Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile

Autores
Austin, James; Geuna, Silvana Evangelina; Clark, David; Hillan, Dean
Año de publicación
2014
Idioma
inglés
Tipo de recurso
artículo
Estado
versión publicada
Descripción
Magnetic modelling can be a powerful tool for understanding the architecture of numerous types of mineralized systems; e.g., iron ore, IOCG and porphyry deposits. In such modelling, the induced component is generally assumed to be dominant, whereas remanent magnetization is often neglected and, furthermore, the effects of self-demagnetization are commonly ignored. We present rock property measurements (magnetic susceptibility and remanent magnetization) from the Candelaria IOCG deposit in northern Chile. The results demonstrate that remanence is relatively weak (b20% of induced) and that the causative lithologies have very high magnetic susceptibilities (3–4 SI), which makes them highly prone to self-demagnetization. The rock property results were used to constrain a simplified forward model in which the causative bodies are modelled as a series of sub-horizontal highly magnetic sheets, corresponding to “mantos”. These “mantos” occur north and south of Candelaria, sub-perpendicular to a splay off the Atacama Fault Zone. We demonstrate that Candelaria's unusual magnetic anomaly is due to a combination of its highly magnetic sub-horizontal architecture, and self-demagnetization effects. A further simplified model was used to calculate two synthetic anomalies, one ignoring and the other incorporating the self-demagnetization effect. These synthetic anomalies demonstrate that the magnetic anomaly amplitude is suppressed by up to approximately 50% at Candelaria due to selfdemagnetization, and that the induced magnetization is also slightly rotated from the regional inducing field towards the plane of the “mantos”. The dominant paleomagnetic component recorded by the Candelaria deposit and host rocks is a normal polarity remanence of moderate to high stability which is interpreted to have been acquired during the mid-Cretaceous alteration and mineralisation event(s) that generated the magnetic minerals (predominantly magnetite). However, the presence of a reversed polarity overprint component in some samples suggests that the Candelaria deposit and its immediate environs have experienced a post 83 Ma thermal or thermochemical event that has not been previously recognised. The remanence directions of both polarities are rotated clockwise with respect to the expected directions for mid-Cretaceous/Early Tertiary fields, indicating clockwise rotation of the Candelaria area, including the adjacent batholith, through at least 45° since the acquisition of the normal and reversed remanence components, i.e. since 83 Ma. This case study illustrates the importance of understanding the magnetic behaviour of different ore types, and incorporating self-demagnetization into modelling procedures for highly magnetic targets in mineral exploration.
Fil: Austin, James. Commonwealth Scientific and Industrial Research Organisation; Australia
Fil: Geuna, Silvana Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; Argentina
Fil: Clark, David. Commonwealth Scientific and Industrial Research Organisation; Australia
Fil: Hillan, Dean. Commonwealth Scientific and Industrial Research Organisation; Australia
Materia
Magnetic Modelling
Iron Oxide Copper Gold
Magnetite
Magnetic Susceptibility
Nivel de accesibilidad
acceso abierto
Condiciones de uso
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
Repositorio
CONICET Digital (CONICET)
Institución
Consejo Nacional de Investigaciones Científicas y Técnicas
OAI Identificador
oai:ri.conicet.gov.ar:11336/20016

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network_name_str CONICET Digital (CONICET)
