Ontario Airborne Geophysical Surveys Magnetic Supergrids

ONTARIO GEOLOGICAL SURVEY

Geophysical Data Set 1037—Revised

Ontario Airborne Geophysical Surveys Magnetic Supergrids

by

Ontario Geological Survey

2017

Users of OGS products are encouraged to contact those Aboriginal communities whose traditional territories may be located in the mineral exploration area to discuss their project.

© Queen’s Printer for Ontario, 2017

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Contents

CREDITS .................................................................................................................................................... iv DISCLAIMER ............................................................................................................................................ iv CITATION .................................................................................................................................................. iv NOTE ......................................................................................................................................................... iv

1. Introduction .................................................................................................................................................. 1

2. Aeromagnetic Data Acquired Before 1999 ................................................................................................ 1

3. Aeromagnetic Data Acquired from 1999 to 2003 ...................................................................................... 3 4. Creation of Updated Supergrids ................................................................................................................. 3

4.1. Abitibi Magnetic Supergrid ............................................................................................................. 5 4.2. Bamaji–Vickers Magnetic Supergrid............................................................................................... 6 4.3. Fort Hope–James Bay–Attawapiskat Supergrid .............................................................................. 7 4.4. Quetico Supergrid ............................................................................................................................ 8 4.5. Red Lake–Stormy Lake Supergrid .................................................................................................. 9 4.6. Schrieber Supergrid ......................................................................................................................... 10 4.7. Southeast Ontario Supergrid ............................................................................................................ 10

5. References ..................................................................................................................................................... 11

Appendix A. Construction of Previous Supergrids........................................................................................ 12

Appendix B. Grid Archive Definition ............................................................................................................. 14

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FIGURES 1. Locations of the updated magnetic supergrids ............................................................................................ 4

TABLES 1. Final continuation height and grid cell size of the supergrids ..................................................................... 4

2. Abitibi supergrid component surveys and merging parameters .................................................................. 5

3. Bamaji–Vickers supergrid component surveys and merging parameters.................................................... 6

4. Fort Hope–James Bay–Attawapiskat supergrid component surveys and merging parameters ................... 7 5. Quetico supergrid component surveys and merging parameters ................................................................. 8

6. Red Lake–Stormy Lake supergrid component surveys and merging parameters ....................................... 9

7. Schrieber area supergrid component surveys and merging parameters....................................................... 10

8. Southeast Ontario supergrid component surveys and merging parameters ................................................. 10

A-1. Abitibi supergrid, 2003 ............................................................................................................................... 12

A-2. Bamaji–Vickers supergrid, 2003 ................................................................................................................. 13 A-3. Dryden supergrid, 1999 ............................................................................................................................... 13

A-4. Fort Hope–James Bay–Attawapiskat supergrid, 2003 ................................................................................ 13

A-5. Schreiber supergrid, 2003 ........................................................................................................................... 13

iv

CREDITS List of accountabilities and responsibilities.

• Renée-Luce Simard, Senior Manager, Earth Resources and Geoscience Mapping Section,Ontario Geological Survey (OGS), Ministry of Northern Development and Mines (MNDM)– accountable for the geophysical survey projects, including contract management

• Desmond Rainsford, Senior Geoscience Leader – Geophysics, Earth Resources and GeoscienceMapping Section, Ontario Geological Survey – compilation and levelling of supergrids

• Angela Carter–McAuslan, student assistant, Earth Resources and Geoscience Mapping Section,Ontario Geological Survey – created initial recompilation grids

DISCLAIMER Every possible effort has been made to ensure the accuracy of the information presented in this report and the accompanying data; however, the Ministry of Northern Development and Mines does not assume liability for errors that may occur. Users should verify critical information.

CITATION Parts of this publication may be quoted if credit is given. It is recommended that reference to this publication be made in the following form: Ontario Geological Survey 2017. Report on magnetic supergrids, 14p. [PDF document]; report in

Ontario airborne geophysical surveys, magnetic data, grid data (ASCII and Geosoft® formats), magnetic supergrids; Ontario Geological Survey, Geophysical Data Set 1037—Revised.

