Bulk Fe Content Research Articles

Magnetic susceptibility variations in carbonates of the La Vid Group (Cantabrian Zone, NW-Spain) related to burial diagenesis

The carbonates of the Lower Devonian La Vid Group in the Cantabrian Zone (NW-Spain) reveal distinct variations in low-field magnetic susceptibility (MS) from base to top. There is good correlation between MS-variations and bulk Fe-content. A predominance of paramagnetic minerals (Fe-carbonate cements, pyrite, Fe-chlorite), mainly responsible for these MS-variations, is evidenced by optical methods, temperature-dependent MS-measurements and high-field magnetisation behaviour. These minerals are members of the diagenetic mineral assemblage formed during migration of a reducing Fe-bearing fluid. We interpret the variation in MS to reflect two stages of Fe-bearing mineral precipitation with an earlier Fe-carbonate and a later Fe-chlorite crystallisation; the latter restricted to interbedded carbonates and shales. Furthermore, porosity has an additional influence on the MS-signature, with high values in coarse-grained sandstones and carbonates, and lower values in fine-grained dolostones and limestones. This study highlights the influence of diagenetic mineral formation on MS-variations in carbonate-bearing successions.

生物起源珪藻土からの高純度シリカの製造について

Diatomaceous earth, which is found throughout the world, is mainly composed of diatom crusts associated with a small amount of clay and detrital rocks. The diatom crust, amorphous silica, is characterized by dissolution in caustic alkaline solution. In this study we examined the distribution of silica and trace elements leached from diatomaceous earth by 10 w / v % NaOH solution in detail. The results are as follows:(1) 31 diatomite samples of seawater origin were collected from 4 ore deposits located in Akita Prefecture and 28 samples of freshwater origin were collected from 2 ore deposits in Okayama and Oita Prefecture. The specimens mainly consisted of a white or grayish white assemblage of diatoms in the range of μ ∼ mm order.(2) By qualitative analysis, abundant silica and small amounts of 16 elements in dissolved solutions were detected, while the presence of 26 elements in bulk specimens were confirmed. Taking into account the sensitivities of the AAS and ICP-AES analyses, Si, Al, K, Fe and B were quantitatively analyzed. An abundance of silica extracted from diatomite reached 86 ∼ 98 % in bulk samples, Al, K and Fe content were relatively high in the range of 25,000 ∼ 200 ppm. B was present at the less than 150 ppm. Based on similarities among the distribution patterns of each element, it was observed that Silica and B were derived from diatoms, and Al, K and Fe from detrital rocks.(3) The need for high quality silica as a raw material has been increasing, and reserves of high purity quartz will be exhausted in the near future; thus, how to produce high quality silica from diatomaceous earth is of great importance. In particular, the B content in silica must be very low below a few ppm. At present, some solutions extracted from diatomite with a freshwater origin have lower concentrations (4.3 ∼ 13 ppm) than those of seawater origin(80 ∼ 150 ppm). From the data we suggest that diatomaceous earth should be considered as a potential source of high purity silica.

Light noble gases and cosmogenic radionuclides in Estherville, Budulan, and other mesosiderites: Implications for exposure histories and production rates

Abstract— We report measurements of 26AI, 10Be, 41Ca, and 36Cl in the silicate and metal phases of 11 mesosiderites, including several specimens each of Budulan and Estherville, of the brecciated meteorite Bencubbin, and of the iron meteorite Udei Station. Average production rate ratios (atom/atom) for metal phase samples from Estherville and Budulan are 26Al/10Be = 0.77 ± 0.02; 36Cl/10Be = 5.3 ± 0.2. For a larger set of meteorites that includes iron meteorites and other mesosiderites, we find 26Al/10Be = 0.72 ± 0.01 and 36Cl/10Be = 4.5 ± 0.2. The average 41Ca/36Cl production rate ratio is 1.10 ± 0.04 for metal separates from Estherville and four small iron falls. The 41Ca activities in dpm/(kg Ca) of various silicate separates from Budulan and Estherville span nearly a factor of 4, from <400 to >1600, indicating preatmospheric radii of >30 cm. After allowance for composition, the activities of 26Al and 10Be (dpm/kg silicate) are similar to values measured in most ordinary chondrites and appear to depend only weakly on bulk Fe content. Unless shielding effects are larger than suggested by the 36Cl and 41Ca activities of the metal phases, matrix effects are unimportant for 10Be and minor for 26Al.Noble gas concentrations and isotopic abundances are reported for samples of Barea, Emery, Mincy, Morristown, and Marjalahti. New estimates of 36Cl/36Ar exposure ages for the metal phases agree well with published values. Neon‐21 production rates for mesosiderite silicates calculated from these ages and from measured 21Ne contents are consistently higher than predicted for L chondrites despite the fact that the mesosiderite silicates have lower Mg contents than L chondrites. We suggest that the elevation of the 21Ne production rate in mesosiderite silicates reflects a “matrix effect,” that is, the influence of the higher Fe content of mesosiderites, which acts to enhance the flux of low‐energy secondary particles and hence the 21Ne production from Mg. As 10Be production is relatively insensitive to this matrix effect, 10Be/21Ne ages give erroneously low production rates and high exposure ages. By coincidence, standard 22Ne/21Ne based “shielding” corrections give fairly reliable 21Ne production rates in the mesosiderite silicates.

