593 resultados para trace elements in minerals
Resumo:
Hydrothermal deposits "sensu stricto" have been recovered during the FAMOUS cruise and Leg 54 of the Deep Sea Drilling Project near the Galapagos Spreading Centre. The studied sediments, mainly composed of clay material, have very poor REE concentrations, below about ten ppm. The shale-normalized patterns are characterized by a significant enrichment in heavy rare earths and show a negative Ce anomaly. The magnitude of this anomaly fluctuates but is generally lower than the seawater Ce anomaly. The geochemical characteristics of these hydrothermal deposits are in contrast with those of metalliferous sediments which are more enriched in trace elements, especially in REE.
Resumo:
The study of vertical distribution of Mo, V, Co, Ni, and Cu in mass of Black Sea sediments showed that maximum concentrations occur in sapropelic muds of ancient Black Sea deposits. A special study of sapropels samples showed a sufficiently clear correlation of Cu, Ni, Mo, and V contents with organic carbon contents; Co contents do not show such a correlation, but show one with contents of pyrite sulfur. A study of fractions of bitumen, free humic and fulvic acids showed that some part of metal contents in the sediments is bound with organic matter. It is shown that increased concentrations of trace elements in sapropels result from removing of dissolved metals from seawater by organic detritus during deposition on the bottom, in vivo concentration of metals in plankton organisms is of secondary importance.
Resumo:
One of the objectives of the Cape Roberts Project is to study the tectonic history of the western Ross Sea region. Timing of the uplift of the Transantarctic Mountains, which are adjacent to the drillsite, will be a component of the tectonic studies (International Steering Committee, 1994; Cale Roberts Science Team, 1998a). The study of the clast samples from the core will be an important means of providing insight into the timing of uplift of the Transantarctic Mountains. Tholeiitic igneous rocks of the Jurassic (180 Ma) Ferrar large igneous province (FLIP) are widespreaded along the Transantarctic Mountains and have the potential to provide distinct indicators of erosion during uplift of the mountains. In the Transantarctic Mountains adjacent to the Cape Roberts drill site the FLIP is represented by lavas and pyroclastic of the Kirkpatrick basalts and by thick Ferrar dolerite sills which intrude the Beacon Supergroup sediments and, occasionally, the granitic basement rocks. In the Prince Albert Mountains, the youngest Kirkpatrick basalt lava is over 150 m thick, and has a very distinct high TiO2 chemical composition which is unique in the FLIP. If such rocks can be identified in the core they may provide precise timing of the initiation of uplift and denudation of the Transantarctic Mountains. Here we report on an examination of 20 Ferrar dolerite clasts. This brief report is intended as a pilot study to the examination of FLIP clasts from older drillcore.
Resumo:
The timing and nature of the penultimate deglaciation, also known as Termination II (T-II), is subject of controversial discussions due to the scarcity of precisely-dated palaeoclimate records. Here we present a new precisely-dated and highly-resolved multi-proxy stalagmite record covering T-II from the high alpine Schafsloch Cave in Switzerland, an area where climate is governed by the North Atlantic. The inception of stalagmite growth at 137.4 ± 1.4 kyr before present (BP) indicates the presence of drip water and cave air temperatures of above 0 °C, and is related to a climate-induced change in the thermal state (from cold-to warm-based) of the glacier above the cave. The cessation of stalagmite growth between 133.1 ± 0.7 and 131.9 ± 0.6 kyr BP is most likely related to distinct drop in temperature associated with Heinrich stadial 11. The resumption of stalagmite growth at 131.9 ± 0.6 kyr BP is accompanied by an abrupt increase in temperature and precipitation as indicated by distinct shifts in the oxygen and carbon isotopic composition as well as in trace element concentrations. The mid-point of T-II is around 131.8 ± 0.6 kyr BP in the Schafsloch Cave record is significantly earlier compared to the age of 129.1 ± 0.1 kyr BP in the Sanbao Cave record from China. The different ages between both records can be best explained by the competing effects of insolation and glacial boundary forcing on seasonality and snow cover extent in Eurasia.
