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Gablina I.F.,Russian Academy of Sciences | Demina L.L.,Russian Academy of Sciences | Dmitrenko O.B.,Russian Academy of Sciences | Os'kina N.S.,Russian Academy of Sciences | And 3 more authors.
Oceanology | Year: 2011

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms, as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone of Fe-Mn crusts. © 2011 Pleiades Publishing, Ltd.

Silantyev S.A.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry | Krasnova E.A.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry | Cannat M.,CNRS Paris Institute of Global Physics | Bortnikov N.S.,RAS Institute of Geology and Mineralogy | And 2 more authors.
Geochemistry International | Year: 2011

This study aimed at reconstructing the sequence of events in the magmatic and metamorphic evolution of peridotites, gabbroids, and trondhjemites of the oceanic core complexes of the Ashadze and Logachev hydrothermal vent fields. The study object was the collections of plutonic rocks made during cruises 22 and 26 of the R/V Professor Logachev, Cruise 41 of the R/V Akademik Mstislav Keldysh, and the Russian-French expedition Serpentine aboard the R/V Pourquoi pas? The data reported here suggest that the oceanic core complexes of the Ashadze and Logachev fields were formed via the same scenario in the two MAR regions. On the other hand, the analysis of petrological and geochemical characteristics of the rocks indicated that the oceanic core complexes of the MAR axial zone between 12°58′ and 14°45′N show a pronounced petrological and geochemical heterogeneity manifested in variations in the degree of depletion of mantle residues and the Nd isotopic compositions of the rocks of the gabbro-peridotite association. The trondhjemites of the Ashadze hydrothermal field can be considered as partial melting products of gabbroids under the influence of hydrothermal fluid. It was supposed that the presence of trondhjemites in the MAR oceanic core complexes can be used as a marker for the highest temperature deep-rooted hydrothermal systems. Perhaps, the region of the MAR axial zone in which petrologically and geochemically contrasting oceanic core complexes are spatially superimposed served as sites for the development of large hydrothermal clusters with a considerable ore-forming potential. © 2011 Pleiades Publishing, Ltd.

Rusakov V.Y.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry | Shilov V.V.,Polar Marine Geological Prospecting Expedition | Ryzhenko B.N.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry | Gablina I.F.,Russian Academy of Sciences | And 4 more authors.
Geochemistry International | Year: 2013

New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated. © 2013 Pleiades Publishing, Ltd.

Cherkashev G.A.,Gramberg All Russian Institute of Geology and Mineral Resources of the World Ocean VNIIOkeangeologiya | Ivanov V.N.,Polar Marine Geological Prospecting Expedition | Bel'tenev V.I.,Polar Marine Geological Prospecting Expedition | Lazareva L.I.,Polar Marine Geological Prospecting Expedition | And 7 more authors.
Oceanology | Year: 2013

The optimal set of prospecting methods, including geophysical (geoelectrical), geological (mineralogical-geochemical), and hydrological observations, was developed during the long-term investigations of the sulfide mineralization in the northern equatorial zone of the Mid-Atlantic Ridge. The application of these methods made it possible to discover six massive sulfide deposits and considerably extend the boundaries of another two ore objects. The ores associated with ultramafic rocks are characterized by elevated Cu, Au, and Co concentrations. It is established that the ore formation was a multistage process that resulted in the accumulation of large deposits (over 10 million tons). © 2013 Pleiades Publishing, Inc.

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