Thermal alteration of the magnetic mineralogy in ferruginous rocks

Hirt, Ann M.; Gehring, A. U.

doi:10.1029/91jb00573

Cited by 78 publications

(48 citation statements)

References 17 publications

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“…The values of χ FD % in the mineralized sample of 2-14 nm magnetite nanoparticles and Mössbauer spectroscopy identified a significant proportion of SP particles. The results of a magnetic susceptibility versus temperature experiment of the 2-14 nm sample that was repeated in rapid succession suggest the formation of new magnetite nanoparticles, which is similar to the results obtained by Hirt and Gehring (1991).…”

Section: Introductionsupporting

confidence: 74%

“…Berthierine is typically paramagnetic at room temperature. Hirt and Gehring (1991) found that magnetite is created in heating experiments, and this certainly occurred during a number of hydrothermal processes in our study area. This occurrence can explain the Mössbauer spectrum obtained in our case, which is the emerging of a ferromagnetic phase.…”

Section: Mössbauer Spectroscopymentioning

confidence: 99%

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Natural magnetite nanoparticles from an iron-ore deposit: size dependence on magnetic properties

et al. 2009

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We report on the discovery of magnetite nanoparticles ranging in size from 2 to 14 nm in the mineralized zones of the Peña Colorada iron-ore deposit, southern Mexico. Micrometric scale magnetite was magnetically reduced and divided into distinct size ranges: 85-56 μm, 56-30 μm, 30-22 μm, 22-15 μm, 15-10 μm, 10-7 μm and 7-2 μm. Nanometric-scale magnetite in the size range 2-14 nm was identified. The magnetite was characterized by X-ray diffraction, transmitted and reflected light microscope, high-resolution transmission electron microscopy (TEM), high angle annular dark field, Mössbauer spectroscopy and its magnetic properties. Crystallographic identification of nanostructures was performed using high-resolution TEM. Characteristic changes were observed when the particles make the size transition from micro-to nanometric sizes, as follows: (1) frequency-dependent magnetic susceptibility percentage (χ FD %) measurements show high values (13%) for the 2-14 nm fractions attributed to dominant fractions of superparamagnetic particles; (2) variations of χ FD % < 4.5% in fractions of 56-0.2 μm occur in association with the presence of microparticles formed by magnetite aggregates of nanoparticles (<15 nm) embedded in berthierine; (3) Mössbauer spectroscopy results identified a superparamagnetic fraction; (4) nanometric and 0.2-7 μm grain size magnetite particles require a magnetic field up to 152 mT to reach saturation during the isothermal remanent magnetization experiment; (5) coercivity and remanent magnetization of the magnetite increase when the particle size decreases, probably due to parallel coupling effects; (6) twomagnetic susceptibility versus temperature experiments of the same 2-14 nm sample show that the reversibility during the second heating is due to the formation of new magnetite nanoparticles and growth of those already present during the first heating process.

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Section: Introductionsupporting

confidence: 74%

Section: Mössbauer Spectroscopymentioning

confidence: 99%

Natural magnetite nanoparticles from an iron-ore deposit: size dependence on magnetic properties

et al. 2009

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“…Some are SEDEX in origin (Damyanov and Vassileva, 2001;Xu and Veblen, 1996;Kimberley, 1989;Curtis andSpears, 1968 Wiewiora et al, 1998), other sulfide massive volcanogenic (Slack et al, 1992), metamorphic origin (Wybrecht et al, 1985), and associated to bauxite and laterite (White et al, 1985;Toth and Fritz, 1997). These minerals also occur in Northampton ironstone (Hirt and Gehring, 1991), in paleosol near Waterval Onder, South Africa (Retallack, 1986), in the oolitic ironstone beds, Hazara, Lesser Himalayan Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. thrust zone (Yoshida, 1998), in metamorphic rock in the Sierra Albarrana pegmatite body (Del Mar Abad-Ortega and Nieto, 1995), in the coal-swamp deposits in Paleogene and Upper Triassic coal, Japan (Iijima and Matsumoto, 1982).…”

