Combined 3‐D interpretation of airborne, surface, and borehole vector magnetics at the McConnell Nickel deposit

Abstract

The McConnell nickel deposit is an elliptical amphibolite-biotite quartz diorite pod within the Sudbury Metabreccia that surrounds the main mass of the Sudbury Igneous Complex. The geometry of the deposit is tabular with a strike length of approximately 152 m and depth of 610 m. Various magnetic surveys were conducted in this study area. A regional aeromagnetic survey was conducted by the Ontario Geological Survey. A more detailed ground magnetics survey and borehole magnetic survey are used in the interpretation of the character of the causative body. Five boreholes which intersect the deposit at 40 m, 105 m, 135 m, 210 m, and 250 m provide good lithological control of the deposit with depth. Eight other boreholes used in this study did not have logged lithology, but all 13 holes were logged with gamma ray, density, spectral gamma-gamma, IP, resistivity, SP, magnetic susceptibility, temperature, and three-component magnetic field probes. Only the measurements of magnetic susceptibility and three-component magnetic field measurements and their interpretation will be discussed in this paper. Three-component magnetic vector surveys show different signatures for boreholes that pass through a magnetic source body, and for holes that are adjacent to the source body. Using inverse models of the surface magnetic data, values of magnetic susceptibility and magnetic remanence direction and intensity for the various lithological units are estimated. Modelling of the subsurface data reveals fine structure within the ore body and may be used to estimate the direction and distance to the magnetic bodies.

The Lake Bosumtwi meteorite impact structure, Ghana—A magnetic image from a third observational level

“…Measuring the full magnetic vector presents many advantages, namely: a) differentiation of 2-D and 3-D magnetic source bodies, b) separation of the geometrical aspects of the source body from the geometrical aspects of the effective magnetic field, and c) an estimate of the orientation and magnitude of the remanent magnetic vector (Morris et al 1995;Mueller et al 1998). However, little has been published on the application of vector magnetic data as compared to its total magnetic field counterpart (Collar et al 2005).…”

“…Borehole vector magnetic measurements can provide constraints on the depth distribution of anomalous source bodies, and differentiate between source body geometry and magnetic field geometry effects (Mueller et al 1998;Morris et al 2007). Figure 1 shows the calculated surface and borehole total magnetic fields due to a 100 ×100 × 100 m magnetized prism that extends from 100 to 200 m below the surface.…”

Application of 3D magnetic amplitude inversion to iron oxide-copper-gold deposits at low magnetic latitudes: A case study from Carajás Mineral Province, Brazil

“…A similar approach based on parametric inversion is to invert for the magnetization vectors within causative bodies together with their geometric shapes. Mueller et al (1997) use this approach to interpret borehole magnetic data in the presence of strong remanent magnetization. Foss and McKenzie (2011) apply this approach to multiple sources to model complex anomalies.…”

Reorientation of three‐component borehole magnetic data

“…The error in azimuth strongly increases with decreasing inclination (Mueller et al . ). Fieberg () estimates an azimuthal orientation error of 6° for a drill hole inclination of 0.5°.…”