NOTE If you wish to reproduce any of the text, tables or illustrations in this report, please write for permission to the Manager, Publication Services, Ministry of Northern Development and Mines, 933 Ramsey Lake Road, Level A3, Sudbury, Ontario P3E 6B5.

Report on Magnetic Supergrids

Geophysical Data Set 1037—Revised 1

1. IntroductionMagnetic “supergrids” are merged grids combining data from adjoining high-resolution aeromagnetic surveys. The supergrids provide the user with a wider view of the magnetic field and the convenience of having a single grid rather than multiple grids from several surveys. The supergrids achieve a near-seamless merge of adjacent surveys using procedures that are described in this report. Magnetic “supergrids”, merging 22 adjoining, high-resolution magnetic surveys in Ontario, were first created in 1999 (Ontario Geological Survey 1999a). This compilation was subsequently revised in 2003 (Ontario Geological Survey 2003a) with the inclusion of magnetic data from 33 additional surveys. This revision incorporates the results from 54 additional high-resolution aeromagnetic surveys. The updated magnetic supergrids now cover approximately 35% of Ontario.

In an ideal world, there would be no need for any adjustments to magnetic data or grids in order to get a seamless fit between survey boundaries. In theory, one should be able to measure the magnetic field at the same location above the Earth, but at different times, and obtain the same magnetic value after all corrections have been applied. In aeromagnetic survey practice, it is common that data mismatches occur where surveys overlap. The possible contributing factors include

• accuracy of survey navigation and flight path recovery;

• type and noise envelope of the magnetometer;

• differing flight-line directions;

• variations in magnetic sensor height and orientation;

• magnetometer sampling rate;

• techniques used to measure errors and correct the data (e.g., diurnal, International GeomagneticReference Field (IGRF), levelling);

• variations in the diurnal activity; and

• changes in the ground conditions between surveys (e.g., cultural effects)

As a result, it is necessary to use a series of secondary levelling procedures to obtain a seamless fitbetween survey boundaries. These procedures are described in this report.

2. Aeromagnetic Data Acquired Before 1999The following description has largely been excerpted and edited from the previous supergrid report (Ontario Geological Survey 2003a).

High-resolution airborne magnetic and electromagnetic surveys, over major greenstone belts, were initiated in 1975 by the Ontario Department of Mines (currently known as the Ontario Geological Survey) to aid geological mapping and mineral exploration. During the period 1975 to 1992, 32 airborne surveys were flown and processed by different survey contractors and subcontractors. The 2 earlier surveys, Matachewan area and Bamaji–Fry lakes area, were acquired in analogue form and the remaining 30 surveys were recorded digitally. The surveys were flown at a nominal flight-line spacing of 200 m, with the exception of the James Bay Cretaceous Basin (Onakawana–James Bay) survey, which was flown at a flight-line spacing of 1000 m.



There are significant differences in the quality of data acquisition and the original processing of older and newer surveys. The surveys, flown more recently, were designed and executed using state-of-the-art specifications, equipment and technology; whereas some of the older surveys, although conducted to the then-prevailing industry standards, were poorly processed. In many cases, for older surveys, the local map co-ordinates were registered in map inches on uncontrolled or semi-controlled photo-mosaics. The vast amount of digital data, collected by the survey contractors, were archived on 9-track tapes of different sizes and densities, in numerous incompatible data formats and file structures, many of which were difficult to access. For this reason, the archival digital data remained largely inaccessible to the public.

To alleviate many of these problems, and to bring the archival data set of all 32 airborne magnetic and electromagnetic (AMEM) surveys to modern data storage, digital processing and interpretation standards, a recompilation and reprocessing project was initiated under the Northern Ontario Development Agreement (NODA). This included approximately 450 000 line-kilometres of AMEM data, which were recompiled and reprocessed to correct any errors in the original data sets, to compute new derived products and to produce revised electromagnetic anomaly databases, using state-of-the-art geophysical data processing and imaging techniques.

