GDS1104-REV - SCHREIBER AREA, Magnetic and … and Electromagnetic Data Geophysical ... Ontario airborne geophysical surveys, magnetic and electromagnetic ... sector exploration risk

Report on Schreiber Airborne Geophysical SurveyGeophysical Data Set 1104 - Revised

SCHREIBER AREA

Ontario Airborne Geophysical SurveysMagnetic and Electromagnetic DataGeophysical Data Set 1104 - Revised

Ontario Geological SurveyMinistry of Northern Development and MinesWillet Green Miller Centre933 Ramsey Lake RoadSudbury, Ontario, P3E 6B5Canada


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TABLE OF CONTENTS

CREDITS ........................................................................................................................................................................ 2

DISCLAIMER ................................................................................................................................................................ 2

CITATION...................................................................................................................................................................... 2

1) INTRODUCTION................................................................................................................................................. 3

2) SURVEY LOCATION AND SPECIFICATIONS ............................................................................................. 4

3) AIRCRAFT, EQUIPMENT AND PERSONNEL .............................................................................................. 6

4) DATA ACQUISITION ......................................................................................................................................... 9

5) DATA COMPILATION AND PROCESSING................................................................................................. 10

6) MICROLEVELLING AND GSC LEVELLING ............................................................................................. 14

7) FINAL PRODUCTS ........................................................................................................................................... 25

8) QUALITY ASSURANCE AND QUALITY CONTROL................................................................................. 26

REFERENCES ............................................................................................................................................................. 30

APPENDIX A TESTING AND CALIBRATION................................................................................................... 32

APPENDIX B PROFILE ARCHIVE DEFINITION ............................................................................................. 37

APPENDIX C ANOMALY ARCHIVE DEFINITION.......................................................................................... 41

APPENDIX D GRID ARCHIVE DEFINITION .................................................................................................... 43

APPENDIX E GEOTIFF AND VECTOR ARCHIVE DEFINITION ................................................................. 44

APPENDIX F KEATING CORRELATION ARCHIVE DEFINITION............................................................. 45


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CREDITS

This survey is part of the Operation Treasure Hunt geoscience initiative, funded by the OntarioGovernment.

List of accountabilities and responsibilities:� Andy Fyon, Senior Manager, Precambrian Geoscience Section, Ontario Geological Survey

(OGS), Ministry of Northern Development and Mines (MNDM) – accountable for the airbornegeophysical survey projects, including contract management

� Stephen Reford, Vice President, Paterson, Grant & Watson Limited (PGW), Toronto, Ontario,OTH Geophysicist under contract to MNDM, responsible for the airborne geophysical surveyproject management, quality assurance (QA) and quality control (QC)

� Lori Churchill, Project and Results Management Coordinator, Precambrian GeoscienceSection, Ontario Geological Survey, MNDM – manage the project-related milestoneinformation

� Zoran Madon, OTH Data Manager, Precambrian Geoscience Section, Ontario GeologicalSurvey, MNDM – manage the project-related digital and hard copy products

� Fugro Airborne Surveys, High-Sense office, Richmond Hill, Ontario - data acquisition and datacompilation.

DISCLAIMER

To enable the rapid dissemination of information, this digital data has not received a technical edit.Every possible effort has been made to ensure the accuracy of the information provided; however,the Ontario Ministry of Northern Development and Mines does not assume any liability orresponsibility for errors that may occur. Users may wish to verify critical information.

CITATION

Information from this publication may be quoted if credit is given. It is recommended thatreference be made in the following form:

Ontario Geological Survey 2003. Ontario airborne geophysical surveys, magnetic andelectromagnetic data, Schreiber area; Ontario Geological Survey, Geophysical Data Set 1104 -Revised.


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1) INTRODUCTION

Recognising the value of geoscience data in reducing private sector exploration risk andinvestment attraction, the Ontario Government embarked on “Operation Treasure Hunt” (OTH).The OTH initiative comprises a three-year, $29 million program that commenced April 1, 1999. Itincorporates:

� airborne geophysics (high-resolution magnetic/electromagnetic surveys and someradiometric surveys)

� surficial geochemistry (lake sediments and indicator minerals)� bedrock map compilation� methods development (e.g. electro-geochemical modelling applied to exploration and 3-D

geological/geophysical modelling)� delivery of digital data products.

The OGS was charged with the responsibility to manage OTH. The OGS sought advice about themineral industry needs and priorities from its OGS Advisory Board – a stakeholder boardincluding representatives from the Ontario Mining Association, Ontario Prospectors Association,Prospectors and Developers Association, Aggregate Producers Association of Ontario, Chairs ofOntario University Geology Departments, Canadian Mining Industry Research Organisation andGeological Survey of Canada. The OGS Advisory Board mandated a Technical Committee toadvise the OGS on geographic areas of interest within Ontario where collection of new data wouldmake the greatest impact on reducing exploration risk. Various criteria were assessed, including:

� commodities and deposit types sought� prospectivity of the geology� state of the local mining industry and infrastructure� existing, available data� mineral property status.

In late 1999, MNDM commenced an ambitious program of airborne magnetic and electromagneticsurveys as part of OTH geoscience initiative. The project involved four survey contractors, fivedifferent electromagnetic systems and more than 105,000 line-km of data acquisition.

The airborne survey contracts were awarded through a Request for Proposal and ContractorSelection process. The system and contractor selected for each survey area were judged on manycriteria, including the following:

� applicability of the proposed system to the local geology and potential deposit types� aircraft capabilities and safety plan� experience with similar surveys� QA/QC plan� capacity to acquire the data and prepare final products in the allotted time� price-performance.

In February 2002, PGW was retained by MNDM to microlevel and level to a common datum allOTH aeromagnetic surveys. Any OTH surveys adjacent to existing AMEM surveys weresubsequently merged to form supergrids. PGW commenced this project in March 2002.


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2) SURVEY LOCATION AND SPECIFICATIONS

The Schreiber survey area is located in northern Ontario (Figure 1), straddling the boundarybetween the western ends of the Wawa and Quetico Subprovinces within the Superior Province. Itincorporates Archean metavolcanic, metasedimentary and intrusive rocks. Overburden cover in thearea is generally thin except for areas straddling drainage channels. The commodities soughtinclude gold, volcanogenic massive sulphides, intrusion-related nickel-platinum group elementsand alkalic intrusion-related mineralization . The High-Sense frequency-domain electromagneticand magnetic system, mounted on a helicopter platform, was selected by MNDM to conduct thesurvey.

Figure 1: Schreiber survey area.

The airborne survey and noise specifications for the Schreiber survey area were as follows:

a) traverse line spacing and direction� flight line spacing was 200 m� flight line direction was 0� azimuth� maximum deviation from the nominal traverse line location could not exceed 60 m over a

distance greater than 1500 m� minimum separation between two adjacent lines could be no smaller than 140 m or larger

than 260 m


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b) control line spacing and direction� at a regular 1500 m interval, perpendicular to the flight line direction� along each survey boundary (if not parallel to the flight line direction)� maximum deviation from the nominal control line location could not exceed 60 m over a

distance greater than 1500 m c) terrain clearance of the EM receiver bird

� nominal terrain clearance was 30 m� altitude tolerance limited to �15 m except in areas of severe topography� altitude tolerance limited to �10 m at flight line/control line intersections except in areas of

severe topography d) aircraft speed

� nominal aircraft speed was 30 m/sec� aircraft speed tolerance limited to �10.0 m/sec, except in areas of severe topography

e) magnetic diurnal variation

� could not to exceed a maximum deviation of 2.5 nT peak-to-peak over a long chordequivalent to the control line spacing (1500 m)

f) magnetometer noise envelope

� in-flight noise envelope could not exceed 0.1 nT, for straight and level flight� base station noise envelope could not exceed 0.2 nT

g) EM receiver noise envelope� the noise envelope could not exceed:

865 Hz coplanar coil pair - �1 ppm (�2 ppm in rough terrain)4175 Hz coplanar coil pair - �1 ppm (�2 ppm in rough terrain)33000 Hz coplanar coil pair - �5 ppm (�10 ppm in rough terrain)935 Hz coaxial coil pair - �1 ppm (�2 ppm in rough terrain)4600 Hz coaxial coil pair - �1 ppm (�2 ppm in rough terrain)


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3) AIRCRAFT, EQUIPMENT AND PERSONNEL

This section provides a brief description of the geophysical instruments used to acquire the surveydata.

Aircraft

Two Aerospatiale AS350B2 helicopters were used to perform the survey. This model of helicopterprovides a safe platform for this type of survey. The helicopter registered C-GHEX flew theHarrier EM system and completed production flights 1 – 71. The helicopter registered C-FWAUflew the Hawk EM system and completed production flights 104-109. These helicopters flew at anaverage speed of 60 knots while acquiring survey data. The ground sampling distance at 60 knotswas 3.0 metres.

Magnetometer System

The raw total magnetic intensity data were acquired by two Geometrics G-822A cesium vapourmagnetometers. The upper magnetometer was mounted in the magnetics bird 15 metres below thehelicopter and the lower magnetometer was mounted in the EM bird 30 metres below thehelicopter. This provided a vertical magnetic gradiometer configuration with 15 m separation.

Electromagnetic System

Two electromagnetic systems were used to perform the survey, Harrier, and Hawk. Each systemwas composed of electromagnetic transmitter and receiver coils mounted in an 8.43 m long birdtowed below the helicopter on a 30m long cable. The system measured the inphase and quadraturecomponents of five coil pairs operating in the geometry and frequencies listed in the table below.Coil separations were nominally 6.4 m.

Geometry Frequency (Hz)Harrier Hawk

Coaxial 925 925Coplanar 877 851 Coaxial 4,468 4,396Coplanar 4,891 4,740Coplanar 33,840 35,110

Receiver coils measured the secondary field relative to the primary field as seen at the receivercoil. The unit of measurement was parts per million (ppm). In-flight noise levels of ± 1.0 ppmwere normal for the coaxial coil pairs, approximately 1.5 for the low frequency and mid frequencycoplanar coils, and less than 5 ppm for the high frequency coplanar data. Turbulence and culturewere the major causes of electromagnetic noise throughout the survey.

The EM system is electronically and physically complex and requires constant attention forsuccessful operation. The system was monitored using built-in internal calibration coils. Theequipment operator and field quality controller monitored these for each flight. The records are


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contained in table 3 (Appendix A) . Another major concern was to minimize low frequency noise.The amount of low frequency noise or drift was measured by regularly flying outside of groundeffects. This was done at the beginning middle and end of each survey flight. This was onlypartially effective; manual on-line adjustments of EM zero levels were required during dataprocessing.

Radar and Barometric Altimeters

A Terra TRA-3000 radar altimeter recorded terrain clearance. The output from the instrument is alinear function of altitude. The instrument was pre-calibrated by the manufacturer and was checkedafter installation against the barometric and differentially corrected GPS altimeters. This radaraltimeter has a range from 40 to 2500 feet with a system accuracy of ±5% of the flying height.The aircraft also contained a Rosemount 1241M barometric altimeter (FAA certified). Thisaltimeter has an accuracy of ±7 feet for the survey altitude. Both the altimeters were mounted inthe helicopter.

