Screening kimberlite magnetic anomalies in magnetically active areas

Cowan, Duncan; Tompkins, Linda A.; Cowan, S.

doi:10.1071/eg00066

Cited by 12 publications

(9 citation statements)

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“…Keating (1995) proposed a form of correlation filtering which looks for matches with a theoretical model of an idealised kimberlite pipe. Cowan et al (2000) built on Keating's work by combining the results generated from applying multiple filters and other analytical techniques to provide high-level information regarding anomaly characteristics. The drawback with these methods is that they are not flexible enough to recognise anomalies that exhibit significant shape and size variations, for example due to the dominance of remanent over induced magnetism in the source rocks.…”

Section: Detection Of Circular Features In Geoscience Datamentioning

confidence: 99%

Automatic identification of responses from porphyry intrusive systems within magnetic data using image analysis

Holden¹,

Fu²,

Kovesi³

et al. 2011

Journal of Applied Geophysics

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Section: Detection Of Circular Features In Geoscience Datamentioning

confidence: 99%

Automatic identification of responses from porphyry intrusive systems within magnetic data using image analysis

Holden¹,

Fu²,

Kovesi³

et al. 2011

Journal of Applied Geophysics

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“…Euler deconvolution of the total magnetic field was also performed, as it is independent of field inclination and declination (Reid et al, 1990). This technique is one of the methods used to identify kimberlite magnetic anomalies (Cowan et al, 2000). A structural index of 2, corresponding to a magnetic pole, was used.…”

Section: Figmentioning

confidence: 99%

“…In the Kirkland Lake area of northeastern Ontario, Canada, the diameter of the known kimberlite pipes ranges from 100 to 200 m. In the Northwest Territories, their diameter can be as small as 75 m. Brummer et al (1992) show how areromagnetic data can be used to identify previously unknown kimberlites in the Kirkland Lake region; their approach is to look for small, circular, isolated magnetic anomalies. Cowan et al (2000) review techniques that can be used to screen kimberlite magnetic anomalies. Aeromagnetic data enhancement techniques can be used to clarify the expected circular signatures.…”

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confidence: 99%

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Use of the analytic signal to identify magnetic anomalies due to kimberlite pipes

Keating

Sailhac

2004

GEOPHYSICS

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The magnetic signature of most kimberlite pipes is, at high magnetic latitudes, a circular anomaly. At lower magnetic latitudes, it becomes asymmetric; and at the magnetic equator, the anomaly is mostly negative. The shape of the anomaly is also influenced by the presence of remanent magnetization. For a vertical cylinder, the shape of the analytic signal of the magnetic field is nearly independent of field orientation and remanence and always results in a compact, almost circular anomaly. A simple pattern recognition technique, based on a firstorder regression over a moving window, between the analytic signal of the observed magnetic field and the theoretical analytic signal of a magnetic vertical cylinder is an effective tool to identify potential targets. Results where the correlation coefficient between the analytic signal and the theoretical analytic signal within a moving window are above a certain threshold are retained, and additional criteria can later be used to refine the target selection. The method's practical utility is demonstrated by applying it to three different sites. The first is a well-documented area located at high magnetic latitude (Ontario, Canada), the second is at low magnetic latitude (West Africa), and the last one is an area where many pipes have a negative magnetization (Lac de Gras, Canada). INTRODUCTION Kimberlites are the major source of the world's diamonds. Kimberlite is an ultrabasic igneous rock which can occur as sills, dikes, or pipes. Sills and dykes are rarely mined (Gerryts, 1967), and only one in a hundred pipes contains an economic deposit of diamonds (Brummer, 1978; Kamara, 1981). They are found within thick, Archean cratons and adjacent Proterozoic mobile belts (Mitchell, 1991). Pipes are carrot-shaped in

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“…; Cowan et al . ). This is mainly due to the fact that kimberlite pipes have moderate to strong magnetization, with susceptibilities ranging from 1 to 80 × 10 ‐3 SI units (Power et al .…”

Section: Introductionmentioning

confidence: 97%

3D magnetic interpretation of the Regis kimberlite pipe, Minas Gerais, Brazil

Menezes

Terra²

2011

Near Surface Geophysics

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In the present work, high-resolution ground magnetic data are used to unveil the structure of the Regis kimberlite pipe, which is located in a well-known diamondiferous province in the central portion of Brazil. The main tectonic feature of the area is a NW-SE major crustal fracture zone, extending for more than 3000 km within Brazil, along which Regis and several other kimberlite pipes have intruded. The area is located at low magnetic latitude (inclination approximately 27 o south) and the ground magnetic anomaly associated with the Regis pipe appears as an isolated asymmetric dipole-like source caused by magnetization primarily in the direction of the Earth's magnetic field. We inverted this high-resolution magnetic data set in order to recover the 3D effective susceptibility model of the studied pipe. We obtained an asymmetric conical-shaped strongly magnetized body (35 × 10 -3 SI units) extending from 50-720 m depth. Prior to the inversion, the data were upward continued to 30 m above the surface to attenuate high-frequency noise and mitigate inversion artefacts. Our results were used to better define the subsequent drilling positions to thoroughly evaluate the economic potential of the Regis pipe. One available borehole drilled approximately in the centre of the structure corroborates our interpretation. 2007). The magnetic study described herein was initiated prior to

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Screening kimberlite magnetic anomalies in magnetically active areas

Cited by 12 publications

References 0 publications

Automatic identification of responses from porphyry intrusive systems within magnetic data using image analysis

Automatic identification of responses from porphyry intrusive systems within magnetic data using image analysis

Use of the analytic signal to identify magnetic anomalies due to kimberlite pipes

3D magnetic interpretation of the Regis kimberlite pipe, Minas Gerais, Brazil

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