DOCSLIB.ORG

Magnetic Proxy Parameters 525

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetic Proxy Parameters 525 Comp. by: DShiva Date:15/2/07 Time:14:54:18 Stage:1st Revises File Path://spiina1001z/womat/production/ PRODENV/0000000005/0000001725/0000000022/000000A296.3D Proof by: QC by: MAGNETIC PROXY PARAMETERS 525 of terrestrial, synthetic, and lunar ilmenites. Earth and Planetary practice one should look for parameters that describe the essential parts Science Letters, 26: 377–386. of the system. Because these parameters can only describe the system Smirnov, A.V., and Tarduno, J.A., 2002. Magnetic field control of the in an approximate fashion they are termed “proxy parameters” or low-temperature magnetic properties of stoichiometric and cation- “proxies.” There exists a myriad of proxies including the chemical deficient magnetite. Earth and Planetary Science Letters, 194: analysis of inorganic or organic compounds, the number and types 359–368. of living and fossil biota, and the physical properties of a sample, such Snowball, I., and Torii, M., 1999. Incidence and significance of magnetic as grain-size distribution, porosity, magnetic properties, etc. Basically, iron sulphides in Quaternary sediments and soils. In Maher, B.A., and each physical, chemical, or biological parameter that is measurable Thompson, R. (eds.), Quaternary Climates, Environments and reasonably quickly at reasonable cost may serve as proxy to describe Magnetism. Cambridge: Cambridge University Press, pp. 199–230. a complete system. One should realize that up to over several thou- Strangway, D.W., Honea, R.M., McMahon, B.E., and Larson, E.E., sands of data points are rapidly gathered in a case study. Combinations 1968. The magnetic properties of naturally occurring goethite. of two or more of those parameters may yield valuable proxies as well. Geophysical Journal of the Royal Astronomical Society, 15: Another important condition for a parameter to serve as proxy is that 345–359. its meaning must be understood. This pertains to the analytical point Syono, Y., 1965. Magnetocrystalline anisotropy and magnetostriction of view as well as to its functioning in the natural system. In the fol- of Fe3O4–Fe2TiO4 series—with special application to rocks mag- lowing, we outline the merit and potential of the so-called mineral- netism. Japanese Journal of Geophysics, 4:71–143. magnetic proxies. Taylor, R.M., and Schwertmann, U., 1974. Maghemite in soils and its From the analytical viewpoint, the assets of mineral-magnetic or origin. I. Properties and observations on soil maghemites. Clay rock-magnetic proxy parameters are manifold. They include sensitivity, Minerals, 10: 289–298. rapidity, ease of sample preparation, comparatively modestly priced Thorpe, A.N., Minkin, J.A., Senftle, F.E., Alexander, C., Briggs, C., instrumentation for data acquisition, nondestructiveness, and in parti- Evans, H.T. Jr., and Nord, G.L. Jr., 1977. Cell dimensions and cular the ability to sense grain-size variation in the ultrafine grain-size antiferromagnetism of lunar and terrestrial ilmenite single crystals. range. Magnetic properties refer to bulk sample properties in contrast Journal of Physics and Chemistry of Solids, 38:115–123. to (electron) microscopical techniques where often only a small frac- Tucker, P., 1981. Low-temperature magnetic hysteresis properties of tion of a sample can be analyzed. Therefore, mineral-magnetic para- multidomain single-crystal titanomagnetite. Earth and Planetary meters are well suited as proxy parameters. As drawbacks should be Science Letters, 54: 167–172. mentioned that some of the parameters are nonunique, and that their Uyeda, S., 1958. Thermo-remanent magnetism as a medium of palaeo- scales are most often utilized in a relative sense. Often ratios of several magnetism, with special reference to reverse thermo-remanent