spelling Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, ChileAustin, JamesGeuna, Silvana EvangelinaClark, DavidHillan, DeanMagnetic ModellingIron Oxide Copper GoldMagnetiteMagnetic Susceptibilityhttps://purl.org/becyt/ford/1.5https://purl.org/becyt/ford/1Magnetic modelling can be a powerful tool for understanding the architecture of numerous types of mineralized systems; e.g., iron ore, IOCG and porphyry deposits. In such modelling, the induced component is generally assumed to be dominant, whereas remanent magnetization is often neglected and, furthermore, the effects of self-demagnetization are commonly ignored. We present rock property measurements (magnetic susceptibility and remanent magnetization) from the Candelaria IOCG deposit in northern Chile. The results demonstrate that remanence is relatively weak (b20% of induced) and that the causative lithologies have very high magnetic susceptibilities (3–4 SI), which makes them highly prone to self-demagnetization. The rock property results were used to constrain a simplified forward model in which the causative bodies are modelled as a series of sub-horizontal highly magnetic sheets, corresponding to “mantos”. These “mantos” occur north and south of Candelaria, sub-perpendicular to a splay off the Atacama Fault Zone. We demonstrate that Candelaria's unusual magnetic anomaly is due to a combination of its highly magnetic sub-horizontal architecture, and self-demagnetization effects. A further simplified model was used to calculate two synthetic anomalies, one ignoring and the other incorporating the self-demagnetization effect. These synthetic anomalies demonstrate that the magnetic anomaly amplitude is suppressed by up to approximately 50% at Candelaria due to selfdemagnetization, and that the induced magnetization is also slightly rotated from the regional inducing field towards the plane of the “mantos”. The dominant paleomagnetic component recorded by the Candelaria deposit and host rocks is a normal polarity remanence of moderate to high stability which is interpreted to have been acquired during the mid-Cretaceous alteration and mineralisation event(s) that generated the magnetic minerals (predominantly magnetite). However, the presence of a reversed polarity overprint component in some samples suggests that the Candelaria deposit and its immediate environs have experienced a post 83 Ma thermal or thermochemical event that has not been previously recognised. The remanence directions of both polarities are rotated clockwise with respect to the expected directions for mid-Cretaceous/Early Tertiary fields, indicating clockwise rotation of the Candelaria area, including the adjacent batholith, through at least 45° since the acquisition of the normal and reversed remanence components, i.e. since 83 Ma. This case study illustrates the importance of understanding the magnetic behaviour of different ore types, and incorporating self-demagnetization into modelling procedures for highly magnetic targets in mineral exploration.Fil: Austin, James. Commonwealth Scientific and Industrial Research Organisation; AustraliaFil: Geuna, Silvana Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Clark, David. Commonwealth Scientific and Industrial Research Organisation; AustraliaFil: Hillan, Dean. Commonwealth Scientific and Industrial Research Organisation; AustraliaElsevier Science2014-10info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionhttp://purl.org/coar/resource_type/c_6501info:ar-repo/semantics/articuloapplication/pdfapplication/pdfhttp://hdl.handle.net/11336/20016Austin, James; Geuna, Silvana Evangelina; Clark, David; Hillan, Dean; Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile; Elsevier Science; Journal Of Applied Geophysics; 109; 10-2014; 242-2550926-9851CONICET DigitalCONICETenginfo:eu-repo/semantics/altIdentifier/doi/10.1016/j.jappgeo.2014.08.002info:eu-repo/semantics/altIdentifier/url/http://www.sciencedirect.com/science/article/pii/S0926985114002390info:eu-repo/semantics/openAccesshttps://creativecommons.org/licenses/by-nc-sa/2.5/ar/reponame:CONICET Digital (CONICET)instname:Consejo Nacional de Investigaciones Científicas y Técnicas2025-09-29T09:41:40Zoai:ri.conicet.gov.ar:11336/20016instacron:CONICETInstitucionalhttp://ri.conicet.gov.ar/Organismo científico-tecnológicoNo correspondehttp://ri.conicet.gov.ar/oai/requestdasensio@conicet.gov.ar; lcarlino@conicet.gov.arArgentinaNo correspondeNo correspondeNo correspondeopendoar:34982025-09-29 09:41:40.551CONICET Digital (CONICET) - Consejo Nacional de Investigaciones Científicas y Técnicasfalse
