A MINE-FINDER’S GUIDE TO THE LATEST IN GEOPHYSICS

While compiling the material for this annual review article — my first such effort since Dr. Peter Hood’s retirement last year — I had the opportunity to discuss the status of mineral exploration in general, and of exploration geophysics in particular, with people involved in all facets of exploration. The general opinion, which I gleaned from this, reflected short-term pessimism tempered by long-term optimism, particularly as applied to Canada.

Everyone agrees that there are many and complex reasons for the present low level of exploration activity in Canada and other parts of the world. These include perceived difficulties associated with taxation, environmental regulations, aboriginal land rights, withdrawal of land for parks, labor costs and, of course, the world price of metals. Nobody even hinted that the problem was related to a lack of minerals in the ground. In fact, many felt there were still “elephants” to be discovered.

What seems different in this cyclical downturn is that earlier ones were caused primarily by the price of metals fluctuating with the law of supply and demand. This time, however, it is much more complex and is related to a perceived “tarnished image” which we in Canada have acquired, rightly or not. Exploration is taking place outside of Canada basically because the mining industry — domestic and foreign — feels it is unwanted here. To take perhaps the most outspoken example, consider the following quotation in a letter to shareholders from Hecla Mining subsidiary, Acadia Mineral Ventures:

“Uncertainties created by declining metal markets, difficulties in financing exploration projects in Canada regardless of their merits, stringent environmental laws and regulations coupled with unfavorable tax regimes have made the advisability of continuing mineral exploration in most parts of Canada and especially in Ontario less attractive…. Acadia’s officials, like those of many other companies, are of the opinion that mineral exploration in Canada is not attractive.”

The industry recently defined the problem at a Toronto, Ont., conference. The problem and its solution runs something like: Natural resources are neither high on the political agenda nor highly visible in the public eye. At best, the overall view of mining is neutral and its negative impact is largely environmental. To turn this around, public opinion must change for the better. Only then will politicians begin to listen. Of course, a co-ordinated public relations effort is needed to convince a sceptical public that the industry — an environmentally sound industry, that is — is a necessary component to a healthy Canadian economy.

So, what can we do about it? First, improve the image of the mining industry. This must involve not only the industry, but all associated organizations: university geoscience departments, federal and provincial mines departments and geological surveys, the various geological, geophysical and geochemical societies, and other organizations such as the Prospectors and Developers Association of Canada. It cannot be a temporary campaign; it must become an on-going, updated, positive image projection.

Second, if it is accepted that the mineral industry does play a vital role in the economy and future development of the country, then a program to revitalize the flagging mineral exploration component is urgently needed. The Australians have recognized this and their recent establishment of the Centre for Australian Mineral Exploration Technology is an admirable approach to answering this need. The Centre aims to stimulate research to make Australian mining and exploration globally competitive. New master of science programs in modern exploration methods will be offered at two universities. Three chairs in exploration geophysics are either being created or renewed. This joint government/industry/university venture will have total funding of $5 million per year.

Canada’s position as the world leader in exploration technology has been significantly eroded in the past decade, and a similar approach to the Australian model is required immediately lest we lose it completely. Perhaps the Exploration Technology Division of Mitec could serve as the focal point for the revitalization.

But I digress. Whither exploration geophysics, technically speaking? Probably the single development having the greatest impact on geophysical exploration has been the advent of the Global Positioning System (GPS) which permits accurate determination of a surveyor’s position almost instantly, based on triangulation with a set of satellites in stationary orbits.

GPS makes it possible to pinpoint the location of anomalies from the air and to locate them easily on the ground for follow-up. The airborne survey can also take advantage of GPS for keeping the aircraft on line during the survey, as well as provide positional information for real-time processing of the survey data on board the aircraft.

GPS will also play a role in new developments in airborne gravity surveying. It appears that this long-researched area of geophysics is finally paying dividends. A section on airborne gravity may be needed in next year’s article.

Today, there are definitely more data being collected from any given survey than ever before — more windows, more channels, more components — and with more precision. In fact, the technology is evolving more rapidly than we can learn its applications. There is a requirement for geophysicists to think more than ever before. In the old days, we spent most of the time acquiring data using relatively standard techniques and processing methods. Much of the data acquisition should now be done by technicians while the geophysicist spends more time trying to determine what it all means.

Unfortunately, the new geophysicists who are to do this thinking aren’t in the universities. This is another deplorable situation that should be considered for the future. But again I digress.

New areas in which we will likely see technical developments in the next five years include mineral-discriminating techniques such as forms of electro-chemistry, seismo-electricity, and a return to spectral IP investigations. The use of seismic methods in mineral exploration will increase along with a need to compile data on the seismic properties of rocks to support interpretation. New developments in borehole geophysics are expected, along with an increased use of this technology.

In addition, a whole new field of quasi-exploration geophysics is evolving, which might be called environmental geophysics. This area is absorbing at least a few of those exploration geophysicists who might otherwise be unemployed. Their activities can be used in the pre-mine and post-mine studies associated with the environment.

CORPORATE AND INTERNATIONAL HIGHLIGHTS

ABEM AB was divided into two companies in 1992. ABEM Instrument will concentrate mainly on seismics and resistivity. ABEM GeoScience will concentrate mainly on radar and multi-parameter borehole instrumentation.

The biggest single event in Australia this year was the government’s suggestion that the Bureau of Mineral Resources (BMR) be absorbed into the federal scientific research organization, CSIRO. This announcement was made without warning and without seeking any advice from industry. It caused such a hue and cry that the government relented and delayed the move subject to an enquiry. In any event the name of the BMR has been changed to the Australian Geological Survey Organization (AGSO).

Airborne geophysical activity continues in Australia, including fixed-wing EM (electromagnetic) from Geoterrex and World Geoscience. Aerodat of Canada had its first helicopter EM survey in the Australasian region with a contract in New Zealand. Ground geophysics has also been very strong, especially in base metals, with the announcements of discoveries in the Mount Isa area.

