Hydrothermal Fe and Si oxyhydroxide deposits from South Pacific intraplate volcanoes and East Pacific Rise axial and off-axial regions

Abstract

Fe-andSi-rich oxyhydroxide deposits are among the most common hydrothermal materials encountered on the submarine intraplate volcanoes of the Society, Austral, and Pitcairn regions and on accreting plate boundaries of the East Pacific near 21 ø N, 12050 ' N, and 11ø30 • N. Based on field observations and compositional variations, the hydrothermal deposits are divided into four types: (1) Fe oxyhydroxides forming chimneys and mounds, depleted in trace metals (Co + Cu + Zn + Ni < 0.1 •vt %), •vith a total Fe of 27 to 45 •vt percent; (2) Fe oxyhydroxides associated •vith sulfides, enriched in trace metals (Co + Cu + Zn + Ni > 0.4-1%), •vith an iron content of 30 to 50 percent; (3) Fe-Si oxyhydroxides also forming chimneys and mounds enriched in clay (nontronite), depleted in trace metals, •vith Si and Fe contents of 7 to 20 percent and 20 to 30 percent, respectively; and (4) Si-Fe oxyhy&oxides enriched in opaline silica, •vith high Si (>35%) and lo•v Fe (<10%), and strongly depleted in trace metals. Although type 2 represents the alteration products of preexisting sulfides, the other Fe and Si oxyhydroxide deposits are primary lo•v-temperature (<70øC) hydrothermal precipitates forming edifices, mounds, and flat-lying deposits. These hydrothermal deposits have lo•ver total rare earth element (REE) contents (10-200 ppm) than their associated volcanics and have variable anomalies in Ce and Eu. There are no substantial differences in morphology and composition of the Fe and Si oxyhydroxide deposits bet•veen the intraplate and East Pacific Rise regions. Both the intraplate and the EPR deposits are associated with pillo•v lava, sheet flows, hyaloclastites, and hydrothermally altered flows having zones of sulfide and silicate mineralizations, although, up to no•v, no sulfide edifices have been found on the intraplate volcanoes of the South Pacific. Nevertheless, high-temperature solutions have percolated through the volcanics, giving rise to sulfides (pyrite, chalcopyrite) and silicates (quartz, andradite, actinolite) in relatively high temperature (>250øC) mineralized zones. It is believed that the Fe and Si oxyhydroxide deposits of types 1, 3, and 4 are formed during mixing bet•veen descending cold sea•vater and ascending hot hydrothermal fluids in a crustal environment.

Geochemistry and Origin of Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

“…Moorby et al, 1984;Eckhardt et al, 1997;Usui andGlasby, 1998) andhotspot (e.g. De Carlo et al, 1983;Hekinian et al, 1993;Hodkinson et al, 1994;Scholten et vol. 56, no.…”

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

“…Fe oxide deposits are commonly found at hydrothermal vent sites at mid-ocean ridge and back-arc sea floor spreading centers, seamounts associated with these spreading centers, and intraplate seamounts (e.g., Barrett, Taylor, and Lugowski 1987;Alt 1988;Binns et al 1993;Hekinian et al 1993;Stoffers et al 1993;Bogdanov et al 1998;Iizasa et al 1998;Halbach, Halbach, and Lüders 2002). 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…”

“…The mineralogy of these Fe oxide deposits is dominated by poorly ordered Fe oxyhydroxides (Two-XRDline ferrihydrite and goethite), often with significant amounts of amorphous silica (up to 73 wt%) and Mn (up to 14 wt%) (Alt 1988;Juniper and Fouquet 1988;Binns et al 1993;Hekinian et al 1993;Stoffers et al 1993;Fortin, Ferris, and Scott 1998;Iizasa et al 1998;Boyd and Scott 2001;Emerson and Moyer 2002;Kennedy, Scott, and Ferris 2003a).…”

Negative Ce Anomaly in the Indian Banded Iron Formations: Evidence for the Emergence of Oxygenated Deep‐Sea at 2.9‐2.7 Ga

“…This preferential uptake of LREEs has been also confirmed by experiments on REE scavenging (Byrne and Kim, 1990;Koeppenkastrop and De Carlo, 1992). The above-mentioned correlations among REE indices (ΣREE, Eu/Eu*, Ce/Ce*, (La/Yb) N ) of MOR hydrothermal sediments and particulates have not yet been recognized in iron-rich hydrothermal sediments of volcanic arcs (Savelli et al, 1999), back-arc seamounts (Binns et al, 1993), and hot-spots (Hekinian et al, 1993).…”