This work resulted in the followings products that are pertinent to the aeromagnetic data:

1. common data format for all 32 AMEM survey data sets on CD-ROMs;

2. digitized survey data acquired in analogue form;

3. corrected flight path to account for distortions in the photo-mosaics and a digital flight pathreferenced to Universal Transverse Mercator (UTM) co-ordinates;

4. link and level total magnetic field data, from all 32 surveys, to the Single Master AeromagneticGrid for Ontario, which was prepared from the Geological Survey of Canada’s magneticdatabase under an earlier project (Ontario Geological Survey 1999b, 2003c). This process isalso referred to informally as “GSC-levelling”;

5. image-quality total magnetic field grids and profiles for each survey from reprocessed magneticdata; and

6. image-quality second vertical derivative grids of the reprocessed total magnetic field.

A complete description of the magnetic processing techniques applied for all AMEM surveys, and the specific details concerning each individual survey, are provided in the survey report included with each geophysical data set (e.g., Ontario Geological Survey 2003b).

Of the 32 individual aeromagnetic data sets that were compiled in this way, 22 were used to create 6 residual magnetic field and 6 second vertical derivative supergrids.



3. Aeromagnetic Data Acquired from 1999 to 2003The following description has been summarized from the previous supergrid report (Ontario Geological Survey 2003a).

Over the course of the Operation Treasure Hunt initiative, 36 airborne survey data sets were acquired. Of these, 11 new surveys were commissioned by the OGS and 25 were proprietary surveys purchased from industry. The purchased surveys were selected on the basis of location, recency, survey type, survey specifications and data quality.

Building on the previously created supergrids, 6 new grids were created using the same procedures that are detailed in the following sections. The new grids incorporated an additional 32 airborne magnetic surveys, in 6 geographical regions of Ontario. Of these, 5 comprise 40 m × 40 m cell size grids of the total magnetic field and its second vertical derivative. The sixth region (Fort Hope–James Bay–Attawapiskat) comprises 80 m × 80 m cell size grids of the total magnetic field and its second vertical derivative. A summary of the processing parameters used for the creation of the 2003 supergrids is provided in Appendix A.

4. Creation of Updated SupergridsA total of 6 new or revised supergrids were created for this current update. A seventh supergrid (Bamaji–Vickers) remains unchanged, but is included in this publication for completeness. Of the 6 new supergrids, 3 are updates of existing supergrids, 2 are new creations and 1 is an amalgamation of 2 existing supergrids. In total, the data from 54 additional surveys were added to create the new grids. The grid parameters are shown in Table 1 and their locations are displayed in Figure 1. These 7 supergrids comprise 2 203 459 line-kilometres covering an area of approximately 328 186 km2.

In order for adjacent magnetic surveys to be successfully merged, the data from each survey had to be levelled to the Single Master Aeromagnetic Grid for Ontario (Ontario Geological Survey 2003c) and brought to a common survey height. The process of draping individual magnetic surveys onto the Single Master Aeromagnetic Grid is known as “GSC-levelling” and is described by Reford et al. (1990). Bringing magnetic grids to a common height is achieved through a process of either upward or downward continuation (Bhattacharyya 1967). The final continuation heights of the supergrids range from 45 to 150 m. The continuation heights were chosen to be close to the magnetic sensor heights of the constituent surveys, thereby minimizing the degree of upward or downward continuation required.

Prior to merging, grids were re-projected to a common UTM zone. The UTM zone for each supergrid was chosen according to the UTM zone of the majority of constituent grids. The assignment of surveys to supergrids was based on both proximity and similar flight heights. As a result, abutting supergrids have not been merged because of the differences in continuation height.

The merging process was carried out using Geosoft Limited’s GridKnitTM routine. The “suture” method of merging was chosen both for the residual magnetic field and second vertical derivative grids. The suture line is located within the overlap area of adjacent grids and, during the knitting process, values on either side of the suture line are adjusted to leave a smooth transition between the grids. The suture line can be defined manually, automatically or along the edge of one of the grids. Most often, the automatic option, which defines the suture line along the midpoint of the grid overlap, was used. In some cases, where one grid was entirely within another or where the magnetic data of one grid were markedly superior to the other, a grid-edge suture was selected.



