rpt on heliborne em geophys surv bonar stefansson …
TRANSCRIPT
REPORT ON A HELICOPTER-BORNE
TIME DOMAIN ELECTROMAGNETIC
GEOPHYSICAL SURVEY
Bonar-Stefansson Lake Project
Bonar Township Ontario, Canada
RECEIVEDNOV 1 8 21C3
SEOSCIENCF ASSESSMENT OfFICE
Geotech Ltd.
30 Industrial Parkway. South
Aurora, Ontario L4G 3W2
Tel: 905 841 5004
Fax: 905841 0611
Email: [email protected]
Survey flown in October 2003
Illl l
42B06NB2001 2.26651 BONAR 010
TABLE OF CONTENTS
INTRODUCTION..............................................................................................................................SIJRVEYAREA.....................................................^SURVEY OPERATIONS...................................................................................................................................................5AIRCRAFT AND EQUIPMENT.............................................,..................,.....................................................................61 Akcraft.........................................................................................................................................................................^2 Electromagnetic System...............................................................................................................................................63 Airborne magnetometer...............................................................................................................................................?4 Ancillary Systems ........................................................................................................................................................7
4.1 Radar Altimeter.........................................................4.2 OPS Navigation System......................................................................................................................................74.3 Digital Acquisition System..................................................................................................................................7
5 Base Station.................................................................................................................................................................8PERSONNEL..............................................................................................................................................^DATA PROCESSING AND PRESENTATION...............................................................................................................9DELIVERABLES.............................................................................................................................................10CONCLUSIONS...............................................................................................................................................................l l
TABLE OF FIGURES
FIGURE l - LOCATION MAP ..........................................................................................................................................4FIGURE 2 ..........................................................................................................................6FIGURE 3.........................................................................................................................................................................6
TABLES
TABLE l-SAMPLINGRATES...................................................................................................................
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REPORT ON A HELICOPTER-BORNE TIME DOMAIN ELECTROMAGNETIC SURVEY
Stefansson Lake Block, Bonar Township, Ontario, Canada
INTRODUCTION
This report describes the helicopter-borne geophysical survey carried out on behalf of Larry Gervais by Geotech Ltd. under an agreement dated October 2003. Principal geophysical sensors included a time domain electromagnetic system and a cesium magnetometer. Ancillary equipment included a OPS navigation system and a radar altimeter.
One block, referred to as Stefansson Lake Block in the Bonar Township area, was surveyed. The block is located approximately 125 km west of Timmins. The coordinates of the centre of the area are 83 0 l' 30" W, 480 24' N. The total area of the blocks is 4.4 km2, the total line kilometres flown was 47.7 km. Data acquisition was initiated and completed on October 18th, 2003.
This report describes the survey, the data processing and presentation.
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SURVEY AREA
The survey area is shown in figure l.
Figure l - Location Map
'i i ' i i ' i 'i i
TimminsStefansson Lake Block
Foleyet
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SURVEY OPERATIONS
Survey operations were based out of Timmins.
The nominal EM sensor terrain clearance was 30 m (EM bird height above ground, i.e. helicopter is maintained 65 m above ground). Nominal survey speed was 80 km/hour. The data-recording rates of the data acquisition was 0. l second for electromagnetics and magnetometer, 0.5 second for altimeter, l second for OPS. This translates to a geophysical reading about every 2 metres along flight track. Navigation was assisted by a GPS receiver and data acquisition system, which reports GPS co-ordinates as latitude/longitude and directs the pilot over a pre-programmed survey grid.
The operator was responsible for monitoring of the system integrity. He also maintained a detailed flight log during the survey noting the times of the flight as well as any unusual geophysical or topographic feature.
On return of the aircrew to the base camp the survey data was transferred from a compact flash card (PCMCIA) to the data processing computer.
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AIRCRAFT AND EQUIPMENT
l Aircraft
An Astar BA helicopter, registration C-GOVH - owned and operated by Canadian Helicopters was used for the survey. Installation of the geophysical and ancillary equipment was carried out by Geotech Ltd. in Timmins.