parameters are used to reduce nonuniqueness. The meaning of a ratio magnetism. Japanese Journal of Geophysics, 2:1–123. may change depending on the absolute values of numerator and deno- van der Lugt, W., and Poulis, N.J., 1961. The splitting of the nuclear minator; hence, may vary among case studies. Proper interpretation of magnetic resonance lines in vivianite. Physica, 27: 733–750. a mineral-magnetic data set therefore requires expert training and a Verwey, E.J.W., 1939. Electronic conduction of magnetite (Fe3O4) and feel for potential variability in the data cloud. its transition point at low temperatures. Nature, 44: 327–328. Verwey, E.J.W., and Haayman, P.W., 1941. Electronic conductivity and transition point of magnetite (“Fe3O4”). Physica, 8: 979–987. Magnetism Walz, F., 2002. The Verwey transition—a topical review. Journal of Mineral-magnetic parameters refer to the concentration and properties Physics: Condensed Matter, 14: R285–R340. of iron oxides (and some iron sulfides), minerals that occur in trace Weiss, P., and Forrer, R., 1929. La saturation absolue des ferromagné- amounts in any rock, soil, or even organic tissue. In quantum tiques et les lois d’approche en fonction du champ et de la tempéra- mechanics, electrons are assigned orbital and spin magnetic moments. ture. Annales de Physique,10e série, 12: 279–374. For magnetism, the spin moment is most important: each electron can Weiss, P., and Renger, K., 1914. Die anfängliche Permeabilität von be regarded as a microscopic magnet. In most compounds electrons act Eisen und Magnetit in Funktion der Temperatur und die Abhängig- independently and consequently a very low-magnetic moment is mea- keit der Umwandlungspunkte von der Feldstärke. Archiv für sured in applied magnetic fields and no permanent or remanent Electrotechnik, 2: 406–418. magnetic moment can exist. This is the case in diamagnetic and Zergenyi, R.S., Hirt, A.M., Zimmermann, S., Dobson, J.B., and paramagnetic substances. Diamagnetism—occurring in compounds Lowrie, W., 2000. Low-temperature magnetic behavior of ferrihy- with no unpaired electron spins—is characterized by a small but nega- drite. Journal Geophysical Research, 105: 8297–8303. tive magnetic moment in applied fields. It is a property of all matter because all paired electrons yield a diamagnetic moment. Paramagnet- — — Cross-references ism characteristic of compounds with unpaired electron spins yields a positive magnetic moment that outweighs diamagnetic Iron Sulfides moments very quickly. Magnetic Mineralogy, Changes due to Heating By virtue of exchange interaction, a property described also by Magnetic Proxy Parameters quantum mechanics, the outermost electrons of transition elements Rock Magnetism may act collectively in some compounds, provided that their orbitals Rock Magnetism, Hysteresis Measurements sufficiently overlap. For the first row transition elements, this situation occurs in metal oxides. In nature, iron is the most important element and the collective electron behavior is termed ferromagnetism (sensu lato). Several classes of ferromagnetism are distinguished: ferromag- MAGNETIC PROXY PARAMETERS netism, ferrimagnetism, and antiferromagnetism (Figure M48). Ferromagnetic and ferrimagnetic materials have very large magnetic moments in applied fields, several orders of magnitude larger than a Introduction typical paramagnet. Antiferromagnetic materials ideally would have As a rule, a natural system is complex and the result of the interplay of a net magnetic moment of zero but in reality usually a weak moment numerous constituting parameters. To fully describe such systems, ide- persists. Collective spin behavior gives rise to the existence of perma- ally each (independent) parameter must be known. However, their nent or remanent magnetization, i.e., magnetic moments that remain mere number would imply a