Table 1. Final continuation height and grid cell size of the supergrids.

Supergrid Final Continuation Height (metres)

Final Grid Cell Size (metres)

Final Projection (NAD83 CSRS*)

Abitibi 70 40 UTM 17N Bamaji–Vickers 30 40 UTM 15N Fort Hope–James Bay–Attawapiskat 80 40 UTM 16N Quetico 100 40 UTM 16N Red Lake–Stormy Lake 75 40 UTM 15N Schreiber 45 40 UTM 16N Southeast Ontario 150 40 UTM 18N

*Projection: NAD83 CSRS, North American Datum 1983 using Canadian Spatial Reference System.

Figure 1. Locations of the updated magnetic supergrids.



4.1. ABITIBI MAGNETIC SUPERGRID The updated Abitibi supergrid was built on the previous version and used the same 70 m continuation height. Details on the construction of the previous supergrid are provided in Appendix A. With the exception of 3 data sets (Kidd–Munro, Blake River area; Detour Lake area; and Round Lake batholith area), the magnetic grids were merged without any trend removal. As GSC-levelling had not been performed previously on the Timmins area MEGATEM® survey, this step had to be completed prior to inclusion in the magnetic supergrid. In order to merge the Round Lake batholith area data satisfactorily, the GSC-levelling of this data set had to be redone. Prior to merging, individual grids were downward or upward continued to a common 70 m magnetic sensor height. A summary of the data added to the Abitibi supergrid and the merging parameters are shown in Table 2.

Table 2. Abitibi supergrid component surveys and merging parameters.

Survey Geophysical Data Set (GDS)

Number

Magnetic Sensor Height

(metres)

Continuation Height

(metres)

Original Cell Size (metres)

Order of Merging

Abitibi supergrid (2003) 1037b 70 0 40 1 Kidd–Munro, Blake River area MEGATEM® II 1044b 75 −5 40 2 Timmins area MEGATEM® 1041b 77 −7 40 3 Kamiskotia area MEGATEM® II 1042b 75 −5 40 4 Central Abitibi Destor–Porcupine–Pipestone faults area 1049b 50 20 40 5 Lake Abitibi area 1050b 50 20 40 6 Detour Lake area 1062 80 −10 20 7 Bartlett Dome area MEGATEM® II 1057 75 −5 40 8 Halliday Dome area MEGATEM® II 1043b 75 −5 40 9 Round Lake batholith area 1048b 80 −10 40 10 Shining Tree area (2008) 1064 80 −10 40 11 Kirkland Lake–Larder Lake area 1053b 50 20 40 12 Shaw Dome area 1046b 45 25 40 13 Latchford area 1242 30 40 40 14 Matachewan–Timmins area 1243 51 19 20 15 Burntbush Lake area 1063 80 −10 20 16 Kabinakagami Lake area 1079b 60 10 40 17 Opeepeesway Lake area 1238 40 30 20 18 Magpie River–Missinaibi Lake area 1237 40 30 20 19 Michipicoten area 1010 30 40 40 20

Abbreviation: GDS, Geophysical Data Set.



4.2. BAMAJI–VICKERS MAGNETIC SUPERGRID No further magnetic data have been added to the Bamaji–Vickers supergrids since the previous supergrid update in 2003. For the sake of completeness, the unaltered supergrids have been included in this publication. New, more descriptive file names have been assigned to the supergrids. A summary of the component grids and the merging parameters is provided in Table 3.

Table 3. Bamaji–Vickers supergrid component surveys and merging parameters.