dc.title.none.fl_str_mv Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
title Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
spellingShingle Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
Austin, James
Magnetic Modelling
Iron Oxide Copper Gold
Magnetite
Magnetic Susceptibility
title_short Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
title_full Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
title_fullStr Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
title_full_unstemmed Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
title_sort Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile
dc.creator.none.fl_str_mv Austin, James
Geuna, Silvana Evangelina
Clark, David
Hillan, Dean
author Austin, James
author_facet Austin, James
Geuna, Silvana Evangelina
Clark, David
Hillan, Dean
author_role author
author2 Geuna, Silvana Evangelina
Clark, David
Hillan, Dean
author2_role author
author
author
dc.subject.none.fl_str_mv Magnetic Modelling
Iron Oxide Copper Gold
Magnetite
Magnetic Susceptibility
topic Magnetic Modelling
Iron Oxide Copper Gold
Magnetite
Magnetic Susceptibility
purl_subject.fl_str_mv https://purl.org/becyt/ford/1.5
https://purl.org/becyt/ford/1
dc.description.none.fl_txt_mv Magnetic modelling can be a powerful tool for understanding the architecture of numerous types of mineralized systems; e.g., iron ore, IOCG and porphyry deposits. In such modelling, the induced component is generally assumed to be dominant, whereas remanent magnetization is often neglected and, furthermore, the effects of self-demagnetization are commonly ignored. We present rock property measurements (magnetic susceptibility and remanent magnetization) from the Candelaria IOCG deposit in northern Chile. The results demonstrate that remanence is relatively weak (b20% of induced) and that the causative lithologies have very high magnetic susceptibilities (3–4 SI), which makes them highly prone to self-demagnetization. The rock property results were used to constrain a simplified forward model in which the causative bodies are modelled as a series of sub-horizontal highly magnetic sheets, corresponding to “mantos”. These “mantos” occur north and south of Candelaria, sub-perpendicular to a splay off the Atacama Fault Zone. We demonstrate that Candelaria's unusual magnetic anomaly is due to a combination of its highly magnetic sub-horizontal architecture, and self-demagnetization effects. A further simplified model was used to calculate two synthetic anomalies, one ignoring and the other incorporating the self-demagnetization effect. These synthetic anomalies demonstrate that the magnetic anomaly amplitude is suppressed by up to approximately 50% at Candelaria due to selfdemagnetization, and that the induced magnetization is also slightly rotated from the regional inducing field towards the plane of the “mantos”. The dominant paleomagnetic component recorded by the Candelaria deposit and host rocks is a normal polarity remanence of moderate to high stability which is interpreted to have been acquired during the mid-Cretaceous alteration and mineralisation event(s) that generated the magnetic minerals (predominantly magnetite). However, the presence of a reversed polarity overprint component in some samples suggests that the Candelaria deposit and its immediate environs have experienced a post 83 Ma thermal or thermochemical event that has not been previously recognised. The remanence directions of both polarities are rotated clockwise with respect to the expected directions for mid-Cretaceous/Early Tertiary fields, indicating clockwise rotation of the Candelaria area, including the adjacent batholith, through at least 45° since the acquisition of the normal and reversed remanence components, i.e. since 83 Ma. This case study illustrates the importance of understanding the magnetic behaviour of different ore types, and incorporating self-demagnetization into modelling procedures for highly magnetic targets in mineral exploration.
