MINERAL EXPLORATION: TRENDS AND DEVELOPMENTS IN INSTRUMENTATION (January 01, 1992)

Because of generally low exploration activity, the past year appears to have been an even poorer one than 1990 for the geophysical industry in Canada. A number of Canadian companies have noted that more than three-quarters of their business was overseas. The exception appears to be companies offering data processing and interpretation services; they generally reported increased business. Outside Canada there have been several active exploration areas, notably in Chile and Southeast Asia.

CORPORATE HIGHLIGHTS

On Sept. 25, 1991, Aerodat was purchased by Geonex of Florida (subject to regulatory approval). The main business of Geonex has been the production of digital maps for town planning from photo and satellite imagery.

BGM Airborne Surveys is the newest member of the Australian World Geoscience Group of exploration companies and is based in Houston, TX. During 1991, BGM flew aeromagnetic-radiometric surveys including 81,000 km in Bolivia and 72,000 km in Alaska. Data processing was done in the field.

BRGM Instruments of France has entered into a partnership with Oyo Corp. of Japan to form Iris Instruments. The new company will be the exclusive sales and service representative for BRGM ground geophysical instruments.

A group of more than 24 Canadian geoscience companies has formed an association to market their expertise worldwide. The association is called the Canadian Geophysics Congress (CGC) and is headquartered in Markham, Ont. Offered services include airborne and ground geophysical surveys, geochemical surveys, geological mapping, data processing, interpretation, and training. CGC will also act as the prime contractor on large projects.

Compagnie Generale de Geophysique (CGG) of France has acquired a minority equity position in Dighem Surveys and Processing. The companies were awarded a 16,000-line-kilometre helicopter EM-magnetic-radiometric survey in Ethiopia for polymetallic mineral exploration. The contract includes data acquisition, computer processing, interpretation and training of Ethiopian geophysicists under the technical supervision of the United Nations. The helicopter survey in Yemen completed in 1990 has generated significant follow-up interest.

Geonics, which specializes in the development of EM instruments, was purchased by Swedish Geological AB (SGAB) in July. SGAB also owns ABEM, and it has substantial interests in Phoenix Geophysics and Terraplus (both of Canada) and Terraplus (USA).

The Haileybury School of Mines held another exploration workshop during June, 1991. It focused on the interpretation of data for the most commonly utilized ground and airborne geophysical techniques. The four-day workshop was supported by presentations from a number of the principal instrument and survey contractors and with Ontario Ministry of Northern Development and Mines funding.

MPH Consulting and William Hill Mining Consultants merged last year. The MPH Consulting name was retained, and mining engineering services are offered by the Hill Mining division. Highlights of 1991 activities include a complete review of mining operations in Peru, increased geophysical activity in Mexico, continued application of the Euler depth processing technique to aeromagnetic survey results, and expansion into environmental services.

Multiview Geoservices investigated brine migration from a potash tailings area in Saskatchewan using the Geonics EM47 time-domain EM instrument. The surrounding overburden stratigraphy was mapped with a Geometrics 1225F seismograph, which was also utilized in a seismic refraction survey for a hydroelectric project in Belize. Multiview located a number of abandoned mine workings in northern Ontario using the Pulse Ekko IV radar, Geoscan FM-18 fluxgate gradiometer and Apex MaxMin I-9EM.

Paterson, Grant & Watson (PGW) expanded its staff to 12 full-time geophysicists and added to its Sun computing network. Regional data compilations continued, with projects in Africa, eastern Canada and Minnesota. Major contracts included airborne magnetic-radiometric interpretation, ground truth and training in Sarawak; gravity and magnetic processing and interpretation in Yemen; and projects in Chile, Bolivia, West and South Africa, Mexico, Philippines, Fiji, as well as in Canada and the United States.

Simon Engineering, in Britain, has acquired all assets of the Robertson Group (formerly Robertson Research). A new entity, known as Simon-Robertson will continue to offer mineral consulting, geophysical data processing and interpretation services on a worldwide basis.

Urquhart Dvorak (UDL) and its software division, Geopak Systems, have undergone a corporate reorganization. Additional staff has been hired and computer equipment upgraded, including an IBM 6000 and 486 PCs and the ethernetting of the office environment.

