Richard Stuart Smith

• Ph.D.
• Professor at Laurentian University

Despite abundant empirical evidence, the details of coupled deformation and mass transfer processes within a framework of the crustal architecture of ancient orogens remains enigmatic. Geophysical imaging of the Larder Lake‐Cadillac deformation zone, a well‐endowed crustal‐scale fault system in the Superior Province of the Canadian Shield, characte...

Mineral prospectivity maps were produced for gold in two greenstone belts in the Superior geological province in Ontario, Canada, as part of the Metal Earth Project in the Laurentian University, Sudbury, Ontario. These maps, created using the random forest machine learning algorithm, cover the well-endowed Matheson area, which is in the Abitibi sub...

Unmanned aerial vehicles (UAVs), commonly known as drones, offer several advantages over traditional piloted aircraft. They are characterized by enhanced safety, cost-effectiveness, and the ability to operate in closer proximity to targeted sources. Consequently, magnetic sensors have been adapted or specifically designed for integration onto UAV p...

Enhancing magnetic data is often complicated due to the non-vertical orientation of the geomagnetic field and the orientation of remanent source magnetization. The complication can be reduced by reducing the data to the pole (mathematically making the geomagnetic field vertical), but this reduction process is problematic. The analytic-signal amplit...

The model that is used to explain potential-field data is highly dependent on the constraints applied in the modelling process. Many studies demonstrate the necessity of constraining gravity and magnetic models. However, typically they do not demonstrate the individual enhancements that come as a consequence of integrating each constraint into the...

Gravity data are ‘nonunique’ in that a gravity anomaly can be explained by many bodies with different properties. Similarly, in seismic data, the strength of a reflection is dependent on the product of the density and the seismic velocity, so the nature of a reflection cannot be used to determine the density below an interface when the velocity is...

A data set consisting of 376 broadband and long‐period MT measurements was used to generate the first ever 3D resistivity model of the Archean western Superior Craton. The modeled resistivity structure is compared to coincident seismic reflection data. The observed geophysical signatures are interpreted within the context of the late stages of crus...

The Iraq Southern Desert (SD) needs detailed studies to explore the subsurface, especially the deep and concealed basement. The aim of this work is to interpret the airborne magnetic survey data of the SD, which has a thick Phanerozoic sedimentary cover. The basement has not been imaged by deep seismic or even accessed by exploration wells. Magneti...

When using forward modeling to estimate model parameters, such as the dip, it is also important to estimate the corresponding uncertainty in the model parameters. For gravity data, these uncertainties are dependent on the uncertainty in the Bouguer corrected data. The uncertainty in the gravity meter reading and the height used in the free-air and...

A well-known and essential task in magnetic data interpretation is the structural mapping of basement terranes. Useful tools for analyzing the deep basement are edge-detection filters that normalize the first-/second-order gradients of the magnetic field in three spatial directions. Different edge-detection filters can reveal different structures;...

Three-dimensional depth-to-basement geometry modelling was carried out in the northeastern part of the Sudbury impact structure using the VPmg potential field inversion package implemented within the Mira Geoscience GOCAD mining suite. Along a transect, several geophysical datasets (gravity, high-resolution seismic, audio-frequency and broad-band m...

The Metal Earth project integrates geophysics, geology, geochemistry, and geochronology to improve the understanding of metal endowment in Precambrian terranes. Magnetics (airborne), gravity, magnetotellurics, and reflection seismic methods are the primary geophysical tools employed. Data were collected along 13 transects in the initial phase of th...

We introduce a three-dimensional (3D) generalized spherical multifocusing (GSMF) algorithm to generate a high-resolution 3D stacked volume that is equivalent to a synthesized 3D zero-offset wavefield for crooked-line/3D seismic data. The proposed algorithm can be applied to arbitrary recording geometry from areas with irregular topography, complex...

A high‐resolution seismic reflection transect was acquired over a hard‐rock geological setting along an existing roadway in the Larder Lake area of the Superior Craton of Canada for the Metal Earth project in 2017. This profile, as well as other Metal earth transects, primarily aims to enhance the knowledge and to better understand the subsurface g...

