Partitioning riverine sulfate sources using oxygen and sulfur isotopes: Implications for carbon budgets of large rivers

Abstract Sedimentary pyrite formation links the global biogeochemical cycles of carbon, sulfur, and iron, which, in turn, modulate the redox state of the planet's surficial environment over geological time scales. Accordingly, the sulfur isotopic composition (δ34S) of pyrite has been widely employed as a geochemical tool to probe the evolution of ocean chemistry. Characteristics of the depositional environment and post-depositional processes, however, can modify the δ34S signal that is captured in sedimentary pyrite and ultimately preserved in the geological record. Exploring sulfur and iron diagenesis within the Bornholm Basin, Baltic Sea, we find that higher sedimentation rates limit the near-surface sulfidization of reactive iron, facilitating its burial and hence the subsurface availability of reactive iron for continued and progressively more 34S-enriched sediment-hosted pyrite formation (δ34S ≈ −5‰). Using a diagenetic model, we show that the amount of pyrite formed at the sediment-water interface has increased over the past few centuries in response to expansion of water-column hypoxia, which also impacts the sulfur isotopic signature of pyrite at depth. This contribution highlights the critical role of reactive iron in pyrite formation and questions to what degree pyrite δ34S values truly reflect past global ocean chemistry and biogeochemical processes. This work strengthens our ability to extract local paleoenvironmental information from pyrite δ34S signatures.

δ34S

Biogeochemical Cycle

Sedimentation

10.1130/g48415.1

Cite

Citations (35)

Multiple element mapping and in-situ S isotopes of Au-carrying pyrite of Shuiyindong gold deposit, southwestern China using NanoSIMS: Constraints on Au sources, ore fluids, and mineralization processes

Ore Geology Reviews (2020)

Jian‐Yang Li Jie Li Xuemin Liu Wei Zhai Yi Huang

δ34S

10.1016/j.oregeorev.2020.103576

Cite

Citations (25)

Genesis of the Hatu gold deposit: Constrained by in situ S Pb isotope geochemistry of pyrite

Journal of Geochemical Exploration (2023)

Fang An Yongfeng Zhu Xuwen Wang Yuxuan Li Jianli Qiang

δ34S

Siltstone

10.1016/j.gexplo.2023.107296

Cite

Citations (2)

The world-class Howard’s Pass SEDEX Zn-Pb district, Selwyn Basin, Yukon. Part II: the roles of thermochemical and bacterial sulfate reduction in metal fixation

Mineralium Deposita (2016)

M G Gadd Daniel Layton‐Matthews Jan M. Peter S J Paradis I R Jonasson

The Howard's Pass district of sedimentary exhalative (SEDEX) Zn-Pb deposits is located in Yukon Territory and comprises 14 Zn-Pb deposits that contain an estimated 400.7 Mt of sulfide mineralization grading 4.5 % Zn and 1.5 % Pb. Mineralization is hosted in carbonaceous and calcareous and, to a lesser extent, siliceous mudstones. Pyrite is a minor but ubiquitous mineral in the host rocks stratigraphically above, within, and below mineralization. Petrographic analyses reveal that pyrite has a complex and protracted growth history, preserving multiple generations of pyrite within single grains. Sulfur isotope analysis of paragenetically complex pyrite by secondary ion mass spectrometry (SIMS) reveals that sulfur isotope compositions vary with textural zonation. Within the Zn-Pb deposits, framboidal pyrite is the earliest pyrite generation recognized, and this exclusively has negative δ34S values (mean = −16.6 ± 4.1 ‰; n = 55), whereas paragenetically later pyrite and galena possess positive δ34S values (mean = 29.1 ± 7.5 and 22.4 ± 3.0 ‰, n = 13 and 13, respectively). Previous studies found that sphalerite and galena mineral separates have exclusively positive δ34S values (mean = 16.8 ± 3.3 and 12.7 ± 2.8 ‰, respectively; Goodfellow and Jonasson 1986). These distinct sulfur isotope values are interpreted to reflect varying contributions of bacterially reduced seawater sulfate (negative; framboidal pyrite) and thermochemically reduced seawater sulfate and/or hydrothermal sulfate (positive; galena, sphalerite, later forms of pyrite). Textural evidence indicates that framboidal pyrite predates galena and sphalerite deposition. Collectively, the in situ and bulk sulfur isotope data are much more complex than δ34S values permitted by prevailing genetic models that invoke only biogenically reduced sulfur and coeval deposition of galena, sphalerite, and framboidal pyrite within a euxinic water column, and we present several lines of evidence that argue against this model. Indeed, the new data indicate that much of the base metal sulfide mineralization was emplaced below the sediment-water interface within sulfidic muds under reducing conditions during early diagenesis. Furthermore, thermochemical sulfate reduction provided most of the reduced sulfur within the Zn-Pb deposits.

δ34S

Sulfide Minerals

10.1007/s00126-016-0672-x

Cite

Citations (57)

Development of in situ sulfur four-isotope analysis with multiple Faraday cup detectors by SIMS and application to pyrite grains in a Paleoproterozoic glaciogenic sandstone

Chemical Geology (2014)

T. Ushikubo Kenneth H. Williford James Farquhar David T. Johnston Martin J. Van Kranendonk

δ34S

Isotope Analysis

10.1016/j.chemgeo.2014.06.006

Cite

Citations (76)

Mineralogical Characteristics and Genetic Types of Pyrite with Different Occurrence: Constraints from Spectroscopy, Geochemistry and δ34S Stable Isotopes

Minerals (2023)

Shiyu Ma Miao Shi Cun Zhang Qinyuan Cao

Pyrite is widely distributed in the Earth’s crust and oceanic systems, and it generally occurs as pentagonal dodecahedra, cubic, octahedral, idiomorphic crystals, or dense, massive, granular, and nodular aggregates. In this study, representative pyrite samples from Hunan, Fujian, Jiangxi, Anhui in China and from Peru were collected. By utilizing a range of analytical techniques, including petrography, X-ray diffraction, infrared spectrum, Raman spectrum, major and trace element analysis, as well as sulfur stable isotope analysis, we comprehensively depict the mineralogical and spectroscopic characteristics of pyrite, and the evolution processes of the physical and chemical conditions of mineralization can be qualitatively constrained. The spectroscopic results indicate all samples show a relatively narrow absorption band with weak to moderate intensity in the vicinity of 343 cm−1, which represents the bending vibration of the Fe-[S2]2− molecular bond. The Co content of pyrite exhibits the characteristics of a positive correlation with temperature and a negative correlation with oxygen fugacity, respectively. The δ34S isotopic compositions of colloidal pyrite are in the range of 0.03 to 0.67, which are close to meteoric sulfur and mantle sulfur compositions, while the δ34S values of nodular pyrite fall within the range of granite, indicating the characteristics of mixtures of sulfur sources are mainly related to magmatic activity. Our results provide insight into the formation mechanisms of pyrite in different environments, its mineralization, and the ore genesis of deposits. Moreover, the integrated analytical methods for pyrite are provided, which can define theoretical guidance for the exploration and development of mineral resources.

δ34S

Mineral redox buffer

10.3390/min14010052

Cite

Citations (1)