Val D’Or Geophysique offers a variety of airborne and ground geophysical services in Quebec. These include Dighem helicopter-borne EM and magnetic surveys and the use of I-Power processing software. Ground services offered in addition to the standard techniques include Crone borehole Pulse EM and other logging techniques.

AIRBORNE GEOPHYSICAL

SURVEYING

The capabilities of the various airborne geophysical contractors throughout the world are listed in the table.

Aerodat surveyed last year in Brazil, Chile, Britain, France, Spain, Malaysia and Indonesia as well as in Canada and the United States. Although most projects have a mineral exploration objective, other applications have included engineering and environmental assessment, salvage, bathymetry and ice measurement.

Aerodat carried out a survey for British Nuclear Fuels in an area undergoing intensive study as a possible site for underground nuclear waste disposal. A helicopter magnetic gradiometer-gamma-ray spectrometer-VLF EM survey was flown. Preliminary flight path, aeromagnetic, VLF EM and spectrometer maps were prepared on site as the survey progressed.

During 1991, CGI Controlled Geophysics continued to manage airborne magnetic-EM surveys for exploration companies. Each survey involved advanced processing and a detailed interpretation. The Output EM processing technique was improved and applied to a large number of private and public data sets. Multiple time constant analysis was carried out in difficult areas where traditional interpretation methods have failed to extract the necessary information from the EM data.

Questor Surveys reports that the Questem airborne digital time-domain system was very active in both Canada and the United States during the first half of 1991, but declining exploration activities kept the aircraft on the ground for four months during late summer. Improvements in the atmospheric noise and 60-50 Hz rejection algorithms on the Questem increased productivity levels. On-site processing and interpretations provided clients with exploration targets shortly after flying.

Sander Geophysics has been using a new system, based on combined GPS and INS navigation, on all its aeromagnetic surveys. The company has developed a system for transmitting GPS ground station corrections to the survey aircraft in flight, allowing for very precise navigation along flight lines. Sander is capable of carrying out all data processing and map production in the field.

Trimble Navigation is manufacturing an airborne GPS receiver, called the Aerial Surveyor, in its 4000 series. It provides fixes every 0.5 second with an accuracy of a few metres in the differential mode using Trimvec software. These receivers have been used internationally by airborne geophysical contractors and in Canada are available through Surnav.

Airborne Data Acquisition and Processing

Aerodat has introduced a new PC-based software package named Axis (Aerodat extended imaging system). The system provides shadow map capability, an image mosaic feature for adjacent data sets, and image overlay capability for the comparison of different data of the same area. CADD features are included for custom presentations, and basic GIS tools permit the creation of color overlays such as geological
maps.

Controlled Geophysics has expanded its service bureau through the acquisition of microcomputer hardware including rewritable magneto-optical disc technology. The latter has proven invaluable in dealing with very large data sets. MS DOS-compatible archiving and transcription of data sets is now available to and from a variety of media formats.

Dighem has implemented a complete GPS navigation system for its airborne surveys. This system will either replace or supplement the existing UHF navigation system depending on the survey logistics. A real time differential GPS system was to be acquired early in 1992. Dighem has expanded the capabilities of the field workstation to provide preprocessed data.

The I-Power computer division of Dighem, in co-operation with Geosoft, released the I-Power Vision image processing software system in 1991. This is an upgraded version of the old system developed in response to clients’ requirements for an intuitive, user-friendly system. Also, a worldwide distribution network has been established.

Geosoft has introduced two new gravity and magnetic modelling programs to complement its potential field modelling software. Pmodel computes theoretical gravity and magnetic anomalies that arise from a 2-D or 3-D model. It is designed to solve modelling problems for which the user is interested in a range of answers. For example, an orebody could be represented by a dipping 3-D prism and Pmodel used to calculate a suite of responses from different model dips and depths. The Pmodel system was developed under contract for Noranda Exploration.

Gridepth is a PC implementation of Simon-Robertson’s 3-D Euler deconvolution method for determining the location and depth of the sources of gravity and magnetic anomalies from gridded data sets. Gridepth produces a Geosoft compatible XYZ file of source locations and depths from a single gravity or magnetic grid or image. The image may cover a large area and include any number of diverse geological anomaly sources.

Geosoft has released a new version of its mapping software for earth science data. Notable improvements include full color line work and polygon area fills, solid color filled symbol plotting, and an upgraded graphics system that allows plot files to be edited interactively. The Geosoft graphics system is now supported by other third party developers, including Interpex, I-Power, Sensors & Software, and Geo Acoustics.