Thermal parameters of the Earth's lower mantle

Laboratory and seismological measurements of bulk and shear moduli ( K S and μ S) have been combined to derive the specific temperature and frequency dependencies of pressure, K S and μ S as a function of depth in the lower mantle of the Earth. The results depend on the mineralogical model and temperature profiles chosen, as well as on the bulk Fe content in the lower mantle. If the Fe/Mg+Fe content in the lower mantle does not exceed 0.15, two important conclusions remain after a large variety of models have been investigated. (1) High-frequency (MHz or GHz) laboratory measurements of μ S of mantle phases should be corrected by 3–20% before comparison with seismological data can be done. Dispersion laws such as those provided by the PREM model underestimate this correction. (2) The lower mantle material, described as a Debye solid, cannot be silicon rich (e.g., pure perovskite) and the values of K 0′ are constrained between 3.5 and 3.7.

Sulfide melt-silicate melt distribution coefficients for nickel and iron and implications for the distribution of other chalcophile elements

Distribution coefficients for Fe and Ni between sulfide and silicate melts have been determined as functions of f; O 2 and f; S 2 . Experiments were carried out in a piston-cylinder apparatus at 1450°C and 8 kbars. In a system at sulfide saturation the f; S 2 , f; O 2 and a FeO are interdependent; therefore, it was possible to vary f; O 2 / f; S 2 systematically by changing the bulk Fe content of the starting materials. This was accomplished in two ways, first by varying the sulfide to silicate mass ratio and second by synthesizing silicate starting materials of differing FeO contents. The f; O 2 / f; S 2 was further constrained by the choice of graphite capsule material combined with pre-oxidation of the starting silicate. This produced melts which were saturated or nearly saturated in C-O-S vapor. The f; O 2 and f; S 2 were computed from the independent relationships of f; O 2 / f; S 2 , with vapor and silicate melt compositions. The molar distribution coefficients of Ni and Fe, D(Ni mol) (= X sulf NiSX sil Nio) and D(Fe mol), exhibit strong dependencies on the molar S concentration of the sulfide melt and FeO content of the silicate melt. D(Ni mol) ranges from 1458 to 8857 for sulfide melt S concentrations of 45.8 to 51.1 mol%, respectively. Negative correlations of log D(Ni mol) and log D(Fe mol) with log ( f; O 2 / f; S 2 ) are consistent with reactions between sulfide and oxide components of these elements in both melts and indicate that the controlling equilibrium is MO sil + 1/2 S 2 = MS sulf + 1/2 O 2, (M = metal). The different values of D(Ni wt) reported in the literature can be rationalized in terms of differences in f; O 2 / f; S 2 of the experiments. It is suggested that all chalcophile elements, including PGEs, behave similarly. In particular, it is demonstrated that D(Ir wt) and D(Pd wt) vary directly with the S content of the sulfide melt and indirectly with f; O 2 in published experiments. For the possible range in f; O 2 / f; S 2 of sulfide-saturated magmas in nature, variations in Ds for Ni and the other chalcophile elements of more than one order of magnitude may exist.

The surface composition of lunar soil grains: A comparison of the results of Auger and X-ray photoelectron (ESCA) spectroscopy

ESCA spectra of lunar soil and crushed rock samples are compared to previously obtained Auger spectra of the same samples. The ESCA data confirm the increase of Fe concentration on the surface of soil samples vs. their bulk Fe content; and strongly support the existence of layers on the surfaces of lunar soil grains which are significantly enriched in Fe, some of which is in the Fe° state. The significance of the ESCA information on the major elemental composition of lunar soil grain surfaces for the understanding of the processes that affect the state of the regolith is discussed.