Summary Developments in instrumentation and processing tools have made 3D resistivity surveys an effective approach in delineating complex geological environments. In the performance of these surveys a large number of data points are produced, and the properties of the dataset should be explored to optimize and coordinate interpretation efforts. In this study, a field 3D dataset was geometrically decomposed into near maximum-coupled (so-called radial) and near null-coupled (so-called tangential) subsets and inverted using a 3D approach. The results indicate that these two models may represent the subsurface at regional and local scales and help in the discrimination of different targets. Introduction Mineral exploration generally employs the DC resistivity method to detect and map targets of interest.
An Orion 3D DC/IP/MT survey was conducted over a portion of Landore Resources Canada’s Junior Lake property in Northwestern Ontario in 2012, with a larger follow-up survey conducted in 2014. The survey results provided 3D models that successfully delineated the known B4-7 and VW deposits and provided an enhanced understanding of the three-dimensional geometry of the mineralization. With this improved understanding of their deposits, Landore was better able to plan future efforts to expand the known mineralized zones.
Landore Resources Canada’s Junior Lake property is located approximately 235 km north-northeast of Thunder Bay (Figure 1). The area has been mapped and explored since the early 20th century. Landore Resources Canada acquired the Junior Lake property between 1998 and 2000.
The B4-7 massive sulphide zone was discovered in 1969 based on drill testing of airborne geophysical anomalies. The discovery hole intersected 8.26 m of massive pyrrhotite-pyrite-chalcopyrite, with grades of 0.80% Ni and 0.53% Cu.
In 2004, a helicopterborne magnetic and TDEM survey identified a number of conductors and magnetic features on the Junior Lake property, including the Scorpion Zone that extends west from the B4-7 deposit. In 2005, the VW disseminated/vein sulphide deposit was discovered while following up a conductor identified on the 2004 airborne survey.
A known mineralized zone was successfully mapped in high resolution with the Orion 3D omnidirectional 3D DCIP system. Subsets of the original dataset are used to examine the resolution and mapping capabilities of other approaches to 3D DCIP acquisition. The results show that the high-density omnidirectional method produces superior resolution of geologic structures compared to other methods that collect less dense and directionally biased data.
In recent years, DCIP acquisition has evolved from a purely 2-D method to a variety of systems offering differing levels of three-dimensional acquisition. Offset-injection systems acquire data on multiple parallel receiver lines, with or without orthogonal receiver dipoles. The Orion 3D pole-dipole system, however, uses a network of orthogonal dipoles and a large number of current injections to collect high-density omnidirectional DCIP data throughout the survey area.
To examine the resolution of the high-density omnidirectional approach to 3D DCIP acquisition, we examine the inversion results from an Orion 3D survey that was used to successfully map a known mineralized zone with a high degree of precision.
Subsets of the full dataset have been inverted to evaluate the effectiveness and mapping resolution of lower density methods of data acquisition, including those with unidirectional receiver dipoles, directionally oriented current injection patterns, and roll-along type offset injection surveys.