The Geosoft MapPlot graphics language has also been significantly improved and includes GIS functions to read data from external XYZ files and create custom plots based on that data. This allows users to design custom plots of single line profiles, add annotations and include custom logos on the plot. MapPlot can then be applied to survey data to produce profiles.

Also from Geosoft is new user-programmable Calculator software that allows application of mathematical formulas to Geosoft XYZ files and grid files. Formulas can be as simple as taking the logarithm of a data column or grid, or performing complex calculations using branching and logic.

A new Geosoft version of NetView is able to produce colored 3-D perspective views of gridded data. In particular, the new version is able to drape one grid onto a surface produced by a different grid, and add surface shading if desired. For example, this can be used to drape a gravity grid onto a topography grid so that the relationship between elevation and gravity can be viewed graphically.

During 1991, PGW re-entered the software market, introducing the Gipsi suite of Unix VMS programs designed for workstation-based processing and interpretation. Gipsi offers up-dated versions of all of the proven potential field programs developed by PGW and Geosoft over the past 18 years.

In addition, there are three new releases from PGW. First is Compudrape 1-D and 2-D package for continuing aeromagnetic data between non-parallel surfaces performing the continuation process in the wave number domain, using the state-of-the-art Winograd FFT algorithm. Compudrape has been tested on 20 projects and is now packaged as a stand-alone automated module. The second, Digi, is an interactive digitizing system that has eliminated the use of digitizing tablets and the necessity of hard copy verification maps. Given a scanned image, Digi allows the user to digitize and verify interactively on a workstation several maps in a working day with the same tool. And third is Gridepth, the Euler deconvolution program mentioned earlier

Picodas Group has made its PDAS-1000 data acquisition system more versatile by incorporating an improved magnetic compensation system and a gamma-ray spectrometer option. Picodas has also developed software for magnetic and GPS navigation base station recording on a printer.

Following the introduction of the improved microcomputer module and the SCSI interface, RMS Instruments now offers, in addition to the TCR12 magnetic tape cartridge, two more recording devices. The HDS60 hard disc drive and tape streamer can be operated either in the standard back-up mode or record in parallel with the 40-Mb hard disc. The data format on the removable disc cartridge of the RHD40 is MS DOS compatible providing immediate access to the data on this transportable media.

RMS has made its spectrometer interface module directly compatible with the Exploranium GR820 gamma-ray spectrometer.

UDL has released several processing software packages. All are compatible with Geopak’s RTI CAD system. The spectrometric correction (SC) program for radiometric data was developed to meet Geological Survey of Canada and International Atomic Energy Agency (IAEA) specifications for the processing of data. The program includes corrections for live time, cosmic sources, background radiation, Compton stripping, altitude, sensitivity, filtering (Savitsky-Golay) and ratio calculations. Multi-aircraft and/or multi-season surveys are combined by specifying correction parameters by flight range. The SC program is currently in use on projects sanctioned by the IAEA, including the recovery and reprocessing of vintage data.

The UDL airborne in-field compilation system is based on the field mapper system whose development was supported by National Research Council (NRC) and IRAP funding. This PC-based system enables processing of magnetic, radiometric and EM data and map production during the course of airborne surveys, facilitating the monitoring of data quality and allowing immediate follow-up. Surveys in excess of 50,000 line kilometres are routinely processed.

UDL’s proprietary process known as Acudrape continues aeromagnetic data acquired over an irregular surface to a horizontal plane, or conversely drapes data from a fixed altitude survey onto an undulating surface (either outcropping topography or subsurface magnetic basement) for data enhancement and interpretation.

Aeromagnetic

With the co-operation of Ferderber Geophysics, Gem Systems has successfully flown its Model GSMP-20 potassium optically-pumped magnetometer in a wing-tip installation. The test indicated that the short term noise envelope of the system was well below 0.1 nT for five readings per second and the tracking speed was over 10,000 nT/sec. There is a heading error of about 0.2 nT over 5deg to 85deg. The low noise level of the potassium magnetometer has been confirmed by the Flight Research Laboratory of the NRC in Ottawa.

EG&G Geometrics has recently developed a split beam, self-oscillating, cesium vapor magnetometer as part of its military MK-22 and MK-25 ordnance locator program. The G-822A sensor is now available for commercial airborne survey systems in configurations providing a Larmor signal only. The G-822A System produces better than 0.01 nT peak-to-peak data over a 500-Hz bandwidth at optimum field dip angles. Rotation error is controlled to less than +/-0.15 nT.

