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. (C) 2017 Ben Wernette All Rights Reserved

Stillwater Complex: Overview Modified from Zientek et al., 2002 (C) 2017 Ben Wernette All Rights Reserved

Stillwater Complex: Overview Google Maps: maps.google.com (C) 2017 Ben Wernette All Rights Reserved

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 (C) 2017 Ben Wernette All Rights Reserved

Stillwater Complex: Overview (C) 2017 Ben Wernette All Rights Reserved Stillwater Mining, 2015 Annual Report

Layered Intrusions: A Recipe Economic Layered Intrusions: A Recipe Restricted range of mantle melting https://www.geol.umd.edu/~jmerck/geol212/lectures/13.html (C) 2017 Ben Wernette All Rights Reserved Calculations after Naldrett, 2013

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 (C) 2017 Ben Wernette All Rights Reserved

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 (C) 2017 Ben Wernette All Rights Reserved

Sulfur Isotopes and Crustal Assimilation (C) 2017 Ben Wernette All Rights Reserved

Sulfur Isotopes and Crustal Assimilation Farquhar et al., 2010 (C) 2017 Ben Wernette All Rights Reserved

Evidence of Crustal Assimilation? Modified from Zientek et al., 2002 (C) 2017 Ben Wernette All Rights Reserved Photomicrographs provided by Josh Smith, Indiana University

(C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved Modified from Ripley et al., 2017 (C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved Modified from Ripley et al., 2017 (C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved 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? (C) 2017 Ben Wernette All Rights Reserved

Stillwater …continued…. Polovina and Hudson, 2001 Godel and Barnes, 2008 (C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved Wernette et al., 2017 (submitted)

(C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved Wernette et al., 2017 (submitted) (C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved An Explanation… Preferential alteration of more permeable lithologies Rocks with anomalous δ34S average ≥ 90 % olivine 6(Mg1.50Fe0.50)SiO4 + 3CO2 + 3H2O + 2Ca2+ + 0.5O2 = 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 (C) 2017 Ben Wernette All Rights Reserved

(C) 2017 Ben Wernette All Rights Reserved Thanks! Wernette, 2016 (C) 2017 Ben Wernette All Rights Reserved