substantial analytical operation and in after removal of an external magnetic field. The magnetic properties Comp. by: DShiva Date:15/2/07 Time:14:54:19 Stage:1st Revises File Path://spiina1001z/womat/production/ PRODENV/0000000005/0000001725/0000000022/000000A296.3D Proof by: QC by: 526 MAGNETIC PROXY PARAMETERS of ferromagnets (sensu lato) are dependent on mineral type, tem- mineral; it is one of the endmembers of the titanohematite solid-solution perature, grain size, and strain state of the grain. Subtle variations in series (the other endmember is ilmenite, FeTiO3). Goethite magnetic properties can thus be interpreted in terms of changing con- (a-FeOOH), pyrrhotite (Fe7S8), and greigite (Fe3S4) are often referred centration, grain size, or strain state of the magnetic materials. In a to as minor magnetic minerals. Some copper minerals show magnetic geoscientific context, in turn, these can be interpreted along the lines properties as well but their occurrence is restricted to certain iron of changes in catchment area, in climate, in diagenesis, or in oxidation types. Metallic iron is very rare in terrestrial environments but occurs degree when dealing with a series of lava flows. This is exploited prominently in meteorites. Magnetic minerals can be distinguished from when utilizing magnetic properties as proxy parameters. each other by their Curie point temperature, the temperature above which collective behavior is lost and a paramagnetic substance re- Magnetic minerals mains. When dealing with antiferromagnetic minerals the temperature at which collective behavior is lost, is referred to as Néel point tem- – In nature, magnetic minerals are largely restricted to iron titanium oxi- perature. In practice Curie and Néel temperature are used inter- des that may contain minor amounts of substituted aluminum, chro- changeably. When cooling below the Curie or Néel temperature, mium, manganese, and magnesium. The most important
Load more

Recommended publications
  • CERI 7022/8022 Global Geophysics Spring 2016
    FerrimagnetismI I Recall three types of magnetic properties of materials I Diamagnetism I Paramagnetism I Ferromagnetism I Anti-ferromagnetism I Parasitic ferromagnetism I Ferrimagnetism I Ferrimagnetism I Spinel structure is one of the common crystal structure of rock-forming minerals. I Tetrahedral and octahedral sites form two sublattices. 2+ 3+ I Fe in 1/8 of tetrahedral sites, Fe in 1/2 of octahedral sites. FerrimagnetismII I xmujpkc.xmu.edu.cn/jghx/source/chapter9.pdf Ferrimagnetism III I www.tf.uni-kiel.de/matwis/amat/def_en/kap_2/basics/b2_1_6.html I Anti-spinel structure of the most common iron oxides 3+ 3+ 2+ I Fe in 1/8 tetrahedral sites, (Fe , Fe ) in 1/2 of octahedral sites. FerrimagnetismIV I Indirect exchange involves antiparallel and unequal magnetization of the sublattices, a net spontaneous magnetization appears. This phenomenon is called ferrimagnetism. I Ferrimagnetic materials are called ferrites. I Ferrites exhibit magnetic hysteresis and retain remanent magnetization (i.e. behaves like ferromagnets.) I Above the Curie temperature, becomes paramagnetic. I Magnetite (Fe3O4), maghemite, pyrrhotite and goethite (' rust). Magnetic properties of rocksI I Matrix minerals are mainly silicates or carbonates, which are diamagnetic. I Secondary minerals (e.g., clays) have paramagnetic properties. I So, the bulk of constituent minerals have a magnetic susceptibility but not remanent magnetic properties. I Variable concentrations of ferrimagnetic and matrix minerals result in a wide range of susceptibilities in rocks. Magnetic properties of rocksII I I The weak and variable concentration of ferrimagnetic minerals plays a key role in determining the magnetic properties of the rock. Magnetic properties of rocks III I Important factors influencing rock magnetism: I The type of ferrimagnetic mineral.
