Bill Morris

Identifying structural trend with fractal dimension and topography

A digital elevation model (DEM), derived from light imaging detection and ranging (LiDAR) altimetry data, is used to investigate the fractal characteristics and structural trends of a topographic surface. The study area is located on the southeastern rim of the Sudbury Basin, a meteorite impact feature in Ontario, Canada. Visual interpretation and statistical analysis of fractal dimension (D) indicate that the geological units in the study area are characterized by statistically different distributions of D. In addition, the landscape exhibits two predominant aspect directions: 127° and 290° or ∼SE and NW. High values of D correspond to these predominant aspect directions. Topographic ridgelines exhibit a NE-SW trend, which is perpendicular to that of the highest fractal dimensions and the predominant aspect directions. It is suggested that these ridgelines are topographic expressions of tectonic fabrics present in the various geological units. Genesis of the tectonic fabric is related to the NW-SE–directed shortening of the Sudbury Basin impact crater.

Comparison of fully constrained and weakly constrained unmixing through mine-tailing composition mapping

In recent years, remote-sensing scientists have been developing applications for hyperspectral remote sensing. Analysis techniques, such as linear spectral unmixing, have been used increasingly to solve real-world problems related to vegetation stress detection, mineral prospecting, and environmental monitoring. Information products such as end member fraction maps can be generated by interpreting unmixing results. However, the validity of these maps has not been fully examined. In this paper, two types of constrained linear spectral unmixing techniques are investigated, namely fully constrained and weakly constrained unmixing. Overall, this study revealed that the weakly constrained approach provides more realistic results than the fully constrained technique. From a data-analysis perspective, this study demonstrates that the weakly constrained unmixing can be used successfully when an incomplete list of end members is used in the unmixing, which is almost always the case in reality. In addition, this paper also addresses the scaling issue. When using laboratory spectra as end members for unmixing, proper scaling of the spectra amplitude will reduce errors and, hence, improve unmixing results. The tests were conducted in a mine-tailing site, but the findings derived from this study also apply to other applications.

Mapping mine tailing surface mineralogy using hyperspectral remote sensing

Acid mine drainage resulting from mine tailings poses an environmental threat. An important initial step towards the reclamation of mine tailing sites is to detect the presence of acid-generating, sulphide-rich minerals and determine their spatial distribution. In this study, the potential of hyperspectral remote sensing for characterizing mine tailings is investigated. The study site is located in northern Ontario, Canada, and the data were collected with PROBE-1, an imaging spectrometer that covers the visible, near-infrared, and shortwave-infrared spectral ranges. The results indicate that using the weakly constrained linear spectral unmixing technique PROBE-1 data can provide information on mineral compositions of the tailing surface. The spatial locations and associations of acid-generating source minerals such as pyrite and pyrrhotite along with their oxidation products (e.g., copiapite, jarosite, ferrihydrite, goethite, and hematite) can provide information about the distribution of oxidation processes at the site. This remote mapping technique can be very valuable when attempting to identify abandoned mine-waste sites and the potential risk they might present where there are no a priori knowledge and field samples available.

Mine tailings characterization using PROBE data (preliminary results)

Acid mine drainage (AMD), caused by mine tailings, poses an environmental threat. AMD control is a major challenge facing the mining industries worldwide. An important initial step towards the reclamation of mine tailings sites is to identify the presence of sulphide-rich minerals and their spatial distribution. This study investigated the potential of hyperspectral PROBE data for mine tailings characterization over the Copper Cliffs tailings site in northern Ontario, Canada. The results indicated that PROBE data could provide information on locating oxidation zonations of the tailings. More importantly, it revealed that library mineral spectra could replace the scene-derived endmember spectra to unmix the PROBE image.

Magnetic remanence constraints on magnetic inversion models

A magnetic anomaly is produced when a rock unit has a magnetic contrast with a laterally adjacent rock unit. The cause of this magnetic contrast might be produced by a change in the magnetic susceptibility and/or magnetic remanence of the source bodies. After Vine and Matthews (1963) demonstrated that magnetic anomalies observed over ocean basins record a chronology of ocean floor generation, it was readily apparent that in some instances the genesis of a magnetic anomaly can be dominated by the remanence component. Surprisingly, few investigators have acknowledged that magnetic remanence can have a similar influence on continental magnetic anomalies. The incorporation of magnetic remanence data into a magnetic inversion scheme continues to present a major problem. In this note, we outline the problem and present some approaches that might be used to derive relevant remanence information.