GPS System

A Leica MX9212 (12 channel) GPS receiver was used in the aircraft. The raw positional data weredifferentially corrected on a daily basis with base station GPS data using C3NAV softwaredesigned by the Department of Surveying Engineering at the University of Calgary. Thenavigational unit in the aircraft supplied continuous information to the pilot while flying thesurvey. The Aerodat NAVPILOT navigational system was utilized on the aircraft to provide a leftright indicator for the pilot. The single point GPS positions were logged onto the RMS digitalacquisition system. The GPS positions were recorded in the WGS84 spheroid. The GPS antennawas mounted on the magnetometer bird 15 m below the helicopter.

Base Station Magnetometer

The base station magnetometer was located at the Terrace Bay airport alongside the GPS basestation. Diurnal magnetic data were collected by a cesium vapour Scintrex V1W2321H8magnetometer at a sample rate of once per second. This magnetometer has a 0.1 nT sensitivity, adigital resolution of 0.01 nT, and a range of 20,000 nT to 100,000 nT.

GPS Base Station

A Novatel 3151R GPS receiver was used for the ground GPS recording. The ground station unitwas provided to allow post flight differential processing. Both the airborne and ground unit usedthe GPS satellite time for synchronization. The base station was located at the Terrace Bay airport48° 48’ 55.7004”, N 87° 05’ 22.4410” W, 243.58 m above the WGS84 ellipsoid.

Airborne Digital Recorder

The RMS DGR33 digital acquisition system manufactured by RMS Instruments Limited recordedthe digital data. This system collected the geophysical and ancillary equipment output anddisplayed the data on the GR33 thermal graphic recorder. All the digital acquisition systems


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employed full read after write capability to ensure data reliability. The analog data were monitoredin flight and examined post flight to assure the best data quality.

Video Flight Path Recording

A Sony VHS Model DXC 107 colour video camera was used to visually record the aircraft’s flightpath. This camera operated in conjunction with a Panasonic video recorder. The date, flight, linenumber and time were recorded on the video image for precise correlation. Several randomlychosen flights were checked to ensure positional accuracy.

Personnel

The following chart details the personnel involved in the survey, their title, and the dates duringwhich they worked on the project.

Title Name Period

Operations Manager Zbynek Dvorak 1999/12/01 - 1999/12/02Engineers/Instrument Syed Shah 1999/11/6 - 1999/12/23Operators 2000/01/06 - 2000/01/14

Mark Barry 1999/110/6 - 1999/12/222000/01/03 - 2000/01/06

Chris Kozak 1999/11/05 - 1999/11/111999/11/17 - 1999/12/112000/01/05 - 20000/1/06

Greg Luus 1999/11/30 - 1999/12/4On Site Geophysicist Nick Venter 1999/11/6 - 1999/11/26

Joy Hartzler 1999/11/6 - 1999/12/23,2000/1/3 - 2000/1/14

Tomohiro Kimura 1999/11/26 - 1999/12/232000/1/7 - 2000/1/14

Helicopter Pilot Jean Goyette 1999/11/5 - 1999/12/5 Joel Bretton 1999/11/5 - 1999/11/11

1999/12/5 - 1999/12/22Richard Barette 1999/11/22 - 1999/12/11

Helicopter Mechanics Gaeton Caron 1999/11/5 - 1999/11/27Eddy Perron 1999/11/27 - 1999/12/22

Data Processing Tomohiro Kimura 2000/01/28-2000/06/30Heather Crow 2000/01/21-2000/03/31Joy Hartzler 2000/01/28-2000/04/14Russell Imrie 2000/01/21-2000/07/06


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4) DATA ACQUISITION

Flight Path

Raw positional data were recorded ten times each second in the WGS84 spheroid. The airbornedata were acquired by a Leica MX9212 GPS receiver that updates once a second and were storedon magnetic tape by an RMS DGR33 acquisition system. The raw positional data weredifferentially corrected on a daily basis with base station GPS data using C3NAV softwaredesigned by the Department of Surveying Engineering at the University of Calgary. The basestation GPS receiver was a Novatel 3151R recording at a one second interval.

Magnetic Data

The raw total magnetic intensity data were acquired by two Geometrics G-822A cesium vapourmagnetometers. The upper magnetometer was mounted in the magnetics bird 15 metres below thehelicopter and the lower magnetometer was mounted in the EM bird 30 metres below thehelicopter. The data were recorded on the RMS DGR-33 at ten samples per second.

Radar and Barometric Altimeters

A Terra TRA-3000 radar altimeter and a Rosemount 1241M barometric altimeter (FAA certified)were installed in the helicopter to monitor altitude for the survey. The outputs from thesealtimeters were recorded 5 times per second.

Electromagnetic Data

The EM data were acquired using two High-Sense Aerodat EM birds suspended below thehelicopter on a 30m cable. The operating frequencies for Hawk and Harrier are documented insection 3. The EM data were recorded ten times per second and profiled onto analog charts by theDGR-33 during survey flights. The operator monitored these profiles during data acquisition toensure quality.

Ground Station Data

The GPS and magnetometer base stations were regularly monitored by the field data processorbefore and during the acquisition of survey data. This was done to ensure that diurnal variationsdid not exceed 2.5 nT from a long chord equivalent to the average control line spacing of 1500metres, and that GPS data would be available for post-flight processing. Where re-flights werenecessary the re-flights traversed at least two control lines.


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5) DATA COMPILATION AND PROCESSING

Base Maps

Base maps of the survey area were supplied by the Ontario Ministry of Northern Development andMines.

Projection Description:

Datum: NAD27 (NTv2)*Ellipsoid: Clarke 1866Projection: UTM (Zone: 16N)Central Meridian: 87º00'WFalse Northing: 0False Easting: 500000Central Scale Factor: 0.9996* The geophysical data was collected using the UTM NAD83 datum (WGS84 ellipsoid), thenreprojected to the NAD27 datum (Manitoba, Ontario mean) and finally shifted 2.1 m east and 4.3m south to best approximate the OBM topographic base.

Flight Path

Repeated points caused by the once per second update of the GPS data were defaulted and linearlyinterpolated to produce positional data at ten samples per second. Corrected navigational data wereconverted to NAD27 using the Manitoba/Ontario local datum (major axis=6378206.400, minoraxis=6356583.600, flattening=294.978698, dx=9, dy=-157, dz=-184). UTM NAD27 (Manitoba,Ontario mean) data were then shifted 2.1 metres east and 4.3 metres south to best approximate theOBM topographic base maps in the NTv2 local datum. Positional data are also archived as UTMcoordinates in the NAD83 datum and as latitude and longitude in NAD27 (NTv2) and NAD83.

Magnetic Data

The raw upper and lower magnetic data are archived in the umag_raw and lmag_raw channels.They contain the unedited total magnetic intensity data recorded in the aircraft. The editedmagnetic data are archived in the umag_edit and lmag_edit channels. These channels wereproduced by despiking the raw magnetic data using a 13 4 2 0 spike rejection routine. (See spikerejection at the end of this section). Channels were examined and large spikes were removedmanually. A 5-point moving average filter was applied and a 4th difference was calculated andexamined. The International Geomagnetic Reference Field (IGRF) was calculated for the upperand lower magnetic sensor. These data are archived in the u_igrf and l_igrf channels and werecalculated using year 2000 coefficients based on constant barometric altitudes of 425 m and 410 mabove sea level. The respective IGRF values were subtracted from the edited magnetic values toproduce the umag_igrf and lmag_igrf channels. Spikes were removed from the diurnal data usingspike rejection parameters 13 4 2 0. The data were filtered with a 7-point Hanning filter beforebeing copied to the mag_base_final channel. Diurnal data were subtracted from the IGRF removedmagnetic data and then a base of 58270 nT was added back to produce the mag_igrf_diurn,


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lmag_igrf_diurn channels. The data in these channels were lagged 0.65 seconds for the uppermagnetometer, and 0.75 seconds for the lower before being tie line levelled to produce theumag_lev and lmag_lev channels. These data channels were micro-levelled and corrections lessthan 1 nT were applied to produce the umag_final and lmag_final channels. These data have beengridded using the minimum curvature gridding algorithm and a 40 metre grid cell size. Contourswere threaded through the grid of the upper magnetic sensor to produce the 1:20,000 contourmaps.

The raw vertical magnetic gradient was calculated by subtracting umag_final from lmag_final anddividing by the separation. The result is archived in vg_raw. The edited vertical gradient wasarchived in vg_edit. It was corrected for altitude by having a mean removed on a line by line basis.The vertical gradient data were then gridded and gross errors were removed manually to producethe vg_lev channel. The vg_lev channel was then micro-levelled and corrections less than 0.05nT/m were applied to produce the vg_final channel. This channel was gridded with a 40 m cellsize, and Akima spline interpolation. The grid was then smoothed with a 3 by 3 convolution filterfor presentation.

The second vertical derivative was calculated from the final upper and lower residual magneticfield grids using a Fourier-domain second vertical derivative filter and a low pass Butterworthfilter, with a cut-off wavelength of 200m. The resulting grids have been archived and the grid fromthe upper sensor was used to prepare the 1:50,000 scale shaded relief images.

Possible kimberlite targets were identified from the residual magnetic intensity data, based on theidentification of roughly circular anomalies. This procedure was automated by using a knownpattern recognition technique (Keating, 1995), which consists of computing, over a movingwindow, a first-order regression between a vertical cylinder model anomaly and the griddedmagnetic data. Only the results where the absolute value of the correlation coefficient is above athreshold of 75% were retained. The results are depicted as circular symbols, scaled to reflect thecorrelation value. The most favourable targets are those that exhibit a cluster of high amplitudesolutions. Correlation coefficients with a negative value correspond to reversely magnetisedsources. It is important to be aware that other magnetic sources may correlate well with the verticalcylinder model, whereas some kimberlite pipes of irregular geometry may not.

The cylinder model parameters are as follows:

Cylinder diameter: 200 mCylinder length: infiniteOverburden thickness: 0 mMagnetic inclination: 75.48� NMagnetic declination: 5.69� WMagnetization scale factor: 100Maximum data range: 985.2 nTNumber of passes of smoothing filter: 0Model window size: 15Model window grid cell size: 40 m


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Digital Elevation Model

The digital elevation model was computed from the radar_final and gps_z_asl channels. Becausethe radar altimeter was mounted in the helicopter and the GPSA antenna was on the mag bird a15m offset had to be applied to the DEM channel. The radar_final was produced by applying a 134 2 0 spike rejection to the radar_raw channel, along with a nine point Hanning filter and a 1.6second lag. The differentially corrected height above the NAD27 datum was calculated and then30.42 m was removed to adjust the elevation to metres above sea level. The radar_final channelwas then subtracted to produce a rough DEM. Manual corrections to the rough DEM were appliedto the gps_z_asl and the DEM was recalculated. The DEM was then micro-levelled with nocorrection exceeding 5 metres. Corrections were applied to the gps_z_asl channel. The demchannel contains the final archived digital elevation model. This channel was gridded with a 40 mcell size, and Akima spline interpolation. The grid was then smoothed with a 3 by 3 convolutionfilter for presentation.

