THERMOMAGNETIC ANALYSIS AND ORE GENESIS

1967 ◽  
Vol 4 (6) ◽  
pp. 1119-1125
Author(s):  
E. J. Schwarz
Keyword(s):  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Thermal Conditions ◽  
Natural Remanent Magnetization ◽  
Ore Deposits ◽  
Ore Genesis ◽  
Thermomagnetic Analysis ◽  
Stable Part ◽  
Physical Changes ◽  
Genesis Of Ore Deposits

The potential of rock magnetism in studies on the genesis of ore deposits is examined. It is suggested that techniques based on magnetic properties other than the direction of the stable part of the natural remanent magnetization might prove usefully applicable. More specifically the analysis of the type of remanent magnetization in ores and their wall rocks is suggested as a worthwhile approach in the study of ore genesis. Other methods suggested are based on the occurrence of chemical or physical changes affecting ferromagnetic minerals in ores during heating. It may be possible to relate the results of such experiments to the thermal conditions prevailing at the time of either formation of minerals in ore deposits or acquisition of stable remanent magnetization.

Paleomagnetism of Archean rocks from northwestern Ontario: III. Rock magnetism of the Shelley Lake granite, Quetico Subprovince

1984 ◽  
Vol 21 (8) ◽  
pp. 879-886 ◽  
Author(s):  
David J. Dunlop ◽  
Larry D. Schutts ◽  
Christopher J. Hale
Keyword(s):  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Natural Remanent Magnetization ◽  
Thermal Decay ◽  
Magnetic Phases ◽  
Northwestern Ontario ◽  
Component Type ◽  
Thermal Overprint

The Shelley Lake granite of northwestern Ontario contains five magnetic phases: deuteric and post-crystallization hematites, which are relatively abundant but carry only 1–4% of the natural remanent magnetization (NRM); primary magnetite in coarse (50–500 μm) grains, both optically homogeneous and subdivided by hematite lamellae; micrometre-size secondary magnetite in chloritized biotites; and submicrometre-size magnetite, whose presence is inferred from low blocking temperatures in thermal decay curves of the NRM. The NRM is a composite of type 1 and type 2 remanences, which differ in direction by about 90° (see companion paleomagnetic paper). Both NRM components occur in normal (N) and reverse (R) polarities. Type 1 remanences (1N/1R) have the hallmarks of multidomain (MD) behaviour: high blocking temperatures but low coercivities, exponential alternating field (AF) decay curves, generally MD results of the Lowrie–Fuller test, and MD to transitional values (0.3–10) of the Koenigsberger Qn ratio. Furthermore, intensities of 0.6 Oe (0.06 mT) laboratory thermoremanent magnetizations (TRM's) match those of 1R and some 1N NRM's. We argue on this evidence that 1R and at least part of 1N NRM's are TRM's residing in coarse MD-size primary magnetite. This primary TRM dates from initial cooling of the Shelley Lake pluton around 2580 Ma. Thermal decay spectra of single-component type 2 NRM's (2N/2R) resemble those of 1R. However, the considerable overlap of 2N/2R and 1R blocking temperatures in multivectorial NRM's demonstrates that type 2 remanence must be a chemical or thermochemical rather than a thermal overprint.

scholarly journals On the Primordial Condensation and Accretion Environment and the Remanent Magnetization of Meteorites

1971 ◽  
Vol 13 ◽  
pp. 311-329 ◽  
Author(s):  
Aviva Brecher
Keyword(s):  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Laboratory Data ◽  
Natural Remanent Magnetization ◽  
Parent Body ◽  
Origin And Evolution ◽  
Consistent Model ◽  
Magnetic Remanence ◽  
Condensation Growth ◽  
Theoretical Results