The Canadian Geophysical Congress now has a membership of more than 50 Canadian companies. Some of the key areas in which CGC has considerable experience include instrument design and
manufacture, and software design, as well as airborne and ground data acquisition, processing and manipulation and project management.

In an effort to offset declining business in Canada, Crone has set up joint-venture arrangements with local contractors in Australia and Chile. Surface and borehole time-domain methods are used extensively and Crone’s new three-dimensional borehole EM system is becoming more widely used. In Chile, EM methods have not been used extensively because most deposits are of the porphyry type. However, some of the deposits have massive sulphide zones which could be detected with pulse EM systems. Crone feels that borehole pulse EM surveys will soon be routine for deep holes in Chile.

Dighem delivered complete helicopter-borne geophysical systems to two more Japanese companies in 1992. The latest systems consisted of Dighem multi-frequency EM systems, configured with vertical magnetic gradiometers, multi-channel spectrometers, Totem VLF (very low frequency) systems and real time differential GPS navigation.

Dighem reached an agreement last year with Geodass to offer Dighem surveys in Africa. Geodass operates the instruments, and processes and interprets the data from offices in Johannesburg.

Geonex acquired the world’s first airborne survey company, Aero Service in March, 1992. With the acquisition of Aerodat in September, Geonex has expanded its services to include both helicopter and fixed-wing surveys.

After concentrating for several years on environmental applications, Geonics renewed its relationship with mineral explorationists by introducing new components for Protem time-domain EM systems. Geonics sold Protem equipment to Geoterrex in Australia and has supplied systems in China and Africa.

Quantech has brought a Geonics EM-42 system back to Canada for deep exploration in mature areas. The EM-42 can sound for conductive bodies to depths of several kilometres. There are only three or four of these digital, large transmitter (28 kVA) systems in the world.

Geoterrex, part of the Compagnie Generale de Geophysique (CGG) group, has had an active year in Canada and abroad. The Northwest Territories’ kimberlite rush has provided an increased market for Geotem airborne EM systems and enhanced in-field processing capability. The need for high-quality, detailed magnetics led to the use of a towed-bird magnetometer, bringing the sensor to only 70 metres above the ground and increasing the sampling rate to 10 times per second.

When EG&G Geometrics sold its Mount Sopris division to a private group in May, 1991, many wondered about the future of the Mount Sopris Instrument Co. which was formed. Mount Sopris and a logging service company called Colog, also owned by the group, both operate out of Golden, Colo. The core of the Mount Sopris product line is PC-based surface instrumentation and software. A new portable logger line has also been introduced. New probes and surface instrumentation are planned for the larger Series III line.

MPH Consulting reports that last year’s project highlights included a number of base metal projects in Canada, the evaluation of large copper deposits and mines in Arizona, New Mexico and Chile, and geophysical and geological exploration for diamonds. MPH has also expanded into the field of geotechnical and environmental investigation services as the MPH-AEL Group. These services are offered in joint venture with Angus Environmental Ltd.

The Gipsi division of Paterson, Grant & Watson (PGW), which develops and markets UNIX and VMS software for geophysical data processing, had a record-breaking year with installations in the United States, Chile, the United Kingdom, Australia, South Korea and Newfoundland. Key areas of development include improvements to imaging and data capacity, as well as considerable advances in EM modelling.

PGW has also entered into an agreement with the University of British Columbia to aid in development of advanced modelling techniques as part of the Joint Co-operative Inversion of Geophysical and Geological Data consortium.

As well as representing Geometrics high sensitivity airborne magnetometers in Canada, RMS Instruments reached an agreement with Herz Industries for worldwide manufacture, sales, leases and support of the Totem series of VLF airborne and ground receivers.

Sander had a busy year carrying out high-resolution magnetic surveys, divided almost evenly between work in Canada and other countries. The volume of work in 1992 was higher than in any previous year. Results from one of the foreign projects indicated that such surveys can be of considerable help in porphyry copper exploration.

With a significant increase in high-sensitivity aeromagnetics, Terraquest has undergone corporate reorganization and has moved its corporate head office to Mississauga, Ont.

Urquhart – Dvorak Ltd. (UDL) designed and developed a comprehensive, custom software package for the storage and public distribution of government aeromagnetic survey data. The work was done under contract to the Ontario Geological Survey (OGS).

Marine gravity and magnetics data from the Black Sea were processed, interpreted and plotted on-site by UDL for a consortium of western companies. Clients also asked UDL to re-process existing airborne survey data collected by a number of contractors.

Urtec, through its associated company Canada-China Geoscience, has expanded its activities in China. Major sales to the Ministry of Coal have been made including a number of pulseEKKO ground-penetrating radar systems and training. Business opportunities in the new Commonwealth of Independent States led Urtec to establish an office in Moscow.

World Geoscience Corp. (WGC) is a member of the new Co-operative Research Centre for Mineral Exploration Technologies in Australia. The centre has been established in response to demands for cost-effective and non-invasive exploration methods for mineral exploration. Other partners in the Centre include the CSIRO, AGSO, Macquarie and Curtin universities and the Australian Minerals Industries Research Association.

World Geoscience Inc. (WGI) is a Houston-based affiliate of the WGC group. WGI co-ordinates the activities of both Questor and BGM Airborne Surveys. In addition, WGI has joint venture agreements in Mexico and in Chile to offer airborne surveys there.

WGI has been active this past year in flying more than 300,000 line km. With the recent acquisition of the bulk of the airborne survey assets of Intera Kenting, WGI has a total of five fixed-wing aircraft.

AIRBORNE GEOPHYSICAL SURVEYING

General

The AGSO, formerly BMR, carries out airborne geophysical surveys in order to accelerate the geological mapping of Australia. A new edition of the magnetic anomaly map of Australia with a scale of 1-to-5,000,000 is expected to be published soon.