2 Electromagnetic System
The electromagnetic system was a Geotech Time Domain EM system. The layout is as indicated in Figures 2 below.
VersaTEM Configuration
Magnetometer
Rxloop
Transmitter loop
Figure 2
VersaTEM 30 Hz Base Frequency Sample Times
Location of decay windows
(cam.r ports)
ami: 111:1 i i i7.5 7.7 7.* LI L3 LS
Tx Pulse
D 1 2 34 5 6 7 8 9 10 11 121314 15 16
msec
Half-Waveform
Tx Pulse
Figure 3
Receiver and transmitter coils were concentric and Z-direction oriented. Transmitter coil diameter was 18.5 metres, the number of turns was 5. Receiver coil diameter was 1.1 metre, the number of turns was 60. Transmitter pulse repetition rate was 30 Hz. Peak current was 110 A. Duty cycle was
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Peak dipole moment was 140000 NIA.Wave form - trapezoid.Twenty-six measurement gates were used in the range from 110 us to 6340 us.The transmitter waveform and the receiver decay recording scheme is shown diagrammaticallybelow in Figure 3.Recording sampling rate was 10 samples per second.The EM bird was towed 35m below the helicopter.
3 Airborne magnetometer
The magnetic sensor utilized for the survey was a Geometrics G-823 A, optically pumped cesium vapor magnetic field sensor, mounted in a separate bird towed 15m below the helicopter. The sensitivity of the magnetic sensor is 0.02 nanoTesla (nT) at a sampling interval of 0.1 seconds. The G-823 A Magnetometer consists of a sensor head and sensor driver electronics with CM-201 counter joined by a cable. The magnetometer sends the measured magnetic field strength as nanoTeslas to the data acquisition system via the RS-232 port.
4 Ancillary Systems
4.1 Radar Altimeter
A Terra TRA 3000/TRI30 radar altimeter was used to record terrain clearance. The antenna was mounted beneath the bubble of the helicopter cockpit.
4.2 GPS Navigation System
The navigation system used was a Geotech PC based navigation system utilizing an Ashtech GG24 navigation card, Geotech navigate software, a full screen display with controls in front of the pilot to direct the flight and an Ashtech GPS antenna mounted on the helicopter tail. The co-ordinates of the blocks were set-up prior to the survey and the information was fed into the airborne navigation system.
4.3 Digital Acquisition System
A Geotech data acquisition system recorded the digital survey data on an internal compact flash card. Data is displayed on an LCD screen as traces to allow the operator to monitor the integrity of the system. Contents and update rates were as follows:
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5 Base Station
DATATYPE
IDEM
Magnetometer
OPS Position
RadarAltimeter
SAMPLING
0.1 sec
0.1 sec
1.0 sec
0.5 sec
Table l - Sampling Rates
A combine magnetometer/GPS base station was utilized on this project. A Scintrex CS-2 Cesium vapour magnetometer was used as a magnetic sensor with a sensitivity of 0.001 nT. The base station was recording the magnetic field together with the OPS time at l Hz on a base station computer. The base station magnetometer sensor was installed in Timmins away from electric transmission lines and moving ferrous objects such as motor vehicles. The magnetometer base station's data was backed-up to the data processing computer at the end of each survey day.
Geotech Ltd. - Renort on an Airborne Geonhvsical Survev
PERSONNEL
The following Geotech Ltd. personnel were involved in the project
FieldGeophysicists: Petr KuzminSystem Engineer/Operator: Pavel Tishin
OfficeData Processing/Reporting: Andrei Bagrianski
The survey pilot and the mechanic were employed directly by the helicopter operator — Canadian Helicopters.
Pilot: Philippe Leynaert Mechanic: Patrice Chaput
Overall management of the survey was carried out from the Aurora offices of Geotech Ltd. by Edward Morrison, President.
DATA PROCESSING AND PRESENTATION
Flight Path
The flight path, recorded by the acquisition program as WGS 84 latitude/longitude, was converted into the UTM co-ordinate system in Oasis Montaj.
