Uranium enrichment in metalliferous sediments from the Mid-Atlantic Ridge

Mills, Rachel A.; Thomson, J.; Elderfield, Henry; Hinton, R. W.; Hyslop, Ewan

doi:10.1016/0012-821x(94)00083-2

Cited by 61 publications

(60 citation statements)

References 40 publications

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“…The samples with low U contents yield some of the older ages as well as younger ages. The U contents of sample 34-T8-1-1 (64.60 ± 0.12 ppb), 34-T8-1-2 All these excludes open system conditions with respect to uranium (Lalou et al 1998b;Kuznetsov et al 2015;Mills et al 1994). …”

Section: Resultsmentioning

confidence: 99%

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

Yang

Tao

et al. 2016

Mar Geophys Res

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Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zones at the central volcano, at 50°28 0 E in the ultraslow-spreading Southwest Indian Ridge (SWIR). Twenty-eight subsamples from a relict chimney and massive sulfides were dated using the 230 Th/ 238 U method. Four main episodes of hydrothermal activity were determined according to the restricted results: 68. 9-84.3, 43.9-48.4, 25.3-34.8, and 0.7-17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. The periodic character of hydrothermal activity may be related to the heat source provided by the interaction of local magmatism and tectonism. The estimated mean growth rate of the sulfide chimney is \0.02 mm/yr. This study is the first to estimate the growth rate of chimneys in the SWIR. The maximum age of the relict chimney in Duanqiao hydrothermal filed is close to that of the chimneys from Mt. Jourdanne (70 kyrs). The hydrothermal activity in Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfides are younger than the sulfides from other hydrothermal fields such as Rainbow, Sonne and Ashadze-2. The preliminarily estimated reserves of sulfide ores of Duanqiao are approximately 0.5-2.9 million tons.

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Section: Resultsmentioning

confidence: 99%

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

Yang

Tao

et al. 2016

Mar Geophys Res

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“…Of particular interest are the Fe-rich metalliferous sediments of the Red Sea, which show U-enrichments (up to 31 ppm) similar to Lengenbach magnetite samples (6-15 ppm U), possibly due to adsorption from sea-water (Ku 1969). U-enriched metalliferous sediments are also known from the Mid-Atlantic Ridge (Mills et al 1994). An interpretation of Lengenbach magnetite as formed originally as iron hydroxide sediment is also consistent with the observed elevated Cs contents, an element readily sorbing to Fe-hydroxides.…”

Section: Element Inventor); Of the Lengenbach Mineralisation Comparedmentioning

confidence: 97%

Geochemistry and genesis of the Lengenbach Pb-Zn-As-Tl-Ba-mineralisation, Binn Valley, Switzerland

Hofmann

Knill

1996

Mineral. Deposita

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Abstract. The Lengenbach Pb-Zn-As-TI-Ba mineralisation is located in Triassic dolostones of the Penninic zone in the Swiss Alps where Alpine metamorphism reached upper greenschist to lower amphibolite grade. Geochemical data are used to constrain the origin of this unique occurrence. Two metamorphic redox environments are present: the As(III)-rich zone is controlled by barite-pyrite while the reduced zone contains graphite or pyrrhotitepyrite and formally zerovalent As. The As(III)-rich zone is characterised by a mineral assemblage consistent withfO2 in the stability field of barite + pyrite. An As-(Pb, T1)-rich sulphide melt coexisted with a hydrothermal fluid at > 300 °C in this zone. Mineralised dolostones are anomalous in As, Pb, Ag, T1, Hg, Zn, Ba, Cd, Fe, Cu, Mo, U, V, B, Ga, Cr and possibly Sn and Au (in order of decreasing enrichment). As, Pb and Zn are present in the 0.1 to 1% range, T1 and Ag reach several hundred ppm. Uraninite is concentrated in silicate-rich bands and yields a late Alpine U-Pb age of 18.5 + 0.5 Ma. Pb-and S isotopic variations are interpreted by metamorphic overprinting and re-equilibration within an isochemically metamorphosed mineralisation. Hydrothermal sulphides are more strongly affected by uranogenic Pb than massive Pb-As-sulphides representing a former sulphide melt. The least overprinted mineralisation is characterised by 2°6pb/2°*pb = 18.44 -18.56, 2°TPb/2°4Pb = 15.60 -15.75, 2°Spb/2°4pb = 38.44 -38.84 and ~534S (sulphide) = -25 + 2%0. S isotopic variations are largely a result of sulphide-sulphate re-equilibration yielding temperatures of 450 + 30°C. SVSr/86Sr ratios of mineralised samples are lower than or equal to host dolostones, precluding major infiltration of basement-derived fluids during Alpine metamorphism. The Sr source (87Sr/86Sr close to 0.708) probably was seawater with a radiogenic, detrital mineral component. The genesis of the unique Lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation. Well-crystallised sulphide minerals in Correspondence to: B.A. Hofmann fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid. The primary mineralisation was probably formed at or close below the sea floor and fed by sulphide-poor hydrothermal fluids. Sulphide was largely derived from seawater by open system bacterial sulphate reduction. U, V and Mo may be seawater-derived.