Anglo American reports that the DC-3 aircraft which serves as the survey platform for the Spectrem airborne EM system has been improved by the installation of turboprop engines. Spectrem has undergone an extensive upgrade in which the rms dipole moment of the transmitter has been increased to 300,000 Am2. Improvements to the front-end electronics, resulting in a major reduction in noise levels, have also been made. A computer for real-time signal processing has been installed. Full recording of 512 points per waveform of transmitter signal and X, Y and Z components averaged over 200 milliseconds allows post-flight signal processing to reduce noise levels if required.

During 1992, CGI Controlled Geophysics introduced the digital airborne geophysics project, an extensive compilation of high resolution EM-magnetic surveys flown by the OGS since 1978. More than 400,000 line km. of frequency and time-domain survey are covered. Among the products available are apparent resistivity and time constant, EM profiles and imagery, magnetic derivatives and susceptibilities, Euler deconvolution depth solutions, computer-aided interpretations, digital geology, topography, and Landsat base maps.

Dighem experienced increased exploration levels last year in both Canada and overseas. Th
e improvement in Canada was primarily related to diamond exploration in the Northwest Territories. Activity was relatively quiet for base and precious metals.

Geonex Aerodat continued its focus on international markets. The primary objective of most of the surveys was mineral exploration, including a 20,000-line-km. diamond exploration program in the Northwest Territories, a 36,000-line-km. porphyry copper program in Iran and numerous gold and massive sulphide surveys throughout the world.

Geonex Aerodat has also developed an environmental gradiometer system tailored for mapping magnetic and conductive targets while flying with the sensors as low as five metres above ground.

More than 80,000 line km. were surveyed by Geonex Aero Service in Colombia on behalf of a state-owned oil company as well as in Chile for mineral exploration.

With recent advances in GPS, high-precision airborne gravity has become more feasible. Lacoste & Romberg and ETH Zurich (the Swiss technical university) are advancing the technique. First flights were made in June, 1992. The end product for the Swiss will be a gravity map of their country and for Lacoste & Romberg will be the Model SA, an advanced airborne gravity and data reduction software package.

RMS Instruments reports that in 1992 the automatic aeromagnetic digital compensator (AADC II) has continued to find new applications. Universal Tracking Systems of Australia utilized the compensator on a helicopter system with a Geometrics G-833 helium magnetometer. The sensor was mounted in a nose stinger. The AADC II compensator performed with excellent results.

Another first was the installation of the AADC II on a Piper Navajo, utilizing the Geometrics Model G-822A cesium magnetometer sensor in a tail stinger. The data acquisition and recording system was also supplied by RMS.

Sander further improved its airborne GPS-based navigation system. Additionally, it can utilize intertial and other systems which might supplement the GPS information. Pilots can maintain the aircraft position generally within +/-50 metres of the steering information for the planned line.

At the present time, for military reasons, GPS signals are intentionally transmitted with a slight error, called selective availability. The artificially introduced error is of the order of +/-100 metres in general. This error can be removed by differential flight path recovery. Sander has developed a system to transmit these corrections to the aircraft by radio, and corrections can be carried out while the aircraft is in flight.

Sander is also involved in a major project to develop an airborne gravity survey system. The company has achieved accuracy of five cm. in the determination of the vertical position of the aircraft, which makes it possible to measure gravitational force in flight. The system is scheduled for test flights in 1993.

Sial Geosciences completed a helicopter-supported gravity survey in Manitoba using state-of-the-art positioning and its highly reliable gravity meters. Sial has surveyed more than 4,000 gravity sites since it started offering this service.

Terraquest reports a ninefold increase in total kilometres flown in domestic surveys, particularly for low-level, closely spaced, high-sensitivity surveys encompassing large areas. During 1992, all major aircraft components and geophysical equipment were updated or replaced. Terraquest provides in-field data processing using a 486/50 computer.

Urtec continues to provide airborne resource mapping systems and systems engineering services worldwide. These engineering services focus on matching the end users geophysical needs with available aircraft, local technical support and budget restraints, and offering upgrading to existing airborne platforms.

AIRBORNE DATA ACQUISITION AND PROCESSING

Dighem’s computer division, I-Power, added the display and manipulation of Landsat and Spot data to the Vision imaging system in 1992. Many Vision features are designed for satellite data, including RGB (red-green-blue) overlays allowing examination of several spectral bands simultaneously. New software features include interactive histogram display and manipulation, more universal graphics card support, complete Geosoft data support and output to Targa, TIFF plus other standard image formats.

I-Power has also released a diamond exploration package for the Lac de Gras area of the Northwest Territories. This package, consisting of Vision imaging software and processed GSC aeromagnetic data along with Landsat MSS data, covers the entire region.

Geosoft reports that an inversion-optimization option is available for the GM SYS magnetics-gravity forward modelling program. This option allows the user to refine a model automatically to obtain the best fit to the data. The process pauses between iterations to allow for user evaluation and possible adjustment. Geosoft’s graphics system supports a wider range of printers.

Mapedit has been upgraded with the ability to delete, move and re-size graphic elements such as a color scale bar on the plot. Other improvements include a direct method to change the location of a plot file in world or ground co-ordinates.

An advanced gamma-ray spectrometer option for the Picodas PDAS-1000 data acquisition system was completed last year. The performance of the PDAS-1000 system was upgraded to include 486 computers, an 80-megabyte internal hard disc drive and an 80-megabyte streaming tape backup cartridge recorder. Also introduced was an interface which permits a standard dot matrix printer to be used in real time as a chart recorder. Picodas equipment is marketed by Scintrex.

Picodas software for a GPS navigation base station for post-flight differential corrections is available for some receivers. Advanced GPS navigation software with substantially simplified input of parameters for grid flying was developed. It will run either on the PNAV-2001 navigation computer or any laptop computer.

RMS Instruments added the Model HDS-150 hard disc and streamer tape drive to its line of recording instruments. It produces tapes with a higher capacity, which are more readily compatible to work stations other than those which are PC-based.

Sander has developed a program to calculate the source of magnetic anomalies based on three-dimensional data. The program automatically improves a preliminary estimate to best fit the modelled data to the observed survey data. It is mainly used in Sander’s interpretation service for petroleum exploration.