During April 1991, Geoterrex completed its first real time differential GPS survey offshore from Gabon. The aeromagnetic survey was undertaken using the new Sercel NR103 fast sampling (0.6 second update rate) 10-channel GPS receivers. The high frequ
ency communication link between base station and airborne receivers operated within a range of 400 km achieving positional accuracies of 5 metres.

After the first successful four-sensor triaxial gradiometer system installed on a Cessna Titan 404 aircraft, Poseidon Geophysics of Botswana has built a second with funding from Anglo American. The system incorporates a RMS Instruments AADCII automatic compensator that permits noise levels of 25 pT to be achieved.

BP Exploration of the United Kingdom also incorporated the RMS Instruments AADCII automatic compensator on its Fokker F27. This aircraft has three high sensitivity magnetometers, one at each wing tip and one in a tail stinger.

Sander reports an increasing demand for airborne magnetometer surveys both in Canada and internationally. The company has attributed this increase to the use of GPS navigation which has reduced the costs of airborne surveys, especially in areas where it was previously necessary to set up radio navigation systems. The company is currently operating three fixed-wing aircraft and one helicopter for total field magnetic and vertical magnetic gradient surveys.

In late 1991 Scintrex’s new CS-2 cesium sensor was tested by the Flight Research Laboratory of the NRC and the Australian Geophysical Research Institute. The CS-2 offers a +/-0.25 nT heading error within a common orientation range of +/-30deg with instrumental noise below 0.001 nT RMS. The CS-2 has been operated in -25degC temperatures in the Arctic.

AIRBORNE

ELECTROMAGNETIC

Aerodat’s new five-frequency helicopter EM system has completed over 10,000 line kilometres of production surveys in North America. A unique feature of this system is the use of two coaxial-coplanar coil pairs to aid in the recognition of deep orebodies, as well as three horizontal coils for enhanced resistivity mapping.

Dighem introduced the Dighem V five-frequency helicopter EM system in 1991. Typically for North American applications, frequencies of 900, 7,200 and 56,000 Hz are employed on the horizontal coplanar coils for resistivity mapping, while common 900 and 7,200 Hz vertical coaxial coils are utilized for locating EM conductors.

Dighem delivered helicopter EM system upgrades to the governments of Germany and Austria in 1991. Both countries had purchased Dighem technology more than 10 years ago. Dowa Mining of Japan completed several Dighem surveys for mineral, environmental and archaeological applications in Asia.

Dighem used its helicopter EM system in the resistivity mode for ground water exploration, displaying color sections to delineate the best drilling targets. In addition, a survey was undertaken for the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia to map areas of low and high water recharge. CSIRO, utilizing the ground results, has been able to define recharge rates.

Dighem reported a small increase in helicopter EM surveys in western Canada and the western United States, including Alaska. However, demand for surveys in the Canadian Shield was relatively low except for some interest in the Northwest Territories.

For Geotem surveys, Geoterrex is now offering processed EM data acquired from measurements taken in the presence of the primary energizing field. This data is proving very useful in delineating weak conductors and mapping geological structure and alteration patterns not detectable in the transmitter-off time.

During 1991, results from an airborne Geotem survey in the Canadian Arctic indicated the presence of IP effects probably associated with permafrost. This is most likely the first case where IP effects have been measured and recognized by an airborne EM system. Numerical modelling of combined EM inductive-IP effects using the new layered earth program Airlyr (developed by Australian Mineral Industries Research Association EM project) support the field results and further modelling is being carried out.

Geoterrex has added a fast (10 samples/sec) cesium vapor magnetometer to its towed Geotem system. This new configuration will improve the mapping capabilities of combined magnetic surveys with no degradation to the measurements of the EM field.

Airborne Radiometric

Interest appears to have been renewed in the use of radiometric surveys for mineral exploration. Dighem presently offers a full spectrum radiometric system with upward-looking crystals. In 1991 surveys were flown in the Cordillera of Canada and the western United States to map alteration zones and to augment the geological data bases of mineral exploration companies.