    [Show full text]
  • Relationships Between Magnetic Parameters, Chemical Composition and Clay Minerals of Topsoils Near Coimbra, Central Portugal
    Nat. Hazards Earth Syst. Sci., 12, 2545–2555, 2012 www.nat-hazards-earth-syst-sci.net/12/2545/2012/ Natural Hazards doi:10.5194/nhess-12-2545-2012 and Earth © Author(s) 2012. CC Attribution 3.0 License. System Sciences Relationships between magnetic parameters, chemical composition and clay minerals of topsoils near Coimbra, central Portugal A. M. Lourenc¸o1, F. Rocha2, and C. R. Gomes1 1Centre for Geophysics, Earth Sciences Dept., University of Coimbra, Largo Marquesˆ de Pombal, 3000-272 Coimbra, Portugal 2Geobiotec Centre, Geosciences Dept., University of Aveiro, 3810-193 Aveiro, Portugal Correspondence to: A. M. Lourenc¸o ([email protected]) Received: 6 September 2011 – Revised: 27 February 2012 – Accepted: 28 February 2012 – Published: 14 August 2012 Abstract. Magnetic measurements, mineralogical and geo- al., 1980). This methodology is fast, economic and can be ap- chemical studies were carried out on surface soil samples plied in various research fields, such as environmental mon- in order to find possible relationships and to obtain envi- itoring, pedology, paleoclimatology, limnology, archeology ronmental implications. The samples were taken over a and stratigraphy. Recent studies have demonstrated the ad- square grid (500 × 500 m) near the city of Coimbra, in cen- vantages and the potential of the environmental magnetism tral Portugal. Mass specific magnetic susceptibility ranges methods as valuable aids in the detection and delimitation between 12.50 and 710.11 × 10−8 m3 kg−1 and isothermal of areas affected by pollution (e.g. Bityukova et al., 1999; magnetic remanence at 1 tesla values range between 253 Boyko et al., 2004; Blaha et al., 2008; Lu et al., 2009; and 18 174 × 10−3 Am−1.
    [Show full text]
  • Rock and Paleomagnetic Investigations Technical Detailed
    NWM-USGS-GPP-06 RO Rock and Paleomagnetic Investigations Technical Detailed Procedure GPP-O NNWSI Project Quality Assurance Program U.S. Geological Survey Effective Date: pepared by: Joseph Rosenbaum Technical Reviewer: Richard Reynolds 'Branch Chief: Adel Zohdy NNWI Project Coordinator: W. Dudley Quality Assurance: P. L. Bussolini 8502210165 841130 PDR WASTE PDR Wm-II NWM-USGS-GPP- 06, RO NWM-USGS-GPP- o RO Page 2 of 13 Rock and Paleomagnetic Investigations 1.0 PURPOSE 1.1 This procedure provides a means of assuring the accuracy, validity, and applicability of the methods used to determine paleomagnetic and rock magnetic properties. 1.2 The procedure documents the USGS responsibilities for quality assurance training and enforcement, the processes and authority for procedure modification and revision, the requirements for procedure and personnel interfacing, and to whom the procedure applies. 1.3 The procedure describes the system components, the principles of the methods used, and the limits of their use. 1.4 The procedure describes the detailed methods to be used, where applicable, for system checkout and maintenance, calibration, operation and performance verification. 1.5 The procedure defines the requirements for data acceptance, documentation and control; and provides a means of data traceability. 1.6 The procedure provides a guide for USGS personnel and their contractors engaged to determining paleomagnetic and rock mag- netic properties and a means by which the Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC) can evaluate these activities in meeting requirements for the NNWSI repository. 2.0 SCOPE OF COMPLIANCE 2.1 This procedure applies to all USGS personnel, and persons assigned by the USGS, who perform work on the procedure as described by the work activity given in Section 1.1, or use data from such activities, if the activities or data are deemed by the USGS Project Coordinator to potentially affect public health and safety as related to a nuclear waste repository.