AEROMAGNETIC

Applied Geophysics has published an interesting brochure entitled “10 Years of Mapping Basement, 1982-92,” which is an overview of the “NewMag” aeromagnetic surveying, primarily for petroleum applications.

Over the last year BGM has flown two very large speculative magnetic surveys over Alaska and Texas. These surveys are over areas that have previously been mapped using aeromagnetics.

New techniques developed by World Geoscience for flying oil basins has resulted in an order of magnitude increase in the amount of information obtained about the structural control of the basin.

Dighem has added a vertical magnetic gradiometer to its existing magnetic, EM, radiometric and VLF-EM survey system. Cesium vapor magnetic gradiometer sensors are located midway between the helicopter and EM bird to provide increased detail.

Geoterrex reports that high-resolution aeromagnetic surveys were completed in Canada, the United States, Greenland, Yemen, Egypt and Argentina. A new airborne digital acquisition system based on a 486 PC has been installed. An additional RMS AADC II compensation system has been added to a leased aircraft to handle the large volume of this year’s work. Many functions have been added to GMaps software for both PC- and UNIX-based systems.

In 1992, Scintrex delivered more than 30 of its CS-2 cesium magnetometer sensors to clients in 10 countries. Advantages of this sensor over its successful predecessor include simpler, more reliable electronics, reduced heading error and expanded active zones. The CS-2 offers a +/-0.25 nT heading error with instrum
ental noise below 0.001 nT. The CS-2 is designed to be used with the series of Picodas MEP magnetometer and gradiometer processors and with the PDAS-1000 data acquisition system.

Sial continued surveying helicopter vertical gradiometry surveys totalling over 11,000 line km. for the GSC, as well as carrying out aeromagnetic data processing. Sial is also reprocessing and repositioning thousands of line kilometres of old aeromagnetic surveys located in Abitibi-Temiscamingue, in an area known for its potentially diamond-bearing rocks.

In addition to the high sensitivity magnetic sensor mounted in a tail stinger, Terraquest has added two more cesium vapor sensors in wing tip pods. This permits accurate delineation of point sources between flight lines. Marketing studies by Terraquest indicate that a resurgence in low-level, high sensitivity aeromagnetic surveys is related to the inability of regional surveys to identify subtle point sources.

Magnetic compensation has also been enhanced by an improvement in the Picodas compensating system and by switching to a Bartington three-axis magnetometer mounted in the tail stinger, two metres from the cesium vapor magnetometer.

Terraquest has upgraded its differential GPS system to the Magnavox MX-4200D with Picodas software. The remote receiver utilizes a 1.0 pps cable to the PDAS-1000 to ensure synchronization between the systems. The base station utilizes GPS receiver time, thereby enabling accurate referral with the remote system. Routine high sensitivity base magnetics are achieved using a Gem Overhauser sensor.

PGW has seen its recent research work come to fruition in the application of Euler deconvolution to aeromagnetic data for locating potential kimberlite pipes. Utilizing the Gridepth package, large volumes of reprocessed GSC or newly-acquired data were rapidly analyzed to locate promising targets for diamonds.

Regional compilation of aeromagnetic data sets continued with the initiation of the South American magnetic mapping project. It will run until 1994, with PGW and partner Getech visiting several countries to acquire data. The final products will include maps and a one-kilometre grid covering the continent. Shield areas are being compiled at a higher resolution for mineral exploration.

PGW completed magnetic compilations of Manitoba and Saskatchewan for the GSC’s national homogeneous aeromagnetic database. The company is providing a full-time geophysicist and short-term expertise for a two-year Canadian International Development Agency project in Thailand.

WGC has recently completed a number of surveys in eastern Indonesia, including three heli-mag surveys for gold and base metals and an offshore survey for hydrocarbons. Additional contracts have been signed and are about to commence.

WGC and Simon Robertson formed a joint project to fly a 20,000-line-km, high-resolution aeromagnetic survey of the eastern portion of the Irish Sea covering the Morcambe Bay gas field. Data processing and interpretation included magnetic depth slicing and two- and three-dimensional Euler techniques to elucidate structure both within the sediments and in underlying basement. The final report included the integration of marine seismic and aeromagnetic data sets.

AIRBORNE ELECTROMAGNETIC

In 1992, Controlled Geophysics established an apparent resistivity calculation service for frequency-domain EM survey data. Digital resistivity and depth nomograms can be produced quickly for any fixed-geometry, frequency-domain EM system over a horizontally stratified earth.

A custom service is available where the geological setting suggests that a complex nomogram should be applied, i.e., in the case where a known conductive or resistive layer of relatively uniform thickness overlays the target horizon. The results will be more accurate than resistivity and depth estimates derived from standard simple forward models. The service is ideal for preparing resistivity maps from older surveys, for producing resistivities for coil pairs not previously processed, and for fine tuning existing data.

Dighem reported a small increase in helicopter electromagnetic surveys in Canada and the western United States in 1992. Demand was primarily fuelled by diamond exploration in the Lac de Gras area of the Northwest Territories.

Dighem incorporated two optional frequencies of 220 Hz and 137,500 Hz into its helicopter EM system. These frequencies are being utilized predominantly in geo-engineering applications.

Dighem has developed a PC-based resistivity modelling package, Digres 1D, for its clients. The program utilizes one-dimensional techniques to approximate two-dimensional resistivity distributions, allowing rapid response estimation of large scale resistivity variations. Results are presented as resistivity sengpiel sections. Digres 1D runs with Microsoft Windows 3.x.

Geoterrex operates two Geotem systems and carried out contracts in Canada, the United States, Greenland, Namibia, Tanzania, Zimbabwe, Ghana and Australia. Geotem developments include a higher repetition rate for the system and selectable base frequency from 75 Hz to 270 Hz. In addition, the system is capable of transmitting variable pulse widths up to 1.9 milliseconds with a corresponding increase in the dipole moment from 4.5×105 to 5.5×105 Am2. This is up to four times the power of currently available airborne EM systems. The large loop area of 231 m2 is unchanged. A new receiver bird has been designed to house multi-axis coils.