GROUND SURVEY TECHNIQUES

Data Processing and

Positioning

Geopak has implemented a technique whereby a digitizing tablet connected into the RTI CAD imaging module permits maps to be registered and transferred interactively to the screen. The imaging capabilities of RTI CAD have been further expanded to permit color ternary presentation that can combine radiometric, geochemical and Landsat information. All Geopak processing packages and modules have been integrated with the RTI CAD system.

Magellan Systems is manufacturing a hand-held, single-channel GPS receiver, the Nav 1000 Pro. It can give survey positions with altitude every 2.5 seconds with a 30-metre accuracy (without selective availability) and in the averaging mode down to about 15 metres when good line-of-sight satellite geometry is available.

MPH Software is the North American distributor of Micromine software, a PC-based interactive program that combines the features of a logging program, statistical package, data base, CAD-style digitizing and editing and reserve calculations. This modular software can often be customized to meet a client’s requirements. MPH offers a wide range of bureau services using Micromine and other software to present data in a variety of forms from raw information to fully evaluated and interpreted results.

Trimble has developed a hand-held, three-channel GPS receiver called Transpack that is the civilian version of the Trimpack GPS receiver built for the US Army and widely utilized during the recent Gulf War. The 2-kg Trimpack tracks up to eight satellites with an update rate of one second providing 15-m RMS positions when selective availability is not operating.

Drillhole Methods

ABEM of Sweden has added to its portable Wellmac digital drillhole logging system. New probes include an upgraded resistivity model that simultaneously measures five parameters, i.e. self-potential, single point resistance, short normal, long normal, and lateral. A calliper probe is also available. The Wellmac logger can use up to seven probes simultaneously to reduce the number of logging runs.

With the assistance of Noranda, Crone Geophysics & Exploration has developed a two-component probe for its standard downhole pulse EM system. This probe consists of two orthogonal coils oriented to measure fields orthogonal to the axis of the probe. The probe was successfully tested at the Stratmat main zone south of Bathurst, NB.

IFG Corp. improved its borehole orientation probe by incorporating software to facilitate logging. Additional software has been developed to compute the three orthogonal magnetic field vectors used in determining the direction of off-hole magnetic anomalies. An orientation probe has also been incorporated into the IFG multi-parameter probe to allow measurements of resistivity, temperature, and magnetic susceptibility in conjunction with the orientation data. All measurements are made with a single probe in one pass of the borehole.

Lamontagne Geophysics has extended the depth capability of its borehole EM system (BH Utem) with a 3,500-metre cable. The data rate of the system’s fibre optic data link was doubled to 5 MBaud to accommodate a higher resolution down-hole encoder. The performance of BH Utem was demonstrated by its direct contribution to two discoveries in the Sudbury Basin announced by Inco in September, 1991. The deeper of these discoveries, the Victor deposit, is more than 2,400 metres below surface.

Electromagnetic

Androtex, in co-operation with PGW, complete
d development and testing of a new fixed-source frequency-domain EM transmitter. The EMS-8 operates with a single sensor measuring the amplitude and phase of the vertical magnetic field. All data are recorded in Geosoft format and can be processed in the field to provide half-space apparent conductivity maps; off-line processing can generate multi-layer conductivity pseudo-sections.

Androtex has also developed an EM prospecting device called EZM-1 in which both transmitter and receiver are enclosed in a single unit. The device has an excellent conductance discrimination and high spatial resolution of closely spaced conductors. Depth and dip estimates are derived from the geometry of the response profiles.

Geo Instruments of Australia continues to improve its basic TEM system, Sirotem. The latest model, RVR-3C, measures three orthogonal vector components. As the Sirotem Mk 3 console has a three-channel input, these components can be recorded simultaneously. The RVR-3C is air-cored and each coil has an effective area of 10,000 m[SF]3. The band width to -3 dB is greater than 80 kHz for two axes and 40 kHz for the other. Other Sirotem improvements include a better means of rejecting sferic noise by installing updated software.

Geonics introduced several new EM products in 1991. For mineral exploration, there is now a digital Protem time-domain receiver, with a three-component receiver coil. New software calculates pseudo-conductivity from VLF magnetic field measurements. Two Protem models have been successfully utilized for exploration in the steep topography of the Iskut River area of British Columbia.