Section: Introductionmentioning

confidence: 99%

Berthierine and chamosite hydrothermal: genetic guides in the Peña Colorada magnetite-bearing ore deposit, Mexico

et al. 2006

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We report the first finding of berthierine and chamosite in Mexico. They occur in the iron-ore deposit of Peña Colorada, Colima. Their genetic characteristics show two different mineralization events associated mainly to the magnetite ore. Berthierine is an Fe-rich and Mg-low 1:1 layer phyllosilicate of hydrothermal sedimentary origin. Its structure is 7Å, d hkl [1 0 0] basal spacing and low degree structural ordering. The phyllosilicate has been identified by a lack of 14Å basal reflection on X-ray diffraction (XRD) patterns. These data were supported by High Resolution Transmision Electron Microscopy (HRTEM) images that show thick packets of berthierine in well defined parallel plates. From the analysis of Fast Fourier Transform (FFT), we found around [1 0 0] reflections of berhierine 7.12Å and corresponding angles of hexagonal crystalline structure. Berthierine has a microcrystalline structure, dark green color, and high refraction index (1.64 to 1.65). Birefringence is low, near 0.007 to null and it is associated to nanoparticles (<15 nm) and microparticles of magnetite (<25 μm), fine grain siderite, and organic matter. Its texture is intergranular-interstratified with colloform banding. The chamosite Mg-rich is of hydrothermal epigenetic origin affected by low-degree metamorphism. It is an Fe-rich 2:1 layer silicate, with basal space of 14Å, d hkl [0 0 1]. The chamosite occurs as lamellar in sizes ranging from 50 to 150 μm. It has intense green color and refraction index from 1.64 to 1.65. The birefringence is near 0.008, with biaxial (-) orientation and a 2V small. It is associated mainly to sericite, epidote, clay, feldspar, and magnetite. Chamosite is emplaced in open spaces filling and linings. Mössbauer spectra of berthierine and chamosite are similar. They show the typical spectra of paramagnetic substances, with two well defined unfoldings corresponding to the oxidation state of Fe +2 and Fe +3 . Chemical composition of both minerals was obtained by an electron probe X-ray micro-analyzer (EPMA). The radio Fe+Mg+Mn vs Si and Al show similar chemical compositions and different XRD patterns in the crystalline structure provoked by the environmental conditions of emplacement. A hydrothermal environment was predominant, occurring before, during, and after the magnetite mineralization. The identification of magnetite nanoparticles supports the hypothesis of a marine environment, specifically exhalative sedimentary (SEDEX) for the berthierine.

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“…Hus [1990] found that room temperature oxidation of siderite created hematite, which acquired a fieldcontrolled, very stable crystalline remanent magnetization and concluded that siderite heated in air did not show magnetic interactions between the dissociation products hematite and maghemite. Hirt and Gehring [1991] studied the low-temperature bulk susceptibility and isothermal remanent magnetization (IRM) of the Northampton ironstone and concluded that siderite-rich samples were mineralogically stable in air over years, in contrast to Ellwood e! al.…”

Section: Introductionmentioning

confidence: 99%

Rock magnetic properties related to thermal treatment of siderite: Behavior and interpretation

Pan¹,

Zhu²,

Banerjee³

et al. 2000

J. Geophys. Res.

118

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Abstract. Detailed analyses of rock magnetic experiments were conducted on the oxidation products of high-purity natural crystalline siderite that were thermally treated in air atmosphere. Susceptibilities increase sharply between 400 ø and 530øC indicative of some new ferrimagnetic mineral phase generation. Both a drop (between 540 ø and 590øC) on the heating cycle and a dramatic increase (from 590øC to 520øC) on the cooling cycle occurred and are well consistent with the characteristic of magnetite. A distinct Hopkinson-type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700øC over and over. It has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite-bearing specimens is changed to a normal magnetic fabric during incremental heating over 410ø-490øC. This is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals. A strong chemical-viscous remanent magnetization could be produced during siderite oxidation in an external field. Rock magnetic experimental results show that magnetite, maghemite, and hematite are the transformation products of high-temperature oxidation of siderite in air. Maghemite was not completely inverted to hematite even at temperature as high as 690øC during incremental thermal treatments. The mineral transformation processes were confirmed by conventional optical microscopic observation, X-ray diffractometry and M6ssbauer spectroscopic analyses. These results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks. We conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments. Furthermore, it is clear that great care should be exercised in thermal demagnetization of siderite-bearing rocks in paleomagnetic, magnetic anisotropy, and rock magnetic studies.

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Thermal alteration of the magnetic mineralogy in ferruginous rocks

Cited by 78 publications

References 17 publications

Natural magnetite nanoparticles from an iron-ore deposit: size dependence on magnetic properties

Natural magnetite nanoparticles from an iron-ore deposit: size dependence on magnetic properties

Berthierine and chamosite hydrothermal: genetic guides in the Peña Colorada magnetite-bearing ore deposit, Mexico

Rock magnetic properties related to thermal treatment of siderite: Behavior and interpretation

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