Abstract
We have studied morphology, mineralogy and geochemical characteristics of Fe-oxyhydroxide deposits from metal-enriched sediments of the active (Wocan-1) and inactive (Wocan-2) hydrothermal sites (Carlsberg Ridge, Northwest Indian Ocean). Fe-oxyhydroxide deposits on the Wocan-1 site are reddish-brownish, amorphous and subangular. They occur in association with sulfides (e.g., pyrite, chalcopyrite and sphalerite) and sulfate minerals (e.g., gypsum and barite). The geochemical composition shows enrichment in transition metals (Ʃ (Cu + Co + Zn + Ni) = ~1.19 wt. %) and low (<0.4 wt. %) values of Al/(Al + Fe + Mn) ratio. The Wocan-2 samples show poorly crystallized reddish brown and yellowish Fe-oxyhydroxide, with minor peaks of goethite and manganese oxide minerals. The mineral assemblage includes sulfide and sulfate phases. The geochemical compositions show two distinct types (type-1 and type-2). The type-1 Fe-oxyhydroxides are enriched in transition metals (up to ~1.23 wt. %), with low values of Fe/Ti vs. Al/(Al + Fe + Mn) ratio similar to the Wocan-1 Fe-oxyhydroxides. The type-2 Fe-oxyhydroxides are depleted in transition metals, with Al/(Al + Fe + Mn) ratio of 0.003–0.58 (mean value, 0.04). The ridge flank oxyhydroxides exhibit an extremely low (mean value ~ 0.01) Fe/Mn ratio and a depleted concentration of transition metals. Our results revealed that the Wocan-1 Fe-oxyhydroxides and type-1 Fe-oxyhydroxides of the Wocan-2 site are in the range of Fe-oxyhydroxides deposits that are precipitated by mass wasting and corrosion of pre-existing sulfides. The type-2 Fe-oxyhydroxides are precipitated from sulfide alteration by seawater in an oxygenated environment relative to type-1. The association of biogenic detritus with the oxyhydroxides of the ridge flanks and the low Fe/Mn ratio suggests hydrogenous/biogenic processes of formation and masked hydrothermal signatures with distance away from the Wocan hydrothermal field.
Highlights
Fe-Si-Mn oxide mineral deposits are formed in various geologic settings such as mid-ocean ridgesMOR [1,2,3]; back-arc spreading centers [4,5,6,7]; submerged island arc volcanoes and hot-spot-associated volcanic intraplate [8,9,10,11,12]
Our results revealed that the Wocan-1 Fe-oxyhydroxides and type-1 Fe-oxyhydroxides of the Wocan-2 site are in the range of Fe-oxyhydroxides deposits that are precipitated by mass wasting and corrosion of pre-existing sulfides
Studies on the origin, morphology and mineral chemistry of Fe oxides and hydroxide deposits of the Wocan field had not been conducted. This present study examines the morphology and chemical compositions of Fe-oxyhydroxide mineral grains separated from metalliferous sediments of the WHF
Summary
MOR [1,2,3]; back-arc spreading centers [4,5,6,7]; submerged island arc volcanoes and hot-spot-associated volcanic intraplate [8,9,10,11,12] They are essential components of modern seafloor deposits [12] and generally occur in the form of sulfide oxidation (e.g., gossan/ferruginous ochre from the sulfide mound at the Trans-Atlantic Geotraverse (TAG) hydrothermal site) [2] and primary precipitations from hydrothermal fluid (e.g., chimneys, mounds and ochres formation in the TAG field) [13]. The first group of oxyhydroxides deposits displays the depleted concentration of transition metals References [15,17] related the influence and activities of microorganisms (e.g., iron-oxidizing chemosynthetic bacteria) to the formation of typical Fe-oxyhydroxide deposits in the Lau Basin and Eastern Manus Basin
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