Composition of sulfide minerals of ODP Hole 209-1268A

This paper presents sulfide mineral occurrence, abundance, and composition in samples from hydrothermally altered peridotite and gabbro recovered during Ocean Drilling Program (ODP) Leg 209 from south of the 15°20'N Fracture Zone on the Mid-Atlantic Ridge at Site 1268. Most of the sulfide minerals occur in veins and halos around veins in serpentinized peridotite. The only sulfide phases reported that occur in proximity to gabbro are those associated with a mafic intrusion into serpentinized peridotite. Sulfide mineral species change predictably downsection but are perturbed coincident with a breccia interpreted to be generated by intrusion of a gabbroic magma. The general downhole trend suggests sulfide mineral precipitation in conditions with decreasing sulfur and oxygen fugacity. Sulfide minerals that indicate precipitation at relatively higher sulfur and oxygen fugacity occur in the central core of the intrusion breccia. Sphalerite makes a fleeting appearance in the sulfide mineral assemblage in samples from the lower part of the intrusion breccia. Strongly contrasting pyrite compositions suggest at least two episodes of pyrite precipitation, but there is no clear morphological distinction between phases. Heazelwoodite, tentatively identified in shipboard examinations, could not be confirmed in this study.

Concentration of hydrogen sulfide in waters of the Black Sea in the layer of its coexistence with oxygen

About 100 parallel determinations of hydrogen sulfide by the volumetric and photometric methods were made in the layer of coexistence of oxygen with hydrogen sulfide (C layer). Thiosulfates were determined simultaneously. Regardless of locations of the stations, determinations by two methods coincided for the entire range of depths of occurrence of the C layer upper boundary. Within the C layer hydrogen sulfide readings obtained by these two independent methods agreed; thiosulfates were not found by direct measurements. Difference in the readings appears at the lower boundary of the C layer and below it, accompanied by appearance of thiosulfates. It is therefore concluded that it is correct to determine the upper boundary of the C layer by the iodometric method and to use concentration of hydrogen sulfide obtained by this method in the C layer to calculate rate of chemical oxidation of hydrogen sulfide in quasistationary processes.

Chemistry of the massive sulfide deposit at DSDP Hole 63-471

We report here chemical analyses of sulfide and other minerals occurring in the massive sulfide deposit cored at Site 471. Details of the mineralogy and inferred paragenesis of the deposit will be reported elsewhere. The sulfide deposit at Site 471 occurs between overlying pelagic sediment and underlying basalt. The deposit is vertically zoned and consists, from top to bottom, of the following mineral assemblages: (1) pyrite, chalcopyrite, and Zn-sulfide in chert and calcite gangue (about 35 cm thick); (2) a 5-cm-thick metalliferous sediment layer described in detail by Leinen (this volume); and (3) a 4-cm-thick chert layer. The overlying sediment is a calcareous silty claystone that contains middle Miocene coccoliths (Bukry, this volume). The underlying basalt has been extensively chloritized and veined with calcite. In places feldspars are albitized, and calcite occurs as pseudomorphs after olivine. Relict textures suggest that the basalt grades into diabase and gabbro with increasing depth. Neither stock work nor disseminated sulfides was observed in the altered rocks.

Rates of sulfide formation and oxidation in the Black Sea waters in February-April 1991

Rate of hydrogen sulfide oxidation in the redox zone of the Black Sea and rate of hydrogen sulfide formation due to bacterial sulfate reduction in the upper layer of anaerobic waters were measured in February-April 1991. These measurements were made using sulfur radioisotope under conditions close to those in situ. It was established that hydrogen sulfide is oxidized in the layer of oxygen and hydrogen sulfide coexistence under the upper boundary of the hydrogen sulfide layer. Maximum rate of hydrogen sulfide oxidation was recorded within the limits of density values dT of 16.20-16.30, while varying in the layer from 2 to 4.5 µmol/day. The average rate of hydrogen sulfide oxidation was 1.5-3 times higher than that during the warm season. Sulfide formation was not observed at most of the stations in the examined lower portion of the pycnocline layer (140 to 400 m). Noticeable sulfate reduction was detected only at one station on the northwestern shelf. Intensified hydrodynamics in the upper layers of the water mass during the cold season can be a probable reason for such noticeable changes in sulfur dynamics in the water mass of the Black Sea. Data suggesting that hydrogen sulfide oxidation proceeds under the hydrogen sulfide boundary indicate absence of the so-called "suboxic zone" in this basin.

Chemical and mineral compositions of sulfide deposits from the Snake Pit hydrothermal field, Mid-Atlantic Ridge rift zone

The Snake Pit hydrothermal field is located on the top of a neovolcanic rise on the Mid-Atlantic Ridge at sea depths between 3460 and 3510 m. It was surveyed during several oceanological expeditions including DSDP Legs. Additional scientific materials were obtained in 2002 and 2003 during expedition onboard R/V Akademik Mstislav Keldysh with two Mir deep-sea manned submersibles. Three eastern hydrothermal mounds (Moose, Beehive, and Fir Tree) are located on the upper part of the eastern slope of the rise over a common fractured pedestal composed of fragments of massive sulfides. The western group of hydrothermal deposits is encountered on the western slope of the axial graben. Within this mature hydrothermal field, which was formed over the past 4000 years, we studied morphology of the hydrothermal mounds, chemistry and mineralogy of hydrothermal deposits, chemistry of sulfide minerals, and isotope composition of sulfur in them.

Ex situ microsensor profiles of sulfide concentration and pH in/outside mat 1 (MSM15/1_492-PUC1) measured during the MSM15/1 cruise in 2010 (Black Sea)

Biogeochemical measurements in sediment cores collected with the submersible JAGO (pusch cores) and a TV-MUC in the Black Sea during MSM15/1, Northwest Crimea (HYPOX Project), at water depths between 152-156 m. A series of microbial mats were sampled on the hypoxic region of the Crimean Shelf. Concentrations of organic carbon (Corg) and nitrogen (N) were measured on finely powdered, freeze-dried subsamples of sediment using a using a Fisons NA-1500 elemental analyzer. For organic carbon determination samples were pre-treated with 12.5% HCl to remove carbonates. Chlorophyll a (chl a), phaeopigments (PHAEO) and chloroplastic pigment equivalents (CPE) was measured according to Schubert et al., (2005; doi:10.1029/2004GC000837) and total hydrolyzable amino acids (THAA) and single amino acid: ASP, GLU, SER, HIS, GLY, THR, ARG, ALA, TYR, MET, VAL, PHE, ILE, LEU, LYS following Dauwe et al., 1998. High-resolution ex situ sulfide and pH microprofiles, were assessed only for station MSM15/1_492_PUC1. "in mat 1, 2 and 3" refers to 3 different profiles in 3 different spots of the microbial mat, whereas "outside mat", a profile outside the microbial mat.