Data processing interpretations and software development have been focused on kimberlites. Study of the in-pulse or on-time Geotem information is adding to the understanding of subtle conductivity changes in the near-surface zone.

In 1992 Geonex Aerodat introduced an integrated six-frequency EM system (three vertical coaxial and three horizontal coplanar coils), vertical magnetic gradiometer and VLF-EM system that utilizes Sercel Syledis UHF navigation with color video backup. In addition, the system utilizes a radar altimeter to monitor terrain clearance, a laser altimeter to record bird height, and a barometric altimeter.

The system was used initially to survey over 20,000 line km in the Lac de Gras area. Due to the broad range of frequencies, layered earth inversions are used to determine the physical characteristics of both the upper layer as well as the underlying kimberlite targets.

Geonex Aerodat also released the Aerodat extended imaging system (AXIS) which runs with Windows. AXIS is used to display and enhance geophysical data in shadow and color formats.

Geonex Aerodat has been licensed by the Canadian Hydrographic Service to carry out helicopter EM surveys specifically for bathymetric applications. It brought the special large bird, four-frequency (45, 350, 2,200 and 33,000 Hz) system into operational status. The through-ice bathymetry system was highly successful in obtaining data over a 1,400-sq.-km. area in the Pelly Bay area of the Northwest Territories.

Geonex Aerodat has successfully tested two new lightweight EM systems. The first utilizes a wide band transmitter and incorporates an advanced digital signal processing receiver within the bird. The second is a two-frequency ice thickness sensor, called Ice Probe, which was developed for the Canadian Coast Guard. Ice Probe was flown off St. Anthony, Nfld., for over 300 km of real time ice thickness profiles.

Questor has made several advances to its Questem system recently. First, a 45-Hz fundamental frequency version, which improves detection of deeply buried conductive targets, is available in addition to the standard 90-Hz unit. Second, an optional towed-bird cesium magnetometer provides 10 samples per second, compared to two per second with a tail-stinger mounted instrument. And third, new data processing products provide three-dimensional conductivity information about the sub-surface.

In 1992 Scintrex was awarded a contract by a Japanese geophysical firm to supply a multi-sensor helicopter-borne system complete with a computer processing system. A Dighem V EM system and Dighem’s I-Power data processing s
ystem were delivered as well as a Scintrex cesium magnetic gradiometer, a Picodas PDAS-1000 data acquisition system, a Picodas PGAM-1000 gamma-ray spectrometer, a VLF-EM system, a Magnavox differential GPS system, a base station magnetometer and a PC-based field verification workstation. Installation and training took place in Japan in December, 1992.

WGC, in conjunction with CSIRO, continued work on developing a time-domain airborne EM system known as Saltmap for soil and groundwater salinity monitoring. It will map changes in conductivity in the top 50 metres of the subsurface.

AIRBORNE RADIOMETRIC

Radiometric surveying by Geoterrex continued, primarily in Australia, employing a Nuclear Data 256-channel analyzer with sodium iodide detector volumes up to 33 litres. Surveys also employ high resolution cesium sensor magnetics and GPS-Doppler positioning. A major gold survey using real time differential GPS was completed in Indonesia.

The Exploranium G-820 gamma-ray spectrometer which has become widely used for airborne geophysics, has been enhanced in response to customer demand. First, the system permits full remote control on the IEEE-488 and RS-232 data ports. Second, for users who want to carry out high speed airborne environmental sampling, the system can be operated up to 10 samples per second with full spectrum data transfer on the IEEE-488 port. Third, it can be used as a full 512-channel spectrometer. The extra data volume is not insignificant but curve fitting for isotope analysis is enhanced, especially for narrow peaks. This is important to some users who work in the lower regions of the spectrum.

Exploranium has utilized the small size and cost of the portable G-256 with a 33-litre crystal pack to provide a very low cost mini-airborne spectrometer. The system software has been modified to permit real time eight ROI channel data output on the RS-232 port. All detector packs can be pre-calibrated on Exploranium’s new 1×1-metre test pads, and full stripping data can be supplied with the system.

In 1992 Scintrex and Picodas delivered several PGAM-1000 airborne gamma-ray spectrometers with GSA-44M and GSA-45M sensor systems. The PGAM-1000 collects, calibrates, displays and stores data received from sodium iodide detectors. Each detector-photomultiplier combination is equipped with its own analog-digital converter and transputer-based signal processing circuitry. This revolutionary approach to processing coincident spectra separately alleviates the problems associated with funnelling the output of all detectors through a common analog-digital converter.

GROUND SURVEY TECHNIQUES

DATA PROCESSING AND POSITIONING

Development of Geopak’s integrated software designed for processing ground data continued, focusing on the RTI-CAD (real time imaging computer assisted drawing) package. Full color high resolution display of three-component ternary data such as radiometrics, geochemistry and Landsat information are included in the package.

In response to induced polarization contractor requests, Geopak’s IP pseudo-section processing package now includes IP2XYZ, a utility program designed to extract two dimensional plan maps from the three dimensional IP data.

Geoscan planned to release Geoplot 2.0, a DOS program for the collection, processing and presentation of data from gradiometer, magnetometer and resistivity surveys, in January, 1993. The structure and approach taken in Geoplot helps minimize the risk of introducing artifacts or applying inappropriate techniques to a data set. A record of every edit and process is maintained with each file, giving full traceability and data integrity.

Instrumentation GDD’s Chain+

Level Model D-92 has been completely redesigned to integrate an electronic notebook which stores and transfers data to a computer at the end of daily surveys. Model D-92 is used for horizontal chaining and can measure the difference in elevations more precisely and in a shorter time than the older Model C-82. As no visual contact is needed between points to be measured, the Chain+Level is especially useful for topographic surveys in densely wooded areas.