Electromagnetic Data

The profile EM data were levelled and assigned co-ordinates based on the flight path data. Rawinphase and quadrature data were de-spiked using a 15 4 2 0 spike rejection. Further spikes wereremoved manually after examination of profile data and then a 7-point Hanning filter was applied.Noise less than one second in wavelength on the low coplanar data was removed using an FFTfilter. Linear interpolation of corrections between high level background checks were applied tothe data, and the data were examined in profile form to look for levelling discrepancies. Minorlevel adjustments were applied where warranted after examination of all frequencies.

The inphase and quadrature data were individually gridded and inspected for levelling errors.Several small errors were noticed which were not related to altitude. A decorrugation filter wasapplied to the inphase and quadrature data separately to create preliminary correction grids. Thecorrections were limited to data where the response was in the range of ±4 ppm and a low passfilter was applied to the corrections. The extent of the low pass filter was carefully designed tohave minimal effect in reducing the amplitudes of conductive areas in either the inphase orquadrature channels. The correction channels were applied to the data to create the final inphaseand quadrature channels used to calculate the resistivity. The data were rigorously analyzed aftereach stage to make sure no anomalies were being introduced or deleted and the final correctionwas a smoothly varying function.

The coplanar resistivities were calculated in ohm-metres from the inphase and quadrature data inparts per million using the Fugro pseudo-layer model (i.e. finite thickness resistive layer over ahomogeneous halfspace). These channels were gridded with a 40 m cell size, and Akima splineinterpolation. The grids were then smoothed with a 3 by 3 convolution filter for presentation.

Anomaly picking was done manually with conductor types and dips assigned by the interpreterbased upon the mid-frequency profiles. Cultural anomalies were verified by power line response,topographic correlation, and examination of the flight path video.


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Spike Rejection

There are four parameters required for the spike rejection method;

LEN Is the number of points to examine. LEN must be an odd number greaterthan 3. The centre point of LEN is the point being operated on.

NREJ Is the number of data values to reject in both the high and low directions.

TOL Is the width tolerance.

NFLT Is the number of Hanning filter points in the post spike rejection smoothingfilter.

LEN data points are examined. The NREJth highest and NREJth lowest values are invalidated.The remaining points are a cluster of assumed acceptable values. The DMIN (minimum) andDMAX (maximum) of the remaining points produce a scatter of DIFF size. TOL is multiplied byDIFF and added to DMAX producing TMAX. TOL is multiplied by DIFF and added to DMINproducing TMIN. If the original central point in the cluster is within the span between TMIN andTMAX, it is accepted and left unchanged.

If the original value is outside the range from TMIN to TMAX, it is rejected and a new point isgenerated using a Hanning filter on the acceptable points in the scatter. When a channel is spikerejected, a smoothing filter of NFLT points is applied to the data prior to writing it to thedestination channel in the database.

Fourth Difference

The fourth difference is defined as:

FDI = XI+2 – 4XI+1 + 6XI – 4Xi-1 + Xi-2

Where Xi is the ith total field sample. The fourth difference in this form has units of nT. Highfrequency noise should be such that the fourth differences divided by 16 are generally less than±0.1 nT.


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6) MICROLEVELLING AND GSC LEVELLING

Microlevelling

Microlevelling is the process of removing residual flightline noise that remains after conventionallevelling using control lines. It has become increasingly important as the resolution ofaeromagnetic surveys has improved and the requirement of interpreting subtle geophysicalanomalies has increased. The frequency-domain filtering technique known as “decorrugation” hasproven inadequate in most situations, as significant geological signal might be removed along withnoise. In addition, the microlevelling correction is applied to the profile data, whereasdecorrugation corrects only grids. The separation of noise from geological signal and thecorrection of the profiles, are the key strengths of the PGW’s microlevelling procedure.

The PGW microlevelling technique resulted from a new application of filters used in the process ofdraping profile data onto a regional magnetic datum (Reford et al., 1990). It is similar to thatpublished by Minty (1991).

Microlevelling is applied in two steps. The decorrugation steps are as follows:� Grid the flightline data to a specified cell size using the minimum curvature gridding

algorithm.� Apply a decorrugation filter in the frequency-domain, using a sixth-order high pass

Butterworth filter of specified cut-off wavelength (tuned to the flightline separation),together with a directional cosine filter, so that a grid of flightline-oriented noise isgenerated.

� Extract the noise from the grid to a new profile channel.

At this stage, the noise grid may be examined toensure that the flightline noise has been isolated,and to determine what parameters will berequired to separate the true residual flightlinenoise from the high-frequency geological signalincorporated in the filtering described above.

The steps for the microlevelling procedure are asfollows:

� Apply an amplitude limit to clip or zerohigh amplitude values in the noisechannel, if desired.

� Apply a low pass non-linear filter (Naudyand Dreyer, 1968), so that only the longerwavelength flightline noise remains,forming the microlevel correction.

� Subtract the microlevel correction fromthe original data, resulting in the final,microlevelled profile channel.

Decorrugation noise grid


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In the example shown, the data are windowed from an airborne magnetic and electromagneticsurvey flown in the Matachewan area of Ontario, over typical Archean granite-greenstone terrain(Ontario Geological Survey, 1997). Standard corrections (e.g. diurnal, IGRF, conventional tielinelevelling) were applied to the magnetic data. However, a considerable component of residualflightline noise remains, due for example to inadequate diurnal monitoring or tieline levellingdifficulties.

Middle panel: red – decorrugated noise channelgreen – noise channel after zeroing high valuesblue – non-linear filtered noise channel (=microlevel channel)

Lower panel: magenta – original total magnetic fieldgrey – microlevelled total magnetic field

The resultant microlevelled channel can then be gridded for comparison with the original data. Inaddition, it is useful to examine the intermediate noise channels in profile and grid form, to verifythat the desired separation of residual flightline noise and geological signal has occurred.


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Total magnetic field, before microlevelling. Total magnetic field grid, after microlevelling.

Microlevelling can be applied selectively to deal with noise that varies in amplitude and/orwavelength across a survey area. It can also be applied to swaths of flightlines, where moreregional level shifts are a problem due to inadequate levelling to the control lines. This can beparticularly useful on older surveys where tieline data may no longer be available.

Microlevelling will not solve all problems of flightline noise. For example, positioning errors (e.g.poor lag correction) may result in some level shift that microlevelling will reduce. However,shorter wavelength anomalies will still remain mis-aligned. Line-to-line variations in surveyheight result in anomaly amplitude variations. Again, microlevelling will reduce long wavelengthlevel shifts, but cannot compensate for localized amplitude changes.

Decorrugation Parameters

Decorrugation requires a database of geophysical data, oriented along roughly parallel surveylines. Surveys with more than one line orientation should be separated into blocks of consistentline direction. The profile channel to be microlevelled should have had all standard corrections,and conventional tieline levelling, already applied. Only traverse lines should be selected formicrolevelling (i.e. no tie-lines).

Flight Line SpacingThe nominal flightline spacing is required to design the filter parameters. If a survey containsblocks flown at different line spacings, better results will likely be obtained if these blocks aremicrolevelled separately. If one is attempting to remove wider level shifts, across swaths of lines,then the average width of the swath should be specified instead.


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Flight Line DirectionThe nominal flightline direction is required so that the directional filtering incorporated in thedecorrugation process has the correct orientation. Survey blocks flown with different linedirections should be microlevelled separately.

Grid Cell Size for GriddingThe cell size chosen should be small enough so that the residual flightline noise represented in thegrid of original data is well-defined on a survey line basis. Thus, a grid cell size of ¼ the linespacing or smaller is recommended. However, a cell size that is too small (i.e., less than 1/10 theline spacing) will not improve the microlevelling results, and will increase the processing timerequired.

Decorrugation cut-off wavelengthThis parameter defines the cut-off wavelength of the sixth-order, high-pass Butterworth filter, thatis combined with a directional cosine filter (power of 0.5) oriented perpendicular to the flightlinedirection, to extract the residual flightline noise component from the grid of the original data. Awavelength of four times the line spacing has typically proven to produce the best results. Settingthis wavelength too small will not give the filter enough width to isolate the effect of eachflightline. Setting it too large will extract more geological signal than necessary.

Microlevelling Parameters

Once decorrugation has been applied, it is recommended that the decorrugation grid be reviewedand compared to the original data. This is best done by shaded relief imaging. The purpose is to:

� Ensure that the parameters chosen when decorrugation was applied have properly isolatedthe residual flightline noise.

� Measure the amplitudes (e.g. determine the peak-to-trough amplitude variations betweenthe survey lines) and wavelengths (in the flightline direction) of the residual flightlinenoise, from the decorrugation grid.

Amplitude limit valueThe amplitude limit defines the value estimated by the user as the maximum amplitude of theresidual flight line noise in a survey. If the absolute value of the decorrugation noise channelexceeds the specified amplitude for a given record, then it will be clipped to that value, or zeroed,depending on the mode chosen. This is one of the techniques employed to separate residualflightline noise from geological signal. It is assumed than any responses of higher amplitudereflect geology.

The user should also consider the sources of noise for the particular survey that is beingmicrolevelled. When considering aeromagnetic data, the noise amplitudes produced by somesources (e.g. diurnal variation) are not affected by the geological signal of an area, whereas thenoise amplitudes from others (e.g. height variations) are affected by the geology, particularlywhere the magnetic gradients are strong.

If the user does not want to apply an amplitude limit, than a large value, exceeding the dynamicrange of the decorrugation noise channel, should be specified. This dynamic range can bedetermined from the channel statistics.


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Amplitude Limit ModeThere are two choices for the amplitude limit mode:

Zero mode – This will set any value in the decorrugation noise channel, whose absolute valueexceeds the specified amplitude limit value, to zero prior to application of the non-linear filter.This is suited to areas where the responses exhibit steep gradients (e.g. magnetic survey over near-surface igneous and metamorphic rocks). It has the effect of dividing a simple, high amplituderesponse into three parts: two flanks centred on a zeroed section, allowing a shorter non-linearfilter wavelength to be applied, if appropriate. It also reduces the possibility of this filter distortinga response whose wavelength is close to the filter wavelength.

Clip Mode – This will set any value in the decorrugation noise channel, whose absolute valueexceeds the specified amplitude limit value, to the amplitude limit value (with appropriate sign)prior to application of the non-linear filter. This is suited to areas where the magnetic responsesexhibit shallow gradients (e.g. magnetic survey over sedimentary terrain). It is also applied wherethe wavelengths of the residual flightline noise in the line direction are clearly much greater thanthose of the geological signal in the decorrugation noise grid.

Naudy Filter LengthThe Naudy non-linear low pass filter (Naudy and Dreyer, 1968) is used due to its superior qualitiesfor either accepting or rejecting responses beyond the specified filter length. A linear filter, incontrast, would smear an undesirable, short wavelength response into the filtered data, rather thancompletely remove it. It is applied to the amplitude-limited noise channel, to remove anyremaining geological signal. The filter length is set to half the length of the shortest linear noisesegments visible in the decorrugation noise grid. In most situations, the lengths of these noisesegments will still be considerably larger than the wavelengths of geological signal. The exceptionoccurs where there is strong signal due to geology (e.g. magnetic dykes) that strike subparallel tothe line direction. In such cases, it is wise to choose a fairly long filter length for the first pass ofmicrolevelling, and then shorten the filter length for any subsequent microlevelling applied only tosurvey lines (or parts thereof) where problems remain.