Once inverting potential-field geophysical data an appropriate discretization of the model is required to accurately construct complicated geometries of the causative sources. Rectangular prisms (structured meshes) have limitations to recover and preserve the edges of real geological sources. Here an isoparametric finite-element (FE) methodology is...

Magnetic data are widely available and useful in many exploration and applied-geophysics projects. The magnetic data are usually processed, imaged, and interpreted in commercial software packages. The algorithms used in these packages are sometimes difficult to check or tune, and the code is not available for review. However, these packages often h...

Magnetic susceptibilities measured on outcrop are often assumed to be reasonable values to use when modelling aeromagnetic data. We have undertaken two exercises to understand how useful these measurements are for magnetic modelling. Estimates of apparent magnetic susceptibility can also be derived from aeromagnetic data by mathematical transformat...

Passive seismic methods are considered cost‐effective and environmentally friendly alternatives to active (reflection) seismic methods. We have acquired colocated active and passive seismic surveys over a metal‐endowed Archean granite‐greenstone terrane in the Larder Lake area to investigate the reliability of estimated elastic properties using pas...

Detection and assessment of the deeply buried high-grade uranium deposits in the Athabasca Basin rely on geophysical methods to map conductive rocks. Variable Quaternary surface cover can mask the anomalous signals from depth and affect interpretation of inverted conductivity models. We present the analysis of a number of EM modeling studies and tw...

The dipolar character of magnetic data means that there is a high and a low associated with each source. The relative positions and sizes of these highs and lows, varies depending on the magnetic latitude or the inclination of the Earth’s magnetic field. One method for dealing with this complexity is to transform the data to what would collected if...

Although magmatic- and metamorphic- derived fluids are widely recognized mineralizing agents, the role of crustal architecture in defining source and sink zones within the middle to lower crust and upper mantle of ancient orogens remains enigmatic. The globally largest and best-preserved Archean greenstone belts lie in the Superior Province, Canada...

The horizontal and vertical components of the on-time electromagnetic (EM) response can be used to estimate the parameters of simple models like thin sheets, half-spaces, thin sheets over a lower half-space and a two-layer model. The formulae used in these methods are valid in areas where the on-time response is essentially proportional to the cond...

Parameter estimation in aeromagnetics is an important tool for geological interpretation. Due to aeromagnetic data being highly prevalent around the world, it can often be used to assist in understanding the geology of an area as a whole, or for locating potential areas of further investigation for mineral exploration. Methods that automatically pr...

Recent geological and paleo-magnetic studies from the surface geology suggest a folding of upper crustal Archean basement rocks in the East Range of Sudbury impact crater, but no geophysical evidence from the subsurface has been provided. In the current study, the 3-D geometry of upper-crustal Archean basement rocks below the East Range of the Sudb...

Recent geological and paleo-magnetic studies from the surface geology suggest a folding of upper crustal Archean basement rocks in the East Range of the Sudbury impact crater, but no geophysical evidence from the subsurface has been provided. In the current study, the 3-D geometry of upper-crustal Archean basement rocks below the East Range of the...

The Temagami Geophysical Anomaly (TGA) is situated in the Paleoproterozoic Huronian Supergroup near the southern margin of Archean Superior craton, along strike from the Temagami Greenstone Belt, 50 km northeast of world-class metal endowment in the Sudbury Igneous Complex. It has been attributed to coincidental geophysical responses from Neoarchea...

Formulae for the moments of the magnetic field response can be derived for simple models which have conductivities that vary suddenly as a function of depth (thin and thick sheets) or not at all (half space). In a companion paper we have derived expressions for the moments of a conductivity-depth profile that varies smoothly, taking the form of a G...

The nature of lithospheric evolution and style of the driving tectonic processes during the growth and stabilisation of continental crust in the Archean remain enigmatic. The hotter, rheologically weak Archean crust would be unable to support thick orogens. Thus, gravitational collapse likely occurred when continental fragments became overthickened...

Gold in the Abitibi greenstone belt in the Superior craton, the most prolific gold-producing greenstone terrane in the world, comes largely from complex orogenic mineralizing systems related to deep crustal deformation zones. In order to get a better understanding of these systems, we therefore combined new magnetic, gravity, seismic, and magnetote...