Trimble Navigation claims a significant technical achievement has been made with the development of the new full parallel P-code geodetic surveyor with its sixth-observable technology. Unfortunately, when the GPS becomes fully operational, the P-code upon which many systems rely will be encrypted. This will restrict its high resolution use to authorized (military) users.

The threat of P-code encryption to a secret Y-code has cast a shadow of doubt over processing techniques that rely solely on P-code data. Trimble’s 4000-SSE receiver provides four-observable tracking, even during times of P-code encryption. It continuously tracks P-code with parallel channels when it is available and utilizes cross-correlation measurements during times of encryption. This enables full-cycle L1 and L2 phase signal recovery and dual-frequency code tracking at all times.

DRILLHOLE METHODS

ABEM Geoscience offers the Ramac borehole radar system for mapping rock structures from one borehole or between two. In the latter case, data can be analyzed by tomography. The system operates to a depth of 1,000 metres in the standard version. However, special versions operate down to 2,500 metres and +80degC. The directional sensing antenna makes it possible to determine the location and orientation of a structure or cavity from a single borehole survey.

New Wellmac probes are available including temperature and fluid conductivity and flowmeter. The measuring range for the different resistivity methods has been expanded to 500,000 ohm-meters.

Crone reports that it has been successfully performing three-dimensional borehole pulse EM surveys for the past two years. The method provides all three components of the time-domain EM vector to depths of 2,600 metres or more. Diagnostic anomaly signatures are received on the X and Y components for conductors within a 200-metre search radius. A standard borehole pulse EM survey is performed first, to measure the Z component. The standard probe is then switched with the X-Y probe, which was developed with assistance from Noranda Exploration.

An algorithm was developed which first cleans the primary field measurement to remove much of the secondary field contamination. This cleaned “PP” measurement is then compared to theoretical primary field calculations to determine the X-Y probe’s rotation and correct for it.

A new attachment for the X-Y probe was to be available by the end of 1992. Designed by IFG Corp., it will provide users with a measurement of hole dip and probe rotation using dip meters. This will be more accurate than the primary field comparison method.

Software improvements were also made to the Crone conductive thin plate numerical EM modelling package. It has been upgraded to support additional printers and provide better quality output. For a typical 50-station model the program provides the full 15-eigencurrent solution in 15 seconds on a 486/25 computer.

The Vic drill head from Devico is a steerable diamond core barrel used in place of wedges or downhole directional motors. When borehole surveys show that the hole is off course, the regular core barrel is replaced by the Vic. Locked to the hole by a packer, the Vic’s diamond bit will core the next 1.5 metres on a continuous curve. The deviation may be adjusted between 0.5deg and 1.5deg per metre.

Exploranium offers a borehole probe as an accessory to the G-256 portable spectrometer. The internal 34.5×100-mm sodium iodide crystal gives excellent results in environmental applications. These probes have been run through the GSC’s borehole calibration facilities with excellent results. With the calibration data stored in the memory of the G-256, shallow borehole surveys are very cost effective.

Geoterrex is offering borehole logging services using equipment manufactured by IFG. IFG has developed systems which incorporate digital data acquisition, real time data processing and very high resolution sampling.

IFG has developed a line
of borehole winches for depths ranging from 200-2,000 metres. These winches can be equipped with a DC motor and speed control box, level wind, disc brake, and a slip ring with support for up to eight conductors. The larger winches allow multiple cable types to be used with the same frame.

In co-operation with the German government, IFG has adapted its digital borehole magnetometer to operate on logging cables up to 10,000 metres long. One such probe was used in 1991 as part of a deep drilling research project. It is currently being outfitted with tilt sensors and a gyroscope to allow the vector magnetic field and hole orientation to be measured more accurately.

IFG’s borehole system has been adapted to be compatible with borehole winches made by Crone. In addition, IFG has recently incorporated changes into the new version of its digital data interface (BIN-03) to allow probes from other manufacturers to operate within the IFG system. As a result, the company is able to offer a wider line of probes including fluid resistivity, gamma-gamma, density, and caliper. The current probes include orientation, magnetic field, resistivity, temperature, natural spectral gamma, and magnetic susceptibility.

Mount Sopris has introduced a portable single-conductor borehole logger. The MGX digital logger features a combination control console and winch in a single package which weighs less than 32 kg, including the shipping case. The winch can be equipped with 300 metres of 2.5-mm-diameter or 200 metres of 3.0-mm-diameter cable. A wide variety of measurements are available, including natural gamma, caliper, normal and guard resistivity, SP, flow, gamma-gamma, and neutron.

The electronics include a computer that converts analog and pulse-type log data and depth information into a serial data stream which is fed to a notebook PC for real time display. The data can be printed or stored on disc. A free Logshell demonstration disc is available.

In 1992, Scintrex became the exclusive worldwide representative for Auslog, which produces digital borehole geophysical logging systems. They range from a very portable 12-volt DC battery-powered system capable of logging to 300 metres using a single-conductor cable, to a 115/240-volt AC electric powered system capable of logging to 2,000 metres using a multi-conductor cable. Customized systems capable of logging to greater depths are also available.

Urtec reported that PC-based software developments for the radio wave logger permit tomographic imaging of conductivity changes in host rock. This is particularly useful in locating blind ore zones, water filled fractures and cavities.

ELECTROMAGNETIC

New Protem components from Geonics have significantly reduced the cost of orthogonal component EM surveys. The 3D-3 coil simultaneously senses orthogonal components of the transient EM response, and sends these values in parallel to the Protem digital receiver. The receiver coil is about the size of a suitcase. New software and an enlarged display enable the operator to review ambient noise, decay curves, apparent resistivity or profiles of measurements along the survey line.

At test sites in northwestern Ontario, a high-resolution EM system was configured with the 3D-3 receiver coil, the Protem receiver, the TEM-57 medium-power transmitter and a 5×5-metre multi-turn transmitter loop. With 25-metre separation between transmitter and receiver, the system was able to resolve closely-spaced conductors, and detect conductors that lie parallel to the survey line.