Naudy Filter ToleranceThis parameter sets the amplitude below which the filter will not alter the data. Formicrolevelling, it is recommended that this value be set quite small (e.g. 0.001 nT for magneticdata) as otherwise, the filtered noise channel may contain low amplitude, high frequency chatterthat will then be introduced into the microlevelled channel when the correction is applied.

Quality ControlOnce the microlevelling process has been applied, it is instructive to study five parameters, both inprofile and gridded form: original unmicrolevelled data, decorrugated noise, amplitude-limitednoise, non-linear filtered noise (i.e. microlevel correction) and microlevelled data. This will allowthe user to determine if separation of residual flightline noise from geological signal is satisfactory,and whether any levelling problems remain.

Shaded relief imaging of the total magnetic field and its residual component and/or 1st/2nd verticalderivatives will verify that the residual line noise has been minimised, and that new line noise has


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not been introduced. A grid of the microlevel correction will confirm that geological signal hasnot been removed.

GSC Levelling

In 1989, as part of the requirements for the contract with the Ontario Geological Survey (OGS) tocompile and level all existing GSC aeromagnetic data (<1989) in Ontario, PGW developed arobust method to level the magnetic data of various base levels to a common datum provided bythe Geological Survey of Canada (GSC) as 812.8 m grids. The essential theoretical aspects of thelevelling methodology were fully discussed in Gupta et al. (1989), and Reford et al. (1990). Themethod was later applied to the remainder of the GSC data across Canada and the high-resolutionAMEM surveys flown by the OGS (Ontario Geological Survey, 1996).

Terminology:

Master grid – refers to the 200 metre Ontario magnetic grid compiled and levelled to the 812.8metre magnetic datum from the Geological Survey of Canada.

GSC levelling – the process of levelling profile data to a master grid, first applied to GSC data.

Intra-survey levelling or microlevelling – refer to the removal of residual line noise describedearlier in this chapter; the wavelengths of the noise removed are usually shorter than tie linespacing.

Inter-survey levelling or levelling – refer to the level adjustments applied to a block of data; theadjustments are the long wavelength (in the order of tens of kilometres) differences with respect toa common datum, in this case, the 200 metre Ontario master grid, which was derived from all pre-1989 GSC magnetic data and adjusted, in turn, by the 812.8 metre GSC Canada wide grid.


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Ontario Master Aeromagnetic Grid (Ontario Geological Survey, 1999). The outline for the sample dataset tobe levelled (Vickers) is shown.

The GSC Levelling Methodology

Several data processing procedures are assumed to be applied to the survey data prior to levelling,such as microlevelling, IGRF calculation and removal. The final levelled data is gridded at 1/5 ofthe line spacing. If a survey was flown as several distinct blocks with different flight directions,then each block is treated as an independent survey.

1.Create an upward continuation of the survey grid to 305m

Almost all recent surveys (1990 and later) to be compiled were flown at a nominal terrainclearance of 100 metres or less. The first step in the levelling method is to upward continue thesurvey grid to 305 metres, the nominal terrain clearance of the Ontario master grid. The grid cellsize for the survey grids is set at 100 metres. Since the wavelengths of level corrections will begreater than 10 to 15 kilometres, working with 100 metre or even 200 metre grids at this stage willnot affect the integrity of the levelling method. Only at the very end, when the level corrections areimported into the databases, will the level correction grids be regridded to 1/5 of line spacing.

The unlevelled 100 metre grid is extended by at least 2 grid cells beyond the actual surveyboundary, so that, in the subsequent processing, all data points are covered.

2. Create a difference grid between the survey grid and the Ontario master grid


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The difference between the upward continued survey grid and the Ontario master grid, regridded at100 metres, is computed. The short wavelengths represent the higher resolution of the survey grid.The long wavelengths represent the level difference between the two grids.

Difference grid (difference between survey grid and master grid), Vickers survey.

3. Rotate difference grid so that flight line direction is parallel to grid column or row, if necessary.

4. Apply a first pass of a non-linear filter (Naudy and Dreyer, 1968) of wavelength on the order of15 to 20 kilometres along the flight line direction. Reapply the same non-linear filter across theflight line direction.

5. Apply a second pass of a non-linear filter of wavelength on the order of 2000 to 5000 metresalong the flight line direction. Reapply the same non-linear filter across the flight line direction.

6. Rotate the filtered grid back to its original (true) orientation.


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Difference grid after application on non-linear filtering, Vickers Survey.

7. Apply a low pass filter to the non-linear filtered grid

Streaks may remain in the non-linear filtered grid, mostly caused by edge effects. They must beremoved by a frequency-domain, low pass filter with the wavelengths in the order of 25kilometres.

Level correction grid, Vickers Survey.

8. Regrid to 1/5 line spacing and import level corrections into database.


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9. Subtract the level correction channel from the unlevelled channel to obtain the level correctedchannel.

10. Make final grid using minimum curvature gridding algorithm with grid cell size at 1/5 of linespacing.

Total Magnetic field and Second Vertical Derivative Grids

For most surveys the reprocessed total field magnetic grid was calculated from the finalreprocessed profiles by a minimum curvature algorithm (Briggs, 1974). The accuracy standard forgridding is that the grid values fit the profile data to within 1 nT for 99.98% of the profile datapoints. The average gridding error is well below 0.1 nT.

Minimum curvature gridding provides the smoothest possible grid surface that also honours theprofile line data. However, sometimes this can cause narrow linear anomalies cutting across flightlines to appear as a series of isolated spots.

The second vertical derivative of the total magnetic field was computed to enhance small and weaknear-surface anomalies and as an aid to delineate the contacts of the lithologies having contrastingsusceptibilities. The location of contacts or boundaries is usually traced by the zero contour of thesecond vertical derivative map.

An optimum second vertical derivative filter was designed using Wiener filter theory and matchedto the data (Gupta and Ramani, 1982) of individual survey areas. First, the radially averagedpower spectrum of the total magnetic field was computed and a white noise power was chosen bytrial and error. Second, an optimum Wiener filter was designed for the radially averaged powerspectrum. Third, a cosine-squared function was then applied to the optimum Wiener filter toremove the sharp roll-off at higher frequencies.

The radial frequency response of the optimum second vertical derivative filter is given by:

H2VD(f) = (2f*π)2*(1-exp(-x(f)))

Where x(f) is the logarithmic distance between the spectrum and the selected white noise.


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Survey Specific Parameters

The following decorrugation and microlevelling parameters were used in the Schreiber survey:No microlevelling was required.

The following GSC levelling parameters were used in the Schreiber survey:Distance to upward continue: 275 metresFirst pass non-linear filter length: 10000 metresSecond pass non-linear filter length: 5000 metresLow pass filter cut-off wavelength: 15000 metresComments: lmag_final channel was used to calculate the mag_gsclev channel.


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7) FINAL PRODUCTS

� Residual magnetic field contours with labelled EM anomalies, flight path and topographic dataplot files at a scale of 1:20,000.

� Shaded colour calculated second vertical magnetic derivative, Keating correlation coefficientsand topographic data plot files at a scale of 1:50,000.

� Resistivity (mid-frequency 4891 Hz) with EM anomalies and topographic data plot files at ascale of 1:50,000.

� Residual magnetic field with EM anomalies and topographic data plot files at a scale of1:50,000.

� EM anomaly data base in Geosoft GDB format and CSV format.� Profile archive in Geosoft GDB format and flat ASCII format.� Keating coefficients in Geosoft GDB format and CSV format.� Digital terrain model, residual magnetics (two sensors), GSC levelled magnetic field ,measured

vertical magnetic gradient, second vertical magnetic derivative field (two sensors), secondvertical derivative of the GSC levelled magnetic field, apparent resistivity from low, mid andhigh frequency data in Geosoft .GRD and .GXF format.

� GeoTIFF files of the residual magnetic, second vertical magnetic derivative and mid-frequencyapparent resistivity all combined with the topographic base data.

� Vector files of flight path, EM anomalies, Keating coefficients, residual magnetic contours andmid-frequency apparent resistivity in DXF format.

� Survey report in Word and PDF format.


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8) QUALITY ASSURANCE AND QUALITY CONTROL

Quality assurance and quality control (QA/QC) were undertaken by the survey contractor (FugroAirborne Surveys), by PGW (as OTH Geophysicist), and by MNDM. Stringent QA/QC wasemphasized throughout the project so that the optimal geological signal was measured, archivedand presented.

Survey Contractor

Test Data

Data were acquired for each system at the Reid-Mahaffy test site following the instructions of theMNDM and the OTH Geophysicist. These data were examined and approved by the OTHGeophysicist before survey data acquisition began.

Data Acquisition

On-site quality checks included the following;

� inspect all analog charts to identify problems such as individual channel noise, harmonics,and birdswing/swoop oscillations

� ensure that all analogs have proper and sufficient labelling and annotations� analyse, summarize and store all survey calibration information� systematically annotate and confirm the completeness of all digital flight data and magnetic

base station data, video recordings, magnetic base station data, and flight analogue charts� maintain a logbook of all surveying progress and equipment histories� create and plot post flight analog profiles from the master database as required� at regular intervals, current databases and accompanying files and reports were shipped to

High-Sense’s head office for further QA/QC and continued processing� provide database information to the OTH QC/QA inspection team in Geosoft OASIS

format for their inspection� transcribe raw sampled airborne geophysical data into the master database� adjust channels for time lag as determined by pre-survey tests and calibrations� differentially correct all airborne GPS data and confirm complete coverage of the GPS data

with the master database� inspect the GPS height and produce DEM plots� compute X,Y coordinates in UTM’s create and plot plan views of flight path� inspect all survey lines for adherence to technical specifications regarding line separation,

coverage, and overlap of re-flight lines� verify that base station magnetic data covers the time that airborne data was collected� inspect base station data for adherence to allowable diurnal variation and flag re-flights

where necessary� remove spikes from diurnal data and apply a long wavelength filter� convert radar altimeter data to metres and remove any spikes� calculate traverse-tie line altitude intersection file to ensure that the ground clearance

variations are within the survey specifications


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� use pre and post-flight barometric calibrations to remove daily drift from the barometricaltimeter

� inspect the barometric data remove any spikes and apply a long wavelength filter� visually inspect profiles of the radar, barometric, and GPS altimeters� compute, grid, and compare the DEM calculated from the GPS and radar, with that

calculated from the barometric altimeter and the radar� inspect profiles of raw airborne magnetic data and the fourth difference channel and

remove spikes� grid raw magnetic data and diurnally corrected magnetic data and compare� when survey is complete compute levelling network, apply to magnetic data, grid and

examine, compute and examine second vertical derivative� daily Q coil measurements were recorded and charted to ensure the consistency of all five

frequencies from flight to flight� examine raw EM profiles in ppm for noise harmonics and sferics� remove noise where possible filter and level EM data to produce apparent resistivity grids

which can be examined� compile master grids of all survey data as survey progresses to ensure quality between

flights is acceptable

Office Processing

The office processing was conducted by four data processors; two of them worked as fieldprocessors during the acquisition of the data and ensured continuity with office processing. Tocheck the field data, grids were computed from field data channels and were examined for errors.Flight path was verified by comparison with the video and published topographic maps. Thepositional data were converted to the NTv2 co-ordinates by one processor and the results werecopied into databases for all data processors. The upper and lower magnetic data were processedindependently using the same techniques by two data processors. The results were compared andused to detect errors. The levelling of the electromagnetic data was completed by two dataprocessors using exaggerated scales on profile plots of the data and colour resistivity grids. High-Sense’s RTI-CAD was used to produce on screen colour grids that were shadowed to exaggerateany levelling problems in the magnetic and electromagnetic data. The various steps in processingwere checked by other members of the processing team, and two senior geophysicists monitoredthe entire process. Statistical analysis of all final data channels was computed and examined on aline by line basis for the entire data set to ensure that all data was satisfactory.


