Georgy Cherkashov

Pyrococcus CH1, an obligate piezophilic hyperthermophile: extending the upper pressure-temperature limits for life

A novel hydrothermal site was discovered in March 2007, on the mid-Atlantic ridge during the cruise ‘Serpentine’. At a depth of 4100 m, the site ‘Ashadze’ is the deepest vent field known so far. Smoker samples were collected with the ROV ‘Victor 6000’ and processed in the laboratory for the enrichment of anaerobic heterotrophic microorganisms under high-temperature and high-hydrostatic pressure conditions. Strain CH1 was successfully isolated and assigned to the genus Pyrococcus, within the Euryarchaeota lineage within the Archaea domain. This organism grows within a temperature range of 80 to 108 °C and a pressure range of 20 to 120 MPa, with optima for 98 °C and 52 MPa respectively. Pyrococcus CH1 represents the first obligate piezophilic hyperthermophilic microorganism known so far. Comparisons of growth yields obtained under high-temperature/high-pressure conditions for relative organisms isolated from various depths, showed clear relationships between depth at origin and responses to hydrostatic pressure.

Geodiversity of Hydrothermal Processes Along the Mid‐Atlantic Ridge and Ultramafic‐Hosted Mineralization: a New Type Of Oceanic Cu‐Zn‐Co‐Au Volcanogenic Massive Sulfide Deposit

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Seafloor Massive Sulfides from the Northern Equatorial Mid-Atlantic Ridge: New Discoveries and Perspectives

In addition to the two new hydrothermal fields Krasnov (l6° 38′ N) and Ashadze (13° N) discovered in 2003–2004, some later discoveries were made in the Northern Equatorial segment of the Mid-Atlantic Ridge (MAR). Two new major seafloor massive sulfide (SMS) deposits: Semyenov (13° 31′ N) and Zenith-Victory (20° 08′ N), as well as the now extended Puy des Folles hydrothermal field (20° 30.5′ N), provide enough data to make conclusions about the general characteristics of SMS deposits in the northern equatorial MAR environment. Parameters of SMS deposits, such as their distribution, geological setting, morphology, composition and age, are discussed in this paper. A majority of studied SMS deposits (Ashadze, Logatchev, Semyenov) are associated with uplifted lower crust and mantle rocks (oceanic core complex, or OCC) at the MAR segments with asymmetric mode of accretion. OCC is tectonically uplifted along with detachment faults, which exhume deep-seated rocks onto the seafloor. Detachment faults, in turn, could be the conduits for the circulation of seawater and discharge of hydrothermal fluids. Gabbro-peridotite hosted deposits are characterized by high concentrations of copper, gold and cobalt. The relationship between the size of the deposits and their age is documented.

Two New Hydrothermal Fields at the Mid-Atlantic Ridge

Two new major hydrothermal fields have been discovered in the rift valley of the MAR at 13°N (Ashadze) and l6°38′N (Krasnov). The Ashadze field consists of a cluster of active hydrothermal sites associated with ultramafic rocks and located at the greatest depth in the ocean (4,200 m). By contrast, the Krasnov field consists of inactive sulfide mounds hosted in basalts. The Krasnov is the largest hydrothermal deposit on the MAR (17.4 Mt) so far discovered with iron sulfide as the principal mineral type. By contrast, Cu-Zn sulfides are the major minerals in the Ashadze deposits, which are also enriched in gold and several other metals.

230Th/U chronology of ore formation within the semyenov hydrothermal district (13°31′ N) at the Mid-Atlantic ridge

A radiochemical study was carried out on massive sulfides from Semyenov hydrothermal district at the Mid-Atlantic Ridge. New and published results provide evidence that 230Th/U ages obtained for massive sulfides are reliable. The sulfide deposits from the West, North-West, North-East, and East hydrothermal sites at the Semyenov hydrothermal district were formed between ∼124 ka and ∼37 ka ago. The hydrothermal activity might have started in the eastern part of the district and moved to the west by episodic ore formation.

The oldest seafloor massive sulfide deposits at the Mid - Atlantic Ridge: 230th/u chronology and composition

Abstract A geochronological and geochemical study on 10 samples of seafloor massive sulfides (SMS) from the inactive Peterburgskoye hydrothermal field at the Mid-Atlantic Ridge (MAR) was carried out. The 230Th/U ages of the SMS are the oldest for the Quaternary hydrothermal ores ever found at the ocean floor. According to them the hydrothermal activity at Peterburgskoye field started at least 170 ka and continued down to 63 ka. The oldest hydrothermal ores from this field consist mainly of pyrite and chalcopyrite and have geochemical properties typical for SMS associated with basalts.

Arctic deep-water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean

Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits. The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.

Are modern seafloor massive sulfide deposits a possible resource for mankind: Lessons learned from shallow drilling operations

Massive sulfide deposits from the modern seafloor are often seen as a potential metal resource for humankind. With the existing geochemical database and lacking information on the third dimension for most deposits it seems premature to comment on the economic significance of seafloor massive sulfides. Published geochemical analyses of sulfide samples indicate that some deposits may contain important metal concentrations, however, the data on surface grab samples from these deposits may not relate to the true metal content of these deposits. Results from recent shallow drilling of various hydrothermal systems presented here highlight the importance of seafloor drilling to validate grades and tonnages of seafloor massive sulfides.

Chronology of Hydrothermal Activity Within the Yubileynoye Ore Field (Mid-Atlantic Ridge, 20°08′ N)

This paper reports on the integrated geochronological and geochemical methods used in studying the ore deposits and metalliferous sediments of the Yubileinoye field. This study gives the opportunity to carry out cross dating of hydrothermal deposits, including the 230Th/U dating of sulfides, the 230Th, 14C dating, and foraminiferal analysis of the sediments, and, on this basis, to reconstruct hydrothermal activity over time. It was established that the ores started forming about 100 000–123 000 years ago and were renewed 4–5 times with a frequency of 10–20 ka. As a result, the complex of pyrite-marcasite, chalcopyrite and sphalerite ores and the associated metal-bearing and ore-bearing sediments with consistent geochemical specialization were formed. The integrated geochronological and geochemical studies of the ores and sediments allow us to obtain detailed data on evolution of the hydrothermal ore-formation not only in the certain areas but also for the entire Mid-Atlantic Ridge.

Seafloor Massive Sulfide Deposits: Distribution and Prospecting

Discovery of hydrothermal vents and seafloor massive sulfides (SMS) that contain metals of economic importance due to their high concentrations has generated significant interest among researchers as well as entrepreneurs as an alternative source that can be mined in future. This chapter provides a brief historical review of hydrothermal systems, the distribution, geological setting, morphology, composition, and age as well as formation and source of metals in SMS deposits. The chapter also looks at the criteria for recognition and exploration technologies for SMS deposits.