Magneto-Mineralogical and Physico-Chemical Characterization of the Peña Colorada Iron-Ore, México: Genetic Implications
Abstract
Peña Colorada iron-ores represented by massive-disseminated ore and intergranular magnetite ore. Mössbauer spectroscopy shows differences in both magnetite-ores. Magnetite of massive-disseminated ore has a stable structure, with Fe in oxidation state III (Fe2O3) and Fe in oxidation state II (FeO). Magnetite of intergranular ore has a micro-margin of replacement with particular properties, because have radicals (OH-) in positions corresponding to oxygen, shifting alternatively Fe II by Fe III. Chlorite associated to intergranular magnetite is classified as chamosite (berthierine variety). Berthierine presents structural differences by X-ray diffraction at 550 oC temperature loosing its cristallinity becoming amorphous. Differential and gravimetric thermal analyses of berthierine show typical endo-thermal reactions at 430 oC and 510 oC by dehydratation, and endo-thermal reaction at 980 oC by structural change. We propose contact metamorphism and a hydrothermal phase, pursued by disseminated-massive magnetite deposition as the main processes acting in the formation of the Peña Colorada iron-ore deposit. Intergranular ore is sedimentary exhalative origin deposited together with berthierine. Massive-disseminated and intergranular ore have similar geochemical evolution and different conditions of deposit. Curie temperatures are mostly 580 ± 5oC typical of magnetite. Hysteresis parameters indicate that most samples present PSD to MD behavior. AF demagnetization and isothermal remanent magnetization (IRM) acquisition curves show that NRM and laboratory remanence are carried by MD magnetite in iron ores and PSD-SD magnetite in host rocks. Magnetic Force Microscope images for both ore minerals show good and diffuse magnetic domain definition, respectively. Lack of clarity of the intergranular ore image is due to environment, temperature and formation conditions related to magnetostatic changes and magnetocrystalline anisotropy of grains.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSMGP31A..04R
- Keywords:
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- 1519 Magnetic mineralogy and petrology;
- 1540 Rock and mineral magnetism;
- 1599 General or miscellaneous