    [Show full text]
  • Design of a Curie Point Meter
    BULLETIN 69 DESIGN OF A CURIE POINT METER A. Larochelle Price, 50 cents 1961 DESIGN OF A CURIE POINT METER 3,000-1960-1818 91594-2-1 11 026: General view of Curie point meter GEOLOGICAL SURVEY OF CANADA BULLETIN 69 DESIGN OF A CURIE POINT METER By A. Larochelle DEPARTMENT OF MINES AND TECHNICAL SURVEYS CANADA 91594-2-2 ROGER DUHAMEL. F.R.S.C. QUEEN'S PRINTER AND CONTROLLER OF STATIONERY OTTAWA, 1961 Price 50 cents Cat. No. M42-69 Preface Magnetic properties are rarely used to identify minerals because they are generally difficult to detect or to determine accurately. Ferromagnetic minerals are, however, an exception. Not only can a family of ferromagnetic minerals be identified from its magnetic properties, but individual members of the family can be recognized. The Curie point is one of the most reliable magnetic properties for identifying such minerals. The apparatus described in this bulletin was designed to permit the rapid, accurate measurement of the Curie point of the ferromagnetic minerals in rock specimens, and by this means to identify them. J. M. HARRISON, Director, Geological Survey of Canada OTTAWA, April 28, 1960 v CONTENTS PAGE Introduction 1 General description 1 The torsion balance 2 The recording system 6 The heating element ........ ..... 8 The electromagnet 9 Operation and calibration of the apparatus 12 Practical application . 15 Bibliography 18 Table I. Curie points of specimens of basic intrusive rocks . 16 Plate I. General view of Curie point meter Frontispiece Figure 1. Schematic view of the Curie point meter . 2 2. Longitudinal section of torsion balance 3 3.
    [Show full text]
  • Rock Magnetism of Remagnetized Carbonate Rocks: Another Look
    Downloaded from http://sp.lyellcollection.org/ at University of California Berkeley on July 30, 2013 Rock magnetism of remagnetized carbonate rocks: another look MIKE JACKSON* & NICHOLAS L. SWANSON-HYSELL Institute for Rock Magnetism, Winchell School of Earth Sciences, University of Minnesota, Minnesota, US *Corresponding author (e-mail: [email protected]) Abstract: Authigenic formation of fine-grained magnetite is responsible for widespread chemical remagnetization of many carbonate rocks. Authigenic magnetite grains, dominantly in the super- paramagnetic and stable single-domain size range, also give rise to distinctive rock-magnetic prop- erties, now commonly used as a ‘fingerprint’ of remagnetization. We re-examine the basis of this association in terms of magnetic mineralogy and particle-size distribution in remagnetized carbon- ates having these characteristic rock-magnetic properties, including ‘wasp-waisted’ hysteresis loops, high ratios of anhysteretic remanence to saturation remanence and frequency-dependent susceptibility. New measurements on samples from the Helderberg Group allow us to quantify the proportions of superparamagnetic, stable single-domain and larger grains, and to evaluate the mineralogical composition of the remanence carriers. The dominant magnetic phase is magnetite-like, with sufficient impurity to completely suppress the Verwey transition. Particle sizes are extremely fine: approximately 75% of the total magnetite content is superparamagnetic at room temperature and almost all of the rest is stable single-domain. Although it has been pro- posed that the single-domain magnetite in these remagnetized carbonates lacks shape anisotropy (and is therefore controlled by cubic magnetocrystalline anisotropy), we have found strong exper- imental evidence that cubic anisotropy is not an important underlying factor in the rock-magnetic signature of chemical remagnetization.
    [Show full text]
  • Magnetic Mineral Assemblages in Soils and Paleosols As the Basis for Paleoprecipitation Proxies: a Review of Magnetic Methods and Challenges
    Earth-Science Reviews 155 (2016) 28–48 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies: A review of magnetic methods and challenges Daniel P. Maxbauer a,b,⁎, Joshua M. Feinberg a,b, David L. Fox a a Department of Earth Sciences, University of Minnesota, Minneapolis, MN, United States b Institute for Rock Magnetism, University of Minnesota, Minneapolis, MN, United States article info abstract Article history: Magnetic iron oxide minerals, principally magnetite, maghemite, hematite, and goethite are formed in well- Received 10 August 2015 drained soils in response to a suite of physical, chemical, and biological factors. Despite a wide range of complex- Received in revised form 11 January 2016 ity in the pedogenic processes that lead to magnetic mineral formation, dissolution, and transformation, there are Accepted 26 January 2016 well-documented empirical relationships between various magnetic mineral assemblages in soils with environ- Available online 27 January 2016 mental and climatic conditions. Recently there has been an increase in the number of quantitative magnetic Keywords: paleoprecipitation proxies that have been developed, and there is great potential for magnetic methods to be Paleoprecipitation used in the geologic record to develop reconstructions of past climates. Magnetic paleoprecipitation proxies Proxy have been widely utilized in Quaternary or younger loess–paleosol systems; however, they have yet to be utilized Soil magnetism in the pre-Quaternary fossil record. Future studies of magnetic mineralogy of soils and paleosols should aim to Paleosols explore non-loessic modern soils and pre-Quaternary paleosols with more focus on understanding the interac- Iron oxides tion between magnetic mineral assemblages and soil moisture.