Exploration for new mineral deposits has become increasingly difficult as new discoveries are being found under progressively deeper cover. To better understand and predict orogenic gold mineralization in the Archean Swayze greenstone belt, the essential ingredients of a mineral system are considered: 1) the source of gold and transport fluid ligan...

This contribution focusses on obtaining a better understanding of the subsurface geology of the Chibougamau area, in the NE of the Abitibi greenstone belt (Superior craton), using geophysical data collected along a 128 km long traverse with a rough SW-NE orientation. We have constructed two-dimensional (2D) models of the study area that are consist...

Understanding the spatial controls on mineral deposits is crucial in mineral exploration targeting. This paper uses a combination of spatial data analysis techniques, such as the distance distribution method, Fry, nearest neighbor index, Ripley’s K-function multi-distance, fractal, and kernel density analysis, to better define controls on the distr...

The concept of moments of the electromagnetic response is useful in electromagnetic interpretation. Analytic formulae exist for low-order moments of a few conductivity models, enabling source parameters such as time constant, depth, conductance and conductivity to be estimated from the measured moments of the electromagnetic response. However, most...

When inverting potential-field geophysical data an appropriate discretization of the model is required to accurately construct complicated geometries of the causative sources. Rectangular prisms (structured meshes) have limitations to recover and preserve the edges of realistic geological sources. We use an isoparametric finite-element methodology...

Recently, there was an increase of costs to explore new economical mineral occurrences, while the success of discovery of new deposits has diminished. Therefore, Metal Earth was conceived with the objective to improve understanding of the processes controlling the distribution of mineral endowment, with a focus on Archean greenstone belts of the Ca...

The time decay constant or “tau” of airborne electromagnetic (AEM) systems is commonly used to indicate the presence and relative conductivity or conductance of conductors in the survey area. In fact, it is not a constant because it depends on the system, the survey design and the method of calculation. The system dependence is a consequence of par...

Gravity data have been acquired as part of the geophysical component of the Metal Earth project. Collected data have been processed and will be used to assist geologists in their geological interpretation, while also providing two-dimensional (2-D) and three-dimensional (3-D) models of the subsurface features. The initial models that are constraine...

Magnetic and gravity inversions are used to create 2D or 3D models of the magnetic susceptibility and density, respectively, using potential field data. Unconstrained inversions generate an output based on mathematical constraints imposed by the inversion algorithm. Constrained inversions integrate lithological, structural, and petrophysical inform...

When aeromagnetic data are interpolated to make a gridded image, thin linear features can result in "boudinage" or "string of beads" artifacts if the anomalies are at acute angles to the traverse lines. These artifacts are due to the undersampling of these types of features across the flight lines, making it difficult for most interpolation methods...

Structurally complex zones within orogenic terranes typically correspond to areas where there is interference between multiple fold generations and are known to be favorable pathways for fluid flow because of their higher permeability. In the Canadian Malartic district, gold anomalies have been linked with zones of structural complexity that have b...

The 2D contrast source inversion (CSI) method is introduced for interpreting cross-hole radio imaging (RIM) data. The contrast source is defined as the product of the electric field and the object profile, the latter of which contains information about the conductivity and the permittivity of a model. We built a cost function and used the conjugate...

ABSTRACT Extremely conductive bodies, such as those containing valuable nickel sulfides, have a secondary response that is dominated by an in-phase component, so this secondary response is very difficult to distinguish from the primary field emanating from the transmitter (because by definition they are identical in temporal shape and phase). Hence...

We present two examples of using the contrast source inversion (CSI) method to invert synthetic radio-imaging (RIM) data and field data. The synthetic model has two isolated conductors (one perfect conductor and one moderate conductor) embedded in a layered background. After inversion, we can identify the two conductors on the inverted image. The s...

The magnetic viscosity effects observed at time scales between 0.01 and 10 ms at Opemiska are associated with magnetic grains of variable size in rocks. Recent observations made during a ground time-domain electromagnetic (TDEM) survey at Opemiska are consistent with four aspects of the spatial and amplitude characteristics of a magnetic viscosity...

