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Summary Deriving time-constants from EM data allows a fast analysis of survey data, but historically time-constants were only derived from transient EM data. The relationship between time-constant and conductance is examined for plate and sphere models for frequency-domain EM data of the RESOLVE system. The results confirm published relationships between the two parameters and indicate that time-constants are underestimated for targets with elevated magnetic permeabilities. Further, the plate model results suggest that RESOLVE data detect highly conductive structures, but don’t resolve their conductances and timeconstants if those values exceed 500 S and 8 ms, respectively. A RESOLVE data set flown initially for kimberlite exploration has been re-analyzed for nickel sulphides. Since the latter are highly conductive, the standard processing products such as apparent resistivity grids, deemed useful for mapping kimberlites, did not provide the optimum resolution for data analysis. The survey area is characterized by strong magnetic and EM responses due to the presence of banded-iron formations and pyrrhotite-rich massive sulphides. In order to determine the strongest conductors, time-constants were derived from the RESOLVE survey data. Due to the strong magnetic response, correction of the RESOLVE data for magnetic permeability resulted in better-resolved time-constants. This was achieved by inverting the data for the conductivity σ and magnetic permeability µr of a layeredearth, followed by the forward modeling of the layer conductivities with µr=1. A comparison of independently derived time-constants and apparent conductances suggests that reliable values derived from the survey data do not exceed 0.4 ms and 200 S, respectively. Conductors with values above 200 S / 0.4 ms are detectable, but not resolvable.

Concurrent with this migration out of the oil and gas industry was more minerals-focused applications which evolved from the migration of 2D GIS applications into 3D applications. This software was designed to be much more suited to the exploration “generalist” and advanced visualization capabilities were typically was appended to the core software which had everyday required functionality. Condor has used one such software called 1

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has used helicopter-mounted electromagnetic (HEM) surveys to identify mine pools within active and abandoned underground coal mines in the eastern United States. Two types of HEM surveys have been tested: frequency domain electromagnetic (FDEM) and time domain electromagnetic (TDEM). Previous surveys have indicated that FDEM surveys can identify flooded mine workings in areas where overburden is less than 50-m thick. However, most mines are deeper than 50 m. This survey attempted to use helicopter TDEM to locate deep, flooded mine workings at challenging sites in southwestern Virginia, an area containing multiple levels of mining, thin seams, and mine water of relatively low conductivity. The rationale behind this choice of field sites was that if the technology worked in this admittedly difficult region, it could be applied to any coalfield. However, the survey was unsuccessful; mine workings known to be flooded were not detected. This paper discusses problems that were encountered, particularly electromagnetic noise, which rendered 25-50 pct of each flight line unusable.

Waste from nickel mining comprises a mixture of fine silicates with a variable amount of sulphides, and iron oxides. Subsequent oxidation of the sulphides results in the formation of environmentally hazardous acid-rich leachate. Identification of the distribution of regions of higher sulphide concentration and resulting leachate ponding represents an important first step towards the implementation of an effective tailings management strategy. Synergistic information regarding the prevalence of Acid Mine Drainage can be derived from combining hyperspectral imagery and topographic data that describe near surface variations with airborne geophysical surveys that describe shallow subsurface variations. Preliminary investigations over the Copper Cliff tailings site, Sudbury Ontario reveal that these parameters can be used to separate tailings with varying compositional and alteration levels, and water bodies of varying acidic levels. On-going oxidation of older tailings and soil development is demonstrated in the hyperspectral data by increased vegetation coverage. Magnetic susceptibility changes are associated with the progressive alteration of magnetite and pyrrhotite to less magnetic hematite. Inductive conductivity variations in tailings are related to the combined effects of sulphide mineral content and the ionic concentration of acid in groundwater. Inversion of conductivity data shows lateral contrasts both between and within adjacent tailings basins.

This paper describes the development of applications for the interactive investigation of three-dimensional geological andgeophysical data, using an Interactive Workbench. The Interactive Workbench is essentially a large (175 cm by 125 cm)light table, on which stereo images are back-projected. The position of the user's head and hands are determined by amagnetic tracking system. The user interacts via a 3D mouse with geoscientific data objects that appear to be placed on orabove the table. A high-end Silicon Graphics Workstation (Onyx2) renders the stereo image 30 times a second for the users current eye position. We have implemented a pen-driven user interface (traditional GUI) as well as virtual tools for positioning, picking and cutting in order to visualize and, in some instances, edit geological objects like horizons, faults,seismic data, well bores, etc.This approach enables geoscientists to more fully exploit three-dimensional geoscientific data by providing them with a trulythree-dimensional display that can be shared (locally or remotely) with others. In addition, the three-dimensional interactivitythat this technology provides can support more productive modeling of geoscientific data and more efficient verification ofthe resulting interpretations.Keywords: Scientific Visualization, Virtual Reality, Geophysical Data, Direct manipulation of virtual objects, ImmersiveDisplay

Summary Airborne EM (AEM) has been the most successful mining geophysical technique ever developed, with approximately 80 deposits discovered (Witherly-1999) since the early 1950s. Almost 80% of these discoveries have been made in Canada and they can be broken down into three main deposit types; massive sulfides, unconformity uranium deposits and diamondiferous kimberlites. All three deposit types tend to occur in relatively close groupings, commonly termed districts or camps. AEM proved particularly effective in screening camps for their endowment of deposits once the existence of a particular deposit type has been established. A review of how AEM was applied in the various camp settings shows that early on explorers developed a set of geophysical and geological search criteria which had a strong empirical relationship to the sought after targets. These pathfinders to discovery are termed Geologically Serendipitous Observations (GSOs). Not only did GSOs help guide work in a given camp, they often proved robust enough that they could be applied to new areas with a high likelihood of success.

Exploration 07, the fifth decennial conference on mineral exploration technology was held in Toronto, Canada, on 9–12 September 2007. For 40 years, these meetings have provided a once-a-decade review of the major developments in the fields of geophysics, geochemistry, remote sensing and data management and processing as they relate to minerals exploration. At Exploration 07, the core program consisted of 54 invited papers, 66 poster and 19 3D theater presentations. In addition there were seven workshops on topics related to the overall conference themes prior to and after the conference. There were over 1200 registered delegates from 60 countries. A short summary of the geophysical component of the program is provided below.

Over the last 50 years, mining companies have frequently made major investments in new geophysical technology. These investments have been made in the belief that such technology would provide them with a competitive exploration advantage. Many of these projects involved new airborne geophysical technology, with the emphasis on electromagnetic (EM) systems. Although in time, such technology frequently has made a major impact on the exploration industry as a whole, the primary sponsors of these developments often did not realize a return that would be considered commensurate with their investment. This paper looks at a selection of some of the major projects, with the emphasis on examining the reasons behind mining companies making such investments, as well as the problems and benefits to both the individual companies and the industry as a whole when new technology is developed in such a manner. While not likely a normal R&D model by other industry standards, this approach has worked reasonably well for the minerals exploration business for the last half century.

The ability to detect and characterize targets of high conductance (>2 000 S) has become a primary technical criteria for airborne EM surveys being flown to explore for nickel sulfide deposits. A variety of commercial airborne EM systems have flown over the same high conductance target as well as a prototype system. These results show what the current capabilities of the various systems and as well, what type of future technology is required to significantly improve the high end conductance aperture of airborne EM technology.

In the last five years the Munali nickel-copper deposit has been subject to a systematic assessment using a variety of airborne and ground geophysical techniques. These results are reviewed here to assess the efficacy of the techniques and define a target model that could be used in the search for similar deposits. 3D modelling and display have been used to aid in this assessment.