    [Show full text]
  • Magnetic Properties of Rocks and Minerals
    MagneticProperties of Rocksand Minerals ChristopherP. Hunt, BruceM. Moskowitz,Subir K. Banerjee 1. INTRODUCTION composition-dependentmagnetic parameters of a varietyof iron-bearingminerals. This is an updatedcollation of magneticparameters of rocksand mineralsfor geologists,geochemists, and geo- 2. MAGNETIC SUSCEPTIBILITY physicists.Since the publication of theprevious edition of Handbookof PhysicalConstants [74], two othercollations Magnetic susceptibilityis a measureof the magnetic have appeared[16, 18]. In addition,selected magnetic responseof a materialto an externalmagnetic field. The parametershave alsobeen assembled[19, 22, 38, 41, 88]. volumesusceptibility k, measuredin dimensionlessunits, is Ratherthan produce a fully comprehensivecollection, we definedas the ratio of thematerial magnetization J (perunit have aimed for high-precisiondata obtainedfrom well- volume) to the weak externalmagnetic field H: characterizedsamples. Bothtables and figures have been used for presentingthe J=kH. (1) data,and best-fit equations have been provided for someof thedisplayed data so that interpolations can be made easily. Alternatively,the specificor masssusceptibility Z, mea- In an attemptto discouragethe useof the outdatedcgs suredin units of rn3kg4, isdefined as the ratio of the material system,all valuesare in theSI system(see Moskowitz, this magnetizationJ (per unit mass)to the weak externalmag- volume). Referenceshave been cited for the sourcesused netic field H: here. However,a morecomprehensive bibliography has alsobeen provided from which
    [Show full text]
  • Magnetic Properties of the Magnetite-Spinel Solid Solution: Curie Temperatures, Magnetic Susceptibilities, and Cation Ordering
    American Mineralogist, Volume 81, pages 375-384, 1996 Magnetic properties of the magnetite-spinel solid solution: Curie temperatures, magnetic susceptibilities, and cation ordering RICHARD J. HARRISON ANDANDREW PurNIS * Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, U.K. ABSTRACT Curie temperatures (Td of the (Fe304)x(MgA1204)1-xsolid solution have been deter- mined from measurements of magnetic susceptibility (x) vs. temperature. The trend in Te vs. composition extrapolates to 0 K at x = 0.27. This behavior is rationalized in terms of the trend in cation distribution vs. composition suggested by Nell and Wood (1989), with Fe occurring predominantly on tetrahedral sites for x < 0.27. High-temperature x-T curves are nonreversible because of the processes of cation or- dering and exsolution, which occur in the temperature range 400-650 0c. The Curie tem- perature of single-phase material is shown to be sensitive to the state of nonconvergent cation order, with a difference in Te of more than 70°C being observed between a sample quenched from 1400 °C and the same sample after heating to 650°C. This interaction between magnetic and chemical ordering leads to thermal hysteresis behavior such that Te measured during heating experiments is approximately 10°Chigherthan that measured during cooling. The hysteresis is due to a reversible difference in the state of cation order during heating and cooling caused by a kinetic lag in the cation-ordering behavior. Samples with compositions in the range 0.55 < x < 0.7 undergo exsolution to a mixture of ferrimagnetic and paramagnetic phases after heating to 650°C.