In inductive electromagnetics, the magnetic field measured in the air at any instant can be considered a potential field. As such, we can invert measured magnetic fields (at a fixed time or frequency) for the causative subsurface current system. These currents can be approximated with a 3D subsurface grid of 3D magnetic (closed loop current) or ele...

Radio-frequency electromagnetic tomography (or radio imaging method) employs radio-frequency (typically 0.1–10 MHz) electromagnetic wave propagation to delineate the distribution of electric properties between two boreholes. Currently, the straight-ray imaging method is the primary imaging method for the radio imaging method data acquired for miner...

Geologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three-dimensional geological model. The initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion. In addition...

The magnetic response of dykes and mafic dyke swarms are typical examples of the type of geological feature that can result in “boudinage” artifacts when the data is interpolated and imaged. In an effort to remove these types of artifacts, a new interpolation method uses a Taylor series expansion of two variables to interpolate a measurement locati...

Geologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three dimensional (3D) geological model. The initial and reference model (used to constrain the inversion) was constructed based on geological information from approximately 965 dr...

The radio imaging method (RIM) is a cross-hole imaging method that uses radio-frequency electromagnetic waves to delineate the electric properties in the borehole plane. In this paper, we describe the two-dimensional (2-D) complex permittivity inversion method of interpreting RIM data and use synthetic data to test its efficacy. The method is based...

Following petrophysical studies, geological and geophysical data compilation, the former Opemiska underground mine of the Chibougamau District was selected for conducting an experimental TDEM ground survey. Fourteen different sites confirmed the variability of the EM response associated with chalcopyrite veins, and the difficulty in relying on an e...

Induced polarization effects have been seen since the 1970s in ground EM data and in airborne EM data since the 1990s. These effects normally manifest themselves as negative amplitudes in transient electromagnetic data. For fixed-wing towed-bird electromagnetic systems, negatives can also occur as a geometric effect, but for systems where the trans...

Electromagnetic exploration methods have important applications for geologic mapping and mineral exploration in igneous and metamorphic terranes. In such cases, the earth is often largely resistive and the most important interaction is between a conductor of interest and a shallow, thin, horizontal sheet representing glacial tills and clays or the...

Resistivity methods are commonly used in mineral exploration to map lithology, structure, sulphides and alteration. In the Athabasca Basin, resistivity methods are used to detect alteration associated with uranium. At the Midwest deposit, there is an alteration zone in the Athabasca sandstones that is above a uraniferous conductive graphitic fault...

We are proposing a new electromagnetic system that is intended for deep exploration of the subsurface. The system comprises one or more three-component transmitters, which can be magnetic dipoles, or for marine exploration electric dipoles. The three transmitter components can be combined so as to direct the primary field in any direction at any lo...

The radio imaging method (RIM) is an electromagnetic crossborehole method with applications in mineral exploration, as well as in the coal industry, where it is used across mine drives. Attenuation of the signal from conductive regions may indicate areas of mineralization, and these conductive effects in general dominate the response. In an effort...

We have developed an alternative strategy for the inevitable deeper inductive electromagnetic (EM) exploration, which will be required as shallow deposits are exhausted. Rather than using very large magnetic moment ground loops, measurement stations are repeated using many smaller sized loops with smaller moments. The multiple transmitter data are...

We have developed a method for displaying or imaging data from a ground-time-domain electromagnetic system and for extracting the geometric parameters of a small conductor. The parameters are determined directly from the data using combinations of the spatial components of the secondary fields and their Hilbert transforms. The position of the targe...

The 3D geologic and structural setting of the Sudbury Structure was predicted by an integration of surface and subsurface geologic data with 2.5D modeling of high-resolution airborne magnetic and gravity data using 3D GeoModeller software. Unlike other CAD-based 3D software, GeoModeller uses the field interpolator method, whereby contacts of rock u...

Downhole density, gamma radioactivity, and magnetic susceptibility measurements in five drillholes at the Victoria property (located in the south range of the Sudbury basin) were analyzed to identify homogenous physical units. The fuzzy k-means clustering algorithm was used for unsupervised classification of the data. Four main physical units were...

A novel automatic data interpretation algorithm is presented for modelling airborne electromagnetic (AEM) data acquired over resistive environments, using a single-component (vertical) transmitter, where the position and orientation of a dipole conductor is allowed to vary in three dimensions. The algorithm assumes that the magnetic fields produced...