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OTH Geophysicist

The OTH Geophysicist conducted on-site inspections during data acquisition, focusing initially onthe data acquisition procedures, base station monitoring and instrument calibration. As data wascollected, it was reviewed for adherence to the survey specifications and completeness. Anyproblems encountered during data acquisition were discussed and resolved.

The QA/QC checks included the following:

Navigation Data� appropriate location of the GPS base station� flight line and control line separations were maintained, and deviations along lines were

minimized� verified synchronicity of GPS navigation and flight video� all boundary control lines were properly located� terrain clearance specifications were maintained� aircraft speed remained within the satisfactory range� area flown covered the entire specified survey area� differentially-corrected GPS data did not suffer from satellite-induced shifts or dropouts� GPS height and radar/laser altimeter data were able to produce an image-quality DEM� GPS and geophysical data acquisition systems were properly synchronized� GPS data were adequately sampled

Magnetic Data� appropriate location of the magnetic base station, and adequate sampling of the diurnal

variations� heading error and lag tests were satisfactory� magnetometer noise levels were within specifications� magnetic diurnal variations remained within specifications� magnetometer drift was minimal once diurnal and IGRF corrections had been applied� spikes and/or drop-outs were minimal to non-existent in the raw data� filtering of the profile data was minimal to non-existent� in-field levelling produced image-quality grids of total magnetic field and higher-order

products (e.g. second vertical derivative)

Frequency-domain Electromagnetic Data� selected transmitter-receiver coil configurations and frequencies were appropriate for the

local geology� data behaved consistently between coil pairs� digital and analog phase and gain remained consistent� noise levels were within specifications, and system noise was minimized� bird swing and orientation noise was not evident� sferics and other spikes were minimal (after editing)� cultural (60 Hz) noise was not excessive� regular tests were conducted to monitor system drift and ensure proper zero levels� filtering of the profile data was minimal


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� in-field processing produced image-quality images of individual channels and apparentresistivities for all coplanar coil pairs.

The OTH Geophysicist reviewed interim and final digital and map products throughout the datacompilation phase, to ensure that noise was minimized and that the products adhered to the OTHspecifications. This typically resulted in several iterations before all digital products wereconsidered satisfactory. Considerable effort was devoted to specifying the data formats, andverifying that the data adhered to these formats.

MNDM

MNDM prepared all of the base map and map surround information required for the digital andhard copy maps. This ensured consistency and completeness for all of the OTH geophysical mapproducts. For Schreiber, the base map was constructed from digital files of the 1:20,000 OBM mapseries.

MNDM worked with the OTH Geophysicist to ensure that the digital files adhered to the specifiedASCII and binary file formats, that the file names and channel names were consistent, and that allrequired data were delivered on schedule. The map products were carefully reviewed in digital andhard copy form to ensure legibility and completeness.


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REFERENCES

Akima, H. 1970. A new method of interpolation and smooth curve fitting based on localprocedures; Journal of Association for Computing Machinery, vol. 17, p. 589 - 602.

Briggs, Ian, 1974, Machine contouring using minimum curvature, Geophysics, v.39, pp.39 - 48.

Fairhead, J. Derek, Misener, D. J., Green, C. M., Bainbridge, G. and Reford, S.W. 1997: LargeScale Compilation of Magnetic, Gravity, Radiometric and Electromagnetic Data: The NewExploration Strategy for the 90s; Proceedings of Exploration 97, ed. A. G. Gubins, p.805-816.

Fraser, D.C. 1972. A new multicoil aerial electromagnetic prospecting system; Geophysics, vol. 37, p.518 - 537.

Fraser, D.C. 1978. Resistivity mapping with an airborne multicoil electromagnetic system;Geophysics, vol. 43, p. 144 - 172.

Gupta, V., Paterson, N., Reford, S., Kwan, K., Hatch, D., and Macleod, I., 1989, Single masteraeromagnetic grid and magnetic colour maps for the province of Ontario: in Summary of fieldwork and other activities 1989, Ontario Geological Survey Miscellaneous Paper 146, pp.244-250.

Gupta, V. and Ramani, N., 1982, Optimum second vertical derivatives in geological mapping andmineral exploration, Geophysics, v.47, pp. 1706-1715.

Gupta, V., Rudd, J. and Reford, S., 1998, Reprocessing of thirty-two airborne electromagneticsurveys in Ontario, Canada: Experience and recommendations, 68th Annual Meeting of theSociety of Exploration Geophysicists, Extended Technical Abstracts, p.2032-2035.

Keating, P.B. 1995, A simple technique to identify magnetic anomalies due to kimberlite pipes;Exploration and Mining Geology, vol. 4, no. 2, p. 121 - 125.

Minty, B. R. S., 1991, Simple micro-levelling for aeromagnetic data, Exploration Geophysics, v.22, pp. 591-592.

Naudy, H. and Dreyer, H., 1968, Essai de filtrage nonlinéaire appliqué aux profilesaeromagnétiques, Geophysical Prospecting, v. 16, pp.171-178.

Ontario Geological Survey, 1996, Ontario airborne magnetic and electromagnetic surveys,processed data and derived products: Archean and Proterozoic “greenstone” belts – MatachewanArea, ERLIS Data Set 1014.

Ontario Geological Survey, 1997, Ontario airborne magnetic and electromagnetic surveys,processed data and derived products: Archean and Proterozoic “greenstone” belts – Black River-Matheson Area, ERLIS Data Set 1001.


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Ontario Geological Survey, 1999, Single master gravity and aeromagnetic data for Ontario, ERLISData Set 1036.

Reford, S.W., Gupta, V.K., Paterson, N.R., Kwan, K.C.H., and Macleod, I.N., 1990, Ontariomaster aeromagnetic grid: A blueprint for detailed compilation of magnetic data on a regionalscale: in Expanded Abstracts, Society of Exploration Geophysicists, 60th Annual InternationalMeeting, San Francisco, v.1., pp.617-619.


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APPENDIX A TESTING AND CALIBRATION

The electromagnetic system utilizes a multi-coil coaxial/coplanar technique to energize conductors indifferent directions. The coaxial coils are vertical with their axes in the flight direction. The coplanarcoils are horizontal. The secondary fields are sensed simultaneously by means of receiver coils whichare maximum coupled to their respective transmitter coils. The system yields an in-phase and aquadrature channel from each transmitter-receiver coil-pair.

The electromagnetic calibration procedure involves four stages; primary field bucking, phasecalibration, gain calibration, and zero adjust. At the beginning of the survey, the primary field ateach receiver coil is cancelled, or “bucked out”, by precise positioning of five bucking coils.

The phase calibration adjusts the phase angle of the receiver to match that of the transmitter. Theinitial phase calibration is conducted with a ferrite bar on the ground, and subsequent calibrationsare conducted in the air using a calibration coil in the bird. A ferrite bar, which produces a purelyin-phase anomaly, is positioned near each receiver coil. The bar is rotated from minimum tomaximum field coupling and the responses for the in-phase and quadrature components for eachcoil-pair/frequency are measured. The phase of the response is adjusted at the console to return anin-phase only response for each coil-pair. Phase checks are performed as required.

The ferrite bar phase calibrations measure a relative change in the secondary field, rather than anabsolute value. This removes any dependency of the calibration procedure on the secondary fielddue to the ground, except under circumstances of extreme ground conductivity

Calibrations of the gain, phase and the system zero level are performed in the air before, and aftereach flight. The system is flown to an altitude high enough to be out of range of any secondaryfield from the earth (the altitude is dependent on ground resistivity) at which point the zero, or baselevel of the system is measured. Calibration coils in the bird are activated for each frequency inturn by closing a switch to form a closed circuit through the coil. The transmitter induces a currentin this loop, which creates a secondary field in the receiver of precisely known phase andamplitude. The inphase and quadrature values produced by the calibration test were recorded foreach frequency. This was charted for the duration of the survey and is presented in Table 3. Adeviation in excess of 0.3 ppm from a previous test result would indicate a calibration problem.The bird would have another phase and calibration done and another test at altitude would beconducted.

Several systems tests were performed before the start of the survey. These included a heading testand lag test.

Magnetic Heading Test

The magnetic system was flown in the four cardinal directions over the same point on the ground. Themagnetic data were then diurnal corrected and lagged. The data were compared and the differenceswere calculated. The results are presented in Table 1.


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Table 1

Magnetic Heading Test Upper MagLine # Direction Fiducial Raw Mag Diurnal MAGDL (diur+lag corr.) Difference

nT nT nT metres nT1 N 8460.8 58178.80 58236.10 58204.57 66.352 S 8215.7 58221.39 58236.12 58228.47 56.36 23.93 E 8357.1 58164.98 58235.99 58193.36 54.224 W 8102.2 58168.67 58237.42 58194.32 58.80 .48

Magnetic Heading Test Lower MagLine # Direction Fiducial Raw Mag Diurnal MAGDL (diur+lag corr.) Difference

nT nT nT metres nT1 N 8460.8 58163.65 58236.10 58184.50 66.352 S 8215.7 58218.82 58236.12 58218.06 56.36 33.53 E 8357.1 58146.27 58235.99 58169.86 54.224 W 8102.2 58150.37 58237.42 58171.14 58.80 1.28

Lag Test

The aircraft was flown at low altitudes in opposite directions over a sharp magnetic anomaly (metalrailway tracks) with the navigation system and magnetometer recording. The position of themagnetic high is determined from the navigation system for each line direction. The numericaldifference in position is the 2-way or total lag. The lag to be applied in each direction is the valuedivided by two. The lag value is 0.6 seconds (6 scans). The results are presented in Table 2.

Table 2

Line Positional FidPick

Digital Fid Pick Difference in Fids Lag (s)

1 8460.4 8461.7 1.3 1.32 8218.1 8219.4 1.3 1.3

Electromagnetic System - Internal Calibration Records

The EM system is electronically and physically complex and requires constant attention forsuccessful operation. The system was monitored using built-in internal calibration coils. Theequipment operator and field quality controller monitored these for each flight. The records arecontained in table 3.


