Aeromagnetics, geology and ore environments, I. Magnetite in igneous, sedimentary and metamorphic rocks: An overview

Grant, F. S.

doi:10.1016/0016-7142(85)90001-8

Cited by 168 publications

(87 citation statements)

References 26 publications

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“…A secondary objective of this study is to investigate whether the χ values have frequency dependence and to detect the ultra-fine particles by employing both low frequency and high frequency susceptibility measurements. Understanding magnetic properties through direct measurement of magnetic susceptibility in the field, supported by laboratory studies of magnetic petrophysics and petrology, provides the basis for more effective use of existing aeromagnetic data as a geological mapping and mineral exploration tool as well as for environmental applications (e.g., Grant, 1985;Reeves, 1989;Hunt et al, 1995;Clark, 1997;Ishihara et al, 2002;Alva-Valdivia et al, 2003). The results can also contribute to the improvement of (general) models for prediction of magnetic susceptibilities of tropical soils and/or arid to semi-arid soils important for electromagnetic prospecting (cf Singer et al, 1996;Van Dam et al, 2005Preetz et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Susceptibility of Soils from Eastern Botswana: A Reconnaissance Survey and Potential Applications

Ranganai¹,

Moidaki²,

King³

2015

JGG

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Soil magnetic properties measurements are relatively fast and inexpensive but have been proved to be sufficient for preliminary investigations in diverse socio-developmental issues. This paper presents results of a reconnaissance study of soil colour and magnetic susceptibility (χ) in eastern Botswana, where ~80% of the population resides. The work is a first step to creating a database of rock and soil magnetic properties and to document spatial variations in magnetic properties in the country. These measurements are important as constraints for interpretation of available aeromagnetic data and can also be exploited for environmental soil research (pollution) and land-use planning (agriculture). The soils sampled include derivatives of varying types and provenance such as Archean gneissic granitoids, metamorphosed rocks (granulites), volcano-sedimentary assemblages, Karoo basalts, and alluvial sediments. A soil colour chart was used since soil colours and magnetic properties are diagnostic of its parent rock sources and weathering profiles. Soil magnetic susceptibilities were measured at both low frequency (0.46 MHz, χlf) and high frequency (4.6 MHz, χhf), thus allowing calculation of frequency-dependent susceptibility (χfd, χfd%) for detecting ultra-fine ferromagnetic minerals.It was found that soils with Hues ranging from 7.5YR to 10YR have appreciable amount of magnetic materials and soils with Hues of 2.5YR are generally nonmagnetic. The results of soil magnetic susceptibility profiles show spatial variation closely related to the variation in basement rocks, which provides excellent evidence that the magnetic susceptibility variation reflects basement rocks or bedrock composition (soil parent material). In relation to the Botswana physiographic units, soils from the hardveld (Precambrian) show the highest susceptibilities, followed by those from the sandveld, with the lowest values being from the alluvial. The frequency dependent magnetic susceptibilities indicate the presence of ultra-fine super-paramagnetic minerals such as magnetite/maghemite. It is suggested that a systematic and continuous programme of rock and soil magnetic measurements would benefit various socio-economic and development priority sectors of Botswana. This also applies to many developing countries in Africa where soil physics and measurement of soil susceptibility in particular, is generally still at an embryonic stage.

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Section: Introductionmentioning

confidence: 99%

Magnetic Susceptibility of Soils from Eastern Botswana: A Reconnaissance Survey and Potential Applications

Ranganai¹,

Moidaki²,

King³

2015

JGG

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“…Our contribution does not discuss the event of secondary magnetite creation in the processes of mechanical deformation and repetitive alterations, which are responsible for increase of magnetic properties (Grant et al 1985). Clarification of these factors requires ad- ditional investigation.…”

Section: Magnetic Properties Of Minerals and Rocksmentioning

confidence: 99%

Magnetic field of the Western Carpathians (Slovakia): reflections on the structure of the crust