    [Show full text]
  • 8. Data Report: Paleomagnetic and Rock Magnetic Characterization of Rocks Recovered from Leg 173 Sites1
    Beslier, M.-O., Whitmarsh, R.B., Wallace, P.J., and Girardeau, J. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 173 8. DATA REPORT: PALEOMAGNETIC AND ROCK MAGNETIC CHARACTERIZATION OF ROCKS RECOVERED FROM LEG 173 SITES1 Xixi Zhao,2 Brent D. Turrin,3 Mike Jackson,4 and Peter Solheid4 ABSTRACT We present detailed paleomagnetic and rock magnetic results of rock samples recovered during Leg 173. The Leg 173 cores display a multi- component magnetization nature. Variations in magnetic properties correlate with changes in lithology that result from differences in the 1Zhao, X., Turrin, B.D., Jackson, M., abundance and size of magnetic minerals. The combined investigation and Solheid, P., 2001. Data report: suggests that the magnetic properties of the “fresher” peridotite sam- Paleomagnetic and rock magnetic ples from Site 1070 are controlled mainly by titanomagnetite, with a characterization of rocks recovered from Leg 173 sites. In Beslier, M.-O., strong Verwey transition in the vicinity of 110 K, and with field- and Whitmarsh, R.B., Wallace, P.J., and frequency-dependent susceptibility curves that resemble those of tita- Girardeau, J. (Eds.), Proc. ODP, Sci. nomagnetites. These results are in excellent agreement with thermo- Results, 173, 1–34 [Online]. Available magnetic characteristics where titanomagnetites with Curie tempera- from World Wide Web: <http:// ture ~580°C were identified from the “fresher” peridotites. In contrast www-odp.tamu.edu/publications/ 173_SR/VOLUME/CHAPTERS/ to the magnetic properties observed from the “fresher” peridotites, the SR173_08.PDF>. [Cited YYYY-MM-DD] low-temperature curves for the “altered” peridotites did not show any 2Institute of Tectonics, University of Verwey transition.
    [Show full text]
  • Rock-Magnetism and Ore Microscopy of the Magnetite-Apatite Ore Deposit from Cerro De Mercado, Mexico
    Earth Planets Space, 53, 181–192, 2001 Rock-magnetism and ore microscopy of the magnetite-apatite ore deposit from Cerro de Mercado, Mexico L. M. Alva-Valdivia1, A. Goguitchaichvili1, J. Urrutia-Fucugauchi1, C. Caballero-Miranda1, and W. Vivallo2 1Instituto de Geof´ısica, Universidad Nacional Autonoma´ de Mexico,´ Del. Coyoacan 04510 D. F., Mexico´ 2Servicio Nacional de Geolog´ıa y Miner´ıa, Chile (Received July 14, 2000; Revised December 19, 2000; Accepted January 24, 2001) Rock-magnetic and microscopic studies of the iron ores and associated igneous rocks in the Cerro de Mercado, Mexico, were carried out to determine the magnetic mineralogy and origin of natural remanent magnetization (NRM), related to the thermo-chemical processes due to hydrothermalism. Chemical remanent magnetization (CRM) seems to be present in most of investigated ore and wall rock samples, replacing completely or partially an original thermoremanent magnetization (TRM). Magnetite (or Ti-poor titanomagnetite) and hematite are commonly found in the ores. Although hematite may carry a stable CRM, no secondary components are detected above 580◦, which probably attests that oxidation occurred soon enough after the extrusion and cooling of the ore-bearing magma. NRM polarities for most of the studied units are reverse. There is some scatter in the cleaned remanence directions of the ores, which may result from physical movement of the ores during faulting or mining, or from perturbation of the ambient field during remanence acquisition by inhomogeneous internal fields within these strongly magnetic ore deposits. The microscopy study under reflected light shows that the magnetic carriers are mainly titanomagnetite, with significant amounts of ilmenite-hematite minerals, and goethite-limonite resulting from alteration processes.
