Mineralogical studies of sulfide samples and volatile concentrations of basalt glasses from the southern Juan de Fuca Ridge

Abstract

Sulfide samples obtained from the U.S. Geological Survey's DSRV Alvin dives on the southern Juan de Fuca Ridge closely resemble those from the same area described by Koski et al. (1984). Major minerals include sphalerite, wurtzite, pyrite, marcasite, isocubanite, anhydrite, and chalcopyrite. Equilibrium, if attained at all, during deposition of most sulfides was a transient event over a few tens of micrometers at most and was perturbed by rapid temperature and compositional changes of the circulating fluid. Two new minerals were found: one, a hydrated Zn, Fe hydroxy-chlorosulfate, and the other, a (Mn, Mg, Fe) hydroxide or hydroxy-hydrate. Both were formed at relatively low temperatures. Lizardite, starkeyite, and anatase were found for the first time in such an environment. Sulfide geothermometry involving the system Cu-Fe-S indicates a vent temperature of <328 degrees C for one sample. Fluid inclusion studies on crystals from the same vicinity of the same sample give pressure-corrected homogenization temperatures of 268 degrees and 285 degrees C. Ice-melting temperatures on inclusions from the same sample are about -2.8 degrees C, indicating that the equivalent salinity of the trapped fluid is about 50% greater than that of seawater. Volatile concentrations from vesicle-free basalt glass from the vent field are about 0.013 wt% CO2 and 0.16 wt% H2O, CO2 contents in these samples yield an entrapment depth of 2200 m of seawater, which is the depth from which the samples were collected.

Neutron-induced prompt gamma activation analysis (PGAA) of metals and non-metals in ocean floor geothermal vent-generated samples

“…Sample 917-R4 contained little silicon, no measurable aluminum, and was mainly composed of copper, nickel and zinc sulfides not found in the other samples. These analyses are consistent with the overall mineralogical analyses of other vent samples that were collected from the two geothermal fields that were previously reported [5][6][7][8][9][10][11][12][13][14][15] .…”

“…We analyzed three samples retrieved from the Juan de Fuca Ridge and the East Pacific Rise ocean floor geothermal vents by the research exploration vessel Alvin. [4][5][6][7][8][9][10][11][12][13][14][15] These samples are representative of the types of material retrieved in dives of the Alvin and thus give an excellent demonstration of complete, simultaneous, nondestructive, multi-element analysis with PGAA. The samples also provide an opportunity to look at a wide array of trace elements that may exhibit varying degrees of complexity in their chemistry.…”

Mineralogy and Formation of Black Smoker Chimneys from Brothers Submarine Volcano, Kermadec Arc

“…This crystal habit made accurate compositional measurements of this phase difficult, further complicated by rapid destruction of the phase under the electron microprobe beam. However, the composition indicated an unnamed Zn sulfate chloride hydrate, Zn 12 (OH) 15 (SO 4 ) 3 Cl 3 ·5H 2 O, a phase also found by Brett et al (1987) in chimneys from the southern Juan de Fuca ridge. However, further studies by Nasdala et al (1998) determined the mineral described by Brett et al (1987) was actually gordaite.…”

“…However, the composition indicated an unnamed Zn sulfate chloride hydrate, Zn 12 (OH) 15 (SO 4 ) 3 Cl 3 ·5H 2 O, a phase also found by Brett et al (1987) in chimneys from the southern Juan de Fuca ridge. However, further studies by Nasdala et al (1998) determined the mineral described by Brett et al (1987) was actually gordaite. Thus, we suspect that is the likely mineral found in this study (Table 3).…”

Seafloor Hydrothermal Activity: Black Smoker Chemistry And Chimneys

“…Magnesium silicates and silica (as either amorphous silica or quartz) have also been described from a number of sites. Unusual or new minerals that have been described from one or more sites include caminite (a Mg-hydroxide-sulfate-hydrate) at 210N EPR and other sites (Haymon & Kastner 1986); and a hydrated Zn, Fe-hydroxychlorosulfate, a (Mn, Mg, Fe)-hydroxide or hydroxy hydrate, lizarditc (Mg3Si20s(OH)4), starkeyite (MgS04 ' 4H20), and ana stase (Ti02) at SJdF (Brett et al 1987). Aragonite (CaC03) has only been fo und in MAR samples (Thompson et al 1988).…”