Survey Geophysical Data Set (GDS) Number

Magnetic Sensor Height (metres)

Continuation Height (metres)


Order of Merging

Bamaji supergrid 1037b 120 −90 40 1 Vickers area 1106bd—Revised 30 0 40 2 Gitche Lake area 1206—Revision 1 45 −15 20 3



4.3. FORT HOPE–JAMES BAY–ATTAWAPISKAT SUPERGRID The previous Fort Hope–James Bay–Attawapiskat supergrid had been assembled using an 80 m × 80 m grid cell size. This was appropriate in view of the fact that much of the supergrid comprised the Attawapiskat area, Albany–Atikameg–Attawapiskat rivers area and Albany River–James Bay area surveys, which were generally flown at 400 m line spacing. However, so as to honour the resolution of the mostly high-resolution surveys included in this current update, the supergrid was recreated from the beginning using a 40 m × 40 m grid cell size. In order to obtain satisfactory merges, the GSC-levelling was re-done for the Attawapiskat area, Albany River–James Bay area and Partridge River area surveys. Re-gridding of the GSC-levelled profile data for the Fort Hope area and Coral Rapids area surveys was carried out prior to merging. Trend removal was not required for any of the grids, except for a static shift that need to be applied to the magnetic grid from the Nagagami–Squirrel–Wakashi rivers area survey. Prior to merging, individual grids were downward or upward continued to a common 80 m magnetic sensor height. A summary of the grids used to construct the Fort Hope–James Bay–Attawapiskat supergrid and the merging parameters are provided in Table 4.

Table 4. Fort Hope–James Bay–Attawapiskat supergrid component surveys and merging parameters.

Survey Geophysical Data Set (GDS) Number


(metres)

Continuation Height

(metres)


Order of Merging

Attawapiskat area 1211b 80 0 80 and 40 1 Albany River–James Bay area 1209—Revised 80 0 40 2 Kenogami River area 1227 65 15 50 3 Nagagami–Squirrel–Wakashi rivers area 1225 56 24 40 4 Albany–Atikameg–Attawapiskat rivers area 1212 80 0 40 and 80 5 Kapiskau River east area 1214—Revised 100 −20 50 6 Fort Hope area 1109b 100 −20 40 7 McFaulds Lake area 1068 100 −20 50 8 Webequie area 1059 80 0 40 9 Ekwan River area 1229 48 32 15 10 Onakawana–James Bay area 1030 50 30 200 11 Squirrel River–Otter Rapids–Moose River areas 1228 61 to 127 19 to −47 50 12 Coral Rapids area 1213—Revised 76.5 0 30 13 Mameigwess Lake–Highbank Lake area 1235 various,

continued to 60 20 20 14

Melchett Lake area 1067 80 0 40 15 Moosonee area 1248 80 0 40 16 Partridge River area 1020 38 42 40 17 Kesagami Lake area 1215—Revised 78 0 40 18 Natogami Lake area 1217—Revised 46 34 60 19



4.4. QUETICO SUPERGRID The Quetico supergrid is so named as it covers almost all of the Quetico Subprovince in Ontario. This is a new supergrid and comprises data from recently acquired surveys. No trend removal was required for any of the data sets to obtain satisfactory results, although the GSC-levelling of the Garden–Obonga area survey had to be redone prior to merging. Prior to merging, individual grids were downward or upward continued to a common 100 m magnetic sensor height. A summary of the grids used to construct the Quetico supergrid and the merging parameters are provided in Table 5.

Table 5. Quetico supergrid component surveys and merging parameters.


Number


(metres)

Continuation Height

(metres)


Order of Merging

Lake Nipigon Embayment area 1047b 109 −9 40 1 Garden–Obonga area 1105b—Revised 33 67 40 2 Lac des Mille Lacs–Nagagami Lake area 1078b 122 −22 40 3 Dog Lake area 1246 72 28 40 4 East Nipigon area 1246 106 −6 40 5 Shebandowan area 1021b 41 59 40 6 Flatrock Lake area 1077 126 −26 40 7 Burchell Lake area 1241 64 36 30 8

Geraldton–Tashota area northwest Geraldton–Tashota area southeast

1031b 1032b

56 44 40 9

Atikokan–Mine Centre area 1029 120 −20 40 10 Lumby–Finlayson lakes area 1060a 81 19 40 11 Mine Centre area 1061a 78 22 40 12 Marmion Lake area 1066 100 0 30 13 Mahon Lake area 1077 100 0 40 14 Armstrong–Caribou Lake area 1027 45 55 40 15 Smooth Rock Falls area 1082b 107 −7 40 17 Kapuskasing–Chapleau area 1040b—Revised 124 −24 40 18