Instrumentation GDD has improved the depth penetration (to 1.5 metres) of its Beep Mat EM prospecting instrument. It can discriminate between the presence of conductive material, such as sulphides and magnetite, underneath the shallow glacial material that covers much of the greenstone belts in the Canadian Precambrian Shield. During 1991, Soquem used the Beep Mat in the initial follow-up of airborne Input EM anomalies that resulted in the discovery of Zn-Cu-Ag-Au mineralization on their Dussault property in Quebec.

Most Utem users have taken advantage of the Utem 3D model upgrade offer made by Lamontagne in 1989. The upgrade includes a new calibration-deconvolution capability bringing the long term system response accuracy to the 0.1% level.

For use with Utem common receiver array (CRA) data, Lamontagne has completed the development of correlation processing software and of a CRA modelling capability based on finite plate or half-plane models to permit the definition of deep conductors with multiple loop positions. The data estimate the location and dip of deep conductors and less accurately their depth to more than 800 metres. Layered earth stripping is a software option for locating conductors under deep sedimentary cover.

A Utem test was carried out in Portugal over the famous Neves-Corvo polymetallic deposit, which has been considered difficult to detect by electrical and EM methods. Two 2.5-km test lines were surveyed over the undeveloped Neves deposit that is one of four closely clustered massive sulphide deposits. The Utem 3 data showed clear, broad, long decay anomalies over the deposit which is at 350 metres depth. A case history is available from Lamontagne.

Geochemical

Recognizing the exploration community is placing more importance on accurate sample analyses, Bondar-Clegg has modified its laboratory information system to include results from routine in-house quality control samples. The client is thus able to monitor performance and identify potential problems. The system can also generate summaries of control data. Using this information, the client can calculate the uncertainty of the laboratory data.

Syplot, a general purpose symbol plotting software module, has been added to the Geosoft mapping system. Up to 32 chemical significance ranges can be defined and assigned a symbol pattern, size and color. Syplot allows the merging of other general map graphics with geochemical data.

Scintrex and Rudgeofizika expanded their collaboration for the exploitation of geoelectrochemical technology. Early in 1991 they formed a joint venture called the Geoelectrochemical Surveys Partnership (GECP) headquartered at Scintrex in Concord, Ont. GECP plans to expand its contracting operations in North America and to carry out tests in Australia in 1992.

Rudgeofizika has developed three geoelectrochemical methods (named MPF, TMGM and CHIM) to detect the presence of metallic ions that migrate upward from subsurface mineral deposits. Five Canadian sites tested to date include gold and base metal targets, some lying at depths of 500 metres. Last year, CHIM surveys were done with 30-kg, 30-channel transmitters powered by portable generators and without in-field chemical analysis. These and further improvements are expected to lower costs. The Canadian results remain the confidential property of the sponsors; however, Soviet case histories are available.

Gravity

Scintrex is now offering the standard CG-3 gravity meter with a reading resolution of 0.005 milligals and a standard deviation of 0.01 milligals. Scintrex is also offering a new high resolution option, the CG-3M, which has a resolution of 1 microgal with a standard deviation less than 5 microgals.

Induced Polarization

Androtex has upgraded the software of its six-dipole time-domain IP receiver, model TDR-6. Two of the new features are millisecond display of the transmitter timing test and a power saving mode. Six analog meters allow monitoring of all parameters during simultaneous measurements. With a new version of the data editor, survey results can be presented as a graph on a computer screen facilitating data quality control.

At the 1991 Prospectors and Developers Association of Canada convention, Scintrex introduced a new time-domain microcontroller-based IP receiver, the IPR-12. A 16-line screen permits graphic and alphanumeric displays of instrument status and measured data to the field operator. Such in-field quality control is important because there are 18 parameters measured for each dipole, and up to eight dipoles can be measured simultaneously. The built-in, solid-state memory records all reading information including header information, measured and calculated data. The IPR-12 stacks each cycle and calculates a running average for Vp, SP and each of 14 IP transient windows.

Magnetic

Gem Systems has incorporated further improvements in its GSM-19 Overhauser “walking” magnetometer-gradiometer. It now has a wider range of sample rates, switchable recording modes, a 256-kb memory, faster data transfer, and automatic resumption of magnetic sampling after VLF readings.

Geometrics has recently introduced a new line of proton precession magnetometers with remote telemetry capabilities. The G-876 is enclosed in a small, submersible aluminum and fibreglass housing. A coaxial cable carries data, control signals and power to and from the magnetometer. It is available as a stand-alone system, or as a module for vehicle-borne or marine systems.