Fil: Austin, James. Commonwealth Scientific and Industrial Research Organisation; Australia
Fil: Geuna, Silvana Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; Argentina
Fil: Clark, David. Commonwealth Scientific and Industrial Research Organisation; Australia
Fil: Hillan, Dean. Commonwealth Scientific and Industrial Research Organisation; Australia
description Magnetic modelling can be a powerful tool for understanding the architecture of numerous types of mineralized systems; e.g., iron ore, IOCG and porphyry deposits. In such modelling, the induced component is generally assumed to be dominant, whereas remanent magnetization is often neglected and, furthermore, the effects of self-demagnetization are commonly ignored. We present rock property measurements (magnetic susceptibility and remanent magnetization) from the Candelaria IOCG deposit in northern Chile. The results demonstrate that remanence is relatively weak (b20% of induced) and that the causative lithologies have very high magnetic susceptibilities (3–4 SI), which makes them highly prone to self-demagnetization. The rock property results were used to constrain a simplified forward model in which the causative bodies are modelled as a series of sub-horizontal highly magnetic sheets, corresponding to “mantos”. These “mantos” occur north and south of Candelaria, sub-perpendicular to a splay off the Atacama Fault Zone. We demonstrate that Candelaria's unusual magnetic anomaly is due to a combination of its highly magnetic sub-horizontal architecture, and self-demagnetization effects. A further simplified model was used to calculate two synthetic anomalies, one ignoring and the other incorporating the self-demagnetization effect. These synthetic anomalies demonstrate that the magnetic anomaly amplitude is suppressed by up to approximately 50% at Candelaria due to selfdemagnetization, and that the induced magnetization is also slightly rotated from the regional inducing field towards the plane of the “mantos”. The dominant paleomagnetic component recorded by the Candelaria deposit and host rocks is a normal polarity remanence of moderate to high stability which is interpreted to have been acquired during the mid-Cretaceous alteration and mineralisation event(s) that generated the magnetic minerals (predominantly magnetite). However, the presence of a reversed polarity overprint component in some samples suggests that the Candelaria deposit and its immediate environs have experienced a post 83 Ma thermal or thermochemical event that has not been previously recognised. The remanence directions of both polarities are rotated clockwise with respect to the expected directions for mid-Cretaceous/Early Tertiary fields, indicating clockwise rotation of the Candelaria area, including the adjacent batholith, through at least 45° since the acquisition of the normal and reversed remanence components, i.e. since 83 Ma. This case study illustrates the importance of understanding the magnetic behaviour of different ore types, and incorporating self-demagnetization into modelling procedures for highly magnetic targets in mineral exploration.
publishDate 2014
dc.date.none.fl_str_mv 2014-10
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
http://purl.org/coar/resource_type/c_6501
info:ar-repo/semantics/articulo
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/11336/20016
Austin, James; Geuna, Silvana Evangelina; Clark, David; Hillan, Dean; Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile; Elsevier Science; Journal Of Applied Geophysics; 109; 10-2014; 242-255
0926-9851
CONICET Digital
CONICET
url http://hdl.handle.net/11336/20016
identifier_str_mv Austin, James; Geuna, Silvana Evangelina; Clark, David; Hillan, Dean; Remanence, self-demagnetization and their ramifications for magnetic modelling of iron oxide copper-gold deposits: An example from Candelaria, Chile; Elsevier Science; Journal Of Applied Geophysics; 109; 10-2014; 242-255
0926-9851
CONICET Digital
CONICET
dc.language.none.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv info:eu-repo/semantics/altIdentifier/doi/10.1016/j.jappgeo.2014.08.002
info:eu-repo/semantics/altIdentifier/url/http://www.sciencedirect.com/science/article/pii/S0926985114002390
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
eu_rights_str_mv openAccess
rights_invalid_str_mv https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
dc.format.none.fl_str_mv application/pdf
application/pdf
dc.publisher.none.fl_str_mv Elsevier Science
publisher.none.fl_str_mv Elsevier Science
dc.source.none.fl_str_mv reponame:CONICET Digital (CONICET)
instname:Consejo Nacional de Investigaciones Científicas y Técnicas
reponame_str CONICET Digital (CONICET)
collection CONICET Digital (CONICET)
instname_str Consejo Nacional de Investigaciones Científicas y Técnicas
repository.name.fl_str_mv CONICET Digital (CONICET) - Consejo Nacional de Investigaciones Científicas y Técnicas
repository.mail.fl_str_mv dasensio@conicet.gov.ar; lcarlino@conicet.gov.ar
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