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Table 3

Electromagnetic System - Internal Calibration RecordsFlt # Date Time L9XI L9XQ M4XI M4XQ L8PI L8PQ M4PI M4PQ H3PI H3PQCalib 07-Nov 1.9 1.7 2.0 2.0 1.9 1.8 1.7 1.6 2.0 1.7

1 11-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.71 11-Nov end 1.9 1.7 2.0 2.0 1.9 1.8 1.6 1.5 2.0 1.72 12-Nov start 1.9 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.72 12-Nov end 1.9 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.73 12-Nov start 1.8 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.73 12-Nov end 1.9 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.74 14-Nov start 1.9 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.74 14-Nov end 1.9 1.7 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.75 14-Nov start 1.9 1.9 2.1 2.0 1.9 1.8 1.7 1.6 2.0 1.75 14-Nov end 1.9 1.7 2.0 2.0 1.9 1.8 1.7 1.6 2.0 1.76 15-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.76 15-Nov end 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.77 15-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.77 15-Nov end 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.78 15-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.78 15-Nov end 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.79 16-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.79 16-Nov end 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.7

10 16-Nov start 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.710 16-Nov end 1.9 1.7 2.1 2.0 1.8 1.8 1.7 1.6 2.0 1.711 18-Nov start 1.9 1.7 2.0 2.0 1.8 1.8 1.7 1.6 2.1 1.711 18-Nov end 1.8 1.7 2.0 2.0 1.8 1.8 1.7 1.6 2.0 1.712 20-Nov start 1.9 1.7 1.9 1.9 1.9 1.8 1.7 1.7 2.0 1.612 20-Nov end 1.9 1.7 1.9 1.8 1.8 1.7 1.7 1.7 2.1 1.713 20-Nov start 1.9 1.6 1.9 1.8 1.8 1.9 1.8 1.7 2.1 1.613 20-Nov end 1.9 1.7 1.9 1.8 1.8 1.8 1.7 1.7 2.1 1.614 20-Nov start 1.9 1.7 1.9 1.8 1.8 1.8 1.7 1.7 2.1 1.614 20-Nov end 1.9 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.1 1.615 23-Nov start 1.9 1.6 1.9 1.8 1.8 1.8 1.7 1.5 2.1 1.615 23-Nov end 1.8 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.1 1.616 24-Nov start 1.9 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.1 1.616 24-Nov end 1.9 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.1 1.717 24-Nov start 1.9 1.8 1.9 1.8 1.8 1.8 1.7 1.7 2.1 1.617 24-Nov end 1.9 1.7 2.0 1.8 1.8 1.8 1.7 1.7 2.1 1.618 25-Nov start 1.9 1.8 1.9 1.8 1.8 1.8 1.8 1.7 2.1 1.618 25-Nov end 1.9 1.8 1.9 1.7 1.8 1.8 1.7 1.7 2.1 1.619 25-Nov start 1.9 1.6 2.0 1.8 1.8 1.8 1.8 1.7 2.1 1.619 25-Nov end 1.8 1.7 1.9 1.8 1.8 1.8 1.7 1.7 2.1 1.620 27-Nov start 1.8 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.0 1.920 27-Nov end 1.8 1.7 1.9 1.8 1.8 1.9 1.8 1.7 2.0 1.921 27-Nov start 1.8 1.7 2.0 1.8 1.9 1.8 1.8 1.7 2.0 1.921 27-Nov end 1.8 1.7 1.9 1.8 1.8 1.9 1.8 1.7 2.0 2.022 28-Nov start 1.8 1.7 2.0 1.8 1.8 1.9 1.8 1.7 2.0 1.922 28-Nov end 1.8 1.7 2.0 1.9 1.8 1.9 1.8 1.7 2.0 1.923 28-Nov start 1.8 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.0 1.923 28-Nov end 1.8 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.0 1.924 28-Nov start 1.8 1.7 1.9 1.8 1.8 1.9 1.8 1.7 2.0 1.924 28-Nov end 1.8 1.7 1.9 1.8 1.8 1.8 1.8 1.7 2.0 1.925 29-Nov start 1.8 1.7 1.9 1.8 1.8 1.9 1.8 1.7 2.0 1.925 29-Nov end 1.8 1.7 1.9 1.9 1.9 1.9 1.8 1.7 2.0 1.9


35

Flt # Date Time L9XI L9XQ M4XI M4XQ L8PI L8PQ M4PI M4PQ H3PI H3PQ26 29-Nov start 1.9 1.8 1.9 1.8 1.8 1.8 1.8 1.7 2.0 1.926 29-Nov end 1.9 1.8 1.9 1.9 1.8 1.9 1.8 1.7 2.0 1.927 30-Nov start 1.8 1.7 1.9 1.9 1.8 1.8 1.8 1.7 2.0 1.927 30-Nov end 1.8 1.7 1.9 1.9 1.8 1.8 1.8 1.7 2.0 1.928 30-Nov start 1.8 1.7 1.9 1.9 1.8 1.8 1.8 1.7 2.0 1.928 30-Nov end 1.8 1.7 1.9 1.9 1.8 1.8 1.8 1.7 2.0 1.929 30-Nov start 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.929 30-Nov end 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.930 01-Dec start 1.9 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.930 01-Dec end 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.931 01-Dec start 1.8 1.7 2.1 2.0 1.8 1.9 1.8 1.7 2.0 1.931 01-Dec end 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.932 03-Dec start 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.932 03-Dec end 1.8 1.7 2.2 2.0 1.8 1.9 1.8 1.7 2.0 1.933 05-Dec start 1.8 1.7 2.1 2.0 1.8 1.9 1.8 1.7 2.0 1.933 05-Dec end 1.8 1.7 2.1 2.1 1.8 1.9 1.8 1.7 2.0 1.934 05-Dec start 1.8 1.7 2.2 2.1 1.8 1.9 1.8 1.7 2.0 1.934 05-Dec end 1.8 1.8 2.1 2.1 1.8 1.9 1.8 1.7 2.0 1.935 06-Dec start 1.8 1.7 2.2 2.1 1.8 1.8 1.8 1.7 2.0 1.935 06-Dec end 1.8 1.7 2.2 2.1 1.8 1.9 1.8 1.7 2.0 1.936 07-Dec start 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.936 07-Dec end 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.937 07-Dec start 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.937 07-Dec end 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.938 08-Dec start 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.938 08-Dec end 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.939 08-Dec start 1.8 1.7 2.2 2.0 1.8 1.8 1.8 1.7 2.0 1.939 08-Dec end 1.8 1.7 2.1 2.0 1.8 1.8 1.8 1.7 2.0 1.940 09-Dec start 1.9 1.7 2.2 2.0 1.9 1.7 1.8 1.7 2.0 1.940 09-Dec end 1.8 1.7 2.1 2.0 1.9 1.8 1.8 1.7 2.0 1.941 09-Dec start 1.8 1.7 2.1 2.0 1.7 2.0 1.8 1.7 2.0 1.941 09-Dec end 1.8 1.7 2.1 2.0 1.7 2.0 1.8 1.7 2.0 1.942 11-Dec start 1.8 1.7 2.1 2.0 1.8 1.9 1.7 1.7 2.0 1.942 11-Dec end 1.8 1.7 2.1 2.0 1.8 1.9 1.7 1.6 2.0 1.943 12-Dec start 1.8 1.7 2.1 2.0 1.9 1.9 1.7 1.7 2.0 1.943 12-Dec end 1.8 1.7 2.1 1.9 1.9 1.9 1.7 1.6 2.0 1.944 12-Dec start 1.8 1.7 2.1 2.0 1.9 1.8 1.7 1.7 2.0 1.944 12-Dec end 1.8 1.7 2.1 2.0 1.9 1.9 1.7 1.7 2.0 1.945 12-Dec start 1.8 1.7 2.1 1.9 1.9 1.9 1.7 1.7 2.0 1.945 12-Dec end 1.8 1.7 2.1 2.0 1.9 1.9 1.7 1.7 2.1 1.946 13-Dec start 1.8 1.7 2.0 1.9 1.9 1.9 1.7 1.7 2.0 1.946 13-Dec end 1.8 1.7 2.0 1.9 1.9 1.9 1.7 1.7 2.0 1.947 13-Dec start 1.8 1.7 2.0 1.9 1.9 1.9 1.7 1.7 2.0 1.947 13-Dec end 1.8 1.6 2.0 1.8 1.9 1.9 1.7 1.7 2.0 1.948 14-Dec start 1.6 1.6 1.9 1.9 1.8 1.9 1.7 1.7 2.0 1.948 14-Dec end 1.7 1.6 1.9 1.9 1.8 1.9 1.7 1.7 2.0 1.949 14-Dec start 1.7 1.6 2.0 1.8 1.8 1.9 1.7 1.7 2.0 1.949 14-Dec end 1.7 1.6 1.9 1.8 1.9 1.9 1.7 1.8 2.0 1.950 16-Dec start 1.7 1.7 1.9 2.0 1.9 2.0 1.7 1.8 1.9 1.950 16-Dec end 1.7 1.7 1.9 2.0 1.8 1.9 1.7 1.7 1.9 1.951 17-Dec start 1.7 1.7 1.9 2.0 1.8 2.0 1.7 1.8 1.9 1.951 17-Dec end 1.7 1.7 1.9 2.0 1.8 2.0 1.7 1.8 1.9 1.952 17-Dec start 1.7 1.7 1.9 2.0 1.8 1.8 1.7 1.8 1.9 1.953 17-Dec start 1.7 1.7 1.9 2.0 1.8 1.9 1.7 1.8 1.9 1.9