    [Show full text]
  • 5 Geomagnetism and Paleomagnetism
    5 Geomagnetism and paleomagnetism It is not known when the directive power of the magnet 5.1 HISTORICAL INTRODUCTION - its ability to align consistently north-south - was first recognized. Early in the Han dynasty, between 300 and 5.1.1 The discovery of magnetism 200 BC, the Chinese fashioned a rudimentary compass Mankind's interest in magnetism began as a fascination out of lodestone. It consisted of a spoon-shaped object, with the curious attractive properties of the mineral lode­ whose bowl balanced and could rotate on a flat polished stone, a naturally occurring form of magnetite. Called surface. This compass may have been used in the search loadstone in early usage, the name derives from the old for gems and in the selection of sites for houses. Before English word load, meaning "way" or "course"; the load­ 1000 AD the Chinese had developed suspended and stone was literally a stone which showed a traveller the pivoted-needle compasses. Their directive power led to the way. use of compasses for navigation long before the origin of The earliest observations of magnetism were made the aligning forces was understood. As late as the twelfth before accurate records of discoveries were kept, so that century, it was supposed in Europe that the alignment of it is impossible to be sure of historical precedents. the compass arose from its attempt to follow the pole star. Nevertheless, Greek philosophers wrote about lodestone It was later shown that the compass alignment was pro­ around 800 BC and its properties were known to the duced by a property of the Earth itself.
    [Show full text]
  • Linked to Mineralisation Episode Are Included
    i Exploration and Mining Report 1073R PREDICTIVE MAGNETIC EXPLORATION MODELS FOR PORPHYRY, EPITHERMAL AND IRON OXIDE COPPER-GOLD DEPOSITS: IMPLICATIONS FOR EXPLORATION D.A. Clark, S. Geuna and P.W.Schmidt SHORT COURSE MANUAL FOR AMIRA P700 April 2003 RESTRICTED CIRCULATION This report is not to be cited in other documents without the consent of CSIRO Exploration and Mining ______________________ ii CSIRO Exploration and Mining PO Box 136, North Ryde, NSW, Australia iii iv Distribution List Copy No. AMIRA 1-8 Dr N. Phillips, Chief CSIRO Exploration and Mining 9 Mr D.A. Clark 10 Dr S. Geuna 11 Dr P.W. Schmidt 12 Records Section (North Ryde) 13 Copy no. ........................ of 19 copies v Page no. TABLE OF CONTENTS 1. INTRODUCTION 1 2. MAGNETIC PETROPHYSICS AND MAGNETIC PETROLOGY: 4 APPLICATION TO INTERPRETATION OF MAGNETIC SURVEYS AND IMPLICATIONS FOR EXPLORATION 3. MAGNETIC PETROLOGY OF IGNEOUS INTRUSIONS: 46 IMPLICATIONS FOR EXPLORATION AND MAGNETIC INTERPRETATION 4. METHODS OF DETERMINING MAGNETIC PROPERTIES WITHIN 95 MINERALISED SYSTEMS 5. GEOLOGICAL MODELS OF PORPHYRY COPPER (Mo, Au), 122 VOLCANIC-HOSTED EPITHERMAL AND IRON OXIDE COPPER- GOLD SYSTEMS 6. GEOLOGICAL AND GEOMAGNETIC FACTORS THAT 192 CONTROL MAGNETIC SIGNATURES OF PORPHYRY, EPITHERMAL AND IRON OXIDE COPPER-GOLD DEPOSITS 7. PETROPHYSICAL PROPERTIES OF VOLCANO-PLUTONIC 212 TERRAINS, PORPHYRY SYSTEMS, IRON OXIDE COPPER-GOLD SYSTEMS AND VOLCANIC-HOSTED EPITHERMAL SYSTEMS – P700 CASE STUDIES 8. MAGNETIC PROPERTIES OF PORPHYRY, EPITHERMAL AND 226 IRON OXIDE COPPER-GOLD DEPOSITS SYSTEMS - SYNTHESIS 9. MAGNETIC AND OTHER GEOPHYSICAL SIGNATURES OF 238 P700 STUDY AREAS 10. MAGNETIC SIGNATURES OF PORPHYRY, EPITHERMAL AND 274 IRON OXIDE COPPER-GOLD MINERALISATION - REVIEW AND SYNTHESIS 11.
    [Show full text]