Geoterrex reports that EM surveys have been performed using the complete suite of Protem equipment. The low power EM-47 transmitter was used for shallow soundings with environmental applications; the medium power EM-57 has been used for deeper soundings with mining exploration applications; and the high power EM-37 has been used for a variety of surface and borehole mining exploration programs. In Australia, the Zonge GGT-30 transmitter has been used in conjunction with Protem receivers where very high transmitter power is required.

Instrumentation GDD claims its new Beep Mat methodology enables the sampling of up to 75% of airborne anomalies for less than the cost of line cutting. The method involves overlaying airborne surveys with overburden maps to locate areas within airborne anomalies where overburden is less than a metre thick. The Beep Mat is used to cross over the anomaly, zigzagging from one side to the other, 25 metres apart until it beeps over the conductor, and the area responding to the Beep Mat is trenched and sampled. This methodology can allow companies to verify a large number of anomalies with a small budget.

Sagax Geophysics is offering Melis (magneto electric induction system) surveys as a contract service. Melis is a deep penetrating frequency-domain EM technique using a fixed source that can be approximated by a vertical magnetic dipole and which is less sensitive to conductive overburden than larger loop sources.

Sagax claims field surveys and numerical modelling established that the detection of large massive sulphide deposits is possible down to 600 metres. A technical brochure including several case histories is available upon request from Sagax.

GEOCHEMICAL

Scintrex and Rudgeofizika, under the auspices of the Geoelectrochemical Surveys Partnership, completed a number of test surveys in 1992 in Australia using the MPF, TMGM and CHIM geoelectrochemical methods. These methods are used to detect the presence of metallic ions that migrate upward from subsurface mineral deposits.

Urtec provides the Gold Probe, a unique bio-geochemical field method for identifying auriferous soils, sediments and rocks. The Gold Probe analyzes samples for the presence of spores of a universally present microbe. These spores preferentially increase in the presence of free gold. The data are said to be quite specific.

GRAVITY

Lacoste & Romberg has field tested a land gravity meter with a microprocessor and data logger which was first shown as a prototype at the 1991 Society of Exploration Geophysicists convention. Development is continuing on both a simple logger and a more advanced system. Deliveries were scheduled for the end of 1992.

Scintrex reports that the number of CG-3 Autograv users has increased and the breadth of applications is steadily widening. The instruments are in use in over 30 countries for applications including geological mapping, crustal studies, tectonic studies, volcanology, geothermal field development, civil engineering, karst mapping, petroleum and mineral exploration. A study has just been completed and reported upon to the Canadian Space Agency on the feasibility of modifying a CG-3 for use on a planetary rover to be launched later this decade.

INDUCED POLARIZATION

In 1992, Instrumentation GDD introduced two time-domain IP transmitters with power of 650 and 1,400 watts. These transmitters are adapted to rocky environments where a high output voltage of up to two kilovolts is needed. Moreover, in swampy areas, the larger one sends a current which can reach 10 amperes with well placed electrodes. The transmitters can be used for underground IP surveys as well.

Iris Instruments has made a number of improvements to its Elrec 6 IP receiver. Changes include the ability to program 10 fully-independent IP windows for extra flexibility in calculation of Cole-Cole parameters; a monitor function to check the level of noise observed on each dipole before the measurement; increased reading resolution of chargeability (to 0.01 mV/volt); and increased maximum input voltage.

A real-time clock has also been added to the Elrec 6 and each reading is recorded with the date and time measurement. Remote control capability has been introduced and frequency mode is included as a standard mode. The power consumption has been reduced by 80% compared to the previous version and memory has been increased to up to 2,500 readings.

In 1992, Scintrex delivered its new IPR-12 time-domain IP-resistivity receiver to clients in over 12 countries, including several in Canada and the United States. The IPR-
12 is a remarkably powerful yet easy to use instrument. It features graphic and alphanumeric displays of instrument status and measured data. Real time quality control of data is important, as 18 parameters are measured for each dipole, and up to eight dipoles can be measured simultaneously. The IPR-12 stacks each cycle and calculates a running average for primary voltage, SP and each of 14 IP transient windows. The IPR-12 uses D-cell batteries and weighs only seven kilograms.

After over four years of tests and modifications, Instrumentation GDD announced the introduction of a cable system for IP surveys incorporating an amplifier at every electrode. The net result is similar to putting a receiver at every electrode. All noise caused by long wires in multiple dipole receivers is eliminated. Field tests in the Chibougamau area produced successful surveys in less time, with a higher quality and at a lower cost than previously. The receiver operator can switch the amplifiers off to allow the measurement of the ground resistance of the electrodes.

The cable system is made up of 25-metre cables connected by switching boxes. At the beginning of the survey, a continuous chain of seven or more cables is connected. The crew places the receiver at the beginning of the chain and uses the first four cables to take the initial readings. Then, the transmitter, generator and receiver are moved 25 metres, and cables two to five are used to take the second set of readings. To make the third set, the crew would again move the instrumentation and use cables three to six. At the same time, other members of the crew move and reconnect cables No. 1 and No. 2 to the seventh, making them No. 8 and No. 9. The survey can thus be continued without interruption. This much faster method allows continuous readings while the cables are being moved.

MAGNETIC

During 1992, Bartington introduced a range of compact, three-axis magnetic field sensors. The cylindrical MAG-03MC and square-section MAG-03MS are available in four measuring ranges. The 70-T version is suitable for geomagnetic observatories and geotechnical studies. The 100-T and 500-T versions are used in engineering applications and bioelectromagnetics. The 250-T version is marketed for magnetic signature analysis in military applications. The MAG-03MSS, which is submersible to depths of 100 metres, is available in measuring ranges of 70 T and 100 T. Output from these sensors is in the form of three analog voltages, proportional to Bx, By and Bz.

Geometrics G-822L cesium magnetometer has a real time RS-232 interface which combines the speed and sensitivity of a cesium magnetometer with the convenience of automatic data recording and processing on a laptop computer. A comparison survey was conducted with a G-856AX proton precession Memory-Mag and a G-822L cesium magnetometer with the RS-232 interface. The G-822L could have surveyed a 6,000-sq.-m area in two hours. The proton magnetometer survey took eight hours.