The flight path was drawn using linear interpolation between x,y positions from the navigation system. Positions are updated every second and expressed as UTM eastings (x) and UTM northings (y).
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Electromagnetic Data
A three stage digital filtering process was used to reject major sferic events and to reduce system noise. Local sferic activity can produce sharp, large amplitude events that cannot be removed by conventional filtering procedures. Smoothing or stacking will reduce their amplitude but leave a broader residual response that can be confused with geological phenomena. To avoid this possibility, a computer algorithm searches out and rejects the major sferic events. The filter used was a 16 point non-linear filter.
The signal to noise ratio was further improved by the application of a low pass linear digital filter. This filter has zero phase shift which prevents any lag or peak displacement from occurring, and it suppresses only variations with a wavelength less than about l second or 20 metres. This filter is a symmetrical l sec linear filter. The results are presented as stacked profiles of EM voltages for the gate times.
Magnetic Data
The processing of the magnetic data involved the correction for diurnal variations by using the digitally recorded ground base station magnetic values. The base station magnetometer data was edited and merged into the Geosoft GOB database on a daily basis. The aero magnetic data was corrected for diurnal variations by subtracting the observed magnetic base station deviations. The corrected magnetic line data from the survey was interpolated between survey lines using a random point gridding method to yield x-y grid values for a standard grid cell size of approximately 0.2 cm at the mapping scale. The Minimum Curvature algorithm was used to interpolate values onto a rectangular regular spaced grid.
DELIVERABLES
The survey is described in a report, which is provided in four copies. The preliminary and final maps were produced at a scale of l: 10,000.
MAPS
The final results of the survey are presented in a colour magnetic contour map and an EM profiles map at a logarithmic scale. The coordinate/projection system used was WGS84, Universal Transverse Mercator, zone 17. For reference the WGS84 latitude and longitude are also noted on the maps. All the maps show the flight path trace.
The map products are as follows:
l. Total Field Magnetic color contour map on the GPS flight path, on paper in two copies
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2. EM Profile Map at a logarithmic scale of the twenty one gates times (220 - 6340 us) on the GPS flight path, on paper in two copies.3. Total Field Magnetic black and white contour map on the GPS flight path, on paper in two copies4. EM Profile black and white map at a logarithmic scale of the twenty one gates times (220 - 6340 us) on the GPS flight path, on paper in two copies.
DIGITAL DATA on CD-ROM
Four copies of CD-ROMs were prepared to accompany the report. Each CD-ROM contains a digital file of the line data in ASCII format in addition to the maps in Geosoft format. A readme.txt file may be found on the CD-ROM that describes the contents in more detail.
CONCLUSIONS
A time domain electromagnetic helicopter-borne geophysical survey has been completed over the Stefansson Lake Block, Bonar Township, Ontario, Canada. The total areal coverage amounts to 4.4 km2 . Total survey line coverage is 47.7 line kilometres. The principal sensors included a Time Domain EM system and a magnetometer. Results have been presented as colour line maps at a scale of 1:10,000.
No EM anomalies were identified. Two round-shaped (about 500 m in diameter) magnetic anomalies might present some interest. Ground follow-up of those magnetic anomalies should be carried out if favourably supported by other geoscientific data.
Respectfully submitted,
Andrei Bagrianski, Geotech Ltd.
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ONTMIO MINISTRY OF NORTHERN DEVELOPMENT AND MINES
Transaction No:
Recording Date:
Approval Date:
W0360.01795
2003-NOV-17
2003-NOV-19
Work Report Summary
Status: APPROVED
Work Done from: 2003-OCT-18
to: 2003-OCT-18
Client(s):
304026
Survey Type(s):
876097 ALBERTA LTD.
AEM
WgrKReport Details:
Claim# Perform
P 1180890 311,051
P 1180891 38,288
319,339
External Credits:
Reserve:
Perform Approve
311,051
38,288
319,339
SO
Applied Applied Approve
36,400 36,400
34,800 34,800
311,200 311,200
Assign
SO
SO
SO
Assign Approve Reserve
0 S4.651
0 33,488
30 58,139
Reserve Approve o ue Date
34,651 2004-SEP-24
33,488 2004-SEP-24
38,139
38, 1 39 Reserve of Work Reportft W0360.01 795
58,139 Total Remaining
Status of claim is based on information currently on record.
