Abstract
In this study, to better understand the influence of hydrothermal processes on ore metal accumulation in bottom sediments, we examined distribution of Fe, Mn, Cu, Zn, As, and Pb in core of metalliferous sediments from the Pobeda hydrothermal cluster, and in core of non-mineralized (background) carbonate sediments (located 69 km northwards). Mechanisms of Fe, Mn, Cu, and Zn accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including a conditional mobile (F-1, exchangeable complex; F-2, authigenic Fe-Mn oxyhydroxides and associated metals; F-3, metals bound to organic matter/sulfides), and residual (F-4), fixed in crystalline lattices ones. The element contents were determined by the XRF and AAS methods, total carbon (TC) and total organic carbon (TOC) were determined using a Shimadzu TOC-L-CPN. Mineral composition and maps of element distribution in sediment components were obtained using the XRD and SEM-micro-X-ray spectrometry methods, respectively. In metalliferous sediments, according to our data, the major Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis, cfb). In the metalliferous core, average contents (cfb), of Fe and Mn were 32.1% and 0.29%, whereas those of Cu, Zn, Pb, and As, were 0.74%, 0.27%, 0.03%, and 0.02%, respectively. Metalliferous sediments are enriched in Fe, Cu, Zn, Pb, and As, relatively to background ones. The exception was Mn, for which no increased accumulation in metalliferous core was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes mineral debris. Among geochemically mobile fractions, to 80% Fe of the (F-1 + F-2 + F-3) sum was determined in the form of F-2, authigenic oxyhydroxides. The same fraction was a predominant host for Mn in both metalliferous and background sediments (to 85%). With these Fe and Mn fractions, a major portion of Cu, Zn, and Pb was associated, while a less their amount was found in sulfide/organic fraction. In the metalliferous sediment core, maximal concentrations of metals and their geochemically mobile fractions were recorded in the deeper core sediment layers, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that ore metals are mostly accumulated in sediment cores in their contact zone with the underlying serpentinized peridotites.
Highlights
The metalliferous sediments are unconsolidated deep-sea deposits that are formed in the volcanically active areas on the ocean floor [1,2,3,4,5,6,7]
Core 184k is composed of brown coccolite-foraminiferal carbonate sediments soaked with iron hydroxides
CaCO3 content showed a regular decrease from 77% to 20%, at depths of 40 and 70 cm (Figure 2a), where metalliferous sediments became the ore-bearing ones
Summary
The metalliferous sediments are unconsolidated deep-sea deposits that are formed in the volcanically active areas on the ocean floor [1,2,3,4,5,6,7]. The source of the metal-bearing matter in the metalliferous sediments is associated with volcanic rocks in the ocean crust. According to [6,10], about 5% of the hydrothermal ore-bearing matter that enters the ocean in the hydrothermal solutions, are accumulated within the massive bodies at the vents, and about 95% is deposited outside of them. The major partobtained of minerals in of core 184k is presented by calcite, whose content the upper layers,ofexhibitSEM micro-X-ray spectral analysis. 38–42 cm of 17 the ing a65–70 decrease down the core 3 contents those determined above and cm Fe-oxyhydroxides composed major portion and of sediments, forming both by the and TIC analysis
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