Attention is drawn to the fact that neither astronomical observations, nor laboratory data can, as yet, sufficiently constrain models of the origin and evolution of the solar system. But, if correctly approached and interpreted, the magnetic remanence of meteorites could help in constructing a self-consistent model.In the context of various models for the early evolution of a solar nebula, the possible roles assigned to ambient magnetic fields and the paleointensities required to establish the stable natural remanent magnetization (NRM in range 10-4 to 10-1 cgsm) observed in meteorites, are discussed. It is suggested that the record of paleofields present during condensation, growth, and accumulation of grains is likely to have been preserved as chemical (CRM) or thermochemical (TCRM) remanence in unaltered meteoritic material. This interpretation of the meteoritic NRM is made plausible by experimental and theoretical results from the contiguous fields of rock magnetism, magnetic materials, interstellar grains, etc. Several arguments (such as the anisotropy of susceptibility in chondrites, suggesting alignment of elongated ferromagnetic grains, or the characteristic sizes and morphology of carrier phases of remanence, etc.) as well as general evidence from meteoritics (cooling rates, chemical and mineralogical data) can be used to challenge the interpretation of NRM as thermo-remanence (TRM) acquired on a “planetary” parent body during cooling of magnetic mineral phases through the Curie point in fields of 0.2 to 0.9 Oe.Fine-particle theories appear adequate for treating meteoritic remanence, if models based on corresponding types of permanent magnet materials, e.g., powder-ferrites for chondrites; diffusion hardened alloys for iron meteorites, are adopted, as suggested here.Finally, a potentially fruitful sequence of experiments is suggested for separating the useful component of NRM in determining the paleofield intensity and its time evolution.

Rock magnetism as a tool for investigating the use of archaeological artefacts from baked clay

2021 ◽  
Author(s):  
Evdokia Tema ◽  
Enzo Ferrara ◽  
Lorenzo Zamboni ◽  
Marica Venturino ◽  
Margherita Reboldi ◽  
...  
Keyword(s):  
Iron Age ◽  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Magnetic Behavior ◽  
Archaeological Site ◽  
Natural Remanent Magnetization ◽  
Rock Magnetic Properties ◽  
Ring Shape ◽  
Magnetic Analysis

<p>Even though multidisciplinary approaches applied to the investigation of archaeological findings are widely used, the use of rock magnetic properties is still poorly exploited in the determination of the use of ancient artefacts. In this study, we present the results of a combined archaeological, morphological and magnetic analyses applied on the ring-shape clay artefacts found at the archaeological site of Villa del Foro, in Northern Italy. The materials studied are dated between the sixth and the first half of fifth century BC and are found in large quantities in different trenches of the archaeological excavation. To investigate their thermal history and to exploit their possible use as kiln supports, cooking stands, or loom weights, we have investigated their natural remanent magnetization (NRM) and the magnetic mineralogy changes occurred during laboratory heating. Magnetic analysis used for the determination of the firing temperatures show thermal stability up to 500-600 <sup>o </sup>C, while further laboratory heating at 700 <sup>o </sup>C introduces magnetic alteration. Thermal demagnetization of the samples generally shows a strong and stable thermal remanent magnetization. In few cases, a clear secondary component is present, suggesting partial re-heating or displacement at temperatures ranging from 200 <sup>o</sup>C to 450 °C. Such secondary magnetic component can be indicative of a secondary heating or of a displacement of the rings from their initial firing position while still hot. Even though the studied rings belong to casually different morphological typologies, no connection among type and magnetic behavior was observed, suggesting that the ring’s morphology does not define neither their production conditions nor the final use of the artefacts. The estimated firing temperatures of around 600-700 <sup>o</sup>C are compatible with the heating of the rings during their manufacture rather than related to cooking activities. In combination with the archaeological evidence and the morphological analysis it is thus suggested that the rings were used as weight looms and baked only during their production procedures. Such a pilot study can be used as reference for the identification of similar objects found in Italy and Europe during the Iron Age and confirms the great potential of rock magnetic analysis in the investigation of the technology and use of ancient baked clays.</p>

Viscosité magnétique potentielle, aimantation détritique et viscosité réelle d'un sédiment lacustre quaternaire

1987 ◽  
Vol 24 (9) ◽  
pp. 1903-1912 ◽  
Author(s):  
Daniel Biquand ◽  
François Sémah
Keyword(s):  
Remanent Magnetization ◽  
Rock Magnetism ◽  
Viscosity Index ◽  
Natural Remanent Magnetization ◽  
Blocking Temperature ◽  
Magnetic Viscosity ◽  
Paleomagnetic Study ◽  
Temperature Spectra

