Mineralogical and Geochemical Signatures of Metalliferous Sediments in Wocan-1 and Wocan-2 Hydrothermal Sites on the Carlsberg Ridge, Indian Ocean

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.

Inactive Sulfide Ecosystems in the Deep Sea: A Review

“…It is beyond the scope of this review to provide a detailed summary of the diverse mineralogies of and abiotic weathering processes associated with inactive sulfides on midocean ridges, in back-arc basins, or off-axis submarine volcanoes. Competent reviews and studies may be found in, for example, Herzig and Hannington (1995), Lehrmann et al (2018), and Popoola et al (2019).…”

Fractionation Trends and Variability of Rare Earth Elements and Selected Critical Metals in Pelagic Sediment from Abyssal Basin of NE Pacific (Clarion-Clipperton Fracture Zone)

“…The individual Ce, Y, Nd, and La resources are as high as 13,600 Mg, 12,600 Mg, 10,200 Mg and 8200 Mg, respectively [76]. The individual contents of REE and some selected metals (Ni or Co) were higher when compared, e.g., with hydrothermally affected carbonate sediments [22], but definitely lower (except for REE) than in typical metalliferous sediments forming in hydrothermally active seafloor zones [112].…”

Integrated Geochemical Investigations on Fe-Mn Nodules, Polymetallic Sulfides and Fe-Mn Oxides Recovered from Marine Sediments of Carlsberg Ridge, Northwest Indian Ocean

“…Polymetallic sulfides are one of the manifestations of hydrothermal activities with other diverse mineral assemblages such as pyrite/marcasite, chalcopyrite, bornite, covellite, digenite, isocubanite, pyrrhotite, barite, anhydrite, amorphous silica and Fe-oxide and hydroxides [6]. Ferromanganese oxides and crusts are widespread on the ocean floor and are formed through the precipitation of suspended iron and manganese oxyhydroxides owing to the hydrothermal-hydrogenetic supply.…”

“…About 5 g of representative samples at 4 cm interval (e.g., 2 cm, 6 cm, 10 cm……38 cm, 42 cm) were soaked in de-ionized water for 24 hours, and wet-sieved to separate > 63 µm (sand size) fractions. Micro nodules were observed, and further (Figure 1) and ultramafic hosted Tianxiu (Figure 1), and Daxi hydrothermal field on the Non-transform offset along the Carlsberg Ridge [5,6,[24][25][26][27][28][29][30][31].…”