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 rock-property 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.

The Deer Lake Basin in western Newfoundland is of Late Devonian to Permian (?) age and was formed by localized transtension, associated with dextral strike slip along the Cabot Fault zone. The basin infill is dominated by elastic sediments deposited in an alluvial environment. The stratigraphy and architecture of the basin have been studied extensively by surface mapping, though the absence of seismic data has limited interpretation of the depth structure. There is current interest in re-evaluating the petroleum potential of the Deep Lake Basin as part of a study of Palaeozoic sediments bordering and underlying the Gulf of St. Lawrence. Most of the activity in the Deer Lake Basin has focused on the north-west portion where the Lower Carboniferous (Visean) sediments of the Deer lake Group outcrop. The Deer Lake Group forms a gently synform, whose axis trends roughly northeasterly, paralleling the trend of the Cabot Fault. The depth extent of the Deer Lake Group sediments has been inferred from geological mapping and gravity and magnetics, though the sparse data sets have called these interpretations into question. The Centre for Earth Resources Research, in cooperation with Vinland Petroleum, acquired and processed seismic data along two test lines in the northwest portion of the basin. The objectives of the surveys were threefold: i) to determine appropriate parameters for high resolution seismic surveying in this region; ii) to determine the thickness and structure of the Deer Lake Group; and iii) to determine the nature of the ''basement'' to the Deer Lake Group in this part of the basin. The first line (line 1) was a short (similar to 2km) test along the axis of the synform near Reidville. Although successful in imaging the internal structure and thickness of the Deer Lake Group, it was too short to reveal any lateral structure and has insufficient source energy to image the deeper sediments in the basin. The second line (line 2-similar to 12km) along Paddy's Reef Road traversed the east limb of the synform. This line provided good images of the Deer Lake Group and underlying structures.There are several significant features seen in the data. There is a clear change in the reflective character of the sediments on both lines at about 0.7s-0.9s two-way time (TWT). This is interpreted as the base of the Deer Lake Group. the synformal structure of the basin is well imaged at the southwest end of line 2. A number of high-angle faults, both normal and reverse structure of the basin is well imaged at the southwest end of line 2. A number of high-angle faults, both normal and reverse intersect the Upper Carboniferous sediments. Many of these faults are associated with an intensely faulted zone at the base of the Deer Lake Group. This zone is directly along strike from the Fisher Hills block of Anguille Group (Tournaisian and older) exposed to the southwest of line 2 and is interpreted as a flower structure developed in Late Devonian to Early Carboniferous time with subsequent burial in the Late Carboniferous, though with evidence of continuing fault activity throughout the whole Carboniferous period. The flower structure and its associated faults provide numerous opportunities both for migration and entrapment of petroleum.Thermal maturation indicators and geothermal modelling indicate that the lower Deer Lake Group experienced maximum paleotemperatures of 125 degrees C and is well within the oil generation window.

A novel application of the tensor controlled source audio‐magnetotelluric (CSAMT) method was part of a multidisciplinary geophysical study of an existing mine site at Buchans, Newfoundland. The orthogonal components of the horizontal electromagnetic fields used for magnetotelluric and CSAMT interpretation of the earth’s conductivity structure were found to be inappropriate at Buchans because of strong scattering in the electric fields. Instead, the length of the major axes of the electric and magnetic field polarization ellipses and the vertical magnetic field were used as data. The data from two bipole sources demonstrate that the bulk response of the earth in the vicinity of Buchans is predominantly one‐dimensional (1-D). These data were inverted to layered earth models with a first‐order correction for electric field distortions. The parameter space considered during the inversion was contracted substantially by incorporating the vertical magnetic field data and by using depths to interfaces as determined by reflection seismic data. The model resulting from the inversions is essentially a two‐layered earth with an increase in resistivity between 1000–1400 m depth. The contrast in the electrical properties is interpreted to be coincident with the Powerline Fault, a floor thrust of a duplex structure with significant out‐of‐sequence movement. Hence, the thrusting may have caused the emplacement of older fractured, and locally mineralized rocks over younger more competent (resistive) ones.

We present results from the first major vibroseis seismic reflection survey at a mine site in North America. It is demonstrated that conventional high‐stack fold reflection seismic techniques can image fault structures associated with volcanogenic massive sulfide bodies, despite the fact that these structures are locally steeply dipping and produce records with low signal‐to‐noise ratios. The new lines were recorded at the locations of two earlier experimental explosive surveys that failed to image many strong reflectors. The principal reasons for the success of the vibroseis experiment were the proper choice of sweep frequencies for maximum signal‐to‐noise ratio, the use of high‐stack fold, and the careful analysis of velocities and statics during processing. A comparison of the new seismic sections with borehole and other geophysical data indicates that the origin of reflections at Buchans can be attributed to various mechanisms including contrasts in lithologies and rock competence and intrusion of diabase sills into pre‐existing fault zones. The best reflections emanate from shallow‐dipping brittle‐ductile thrust fault zones characterized by fault gouge within broader fractured zones. The two seismic lines presented have proven to be a useful and cost‐effective supplement to existing borehole and geophysical data and have provided enough new information on the nature of thrust faulting at the mine to significantly influence current exploration plans.

Sixteen kilometres of high resolution Vibroseis reflection seismic data have been acquired in the vicinity of the former Buchans mine. Direct identification of the cause of several reflectors is possible because the geology is tightly constrained by underground workings and drill holes both of which locally exceed 1 km depth. Many of the mine-scale thrust faults are imaged as reflectors but conformable and intrusive contacts generally responded poorly. A significant shallow-dipping thrust, the Powerline Fault, is recognized below the orebodies and traced throughout the Buchans area, primarily as a result of the seismic survey. It truncates ore stratigraphy and forms the floor thrust of a large duplex–stack, which hosts all the orebodies. Its presence has negative implications for exploration in the immediate mine area. Several lines of evidence suggest that this fault has a significant component of out-of-sequence movement. A strong reflector 4.5 km below Buchans is correlated with the surface expression of the Victoria River Delta Fault, an important regional structure, newly recognized southeast of Red Indian Lake. This shallow, north-dipping sole thrust forms the structural base of the Buchans Group and brings it above a younger fossiliferous Llanvirn volcanic sequence. This fault is not itself the Red Indian Line but is one of a series of faults that collectively effect substantial geological contrasts in central Newfoundland. The seismic survey was a cost-efficient means of gaining knowledge of Buchans structure, which might otherwise have been acquired at much higher cost and over a longer period of time.