Mineralogy and geochemistry of a sediment‐hosted hydrothermal sulfide deposit from the Southern Trough of Guaymas Basin, Gulf of California

Abstract

Samples dredged from a 15‐m‐high hydrothermal mound atop the flat turbidite pond in the Southern Trough of Guaymas Basin consist of pyrrhotite‐rich massive sulfide, barite, barite + calcite, talc, and opaline silica as well as substrate material composed of fossiliferous, clay‐rich ooze. An 11‐m‐long sediment core taken near the dredge site shows increasing hydrothermal alteration with depth; anhydrite‐filled fractures near the base of the core appear to be channels for hydrothermal discharge. Oxidation of the sulfide‐rich samples to an assemblage of geothite, lepidocrocite, and amorphous Fe oxyhydroxide is ubiquitous. Compared to other massive sulfide deposits on sediment‐starved oceanic ridges, the hydrothermal deposit dredged in Guaymas Basin has a high pyrrhotite/pyrite ratio, a low Zn sulfide and combined ore metal (Cu + Zn + Pb + Ag + Cd) content, and a greater abundance of sulfate, carbonate, and silicate phases. Venting hydrothermal solutions are alkaline with moderately high pH; high Ca, Ba, and SiO2 content; low ƒS2 and ƒo2; and very low transition metal content. Disequilibrium assemblages of pyrrhotite and sulfate minerals form during rapid mixing of this evolved vent fluid with ambient bottom waters at the discharge site. Talc is formed at a temperature near 270°C by mixing or entrainment of Mg‐rich bottom water or pore fluid with upwelling hydrothermal fluid that is saturated with silica. Calcite may precipitate from the alkaline, Ca‐rich fluid during degassing of CO2. The minimum temperature range for sulfide and nonsulfide deposition is approximately 190°–326°C. The composition of hydrothermal deposits, vent solutions, and altered sediment requires that circulating fluids evolve during deep penetration into the basaltic basement complex, further interaction with the organic‐and carbonate‐rich sediment pile, and near‐surface mixing with ambient seawater. Although the stable assemblage albite‐epidote‐clinochlore present at depth in the sediment pile requires very low dissolved Mg and Fe in the altering fluid, the addition of Mg to deeply buried sediment indicates significant recharge of the system by Guaymas Basin bottom water.

Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems: Implications for ore genesis and fluid circulation

“…3). A single value of 21.5‰ for the sulfate sample at the EHF falls within the overall range of sulfate samples from other seafloor hydrothermal fields (from 19 to 25‰; n = 288) (data are from Shanks and Niemitz, 1982;Kerridge et al, 1983;Zierenberg et al, 1984Zierenberg et al, , 1993Koski et al, 1985;Shanks and Seyfried, 1987;Hannington and Scott, 1988;Shanks, 1988, 1994;Kusakabe et al, 1990;Blum and Puchelt, 1991;Iizasa et al, 1992;Peter and Shanks, 1992;Lein et al, 1993;Chiba et al, 1998;Gemmell and Sharpe, 1998;Herzig et al, 1998a, b;Knott et al, 1998;Marumo and Hattori, 1999;Zeng et al, 2002a, b;de Ronde et al, 2003;Kim et al, 2004;. Sulfide minerals from the EPR near 1-2°S have much higher sulfur isotope ratios (pyrite δ 34 S values from 3.0 to 5.8‰, avg.…”

Four-Hundred-and-Ninety-Million-Year Record of Bacteriogenic Iron Oxide Precipitation at Sea-Floor Hydrothermal Vents

“…The formation of such deposits can be attributed to several abiogenic processes: sedimentation from hydrothermal plumes (e.g., Barrett et al 1987;Mills, Elderfield, and Thomson 1993); in situ precipitation from diffuse low-temperature flow through sediments (e.g., Koski et al 1985;Alt 1988), typically 20-100…”

Phyllosilicate minerals in the hydrothermal mafic?ultramafic-hosted massive-sulfide deposit of Ivanovka (southern Urals): comparison with modern ocean seafloor analogues

“…These temperatures are unusually low for hydrothermal talc (Lonsdale et al 1980;Koski et al 1985;Styrt et al 1981;Zierenberg and Shanks 1983) and lower than those estimated for chloritites sampled at comparable depths. A possible explanation is that talc-rich rocks equilibrated with an 18 O-enriched hydrothermal fluid, e.g.…”

“…McLeod and Stanton 1984;Aggarwal and Nesbitt 1984;Costa et al 1983;Koski et al 1985;Kranidiotis and MacLean 1987;Lonsdale et al 1980;Shau and Peacor 1992;Goodfellow and Franklin 1993;Zierenberg et al 1995) and distinct populations characterized by either moderately (FeO £ 4 wt%) or highly ferroan compositions may occur at the same site. Available estimates of the temperatures of formation of hydrothermal talc are in the range 270-420°C (Lonsdale et al 1980;Koski et al 1985;Styrt et al 1981;Zierenberg and Shanks 1983), therefore usually higher than those reported for Mg-rich saponite.…”

“…Main modes of occurrence of talc in modern submarine hydrothermal fields include (i) massive terraces and ledges of ferroan talc associated with pyrrhotite and smectite (Guaymas Basin, Lonsdale et al 1980); (ii) talc intergrown with saponite as replacement of olivine phenocrysts in high-T alteration zones (in association with Fe-oxides and sulfides; hole 504B, Shau and Peacor 1992) and in seafloor altered hyaloclastites representing shallow hydrothermal upflow zones (Sea Cliff, Zierenberg et al 1995); (iii) talc in pyrrhotite-rich hydrothermal mounds (Guaymas Basin, Koski et al 1985;Middle Valley, Goodfellow and Franklin 1993) and in polymetallic sulfide chimneys (East Pacific Rise; e.g. Styrt et al 1981); talc in epigenetic veins associated with anhydrite, Mg-rich saponite, chlorite and sulfides (Atlantis II Deep; Zierenberg and Shanks 1983).…”