4.5. RED LAKE–STORMY LAKE SUPERGRID The Red Lake–Stormy Lake supergrid was built on the 1999 version of the Dryden supergrid rather than the more recent 2003 Stormy Lake supergrid. This was necessary because the Stormy Lake survey (GDS 1107), which had been incorporated into the Stormy Lake supergrid, contained inter-block level errors, which were subsequently fixed and the updated data set republished. Details on the construction of the of the Dryden supergrid are provided in Appendix A. Rather than incorporating the pre-existing Red Lake supergrid, better merges were obtained by adding the component grids individually. Prior to merging, individual grids were downward or upward continued to a common 75 m magnetic sensor height. No trend removal was required for any of the added grids in order to obtain satisfactory merges. A summary of the grids used to construct the Red Lake–Stormy Lake supergrid and the merging parameters are provided in Table 6.

Table 6. Red Lake–Stormy Lake supergrid component surveys and merging parameters.

Survey Data Set Number Magnetic Sensor Height

(metres)

Continuation Height

(metres)

Original Cell Size

(metres)

Order of Merging

Dryden supergrid 45 30 40 1 Stormy Lake area 75 0 40 2 Brooks Lake area 53 22 10 3 Fisher Lake area 75 0 20 4 Docker area 45 30 40 5 Kakagi Lake area 75 0 40 6 Nestor Falls area 59 16 30 7 Rainy River area 120 −45 40 8 Separation Lake area 119 −41 40 9 Lac Seul East area 112 −41 40 10 Red Lake area 129 −54 40 11 Uchi–Bruce lakes area 48 27 40 12 Birch–Confederation lakes area 112 −37 40 13 Whitefeather Forest area 74 0 40 14 North Spirit Lake area 72 0 40 15 Gullrock Lake area 58 17 20 16 Werner Lake area 55 20 20 17 Aerobus Lake area

EDS 1037 GDS 1107b—Revision 1 GDS 1233 GDS 1232 GDS 1203—Revision 1 GDS 1208—Revision 1 GDS 1076 GDS 1002b GDS 1083b GDS 1084b GDS 1028—Revised GDS 1026—Revised GDS 1025—Revised GDS 1058a GDS 1056a GDS 1245 GDS 1230 GDS 1240 76 0 20 18

Abbreviation: EDS, ERLIS Data Set; GDS, Geophysical Data Set.



4.6. SCHRIEBER SUPERGRID The Schrieber area supergrid is a revision of the previous version of the supergrid. This grid was reconstructed in order to remove several small holes in the original supergrid. No new grids were added and no trend removal was required for any of the grids, used in the reconstruction, in order to obtain a satisfactory merge. Prior to re-merging, individual grids were downward or upward continued to a common 45 m magnetic sensor height. A summary of the grids used to reconstruct the Schrieber area supergrid and the merging parameters are provided in Table 7.

Table 7. Schrieber area supergrid component surveys and merging parameters.


Number


(metres)

Continuation Height

(metres)

Original Cell Size

(metres)

Order of Merging

Schreiber area 1104b—Revised 30 15 40 1 Geco–Manitouwadge area 1205b—Revised 45 0 40 2 Hemlo area 1207—Revised 55 −10 40 3

4.7. SOUTHEAST ONTARIO SUPERGRID The Southeast Ontario supergrid is a new supergrid incorporating 4 adjacent surveys. No trend removal was required for any of the grids in order to obtain a satisfactorily merged supergrid. Prior to merging, individual grids were downward or upward continued to a common 150 m magnetic sensor height. A summary of the grids used to construct the Southeast Ontario supergrid and the merging parameters are provided in Table 8.

Table 8. Southeast Ontario supergrid component surveys and merging parameters.


Number


(metres)

Continuation Height

(metres)

Original Cell Size

(metres)

Order of Merging

Renfrew area 1074 133 17 40 1 Eastern Ontario area 1075 210 −60 40 2 Kaladar–Marmora area 1018 153 0 40 3 Bancroft area 1234 86 64 40 4



5. ReferencesBhattacharyya, B.K. 1967. Some general properties of potential fields in space and frequency domain: A review;

Geoexploration, v.5, p.127-143.