Kubeš¹,

Bezák²,

Kucharič³

et al. 2010

Geologica Carpathica

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Abstract:A new digital magnetic map of Slovakia on the scale of 1: 200,000 and 1: 500,000 was compiled at the end of 2008 as the output of database magnetic objects from the whole territory of Slovakia at a scale of 1: 50,000. The variable geological structure of the West Carpathian crust is depicted in the equally variable magnetic field of this region. A sizable number of magnetic anomalies with manifold character have been recognized. The basic anomalies distribution was divided into two groups: anomalies connected with rocks of the pre-Neogene basement and anomalies which originate in Neogene and Quaternary volcanic products. Most of the significant anomalies in the pre-Neogene basement were interpreted, modelled and consequently its geological and tectonic classification was worked out. On the basis of the anomalous field features, the following sources of anomalies have been distinguished: a) known, located on the surface, or at shallow depths verified by boreholes, mainly expressed by simple morphology, b) deep-seated and expressed by complicated morphology, reinterpreted or newly interpreted and also problematic. According to our present knowledge the interpretations are insufficient and remain open for further investigation. The above mentioned sources of magnetic anomalies are classified in terms of tectonic provenience to the main tectonic units.

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“…Analytic signal amplitude (ASA) (Roest et al 1992) was applied on magnetic data to enhance high magnetization areas, considered here as evidence for mafic-ultramafic bedrock according to its common high content on ferromagnetic minerals and common magnetic response (Grant 1985a(Grant , 1985b. ASA also enhances areas away from our interest, like non-mafic ultramafic (highly) magnetic bodies, but it is capable of depicting high magnetization zones despite its dimensions, shape and depth (Roest et al 1992, Nabighian et al 2005.…”

Section: Spatial Database and Methodsmentioning

confidence: 99%

A mineral potential mapping approach for supergene nickel deposits in southwestern São Francisco Craton, Brazil

Motta

Júnior

2016

Braz. J. Geol.

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Southwestern São Francisco Craton makes limit with Brasília thrust-fold belt and involves rocks from Archean to formed during the Brasiliano-Pan Africano Neoproterozoic event, including a mafic-ultramafic belt (Morro do Ferro Greenstone Belt) hosted along the Archean counterpart. This greenstone belt hosts two-nickel deposits (Morro do Níquel and O'Toole, respectively silicate and sulfide types) and occurrences. This study applies an empirical-conceptual model for lateritic nickel deposits formation into geographic information systems with aerogeophysical data (magnetic and gamma-spectrometry) and digital elevation models (terrain relief and slope). Our contribution aims for nickel deposits favorability mapping using a simple mathematical operator over a supporting spatial database translating the conceptual exploration model into evidential layers for geological processes involved on deposit formation. Evidential layers constructed for identification of elements pertaining the supergene nickel mineral system are given by analytic signal amplitude maps, thorium over potassium ratio images, and digital elevation models and slope maps, derived from shuttle radar topography mission digital elevation models. Evidential layers integration through binary layers algebraic sum identified effectively known deposits and occurrences with its outputs highlighting possibilities for unknown resources in this under-explored terrain. KEYWORDS: prospection; mineral exploration; geographic information systems. RESUMO: A região sudeste do estado de Minas Gerais encontra-se no limite do Cráton do São Francisco com um sistema de dobras, empurrão e cisalhamento formados no Neoproterozóico no evento Brasiliano-Pan Africano, com envolvimento de assembleias do arqueano até essa idade e inclui associação de rochas máficas-ultramáficas (Greenstone Belt Morro do Ferro). A esta unidade arqueana estão associados depósitos minerais de níquel (Morro do Níquel e O'To

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Aeromagnetics, geology and ore environments, I. Magnetite in igneous, sedimentary and metamorphic rocks: An overview

Cited by 168 publications

References 26 publications

Magnetic Susceptibility of Soils from Eastern Botswana: A Reconnaissance Survey and Potential Applications

Magnetic Susceptibility of Soils from Eastern Botswana: A Reconnaissance Survey and Potential Applications

Magnetic field of the Western Carpathians (Slovakia): reflections on the structure of the crust

A mineral potential mapping approach for supergene nickel deposits in southwestern São Francisco Craton, Brazil

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