Abstract
In this paper, we conduct a comparative study on the mineralogy and geochemistry of metalliferous sediment collected near the active hydrothermal site (Wocan-1) and inactive hydrothermal site (Wocan-2) from Wocan Hydrothermal Field, on the Carlsberg Ridge (CR), northwest Indian Ocean. We aim to understand the spatial variations in the primary and post-depositional conditions and the intensity of hydrothermal circulations in the Wocan hydrothermal systems. Sediment samples were collected from six stations which includes TVG-07, TVG-08 (Wocan-1), TVG-05, TVG-10 (Wocan-2), TVG-12 and TVG-13 (ridge flanks). The mineralogical investigations show that sediment samples from Wocan-1 and Wocan-2 are composed of chalcopyrite, pyrite, sphalerite, barite, gypsum, amorphous silica, altered volcanic glass, Fe-oxides, and hydroxides. The ridge flank sediments are dominated by biogenic calcite and foraminifera assemblages. The bulk sediment samples of Wocan-1 have an elevated Fe/Mn ratio (up to ~1545), with lower U contents (<7.4 ppm) and U/Fe ratio (<~1.8 × 10−5). The sulfide separates (chalcopyrite, pyrite, and sphalerite) are enriched in Se, Co, As, Sb, and Pb. The calculated sphalerite precipitation temperature (Sph.PT) yields ~278 °C. The sulfur isotope (δ34S) analysis returned a light value of 3.0–3.6‰. The bulk sediment samples of Wocan-2 have a lower Fe/Mn ratio (<~523), with high U contents (up to 19.6 ppm) and U/Fe ratio (up to ~6.2 × 10−5). The sulfide separates are enriched in Zn, Cu, Tl, and Sn. The calculated Sph.PT is ~233 °C. The δ34S returned significant values of 4.1–4.3‰ and 6.4–8.7‰ in stations TVG-10 and TVG-05, respectively. The geochemical signatures (e.g., Fe/Mn and U/Fe ratio, mineral chemistry of sulfides separates, and S-isotopes and Sph.PT) suggest that sediment samples from Wocan-1 are located near intermediate–high temperature hydrothermal discharge environments. Additionally, relatively low δ34S values exhibit a lower proportion (less than 20%) of seawater-derived components. The geochemical signatures suggest that sediment samples from Wocan-2 has undergone moderate–extensive oxidation and secondary alterations by seawater in a low–intermediate temperature hydrothermal environments. Additionally, the significant δ34S values of station TVG-05 exhibit a higher estimated proportion (up to 41%) of seawater-derived components. Our results showed pervasive hydrothermal contributions into station TVG-08 relative to TVG-07, it further showed the increased process of seafloor weathering at TVG-05 relative to TVG-10.
Highlights
Seafloor hydrothermal circulations at the mid-ocean ridges are essential process that controls the heat and chemical exchange from the interior of the earth to the ocean [1,2,3]
Our results showed pervasive hydrothermal contributions into station TVG-08 relative to TVG-07, it further showed the increased process of seafloor weathering at TVG-05 relative to TVG-10
The relative abundance from each station shows that chalcopyrite increases in abundance from station TVG-07 to TVG-08, whereas there is a decrease in the abundance of chalcopyrite and secondary
Summary
Seafloor hydrothermal circulations at the mid-ocean ridges are essential process that controls the heat and chemical exchange from the interior of the earth to the ocean [1,2,3]. The sediments in the vicinity of active high-temperature hydrothermal fields are liable to act as a sink for leached metals from the underlying host rocks, which reflect the composition and temperature of discharged hydrothermal fluid [11,12]. They are characterized by distinct mineralogy and geochemical signatures in comparison to pelagic sediments [13]. After the cessation of high-temperature hydrothermal fluid discharge, the post-depositional seafloor weathering would occur when the sulfides are in contact with the oxygenated seawater, causing the collapse of hydrothermal chimneys and the formation of sulfide mounds. The spatial distribution of surface hydrothermal sediment can reflect the intensity and position of hydrothermal activities of an active hydrothermal field [11], as well as the post-depositional processes and history of an inactive hydrothermal field
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