(Mg1.50Fe0.50)SiO4 + 3CO2 + 3H2O + 2Ca O2 = Ant + Talc + Mt + Dol + Calcite + 2Mg2+
Results in 40% increase of molar volume
Proportion of magmatic sulfur is far greater than secondary sulfur in the Reef
Fractionation factor
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Thanks!
Wernette, 2016
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