Enhancing base-metal exploration with seismic imagingThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Abstract

Commencing in 1988 and continuing for 5 years, Lithoprobe acquired a series of high-resolution seismic experiments within and near base-metal mining camps in Canada, including the Abitibi subprovince of Quebec and Ontario, the world-class Sudbury Ni-Cu mining district, the Buchans mine in Newfoundland, and the Thompson Ni belt in Manitoba. This work, undertaken in close cooperation with the Geological Survey of Canada and major Canadian mining companies, stimulated an intensive and broadened series of followup studies with the common objective of assessing potential applications of multichannel seismic (MCS) imaging for deep mineral exploration and mine development. This research was motivated by a widely recognized disparity between the depths from which ores can be profitably mined (up to 2 km or more) and the resolving depths (typically <500 m) of commonly used geophysical methods for mineral exploration. Initial rockproperty studies established that the expected contrast in acoustic impedance between ores and host rocks should be sufficient to generate observable reflections and (or) scattered waves. For an ore deposit to be directly detectable with MCS, however, it is also necessary for it to meet geometrical criteria including a minimum thickness of 1/8 wavelenth (typically *5 m) and a lateral extent similar to the Fresnel radius (typically *100 m). Both Lithoprobe and followup seismic studies, calibrated with borehole data, reveal that lithologic contacts that are characterized by large impedance contrast and significant lateral continuity, such as igneous intrusive contacts between mafic and felsic rocks, are the most likely features to be imaged with the MCS techniques. In some camps such as Buchans, however, faults and shear zones are better imaged than lithologic contacts. In either case, these studies show that well-designed and carefully processed seismic profiles can provide a valuable geophysical tool for interpreting the stratigraphic and structural framework of mineral systems and, more rarely, direct-detection capabilities for deep ore deposits.Résumé : Débutant en 1988 et se poursuivant pendant 5 ans, Lithoprobe a acquis une série d'essais sismiques de haute ré-solution à l'intérieur et à proximité de camps miniers de métaux de base au Canada, incluant la sous-province de l'Abitibi au Québec et en Ontario, le district minier Ni-Cu de classe mondiale de Sudbury, la mine Buchans à Terre-Neuve et la ceinture de nickel Thompson au Manitoba. Ce travail, entrepris en collaboration étroite avec la Commission géologique du Canada et de grandes compagnies minières canadiennes, a stimulé une série d'études de suivi, intensives et élargies, dont l'objectif commun était d'évaluer des applications potentielles d'imagerie sismique par canaux multiples « MCS -Multichannel Seismic » pour l'exploration minérale en profondeur et le développement de mines. Cette recherche a été motivée par la disparité largement reconnue entre les profondeurs desquelles les minerais peuvent être extraits rentablement (jusqu'à 2 k...

Seismic methods in mineral exploration and mine planning: A general overview of past and present case histories and a look into the future

“…Petrophysical measurements and target considerations Eaton et al (2010) report that it was when laboratory measurements for acoustic properties were being carried out during the Lithoprobe project (e.g., Salisbury et al, 1996) that the strong reflective character of massive sulfide deposits in typical volcano sedimentary rocks was accidentally discovered. Salisbury et al (1996Salisbury et al ( , 2003 performed systematic measurements of velocities and densities of massive sulfides and their host rocks (also see Ji et al, 2002).…”

“…In particular, Eaton et al (2010) present a comprehensive overview of the work undertaken during the Lithoprobe program, a national research project that combined multidisciplinary Earth science studies of the Canadian landmass and surrounding offshore margins (also see Clowes et al, 1984). Lithoprobe was instrumental in establishing acquisition, processing, and interpretation approaches suitable for the hard-rock environment that is typical to several volcanogenic massive sulfide mining camps across Canada.…”

“…However, an important catalyst for the application of seismic methods for mineral exploration was the successful imaging of fault and fracture zones in the hard-rock environment for the characterization of nuclear-waste repository sites (Noponen et al, 1979;Mair and Green, 1981;Green and Mair, 1983;Juhlin et al, 1991;Juhlin, 1995;Cosma et al, 2001;Juhlin and Stephens, 2006). Large-scale seismic investigations in Canada (e.g., Lithoprobe), the USA (e.g., COCORP), Australia (AGSO), Europe (Europrobe), and South Africa (National Geophysics Programme) also were very important in developing the necessary techniques for imaging challenging and complex geologic structures in the crystalline environment (e.g., Ruskey, 1981;Clowes et al, 1984;Milkereit et al, 1992c;Juhlin et al, 1995;Milkereit et al, 1996;Milkereit and Eaton, 1998;Ayarza et al, 2000;, Odgers et al, 1993Calvert et al, 2003;Eaton et al, 2010). Extensive 2D seismic surveys to map the structure and explore for extensions of the gold-bearing Witwatersrand Basin of South Africa commenced in the early 1980s (Campbell and Peace, 1984;Durrheim, 1986;Pretorius et al, 1989;Chambovet et al, 2006).…”

Interpretation of 2D seismic profiles in complex geological terrains: Examples from the Flin Flon mining camp, Canada

“…Seismic reflection methods have found use in a variety of hardrock exploration applications during the last 20 years (e.g., Eaton et al, 2003Eaton et al, , 2010. Although 3D surveys are essential to accurately defining exploration drill targets, 2D seismic profiles still have a useful role to play in mineral exploration because they provide an affordable means of making regional assessments, or of constructing sparse 3D geologic models from a network of seismic profiles.…”

Deep Into the Chibougamau Area, Abitibi Greenstone Belt: Structure of a Neoarchean Crust Revealed by Seismic Reflection Profiling

“…For the Chibougamau area, characteristic seismic wavelengths of 110–380 m derive from measured frequency spectra (17–55 Hz) and from velocities that optimized stacking (6,000–6,500 m·s −1 ). The seismic wavelength determines the resolution and thus the scale at which reflectors between contrasting rock types can be observed (Eaton et al, 2010). Typical vertical resolution is one quarter of the seismic wavelength, and thus 30–110 m, increasing with depth within the Chibougamau seismic section.…”