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 extent 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 a 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 3-component magnetic field probes. Only the measurements of magnetic susceptibility and 3-component magnetic field measurements and their interpretation will be discussed in this paper. 3-component magnetic vector surveys show different signatures for boreholes that pass through a magnetic source body (an onhole source), and for holes that are adjacent to the source body (an offhole source). 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 other offhole magnetic bodies.