Gem Systems has incorporated a number of changes in the GSM-19 magnetometer system and created a new option for the “walking” gradiometer. Similar to an airborne survey, data is recorded as often as twice per second as the instrument travels along the line. At each major fiducial, the operator touches a designated key. The walking gradiometer automatically assigns co-ordinates to all intervening readings.

In addition to the standard Overhauser proton magnetometer, a new GSM-19 conventional proton only magnetometer has been introduced. The instrument can store up to 233,000 readings. Gem has also developed two marine versions of the Overhauser magnetometer. A special GSM-19 option is available for remote control observatory and airborne base station applications.

With the Russian State Optical Institute, Gem is developing a super sensitive gradiometer based on very narrow spectral lines of potassium optically pumped magnetometers for the US Geological Survey. Basic resolution of the gradiometer is 4 fT/m (0.004 pT/m) in a bandwidth of 0.02-0.2 Hz. A gradiometer of that sensitivity represents a breakthrough in total field gradiometry and opens new avenues of applications. The instrument is expected to be commercially available in the spring of 1993.

Geo Instruments has produced two new products. One is a pocket-sized magnetic susceptibility meter, Model GMS-2. It is the smallest and lightest unit of its type on the market covering the full measurement range with a sensitivity of 1×10-5 SI units. It has a unique digital and bar graph display, a large memory, the ability to switch from SI to CGS units at the press of a button, auto ranging, and an RS-232 output which does not require any cable connection. It is ideal for drill core scanning and outcrop mapping.

The other product developed by Geo Instruments is a ground survey system, Model HS-10, which is an outgrowth of its miniaturized helicopter magnetics and radiometrics system. The instrumentation required is now so small that it can be hand carried by one or two persons.

The system is built around a 386 processor which can accommodate up to eight magnetometer counter cards together with multi-channel analyzers for radiometrics and GPS navigation cards. Its modular nature and the use of off-the-shelf products makes it expandable and versatile.

Picodas has announced that the MEP-710, an inexpensive “black box” magnetometer is available. It comes complete with software (acquisition with a real time printer support, verification and reporting) for continuous cesium, helium and potassium magnetometers.

RADAR

Canpolar continues to offer a wide range of non-invasive surveys for the environmental and geotechnical markets. Development is under way on data processing and display routines to present data so that an engineer can see anomalies in the data directly.

Canpolar has been very active in developing a radar system mounted in a van which makes continuous quantitative measurements of electrical properties of the materials over which it passes. For example the thickness and defects in pavement and bridges can be measured every 0.1 metre.

Sensors & Software continued to improve the pulseEKKO line of ground penetrating radar systems. The pulseEKKO 1000 Series first introduced in 1991 incorporates improved stacking capabilities which increase the speed of acquisition. Improved high frequency (225-900 MHz) antenna design has also led to deeper penetration in urban environments.

A rental pool for the pulseEKKO IV system has been established. Applications for rentals have ranged from lava flow mapping in Hawaii, to locating World War II aircraft in Greenland glaciers, to environmental site investigations.

RADIOACTIVITY

Exploranium announced that all its spectrometers are calibrated on 1×1-metre pads. The G-256 portable spectrometer can carry out direct assay on the data to an accuracy of 0.1 ppm eU/eTh and 0.1% potassium, using the 14 calibration constants derived on the pads and stored in memory.

RESISTIVITY

Effective March, 1992, Scintrex became the worldwide representatives for Campus Geophysics, the manufacturer of the Geopulse resistivity system. The instrument is not only a signal enhancement resistivity meter, it is also an electrical imaging system and a sounding system capable of surveying to depths of 400 metres. Electrical imaging is achieved by the Geopulse and a MRT computer-controlled, multi-electrode array and switching system.

SEISMIC

ABEM Instrument has introduced a number of improvements to its Terraloc Mark 6 high resolution seismograph. These changes include: a sampling rate that varies from 25 microseconds to two milliseconds; a selectable record length to 16,384 samples; built-in software supporting a small roll-along method without a special switch; and in-field quality control through a range of multi- or single-trace view modes and frequency spectrum analysis (FFT).

Geometrics has introduced a new exploration seismograph, the SmartSeis S12, which is the first of a new generation of products which can collect and process data from 12 geophones. The SmartSeis contain
s a 386 computer with programs to analyze refraction data, plotting a geologic section in the field. It also has programs to assist quality control of reflection data.

The SmartSeis simplifies data collection through use of automatic gain selection and high-resolution acquisition circuitry adopted from digital audio. The data are saved on an internal floppy disk, which can be read on PCs for final processing with any of several available programs. The SmartSeis S12 has a 16-bit analog-digital converter and instantaneous floating point amplifier, making it capable of high quality data acquisition for refraction, reflection and borehole surveys. Follow-on products available in early 1993 will include systems with more channels.

Sial is offering a full range of data acquisition and processing for high resolution seismic reflection and standard land and marine seismic reflection. This service evolved after a seismic reflection survey was completed by Sial’s crew on the Goldex-Ormico orebody, near Malartic, Que. The discovery of a mineralized extension to the existing orebody was the result of two deep drillholes that intersected favorable seismic reflectors interpreted by Sial’s personnel to be at a depth of 800 meres.

Patrick Killeen received his Ph.D in geophysics in 1971 from the University of Western Ontario. After three years as head of the Radiation Methods Section at the Geological Survey of Canada, Killeen, because of his work in gamma ray spectral logging, helped establish in 1981 the Borehole Geophysics Section. He heads this group today. He is also an editor for the Journal of Applied Geophysics and the Journal of Nuclear Geophysics and past president of the Minerals and Geotechnical Logging Society. Dr. Killeen is involved in research to integrate nuclear, electrical, thermal, magnetic and electromagnetic logging techniques for mineral exploration.