We show the advantages of using multi-component transmitter–receiver systems for determining the geometry of a compact planar target whose electromagnetic response can be approximated by a dipole. Our approach is based on a modified version of an algorithm that we previously published using a single-component (vertical) transmitter. Tests on synthe...

Many ground controlled-source electromagnetic (EM) systems have been deployed, and under ideal conditions these systems are capable of detecting large conductors to depths of approximately 800 m; however, more common detection limits are less than 400 m.Although these systems have been used with great success, they may experience two weaknesses whe...

Summary Magnetic susceptibility, density, and gamma ray counts are three physical properties measured within a hole drilled at Victoria property, were used to identify rock types. The fuzzy k-means clustering algorithm was used to divide the data into different clusters, each of which represented a rock group with similar physical properties charac...

Two coincident high-resolution airborne gravity and magnetic profiles of the Sudbury structure were forward modelled to better understand the geology of the structure at depth. A north–south profile was used to further investigate the deep geological setting of the Sudbury Igneous Complex (SIC) along Lithoprobe seismic transect, while an east–west...

The conductance of an infinite uniformly conductive thin sheet can be calculated using the ratio of the temporal gradient and the spatial gradient in the normal direction of any component (or combination of components) of the secondary magnetic field. With standard borehole electromagnetic (BHEM) systems, the temporal gradient can either be measure...

With the inductive electromagnetic geophysical method, the laterally varying conductance of thin sheet models can be estimated either through a direct transform of the measured data or through inversion. The direct transform (called the simplified solution) does not require grid or line data and is simple enough to be performed in the field because...

Mine waste, variable overburden, and the saprolite associated with nickel laterites have conductivity thicknesses (conductances) that vary laterally. In order for electromagnetic methods to be used to easily map lateral changes in conductance over thin-sheet-like bodies such as these, a simple conductance estimation method has been developed from P...

In the period from 2008 to 2012, the topic of electromagnetic (EM) induction methods applied to mineral exploration has been the subject of more than 50 papers in journals and more than 300 extended abstracts presented at conferences (about 100 of which contain developments worthy of mentioning). Most of the work at the universities has been on mod...

The Nickel Rim South property is located entirely within MacLennan Township, 22 kilometers northeast of Sudbury, Ontario, Canada. The occurrence of conductive sulphides in an otherwise highly resistive host rock makes it an ideal place for exploring and mapping using high frequency electromagnetic methods. The FARA radio imaging (RIM) system was de...

In order to obtain an accurate EM response with modelling software, most people assume that it is necessary to know or specify the excitation current waveform (or its derivative) precisely. A mathematical analysis shows that accurate model results can be obtained during the off time if the amplitude of the waveform is specified precisely in the lat...

A discrete conductive sphere model in which current paths are constrained to a single planar orientation (the ‘dipping sphere’) is used to calculate the secondary response from Geotech Ltd’s VTEM airborne time domain electromagnetic (EM) system. In addition to calculating the time constants of the B-field and dB/dt responses, we focus on the time-c...

The detection of conductive bodies is an important capability when exploring for massive sulfide deposits or looking for unexploded ordnance. When these bodies are buried below conductive overburden or embedded in conductive material, the use of an electromagnetic system to identify the bodies becomes problematic because the response of the overlyi...

The Sudbury Structure is one of the most studied geologic structures in the world due to its enigmatic nature and mineral wealth. The available geologic work from the literature and mining industry operations accumulated for more than a century was recently assessed and compiled into a bedrock geologic map. Most regional geophysical investigations...

The SLUTH method requires first-order derivatives at two or more different heights above the ground and can estimate the location and depth of source bodies from magnetic data. Results of this method are independent of a specific model type and can be used to estimate the most appropriate model (structural index). This paper presents a grid impleme...

A versatile discrete conductor model is used to generate the maximum signal-to-noise ratio along an airborne electromagnetic (AEM) profile. By varying the position of the conductor below and to the side of the airborne traverse, a sensitivity cross-section can be generated that shows the volume of material that influences the AEM response. This typ...