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“…P 2 O 5 displays little systematic change with depth, though a couple of samples are strongly enriched in phosphorous, which is most likely the result of adsorption of phosphates onto Fe-oxyhydroxides (e.g., Mills et al, 1994).…”

Section: Vfementioning

confidence: 99%

“…These data suggest that both U and P are adsorbed onto Fe-oxyhydroxides in the rocks. It may be possible that discrete secondary phosphate phases contain U (Mills et al, 1994), but there is no direct evidence for this. The increase in U in altered basalts is demonstrated in a plot of Th/U vs. U on which Th/U decreases from an original value of 2.5 (e.g., Sun and McDonough, 1989) with increasing U content.…”

Section: Trace Elementsmentioning

confidence: 99%

Alteration of Upper Ocean Crust in a Ridge-Flank Hydrothermal Upflow Zone: Mineral, Chemical, and Isotopic Constraints from Hole 896A

Teagle¹,

Alt²,

Bach³

et al. 1996

Proceedings of the Ocean Drilling Program, 148 Scientific Results

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Hole 896A penetrates into the upper volcanic section of a ridge-flank hydrothermal upflow zone. Analyses of the secondary mineralogy and chemistry, whole-rock geochemistry, and oxygen, carbon, and strontium isotope ratios of whole rocks and secondary minerals were conducted to constrain the chemical and thermal evolution of hydrothermal alteration and its effects on the upper crust at Site 896.Celadonite ± Fe-oxyhydroxides are the earliest secondary minerals and formed at low temperatures. N -11). A second generation of carbonates formed at higher temperatures (47°-67°C), from seawater-derived fluids with lowered Mg/Ca and Sr/Ca ratios and elevated Fe, and Mn concentrations. Trace-element chemistry of the high-temperature carbonates in general, and the lower 87 Sr/ 86 Sr of rare high-temperature aragonites (0.7079-0.7084) suggest more restricted circulation of seawater and reducing conditions. The higher temperature carbonates formed at temperatures consistent with the present-day thermal regime at Site 896; a ridge-flank hydrothermal upflow zone with basement temperatures greater than 50°C.All rocks from Hole 896A have interacted with seawater at low temperatures, and samples commonly record the integrated legacy of superimposed alteration processes. The most intense chemical changes have occurred within hyaloclastite and fragmentation breccias that comprise at least 5% of the uppermost oceanic crust at Site 896.The sequence of alteration processes present in Hole 896A is broadly similar to that recorded in the upper crust (above 300 m sub-basement) of Hole 504B, which is located approximately 1 km to the northwest, in a zone of average regional heat flow. The main differences between the material from Holes 896A and 504B is the greater abundance of carbonates, and hyaloclastite and fragmentation breccias, and the common occurrence of thick ( l cm) saponite veins in the new hole.

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Uranium enrichment in metalliferous sediments from the Mid-Atlantic Ridge

Cited by 61 publications

References 40 publications

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

Geochemistry and genesis of the Lengenbach Pb-Zn-As-Tl-Ba-mineralisation, Binn Valley, Switzerland

Alteration of Upper Ocean Crust in a Ridge-Flank Hydrothermal Upflow Zone: Mineral, Chemical, and Isotopic Constraints from Hole 896A

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