Effects of deep magmatic degassing and shallow seawater circulation on trace element and sulfur cycling in submarine hydrothermal systems: Insights from the Shijuligou analog, North China

• Published in: Gondwana research 2024-10, Vol.134, p.187-208
• Main Authors: Meng, Xingwei, Li, Xiaohu, Zoheir, Basem, Chu, Fengyou, Chen, Ling, Zhu, Jihao, Li, Zhenggang, Yang, Kehong, Jin, Xianglong
• Format: Article
• Language: English
• Subjects: Magmatic degassing; Seafloor hydrothermal systems; Seawater circulation; Sulfur isotopes; Trace elements
• ISSN: 1342-937X
• DOI: 10.1016/j.gr.2024.07.009

[Display omitted] •Vertical variations in trace elements within the Shijuligou VMS deposit are mainly controlled by physicochemical conditions, magmatic degassing, and seawater circulation.•A broad sulfur isotope range of −3.36 to 19.84 ‰ in the Shijuligou VMS deposit is caused by deep magmatic degassing and shallow seawater circulation.•Elemental and sulfur isotopic signatures of magmatic degassing could be obscured by subsequent shallow seawater circulation.•Chemical variations, along with Pb and S isotopic data, suggest the Shijuligou VMS deposit resembles a fossil analog of immature, subduction-influenced submarine hydrothermal systems. Limited access to modern subseafloor sulfides hampers our understanding of the link between magmatic volatile influx and the cycling of trace elements and sulfur, as well as the effect of the subsequent shallow seawater circulation on these processes. Hence, we studied a well-preserved fossil analog of submarine hydrothermal systems – the Shijuligou volcanogenic massive sulfide (VMS) deposit from the North Qilian Mountains in North China to examine variations in elements and isotopes of subseafloor sulfides vertically. The vertical distribution of trace elements in subseafloor sulfides is strongly controlled by temperature gradients and redox states during the interaction between hot fluids and seawater beneath the paleo-seafloor. While the enrichment of elements like As, Sb, and Au (median: 1335, 43.7, and 0.30 ppm, respectively, n = 21) and negative δ34S values (mean: −3.07 ‰, n = 7) of euhedral pyrites in the jasper, along with the precipitation of high sulfidation minerals (e.g., enargite), suggest the input of magmatic volatiles into hydrothermal systems. During the shallow seawater-hydrothermal circulation, pyrites in the veined and stockwork zones exhibit distinctly elevated δ34S values (up to 15.74 ‰), accompanied by increased concentrations of wall-rock-derived elements (e.g., Cu, Ni, Si, and Ti) and low-temperature-responsive elements (e.g., Pb, Zn, and Cd). Sulfur isotopes of sulfides vary significantly from the surface to the deep ore zones, ranging from −3.36 to 19.84 ‰ (mean: 9.25 ‰, n = 37). The negative δ34S values of pyrites at the paleo-seafloor are due to the addition of H2S derived from the disproportionation of magmatic SO2. The increased δ34S values of stockwork and disseminated sulfides at depth are attributed to the progressive reduction of seawater sulfates by ferrous iron released from the alte