The magnetic viscosity of sediments, as indicated by thermal demagnetization of natural remanent magnetization (NRM), depends on two main parameters: (i) the specific magnetic viscosity of the material and (ii) the efficiency of the primary magnetization process. In an attempt to determine the relative importance of these two variables, we studied a Lower Pleistocene lacustrine sequence bearing a primary reversed detrital remanent magnetization (DRM).Using natural samples and small cores made of crushed sediment, our study is based on the thermodynamic theory of rock magnetism developed by L. Néel, who established an equivalence between time and temperature, that is, between viscous remanent (VRM) and thermoremanent (TRM) magnetization processes. The determination of the blocking temperature spectra from 20 to 152 °C allows us to calculate the maximum theoretical VRM acquired in situ at each horizon, while the detailed thermal study of the NRM permits an appraisal of the DRM quality. This leads us to define a geological viscosity index, which accounts, in a rather convincing manner, for the behaviour of the samples observed during the classical paleomagnetic study. For the section studied, it appears that the variations of this index are closely correlated with the efficiency of the DRM acquisition process.

scholarly journals ARCHAEOMAGNETIC STUDIES IN KILNS FROM N. GREECE

2017 ◽  
Vol 43 (4) ◽  
pp. 1888 ◽  
Author(s):  
E. Aidona ◽  
D. Kondopoulou ◽  
M. Alexandrou ◽  
N. Ioannidis
Keyword(s):  
Magnetic Field ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Archaeological Sites ◽  
Isothermal Remanent Magnetization ◽  
Thermomagnetic Analysis ◽  
Intensity Measurements ◽  
Magnetic Carriers ◽  
Characteristic Component

Archaeomagnetism combines the magnetic properties of baked materials with Archaeology. The archaeomagnetic method can be applied to any kind of permanent - in situ or displaced- burnt structures, such as kilns, ovens, hearths, burnt floors, tiles, bricks and pottery fragments, the latter for intensity measurements only. In this study we present the latest archaeomagnetic results from archaeological sites which are distributed in N. Greece (Polymylos, Sani, Thesssaloniki). The Natural Remanent Magnetization (NRM) and the magnetic susceptibility of the samples have been initially measured. The samples have been subjected to magnetic cleaning (AF and Thermal demagnetizations) and this procedure revealed the characteristic component of the ancient magnetic field. Rock magnetic experiments such as acquisition of the Isothermal Remanent Magnetization (IRM) and thermomagnetic analysis have been performed in pilot samples in order to identify the main magnetic carriers. Finally the secular variation curves for Greece and the SCHA.DIF.3K model were used in order to date these archaeological structures. This dating improved or modified the estimated archaeological ages.

MAGNETIC PROSPECTING FOR IRON ORES IN JAMAICA

Geophysics ◽  
1955 ◽  
Vol 20 (3) ◽  
pp. 593-614 ◽  
Author(s):  
S. A. Vincenz
Keyword(s):  
Remanent Magnetization ◽  
Iron Ore ◽  
Ground Surface ◽  
Natural Remanent Magnetization ◽  
Ore Deposits ◽  
Small Scale ◽  
Rough Terrain ◽  
Near Surface ◽  
Ore Bodies ◽  
Iron Ore Deposits

Two ground magnetometer surveys over iron ore deposits in Jamaica are described and the results of the observations interpreted. An improvised but economical technique is used to measure the main magnetic properties of ore samples obtained from surface exposures, and a suitable statistical analysis is applied to determine the significance of these observations. The interpretation of the magnetic profiles, carried out on the basis of these observations, is complicated by the non‐uniformity of the natural remanent magnetization of the ores and the roughness of Jamaican topography. The ambiguities due to the latter factor are diminished by taking into account in the computations the changes in the elevation of the ground surface. The results of the interpretation are on the whole successful and give the approximate sizes and positions of the main ore bodies. A conclusion is reached that, in the case of small‐scale near‐surface deposits whose approximate position is already known, ground magnetometer surveys can be superior to those made from the air because of their smaller cost and greater power of resolution in rough terrain.

Natural remanent magnetization studies of a layered Breccia Boulder from the lunar highland region

The Moon ◽  
1975 ◽  
Vol 14 (3-4) ◽  
pp. 473-481 ◽  
Author(s):  
S. K. Banerjee ◽  
G. Swits
Keyword(s):  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Highland Region

Contributions of Cretaceous Quiet Zone natural remanent magnetization to Magsat anomalies in the Southwest Indian Ocean

1994 ◽  
Vol 99 (B6) ◽  
pp. 11923-11936 ◽  
Author(s):  
Lawrence G. Fullerton ◽  
Herbert V. Frey ◽  
James H. Roark ◽  
Herman H. Thomas
Keyword(s):  
Indian Ocean ◽  
Remanent Magnetization ◽  
Natural Remanent Magnetization ◽  
Southwest Indian Ocean
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