Hydrothermal mineralization along submarine rift zones, Hawaii

Abstract

This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe-Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ-MnO 2 . The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn-cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and

Molybdenum isotopes in hydrothermal manganese crust from the Ryukyu arc system: Implications for the source of molybdenum

“…Previous studies have reported high molybdenum (Mo) concentrations (~100-1000 ppm) in these Mn oxides (e.g. Hodkinson et al, 1994;Hein et al, 1996;Glasby et al, 1997;Kuhn et al, 2003). However, the mechanism responsible for the enrichment of Mo in hydrothermal Mn crust is poorly understood.…”

“…Cronan et al, 1982;Usui et al, 1986), and near hot spot volcanoes (e.g. Hodkinson et al, 1994;Hein et al, 1996). The Mn oxides are considered to have precipitated at high growth rates (100-1000 mm/Myr) from reducing hydrothermal solutions as they mix with oxygenated seawater (Takematsu et al, 1989;Glasby, 2006).…”

“…Generally, hydrothermal Mn crusts are characterized by low Fe/Mn ratios and, with the exception of Mo, low contents of manganophile elements such as Co, Ni, Cu, and Zn (e.g. Hodkinson et al, 1994;Hein et al, 1996;Glasby et al, 1997;Kuhn et al, 2003). These characteristics contrast with those of other modern deep-ocean Mn oxides, such as hydrogenous ferromanganese crusts (Fe-Mn crusts) and Mn nodules, which have higher Fe/Mn ratios and are enriched in manganophile elements (e.g.…”

Weathering fluxes and sediment provenance on the SW Scottish shelf during the last deglaciation

“…One caveat is that marine FeMn nodules may not have exactly the same phases as extracted in the leachates. Ferromangenese nodules contain variable proportions of vernadite, amorphous Fe oxyhydroxides and aluminosilicate minerals (Hein et al, 1996), whereas the leachates are thought to be almost exclusively FeMn oxyhydroxides. At least the leaching reagents target only the most labile FeMn phases dominated by ferrihydrite and lepidocrocite; (Poulton and Canfield, 2005).…”

Geochemical studies on Permian manganese deposits in Guichi, eastern China: Implications for their origin and formative environments

“…These diagenetic deposits may be composed of Mn carbonates or oxides. Hydrothermal manganese deposits which are characterized by high Mn/Fe and low trace metal concentrations (Hein et al, 1996;Hein et al, 1994), are directly precipitated from low-temperature hydrothermal solutions Ingram et al, 1990) and generally have laminated and stratabound forms .…”