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

Abstract

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

An aspect of the subsurface structure of the Burdur-Isparta area, SW Anatolia, based on gravity and aeromagnetic data, and some tectonic implications

“…The analytic signal method has been used extensively in magnetic interpretation (e.g., Nabighan, 1972;Roest et al, 1992;Mohan and Babu, 1995;Hsu et al, 1998;Harikumar et al, 2000;Bastani and Pedersen, 2001;Salem et al, 2002;Rajaram, 2003, 2004;Keating and Sailhac, 2004). This signal exhibits maxima over magnetization contrasts, independent of the ambient magnetic field and source magnetization directions.…”

Treatise on the Resolution of the diamond problem after 200 years

“…Such magnetic distinction has led to the location of diamond bearing Kimberlite based on airborne measurements of variations in the earth's magnetic field on the basis of so called magnetic anomalies [50]. Here this Resolving model on the basis of the Little Effect is consistent with the natural formation of diamond in the earth's mantle.…”

Locating anomalies by gravity gradiometry using the matched filter with a probabilistic assessment

“…Finally, we mention that cave detection on Mars plays an important role in the search for extraterrestrial life, where caves are known to harbor their own micro-climates (Wynne et al, 2008). The matched filter is not widely employed in geophysics; examples include the detection of dikes using magnetic data (Naudy, 1971), the detection of sea mounts from satellite altimetry (White et al, 1983), and the detection of kimberlites from magnetic data (Keating, 1995). Our exposition in terms of gravity gradients thus illustrates a relatively new (at least different) technique.…”