Effect of signal amplitude on magnetic depth estimations

The magnetic signal generated over any source can be analyzed in terms of the two basic components of any wave: frequency (λ) and amplitude (A). With respect to magnetics, the frequency will be a function of the magnetic source body depth and geometry, while the amplitude is a function of magnetization intensity (magnetic susceptibility and natural remanent magnetization, NRM, if present). Many processing and interpretation methods developed over the last 50 years take advantage of the intrinsic relationship between frequency and depth to generate a variety of depth-estimation routines. Furthermore, many methods are independent of magnetic susceptibility (and therefore amplitude) contrasts since the methods incorporate some sort of mathematical expression that nulls the effect of varying susceptibilities.

Integration of lithological, geophysical, and remote sensing information: a basis for remote predictive geological mapping of the Baie Verte Peninsula, Newfoundland

The Baie Verte Peninsula is a geologically complex area on the northwest coast of Newfoundland. The region is composed of multiple geological domains and has undergone extensive tectonic activity, uplift, and deformation, producing multiple unconformity surfaces. In addition, multiple phases of intrusion, some with volcanic cover sequences, add to the complexity of the geological model. This study concentrates on establishing a basic framework of the spatial relationships between individual lithological units and their contained mineral deposits from remotely sensed data. Of primary interest is providing basic lithological discrimination, which could form the basis of future field mapping. Multiple thematic maps were produced from compilations of satellite imagery, aerial photography, high-resolution digital elevation maps (DEMs), airborne radiometrics, and aeromagnetics. Common edge boundaries within the geophysical and spectral data were used to discriminate regions having similar physical and mineralogical signatures. The resulting patterns provide a proxy, or remote predictive method, for recognition of the distinct geological features within the study area. Furthermore, the techniques and methods introduced in this paper can be applied to other areas for producing presurvey geological templates.

An assessment of topographic effects on airborne and ground magnetic data

Recent advances in magnetic surveying have focused on achieving higher levels of instrument sensitivity and better definition of the morphology of the magnetic field through the use of measured magnetic field gradients. Images derived from these high-resolution magnetic surveys are widely used as a direct proxy for geologic mapping, especially in areas of limited surface exposure. Commonly, this involves the application of skeletonization (e.g., multiscale edges, or “worms”), Euler, and/or wavelet-based processing routines to generate estimates of the location, and morphology of the edges of anomalous source bodies. The primary assumption for all of these image- (map-) based data processing routines is that the observed magnetic data set provides an unbiased representation of the magnetic mineral variation in the surface and subsurface geology. This assumption may be valid when the observed magnetic anomalies are greater than 5000 nT and the topography is relatively flat, but it is certainly not valid whe...

Qualitative geophysical interpretation of the Sudbury Structure

AbstractThe 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 of the Sudbury Structure have been quantitative — modeling and depth estimation without a clear definition of surface control. Airborne total magnetic intensity data over the Sudbury Structure were compiled, processed, and interpreted, to define magnetic stratigraphy boundaries and near-surface lineaments. Traditional directional and normalized derivatives were computed to enhance the high-frequency information in the magnetic field. Available airborne frequency-domain electromagnetic (EM) data were also interactively interpreted along profiles and in a gridded format to isolate conductive structures. On-screen geographic information system-based informa...

High-resolution magnetic mapping of contaminated sediments in urbanized environments

The remediation of contaminated sediments in industrialized harbors and waterways is a growing environmental concern in North America. More than 100 marine ports and 42 inland harbors in the Great Lakes basins are currently listed by U.S. and Canadian regulatory agencies as having severe habitat and water-quality impairments due to bottom-sediment toxicity. Current approaches to remediation include sediment dredging and removal, capping with clean sediment, and in-situ treatment with oxidants.