Crystal LaFlamme

Anomalous sulfur isotopes trace volatile pathways in magmatic arcs

The cycle of sulfur, an important volatile in Earth9s crust, is the driver of many significant processes such as biological evolution, climate change, and the formation of ore deposits. This study investigates the ancient cycle of volatiles by tracing the indelible signal of anomalous sulfur isotopes, expressed as Δ 33 S ≠ 0, to illuminate the pathway of sulfur recycling through magmatic arcs. We selected the ca. 2.0 Ga Glenburgh gold deposit in the Glenburgh magmatic arc of Western Australia as a natural laboratory for this study. High-precision multiple sulfur isotope analyses of samples from the Glenburgh gold deposit and surrounding granitoid rocks yield the largest known sulfur isotope anomalies (Δ 33 S up to +0.82‰) in rocks <2.33 Ga globally. These data indicate that sulfur, and possibly gold, originated from multiple geochemical reservoirs in sedimentary rocks subducted beneath the magmatic arc, one of which is >2.33 Ga. Multiple sulfur isotope data are able to clarify a process that is cryptic to most other currently available data sets, showing that the cycling of volatiles and metals in arc settings occurs on very large scales, from the atmosphere-hydrosphere through to the lithosphere during crustal generation.

Atmospheric sulfur in the orogenic gold deposits of the Archean Yilgarn Craton, Australia

The origin of sulfur and gold in Archean orogenic gold systems should provide significant insights into the dynamics of fluid movement in the crust of the early Earth, but is poorly constrained and highly debated. Our natural laboratory to address this knowledge gap is the metal-endowed Yilgarn Craton (Western Australia), where we measured the multiple sulfur isotope signatures of representative sulfide-bearing auriferous samples from 24 Archean orogenic gold deposits varying in size and geological setting. Utilizing chemically conservative mass-independent fractionated sulfur (MIF-S) isotope signatures, we fingerprinted a major source of sulfur in these deposits. Contrary to previous studies, our data show that they display MIF-S isotope anomalies, with Δ 33 S values ranging from –1.18‰ to +2.04‰; most of the studied deposits show a sulfur signature that is consistent with a crustally derived source. Unlike smaller deposits, which may form with sulfur derived from a single sedimentary sulfur source, therefore providing a coherent Archean atmospheric signal in their Δ 33 S-Δ 36 S slope (~0.9–1.5), the formation of giant deposits may require sourcing from a wider range of sulfur reservoirs and using different processes, as reflected in their apparently random Δ 33 S-Δ 36 S slopes.

Atmospheric sulfur is recycled to the crystalline continental crust during supercontinent formation

The sulfur cycle across the lithosphere and the role of this volatile element in the metasomatism of the mantle at ancient cratonic boundaries are poorly constrained. We address these knowledge gaps by tracking the journey of sulfur in the assembly of a Proterozoic supercontinent using mass independent isotope fractionation (MIF-S) as an indelible tracer. MIF-S is a signature that was imparted to supracrustal sulfur reservoirs before the ~2.4 Ga Great Oxidation Event. The spatial representation of multiple sulfur isotope data indicates that successive Proterozoic granitoid suites preserve Δ33S up to +0.8‰ in areas adjacent to Archean cratons. These results indicate that suturing of cratons began with devolatilisation of slab-derived sediments deep in the lithosphere. This process transferred atmospheric sulfur to a mantle source reservoir, which was tapped intermittently for over 300 million years of magmatism. Our work tracks pathways and storage of sulfur in the lithosphere at craton margins.The long-term evolution of the sulfur budget in the lithosphere is poorly constrained. Here, using mass independent isotope fractionation as an indelible tracer, the authors track the pathway of sulfur from the Earth’s surface to punctuated episodes of granitoid magmatism during collisional orogenesis.

The multiple sulfur isotope architecture of the Golden Mile and Mount Charlotte deposits, Western Australia

The Golden Mile and Mount Charlotte deposits in the Kalgoorlie Terrane, Western Australia, display three main mineralization styles: Fimiston, comprised of interconnected shear zones associated with ankerite-pyrite ± hematite- ± magnetite-gold-telluride alteration; Oroya, made up of breccia bodies with V-muscovite-ankerite-pyrite ± pyrrhotite-gold-telluride alteration; and Mount Charlotte, which consists of vein arrays with symmetrical ankerite-sericite-albite-pyrite ± pyrrhotite ± gold alteration. Pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes. The δ 34 S, Δ 33 S, and Δ 36 S analyses on pyrite grains from the different mineralization styles, including oxidized and reduced sulfide-oxide assemblages, reveal (1) a large variation in δ 34 S (from − 12.6 to + 23.5‰), and (2) a previously unrecognized occurrence of anomalous Δ 33 S and Δ 36 S signatures (from − 1.0 to + 1.1‰ and from − 2.3 to + 0.9‰, respectively). It is argued that the mineralizing fluids that formed the Golden Mile and Mount Charlotte deposits record mixing among three components: mantle sulfur, oxidized seawater sulfur (e.g., SO 4 ), and reduced elemental sulfur (e.g., S 8 ). Petrographic evidence in conjunction with Δ 33 S and Δ 36 S data suggest that MIF-S was acquired during the deposition of shales and basalts present in the Kalgoorlie Terrane and later mixed with mantle-derived sulfur during the mineralization events. The negative δ 34 S values that predominate in Fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore-forming process, as reflected by the presence of hematite-pyrite-magnetite-gold assemblages. Conversely, the positive δ 34 S values that dominate in the Mt Charlotte and Oroya mineralization styles reflect a reducing environment, as reflected by the presence of pyrite-pyrrhotite-gold assemblages.

Actively forming Kuroko-type VMS mineralization at Iheya North, Okinawa Trough, Japan: new geochemical, petrographic and δ34S isotope results

Actively forming Kuroko-type VMS mineralisation at Iheya North, Okinawa Trough, Japan: New geochemical, petrographic and δS isotope results Christopher Yeats, Steve Hollis, Crystal LaFlamme, Angela Halfpenny, Marco Fiorentini, JuanCarlos Corona, Gordon Southam, Richard Herrington and John Spratt Mineral Resources Flagship, CSIRO, Perth, Australia Geological Survey of New South Wales, Maitland, Australia iCRAG and School of Earth Sciences, University College Dublin, Dublin, Ireland (steve.hollis@icrag-centre.org) Centre for Exploration Targeting, University of Western Australia, Perth, Australia Microscopy & Microanalysis Facility, John de Laeter Centre, Curtin University, Perth, Australia Department of Geological Sciences & Environmental Studies, Binghamton University, USA School of Earth Sciences, University of Queensland, Australia Department of Earth Sciences, Natural History Museum, London, UK