36

Flt # Date Time L9XI L9XQ M4XI M4XQ L8PI L8PQ M4PI M4PQ H3PI H3PQ53 17-Dec end 1.7 1.7 1.9 2.0 1.8 1.8 1.7 1.8 1.9 1.954 18-Dec start 1.7 1.7 1.9 2.0 1.9 1.8 1.7 1.8 2.0 1.955 18-Dec start 1.7 1.7 1.9 2.0 1.9 1.8 1.7 1.8 2.0 1.955 18-Dec end 1.7 1.6 1.9 1.9 1.9 1.8 1.7 1.8 2.0 1.956 21-Dec start 1.7 1.7 1.9 2.0 2.0 1.6 1.7 1.8 1.9 1.956 21-Dec end 1.7 1.7 1.9 2.0 2.0 1.6 1.7 1.8 1.9 1.957 21-Dec start 1.7 1.7 1.9 2.0 2.0 1.6 1.7 1.8 1.9 1.957 21-Dec end 1.7 1.8 1.9 2.0 2.0 1.6 1.7 1.8 1.9 1.958 22-Dec start 1.7 1.7 1.9 2.0 2.0 1.7 1.7 1.9 1.9 1.958 22-Dec end 1.7 1.7 1.9 2.0 2.0 1.6 1.7 1.9 1.9 1.959 07-Jan start 1.8 1.6 2.0 2.0 1.9 1.8 1.7 1.8 1.9 1.959 07-Jan end 1.8 1.6 2.0 2.0 1.8 1.8 1.7 1.8 1.9 1.960 07-Jan start 1.8 1.6 2.0 2.1 1.8 1.8 1.7 1.8 1.9 1.960 07-Jan end 1.8 1.6 2.0 2.1 1.8 1.8 1.7 1.8 1.9 1.961 08-Jan start 1.8 1.6 2.1 2.1 1.8 1.8 1.6 1.6 2.0 1.961 08-Jan end 1.7 1.6 2.1 2.1 1.8 1.9 1.6 1.6 2.0 1.962 09-Jan start 1.7 1.6 2.1 2.1 1.8 1.9 1.6 1.6 2.0 1.962 09-Jan end 1.7 1.6 2.1 2.0 1.8 1.9 1.6 1.6 2.0 1.963 09-Jan start 1.7 1.6 2.1 2.1 1.8 1.9 1.6 1.6 2.0 1.963 09-Jan end 1.7 1.6 2.1 2.1 1.8 1.8 1.6 1.6 2.0 1.964 11-Jan start 1.7 1.6 2.1 2.1 1.8 1.8 1.6 1.6 2.0 1.964 11-Jan end 1.7 1.6 2.1 2.1 1.8 1.9 1.6 1.6 2.0 1.965 12-Jan start 1.7 1.7 2.1 2.2 1.8 1.9 1.6 1.7 1.9 1.965 12-Jan end 1.7 1.7 2.1 2.1 1.7 1.9 1.7 1.7 1.9 1.966 12-Jan start 1.7 1.7 2.1 2.2 1.7 1.9 1.6 1.7 1.9 1.966 12-Jan end 1.7 1.7 2.1 2.2 1.7 1.9 1.6 1.7 1.9 1.967 12-Jan start 1.7 1.7 2.1 2.2 1.7 1.9 1.6 1.7 1.9 1.968 13-Jan start 1.7 1.7 2.1 2.2 1.7 1.9 1.6 1.7 1.9 1.968 13-Jan end 1.7 1.7 2.0 2.2 1.7 1.9 1.6 1.7 1.9 1.969 13-Jan start 1.7 1.7 2.2 2.2 1.7 1.9 1.6 1.7 1.9 1.969 13-Jan end 1.7 1.7 2.2 2.2 1.7 1.9 1.6 1.7 1.9 1.970 14-Jan start 1.7 1.7 2.2 2.2 1.8 1.9 1.6 1.7 1.9 1.970 14-Jan end 1.7 1.7 2.2 2.1 1.7 1.9 1.6 1.7 1.9 1.971 14-Jan start 1.7 1.7 2.2 2.1 1.7 1.9 1.6 1.7 1.9 1.971 14-Jan end 1.7 1.7 2.2 2.1 1.7 1.9 1.6 1.6 1.9 1.9


37

APPENDIX B PROFILE ARCHIVE DEFINITION

Survey 1104 was carried out using the frequency-domain High-Sense Aerodat electromagnetic andmagnetic system, mounted on a helicopter platform.

Data File LayoutThe files for the Schreiber Geophysical Survey 1104 are archived as a 6 CD set, with the filecontent divided as follows:

CD – 1104a- ASCII (GXF) grids.- EM anomaly database (CSV format)- Keating correlation (kimberlite) database (CSV format)- DXF files of entire survey block at 1/50,000 for:

- Flight path- EM anomalies- Keating correlation (kimberlite) anomalies- Total field magnetic contours- Apparent resistivity (4891 Hz) contours

- GEOTIFF images (200 dpi) of the entire survey block at 1/50,000 for:- Total field colour magnetics with base map- Colour shaded relief of 2nd vertical derivative with base map- Colour apparent resistivity (4891 Hz) with base map.

- Project report (Word97 and PDF formats)

CD – 1104b- Geosoft binary (GRD) grids.- EM anomaly database (GDB format)- Keating correlation (kimberlite) database (GDB format)- DXF files of entire survey block at 1/50,000 for:

- Flight path- EM anomalies- Keating correlation (kimberlite) anomalies- Total field magnetic contours- Apparent resistivity (4891 Hz) contours

- GEOTIFF images (200 dpi) of the entire survey block at 1/50,000 for:- Total field colour magnetics with base map- Colour shaded relief of 2nd vertical derivative with base map- Colour apparent resistivity (4891 Hz) with base map.

- Project report (Word97 and PDF formats)


38

CD – 1104c (2 volumes)- Profile database in ASCII (XYZ) format (flightlines 10-2260)- Profile database in ASCII (XYZ) format (flightlines 2261-3780, tielines 9010-10120)- EM anomaly database (CSV format)- Keating correlation (kimberlite) database (CSV format)- Project report (WORD97 and PDF formats)

CD – 1104d (2 volumes)- Profile database (Geosoft GDB format) (flightlines 10-2260)- Profile database (Geosoft GDB format) (flightlines 2261-3780, tielines 9010-10120)- EM anomaly database (Geosoft GDB format)- Keating correlation (kimberlite) database (Geosoft GDB format)- Project report (WORD97 and PDF formats)

Coordinate SystemsThe profile and electromagnetic anomaly data are provided in four coordinate systems:

� Universal Transverse Mercator (UTM) projection, Zone 16N, NAD27 datum (NTv2) localdatum;

� Universal Transverse Mercator (UTM) projection, Zone 16N, NAD83 datum, NorthAmerican local datum;

� Latitude/longitude coordinates, NAD27 datum (NTv2) local datum; and� Latitude/longitude coordinates, NAD83 datum, North American local datum.

The gridded data are provided in the two UTM coordinate systems.

Line NumberingThe line numbering conventions for survey 1104 are as follows:Flightlines 10 -3780Tielines 9010-9300Boundary Tielines 100010-10120

Profile DataThe profile data are provided in two formats, one ASCII and one binary:

� thschreiber.xyz - flat ASCII file� thschrieber.gdb - Geosoft OASIS montaj binary database file (no compression)

Both file types contain the same set of data channels, summarized as follows:

Channel Name Description Units

flight flight number date local date YYYYMMDD fiducial fiducial number x_nad27 easting in UTM co-ordinates using NAD27 datum metres y_nad27 northing in UTM co-ordinates using NAD27 datum metres z_nad27 elevation in UTM co-ordinates using NAD27 datum metres x_nad83 easting in UTM co-ordinates using NAD83 datum metres y_nad83 northing in UTM co-ordinates using NAD83 datum metres


39


z_nad83 elevation in UTM co-ordinates using NAD83 datum metreslat_nad27 latitude using NAD27 datum degreeslong_nad27 longitude using NAD27 datum degreesgps_x_raw raw GPS X using NAD83 datum metresgps_y_raw raw GPS Y using NAD83 datum metresgps_z_raw raw GPS Z using NAD83 datum metresgps_base_x GPS base station data - X location as WGS84 longitude decimal-degreesgps_base_y GPS base station data - Y location as WGS84 latitude decimal-degreesgps_base_z GPS base station data - Z location as WGS84 latitude decimal-degreesgps_z_asl corrected Z position as height above sea level metres

radar_raw raw terrain clearance of aircraft from radar altimeter metresradar_final corrected terrain clearance of aircraft from radar altimeter metresbaro_raw raw barometric altimeter data metresbaro_final corrected barometric altimeter data metresdem digital elevation model metresmag_base_final corrected magnetic base station data nanoteslasheight_umag upper magnetic sensor height above terrain metresheight_lmag_em lower magnetic and EM sensor height above terrain metres

umag_raw raw magnetic field - upper sensor nanoteslaslmag_raw raw magnetic field - lower sensor nanoteslasumag_edit edited magnetic field - upper sensor nanoteslaslmag_edit edited magnetic field - lower sensor nanoteslasu_igrf local (upper sensor) IGRF field nanoteslasl_igrf local (lower sensor) IGRF field nanoteslasumag_igrf IGRF-corrected magnetic field - upper sensor nanoteslaslmag_igrf IGRF-corrected magnetic field - lower sensor nanoteslasumag_igrf_diurn diurnally-corrected magnetic field - upper sensor nanoteslaslmag_igrf_diurn diurnally-corrected magnetic field - lower sensor nanoteslasumag_lev levelled magnetic field - upper sensor nanoteslaslmag_lev levelled magnetic field - lower sensor nanoteslasumag_final micro-levelled magnetic field - upper sensor nanoteslaslmag_final micro-levelled magnetic field - lower sensor nanoteslaslmag_gsclev GSC levelled magnetic field nanoteslasvg_raw vertical gradient from raw upper and lower mag values nanoteslas/ metrevg_edit vertical gradient from edited upper and lower mag values nanoteslas/ metrevg_lev vertical gradient from levelled upper and lower mag values nanoteslas/ metrevg_final vertical gradient from microlevelled upper and lower mag values nanoteslas/ metrecxi_925_raw raw coaxial inphase at 925 Hz parts per millioncxq_925_raw raw coaxial quadrature at 925 Hz parts per millioncxi_4468_raw raw coaxial inphase at 4468 Hz parts per millioncxq_4468_raw raw coaxial quadrature at 4468 Hz parts per millioncpi_877_raw raw coplanar inphase at 877 Hz parts per millioncpq_877_raw raw coplanar quadrature at 877 Hz parts per millioncpi_4891_raw raw coplanar inphase at 4891 Hz parts per millioncpq_4891_raw raw coplanar quadrature at 4891 Hz parts per millioncpi_33840_raw raw coplanar inphase at 33840 Hz parts per millioncpq_33840_raw raw coplanar quadrature at 33840 Hz parts per millioncxi_925_filt edited and filtered coaxial inphase at 925 Hz parts per millioncxq_925_filt edited and filtered coaxial quadrature at 925 Hz parts per millioncxi_4468_filt edited and filtered coaxial inphase at 4468 Hz parts per millioncxq_4468_filt edited and filtered coaxial quadrature at 4468 Hz parts per million


40


cpi_877_filt edited and filtered coplanar inphase at 877 Hz parts per millioncpq_877_filt edited and filtered coplanar quadrature at 877 Hz parts per millioncpi_4891_filt edited and filtered coplanar inphase at 4891 Hz parts per millioncpq_4891_filt edited and filtered coplanar quadrature at 4891 Hz parts per millioncpi_33840_filt edited and filtered coplanar inphase at 33840 Hz parts per millioncpq_33840_filt edited and filtered coplanar quadrature at 33840 Hz parts per million

cxi_925_lev final levelled coaxial inphase at 925 Hz parts per millioncxq_925_lev final levelled coaxial quadrature at 925 Hz parts per millioncxi_4468_lev final levelled coaxial inphase at 4468 Hz parts per millioncxq_4468_lev final levelled coaxial quadrature at 4468 Hz parts per millioncpi_877_lev final levelled coplanar inphase at 877 Hz parts per millioncpq_877_lev final levelled coplanar quadrature at 877 Hz parts per millioncpi_4891_lev final levelled coplanar inphase at 4891 Hz parts per millioncpq_4891_lev final levelled coplanar quadrature at 4891 Hz parts per millioncpi_33840_lev final levelled coplanar inphase at 33840 Hz parts per millioncpq_33840_lev final levelled coplanar quadrature at 33840 Hz parts per millionpower 60 Hz power line monitor

ares_877 apparent resistivity from coplanar coil pair - 877 Hz ohm metresares_4891 apparent resistivity from coplanar coil pair - 4891 Hz ohm metresares_33840 apparent resistivity from coplanar coil pair - 33840 Hz ohm metresares_877_depth depth from coplanar coil pair - 877 Hz metresares_4891_depth depth from coplanar coil pair - 4891 Hz metresares_33840_depth depth from coplanar coil pair - 33840 Hz metrestime_utc UTC time secondstime_local local time secondslat_nad83 latitude using NAD83 datum decimal-degreeslong_nad83 longitude using NAD83 datum decimal-degreesmag_base_raw raw magnetic base station data nanoteslas

line_number full flightline number (flightline and part numbers)line flightline numberline_part flightline part number