Resumo:
Contents and distributions of Cu, Ni, Co, V, Cr, Zn, Pb, Mo, W, and Zr in near-coast and pelagic sediments of the Northern Indian Ocean are under consideration in the paper. Chemical analyses showed enrichment of pelagic clayey radiolarian oozes by Mn, Cu, Ni, Co, Pb, W, and Mo. According to enrichment factors these elements have the following order: Mo> Mn> Cu> Ni> Co> Pb> W. Enrichment of pelagic sediments from the Indian Ocean is mainly determined by the mechanism of the sedimentation process. Enrichment factors of Cu, Ni, Co, W, Mo, and Mn in pelagic sediments of the North Indian Ocean are intermediate between ones in pelagic sediments of the Pacific and Atlantic Oceans.
Resumo:
Basement intersected in Holes 525A, 528, and 527 on the Walvis Ridge consists of submarine basalt flows and pillows with minor intercalated sediments. These holes are situated on the crest and mid- and lower NW flank of a NNW-SSE-trending ridge block which would have closely paralleled the paleo mid-ocean ridge. The basalts were erupted approximately 70 Ma, a date consistent with formation at the paleo mid-ocean ridge. The basalt types vary from aphyric quartz tholeiites on the Ridge crest to highly Plagioclase phyric olivine tholeiites on the flank. These show systematic differences in incompatible trace element and isotopic composition, and many element and isotope ratio pairs form systematic trends with the Ridge crest basalts at one end and the highly phyric Ridge flank basalts at the other. The low 143Nd/144Nd (0.51238) and high 87Sr/86Sr (0.70512) ratios of the Ridge crest basalts suggest derivation from an old Nd/Sm and Rb/Sr enriched mantle source. This isotopic signature is similar to that of alkaline basalts on Tristan da Cunha but offset by somewhat lower 143Nd/144Nd values. The isotopic ratio trends may be extrapolated beyond the Ridge flank basalts (which have 143Nd/144Nd of 0.51270 and 87Sr/86Sr of 0.70417) in the direction of typical MORB compositions. These isotopic correlations are equally consistent with mixing of depleted and enriched end-member melts or partial melting of an inhomogeneous, variably enriched mantle source. However, observed Zr-Ba-Nb-Y interelement relationships are inconsistent with any simple two-component model of magma mixing or partial melting. They also preclude extensive involvement of depleted (N-type) MORB material or its mantle sources in the petrogenesis of Walvis Ridge basalts.
Resumo:
The comparison of Mn/Fe, Co/Ni, Co/Fe, Ni/Mn, and Cu/Fe ratios is presented and it is noticed that Co/Ni and Ni/Mn ratios of nodules fairly coincide with those of coexisting sediments. This agreement suggests that Mn, Ni, and Co are accumulated in both nodules and sediments at about the same rates. According to the calculation of Somayajulu et al. similar consideration is also applicable to Cu. Results are, however, implying that Cu co-precipitates with Fe, rather than Mn.
Resumo:
The gross changes in concentrations of several trace elements in seawater after contact with ferro-manganese particle suspensions has been determined. Cobalt, Fe, and Zn concentrations in the seawater were greatly increased after contact with the par¬ticles. The concentrations of Rb, U, Cs, Sb, and Ag were altered to a lesser degree by this treatment. Similar results were observed where seawater was con¬tacted with suspensions of pelagic sediments. Of the trace elements measured, cobalt and iron appear to be the best elemental indicators of the presence of manganese mining effluents in the ocean. The addi¬tions of the essential elements Co, Fe and Zn toge¬ther with nutrients from the bottom waters may pro¬duce increased biological productivity. However, the toxic trace metals, such as Hg, Cu and Cd which could enter ocean water from the nodules and sedi¬ment and which may be high in effluent-affected areas should be investigated before conclusions as to the likely impact can be reached. Trace element analysis of seawater samples collected at a Pacific Ocean manganese nodule dredging site showed high t race element concentrations, but these are believed to have resulted from contamination during sample collection or storage rather than from the dredging operations.