Geometrics is also manufacturing a civilian version of its cesium vapor magnetometer produced for the U.S. military. The G-822 magnetometer has a 0.1-gamma sensitivity and seven-times-per-second data sampling. Data output is visual and audible, optimizing the system for ground search applications.

Geometrics has recently released MagLoc, a data processing and contouring software package for proton magnetometers that replaces the older MagPac. MagLoc not only includes data transfer and diurnal correction routines, but also generates XYZ ASCII files for input into commercial contouring packages. MagLoc is menu-driven, includes gradiometer support, works as a real time data logger for the G-856 or G-866 magnetometers, and generates an on-screen color graphic representation of the survey grid. This software is available free on request to users of Geometrics magnetometers.

Radar

Multiview has completed a survey at a mine near Copiapo, Chile, using the Sensors & Software Pulse Ekk
o IV GPR. Antennas operating at frequencies of 50, 25 and 12.5 MHz mapped rock lithology 60 metres below the surface. The survey aided in the definition of an altered zone thought to control mineralization in a fractured volcanic sequence.

Sensors & Software has developed a new high frequency GPR, the Pulse Ekko 1000 that extends the range of Pulse Ekko systems from 12.5 to 1,000 MHz. It is designed for high definition shallow depth applications that include engineering and mine structure integrity. The company has also developed a new color plotting package. The illustration shows a radar profile cross-section plotted using the new software across two cylindrical storage tanks buried less than a metre below asphalt. The top of each tank coincides with the apex of each of the hyperbolas.

Resistivity

ABEM has introduced a new multi-electrode resistivity system, called Multimac, that consists of a Terrameter SAS 300C control unit, a distributor box, four two-conductor cables, addressable electrode switchers, and a Geomac III computer. After the electrode arrays are set up, the system is run unattended by Multi-master software that stacks and overlaps the recorded values. Interpretation is subsequently carried out using the ABEM Super-VES software.

Campus Geophysical Instruments of the United Kingdom recently launched Geopulse, a signal enhancement resistivity meter. The instrument has high stability and is accurate over the range 200,000 ohms to 0.0005 ohm. Modules for the Geopulse are also available for controlling the Campus MRT and other imaging electrode arrays, making possible the automatic measurement of 2-D resistivity sections from shallow depths down to 200 metres.

The Geoliner saline mapper (a vehicle-drawn EM resistivity-magnetic system) of Tesla-10 in Australia has been improved with the addition of a cesium vapor magnetometer for high density data collection. A foot-borne variant of this is now available. GPS satellite positioning has been successfully employed with the Geoliner.

Zonge Engineering and Research offers three transmitters that can be utilized for time- or frequency-domain IP, resistivity, complex resistivity, time-domain EM and controlled-source audiomagnetotelluric surveys to power a loop or ground dipole. The GGT-3 transmitter has a 3.5-kVA output, the GGT-10 has a 10-kVA output, and the GGT-30 has a 30-kVA output. All operate over the direct current frequency range to 8 kHz.

Seismic

ABEM is manufacturing a microprocessor-controlled reflection-refraction seismograph called the Miniloc. In its automatic refraction mode, the operator uses three geophones and 36 shot points in a pre-set 108-metre layout profile. The time-distance curves may be displayed on the screen along with the interpreted seismic cross-section.

ABEM has introduced the Mark 6 version of the Terraloc reflection-refraction seismograph. The seismograph can be expanded to 48 channels, and it uses instantaneous floating point amplifiers and 18 bit analog-digital converters.

The Geometrics ES-2401 reflection-refraction seismograph is now available in the X version with 24, 48, 72, 96, or 120 channels. The larger systems are particularly suited to tomographic surveys, deeper reflection and large scale refraction surveys. Another improvement is the introduction of new software to carry out basic geophysical calculations for quality control in the field. The new software can be loaded directly from a floppy disc and is available at no charge.

SPECIALIZED ABBREVIATIONS

USED IN THIS ARTICLE

EM electromagnetic

FFT fast Fourier transform

GIS geographic information

systems

GPR ground penetrating

radar

GPS global positioning

system

INS inertial navigation

system

IP induced polarization

RMS root mean square

RTI real time imaging

SP self-potential

TEM time-domain

electromagnetic

VLF very low frequency

1-D one-dimensional

2-D two-dimensional

3-D three-dimensional