41

APPENDIX C ANOMALY ARCHIVE DEFINITION

Electromagnetic Anomaly DataThe electromagnetic anomaly data are provided in two formats, one ASCII and one binary:

� thscanomaly.csv – ASCII comma-delimited format (Microsoft Excel file)� thscanomaly.gdb – Geosoft OASIS montaj binary database file



x_nad27 easting in UTM co-ordinates using NAD27 datum metresy_nad27 northing in UTM co-ordinates using NAD27 datum metresfiducial fiducialflight flight numberdate local date YYYYMMDDline_number full flightline number (flightline and part numbers)line flightline numberline_part flightline part numberx_nad83 easting in UTM co-ordinates using NAD83 datum metresy_nad83 northing in UTM co-ordinates using NAD83 datum metreslong_nad27 longitude using NAD27 datum decimal-degreeslat_nad27 latitude using NAD27 datum decimal-degreesares_877 apparent resistivity for coplanar transmitter-receiver coil pair - 877 Hz ohm-metresares_4891 apparent resistivity for coplanar transmitter-receiver coil pair - 4891 Hz ohm-metresares_33840 apparent resistivity for coplanar transmitter-receiver coil pair - 33840 Hz ohm-metresares_877_depth apparent depth calculated from coplanar transmitter-receiver coil pair - 877 Hz metresares_4891_depth apparent depth calculated from coplanar transmitter-receiver coil pair - 4891 Hz metresares_33840_depth apparent depth calculated from coplanar transmitter-receiver coil pair - 33840 Hz metrestime_utc UTC time secondstime_local local time seconds after midnightlong_nad83 longitude using NAD83 datum decimal-degreeslat_nad83 latitude using NAD83 datum decimal-degreesheading direction of flight degrees azimuthanomaly_type anomaly classificationanomaly_type_no anomaly classification numbermag_correlation magnetic correlation nanoteslasvert_half-plane_conductance conductance of vertical half-plane model siemensvert_half-plane_depth depth of vertical half-plane model metresdip direction of dipping angle of conductor degrees azimuthcxi_4468_lev levelled coaxial inphase at 4468 Hz parts per millioncxq_4468_lev levelled coaxial quadrature at 4468 Hz parts per millioncpi_4891_lev levelled coplanar inphase at 4891 Hz parts per millioncpq_4891_lev levelled coplanar quadrature at 4891 Hz parts per millioncxi_925_lev levelled coaxial inphase at 925 Hz parts per millioncxq_925_lev levelled coaxial quadrature at 925 Hz parts per millioncpi_877_lev levelled coplanar inphase at 877 Hz parts per millioncpq_877_lev levelled coplanar quadrature at 877 Hz parts per millioncpi_33840_lev levelled coplanar inphase at 33840 Hz parts per millioncpq_33840_lev levelled coplanar quadrature at 33840 Hz parts per millionanomaly_no nth anomaly along the survey linehor_sheet_conductance conductance of horizontal plate model siemenshor_sheet_depth depth of horizontal plate model metres


42


anomaly_id unique anomaly identifierheight_em electromagnetic receiver height metres above terraindem digital elevation model metres above sea level

The unique anomaly identifier (anomaly_id) is a ten digit integer in the format 1LLLLLLAAAwhere 'LLLLLL' holds the line number (and leading zeroes pad short line numbers to six digits).The 'AAA' represents the numeric anomaly identifier (anomaly_no) for that line padded withleading zeroes to three digits. For example, 1000101007 represents the seventh anomaly on Line101. When combined with the survey number (survey_no), the anomaly identifier provides anelectromagnetic anomaly number unique to all surveys archived by the Ontario Geological Survey.

The codes for anomaly_type and anomaly_type_number are as follows:B 1D 2S 3L 4

B: Bedrock - an anomaly whose response matches that of a bedrock conductor, but not thin and/ornear vertical. This anomaly type might include other shapes of conductors: roughly pod-shaped,thick dykes, short strike length bodies, or conductors sub-parallel to the flight path.

D: Dyke - an anomaly whose shape matches that of a steeply dipping thin dyke-like conductor.The thickness appears to be less than about 3 m. These are commonly conductors in steeply-dipping geology, but may also be conductive shear zones.

S: Flat lying conductors - generally surficial. Typical geologic anomalies might be conductiveoverburden, swamps or clay layers. They would not appear to be conductive at depth.

L: Line current - an anomaly with the shape typical of line currents - typically cultural (humansources) such as power lines, train tracks, fences, etc.


43

APPENDIX D GRID ARCHIVE DEFINITION

Gridded Data

The gridded data are provided in two formats, one ASCII and one binary:� *.gxf - ASCII Grid eXchange Format (revision 3.0)� *.grd - Geosoft OASIS montaj binary grid file (no compression)� *.gi - binary file that defines the coordinate system for the *.grd file

The grids are summarized as follows:thscmagu27.grd/.gxf IGRF-corrected magnetic field from the upper magnetic sensor in nanoteslas (UTM

coordinates, NAD27 datum)thscmagu83.grd/.gxf IGRF-corrected magnetic field from the upper magnetic sensor in nanoteslas (UTM

coordinates, NAD83 datum)thscmagl27.grd/.gxf IGRF-corrected magnetic field from the lower magnetic sensor in nanoteslas (UTM

coordinates, NAD27 datum)thscmagl83.grd/.gxf IGRF-corrected magnetic from the field lower magnetic sensor in nanoteslas (UTM

coordinates, NAD83 datum)thscmaggsc27.grd/.gxf GSC levelled magnetic field from the lower magnetic sensor in nanoteslas (UTM

coordinates, NAD27 datum)thscmaggsc83.grd/.gxf GSC levelled magnetic field from the lower magnetic sensor in nanoteslas (UTM

coordinates, NAD83 datum)thscmvg27.grd/.gxf measured vertical magnetic gradient in nanoteslas per metre (UTM coordinates, NAD27

datum)thscmvg83.grd/.gxf measured vertical magnetic gradient in nanoteslas per metre (UTM coordinates, NAD83

datum)thsc2vdu27.grd/.gxf second vertical derivative of the IGRF-corrected magnetic field from the upper magnetic

sensor in nanoteslas per metre squared(UTM coordinates, NAD27 datum)thsc2vdu83.grd/.gxf second vertical derivative of the IGRF-corrected magnetic field from the upper magnetic

sensor in nanoteslas per metre squared (UTM coordinates, NAD83 datum)thsc2vdl27.grd/.gxf second vertical derivative of the IGRF-corrected magnetic field from the lower magnetic

sensor in nanoteslas per metre squared(UTM coordinates, NAD27 datum)thsc2vdl83.grd/.gxf second vertical derivative of the IGRF-corrected magnetic field from the lower magnetic

sensor in nanoteslas per metre squared (UTM coordinates, NAD83 datum)thsc2vdgsc27.grd/.gxf second vertical derivative of the GSC levelled magnetic field from the lower magnetic

sensor in nanoteslas per metre squared(UTM coordinates, NAD27 datum)thsc2vdgsc83.grd/.gxf second vertical derivative of the GSC levelled magnetic field from the lower magnetic

sensor in nanoteslas per metre squared (UTM coordinates, NAD83 datum)thscdem27.grd/.gxf digital elevation model in metres above sea level (UTM coordinates, NAD27 datum)thscdem83.grd/.gxf digital elevation model in metres above sea level (UTM coordinates, NAD83 datum)thscreslow27.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 877 Hz in ohm-metres

(UTM coordinates, NAD27 datum)thscreslow83.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 877 Hz in ohm-metres

(UTM coordinates, NAD83 datum)thscresmid27.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 4891 Hz in ohm-metres

(UTM coordinates, NAD27 datum)thscresmid83.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 4891 Hz in ohm-metres

(UTM coordinates, NAD83 datum)thscreshigh27.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 33840 Hz in ohm-metres

(UTM coordinates, NAD27 datum)thscreshigh83.grd/.gxf apparent resistivity for coplanar transmitter-receiver coil pair - 33840 Hz in ohm-metres

(UTM coordinates, NAD83 datum)


44

APPENDIX E GEOTIFF AND VECTOR ARCHIVE DEFINITION

GeoTIFF Images

Geographically referenced colour images are provided in GeoTIFF format for use in GISapplications.

The images are summarized as follows:

thscmagu27.tif IGRF-corrected magnetic field with topographic base (UTM coordinates, NAD27 datum)thsc2vdu27.tif shadowed second vertical derivative of the IGRF-corrected magnetic field form the upper

magnetic sensor with topographic base (UTM coordinates, NAD27 datum)thscresmid27.tif apparent resistivity for coplanar transmitter-receiver coil pair - 4891 Hz with topographic

base (UTM coordinates, NAD27 datum)

Vector Archives

Vector line work from the maps is provided in DXF ASCII format as follows:

thscem27.dxf electromagnetic anomalies (UTM coordinates, NAD27 datum)thsckc27.dxf Keating correlation targets based on the IGRF-corrected magnetic field grid (UTM

coordinates, NAD27 datum)thscpath27.dxf flight path of the survey area (UTM coordinates, NAD27 datum)thscmag27.dxf contours of the IGRF-corrected magnetic field in nanoteslas (UTM coordinates, NAD27

datum)thscresmid27.dxf contours of the apparent resistivity for coplanar transmitter-receiver coil pair - 4891 Hz in

ohm-metres (UTM coordinates, NAD27 datum)

The layers within the DXF files correspond to the various object types found therein and have intuitive names.


45

APPENDIX F KEATING CORRELATION ARCHIVE DEFINITION

Kimberlite Pipe Correlation Coefficients

The Keating kimberlite pipe correlation coefficient data are provided in two formats, one ASCIIand one binary:

� thsckc.csv - ASCII comma-delimited format (Microsoft Excel file)� thsckc.gdb - Geosoft OASIS montaj binary database file



x_nad27 easting in UTM co-ordinates using NAD27 datum metresy_nad27 northing in UTM co-ordinates using NAD27 datum metresx_nad83 easting in UTM co-ordinates using NAD83 datum metresy_nad83 northing in UTM co-ordinates using NAD83 datum metreslat_nad27 latitude using NAD27 datum decimal-degreeslong_nad27 longitude using NAD27 datum decimal-degreeslat_nad83 latitude using NAD83 datum decimal-degreeslong_nad83 longitude using NAD83 datum decimal-degreesamplitude peak-to-peak anomaly amplitude within window nanoteslascorr_coeff correlation coefficient percent x 10neg_coeff negative correlation coefficient percentnorm_error standard error normalized to amplitude percentpos_coeff positive correlation coefficient percent

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