Resumo:
A detailed description of the ores of Lake Storsjoen was given by Vogt J. H. L., 1915 who pointed out that the ores may be divided into two principal types; first, iron ore with 2% or less of manganese (ex: Ertemalm), and, second, ores with manganese contents of up to 30% (ex: Korinter). The iron-rich ore sometimes occurs as a conglomerate embedded in manganese-rich ores, clearly demonstrating that two distinctly different precipitates are involved. In the iron-rich ore, a concentric structure is common of which light brown layers of loose, almost dusty material alternate with hard and brittle black layers, the thickness of each being 0.5 mm or less. The analyses presented in this paper seem to demonstrate that the composition of the sedimentary ores of Lake Storsjden could result from fluctuations in the composition of ground waters feeding the lake.
Resumo:
The evolution through time of trace element contents (Sr, Mg, Mn, and Fe) of sediments at Sites 549 and 550 is similar to that of previously studied oceanic sites. A comparison with some North Atlantic sites and with outcrops of the Gubbio section (Italy) allowed us to show that 1. A negative correlation between Sr and Mg contents, generally characteristic of pelagic carbonate having undergone diagenesis, is confirmed. 2. Magnesium diagenesis occurs over a relatively short time and is sensitive to the sedimentation rate of each individual time period, whereas Sr diagenesis is a long-term phenomenon and is sensitive to the overall average sedimentation rate at the site. Strontium loss by sediments is related to sediment age (i.e., residence time of sediments in a given diagenetic environment) and could be a rough method of dating individual sediment layers. 3. The nature of the seafloor (oceanic or continental) does not appear to play an important part in the content of Fe and Mn in sediments. Their distribution depends more on mid-oceanic ridge activity, paleodepth (through mediation of CaCO3 dissolution and environment), and distance of the site from the ridge.
Resumo:
Snow samples collected from hand-dug pits at two sites in Simcoe County, Ontario, Canada were analysed for major and trace elements using the clean lab methods established for polar ice. Potentially toxic, chalcophile elements are highly enriched in snow, relative to their natural abundance in crustal rocks, with enrichment factor (EF) values (calculated using Sc) in the range 107 to 1081 for Ag, As, Bi, Cd, Cu, Mo, Pb, Sb, Te, and Zn. Relative to M/Sc ratios in snow, water samples collected at two artesian flows in this area are significantly depleted in Ag, Al, Be, Bi, Cd, Cr, Cu, Ni, Pb, Sb, Tl, V, and Zn at both sites, and in Co, Th and Tl at one of the sites. The removal from the waters of these elements is presumably due to such processes as physical retention (filtration) of metal-bearing atmospheric aerosols by organic and mineral soil components as well as adsorption and surface complexation of ionic species onto organic, metal oxyhydroxide and clay mineral surfaces. In the case of Pb, the removal processes are so effective that apparently ''natural'' ratios of Pb to Sc are found in the groundwaters. Tritium measurements show that the groundwater at one of the sites is modern (ie not more than 30 years old) meaning that the inputs of Pb and other trace elements to the groundwaters may originally have been much higher than they are today; the M/Sc ratios measured in the groundwaters today, therefore, represent a conservative estimate of the extent of metal removal along the flow path. Lithogenic elements significantly enriched in the groundwaters at both sites include Ba, Ca, Li, Mg, Mn, Na, Rb, S, Si, Sr, and Ti. The abundance of these elements can largely be explained in terms of weathering of the dominant silicate (plagioclase, potassium feldspar, amphibole and biotite) and carbonate minerals (calcite, dolomite and ankerite) in the soils and sediments of the watershed. Arsenic, Mo, Te, and especially U are also highly enriched in the groundwaters, due to chemical weathering: these could easily be explained if there are small amounts of sulfides (As, Mo, Te) and apatite (U) in the soils of the source area. Elements neither significantly enriched nor depleted at both sites include Fe, Ga, Ge, and P.