42B06NE2001 2.26651 BONAR 900
2003-Nov-27 13:33 Armstrongjd Page 1 of 1
Ministry ofNorthern Developmentand Mines
Date: 2003-NOV-21
Ministers duDeveloppement du Nord et des Mines Ontario
GEOSCIENCE ASSESSMENT OFFICE 933 RAMSEY LAKE ROAD, 6th FLOOR SUDBURY, ONTARIO P3E 6B5
876097 ALBERTA LTD. BOX 43TIMMINS, ONTARIO P4N 7C5 CANADA
Tel: (888)415-9845 Fax:(877)670-1555
Dear Sir or Madam
Submission Number: 2.26651 Transaction Number(s): W0360.01795
Subject: Approval of Assessment Work
We have approved your Assessment Work Submission with the above noted Transaction Number(s). The attached Work Report Summary indicates the results of the approval.
At the discretion of the Ministry, the assessment work performed on the mining lands noted in this work report may be subject to inspection and/or investigation at any time.
If you have any question regarding this correspondence, please contact STEVEN BENETEAU by email at [email protected] or by phone at (705) 670-5855.
Yours Sincerely,
XVl ^ CRon C. Gashinski
Senior Manager, Mining Lands Section
Cc: Resident Geologist
876097 Alberta Ltd. (Claim Holder)
Assessment File Library
876097 Alberta Ltd. (Assessment Office)
Visit our website at http://wvwv.gov.on.ca/MNDM/LANDS/mlsmnpge.htm Page: 1 Correspondence 10:18885
42B06NE2001 2.26651 BONAR 200
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Survey Specifications:Aircraft: Astar BA helicopter, Registration C-GOVH Flight Line Spacing: 100 metres Nominal terrain clearance 65 metres EM sensor is 35 metres under helicopter Magnetic sensor is 15 metres under helicopter
Instruments:Geotech Time Domain Electromagnetic System with concentric RxATx geometry Geometrics G823A Optically-pumped, High Sensitivity Cesium Magnetometer Mag Resolution 0.02 nT at 10 samples/sec Navigation: Ashtech GG24 Board S Sensor, Update Rate 1 Hz
Contour intervals:
___ _ 10 nT- 50 nT_____ 200 nT
100 O
Scale 1:10000100 200 300 400 500 600 700
metreWGS847UTMzone17N
Bonar-Stefansson Lake Project Bonar Township Ontario, Canada
Geotech IDEM SystemTotal Field Magnetics
Flown and processed by Geotech Ltd.30 Industrial Parkway S.,
Aurora, Ontario, Canada L4G 3W2
October 2003
42B06NE2001 2.26651 BONAR 210
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Survey Specifications:Aircraft: Astar BA helicopter, Registration C-GOVH Flight Line Spacing: 100 metres Nominal terrain clearance 65 metres EM sensor is 35 metres under helicopter Magnetic sensor is 15 metres under helicopter
Instruments:Geotech Time Domain Electromagnetic System with concentric Rx/Tx geometry Geometrics G823A Optically-pumped, High Sensitivity Cesium Magnetometer Mag Resolution 0.02 nT at 10 samples/sec Navigation: Ashtech GG24 Board 8. Sensor, Update Rate 1 Hz
Profiles scale 1 mm = 0,05 pV/A/mM-
(Linear between +/-0 . 2 pV/A/mM-
logarithmic above 0.2 pV/A/mM-
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Geotech IDEM SystemIDEM Profiles
Time Gates 0.22 - 6.34 ms
Flown and processed by Geotech Ltd.30 Industrial Parkway S.,
Aurora, Ontario, Canada L4G 3W2
October 2003
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