Ontario Geological Survey 1999a. Magnetic supergrids, Ontario airborne magnetic and electromagnetic surveys, processed data and derived products, Archean and Proterozoic “greenstone” belts; Ontario Geological Survey, ERLIS Data Set 1037.

——— 1999b. Single master Bouguer gravity and aeromagnetic data for Ontario, Geosoft® format; Ontario Geological Survey, ERLIS Data Set 1036.

——— 2003a. Ontario airborne geophysical surveys, magnetic data, grid data, Geosoft® format, magnetic supergrids; Ontario Geological Survey, Geophysical Data Set 1037b.

——— 2003b. Ontario airborne geophysical surveys, magnetic and electromagnetic data, grid and profile data, ASCII and Geosoft® formats, Armstrong–Caribou Lake area; Ontario Geological Survey, Geophysical Data Set 1027.

——— 2003c. Single master gravity and aeromagnetic data for Ontario, Geosoft® format; Ontario Geological Survey, Geophysical Data Set 1036.

Reford, S.W., Gupta, V.K., Paterson, N.R., Kwan, K.C.H. and Macleod, I.N. 1990. Ontario master aeromagnetic grid: A blueprint for detailed compilation of magnetic data on a regional scale; abstract in Society of Exploration Geophysicists, 60th Annual Meeting, San Francisco, California, SEG Technical Program, Expanded Abstracts 1990, p.617-619, DOI:10.1190/1.1890282.



Appendix A. Construction of Previous Supergrids Appendix Tables A-1 to A-5 summarize the parameters used to construct the previously constructed magnetic supergrids. In cases where the original supergrids published in 1999 were subsequently updated and republished in 2003, the merging parameters have been integrated into a single table.

Abbreviations are used in the following tables: EDS, ERLIS Data Set; GDS, Geophysical Data Set.

Appendix Table A-1. Abitibi supergrid, 2003.


(metres)

Continuation Height

(metres)

Original Grid Cell Size (metres)

Order of Merging

Kirkland Lake area 75 −5 40 1 Matheson area 72 −2 40 2 Temiskaming area 100 −30 25 3 Temagami area 70 0 40 4 Temagami South area 70 0 40 5 Gowan–Evelyn area 45 +25 20 6 Cobalt area 70 0 60 7 Black River–Matheson area 120 −50 40 8 Blake River Syncline area 45 +25 40 9

Detour–Burntbush–Abitibi west and Detour–Burntbush–Abitibi east areas

120 −50 40 10

Kirkland Lake area (1979) 120 −50 40 11 Matachewan area 120 −50 40 12 North Swayze–Montcalm area 120 −50 40 13 Shining Tree area 120 −50 40 14 Swayze area 120 −50 40 15 Timmins area 120 −50 40 16 Robb–Jamieson area 70 0 20 17 Turnbull–Godfrey area 75 −5 40 18 Cochrane area 70 0 40 19

Tyrrell Township (part of Shining Tree area)

90 −20 30 20

Amyot–Browning area 122 −52 30 21 Kapuskasing–Chapleau area 100 −30 40 22 Michipicoten area 30 +40 40 23 Wawa area 45 +25 40 24 Latchford–Redwater area 100 −30 50 25 Kenabeek area 100 −30 40 26 Oba–Kapuskasing area

GDS 1102b—Revised GDS 1101b—Revised GDS 1210—Revision 1 GDS 1103b—Revised GDS 1204—Revision 1 GDS 1202—Revision 1 GDS 1201—Revision 1 GDS 1001 GDS 1006 GDS 1007b GDS 1008b GDS 1022 GDS 1014 GDS 1005b GDS 1003b GDS 1015 GDS 1004b GDS 1221—Revised GDS 1223—Revised GDS 1100b—Revised GDS 1039—Revised

GDS 1200—Revision 1 GDS 1040b—Revised GDS 1010 GDS 1009b GDS 1224 GDS 1224 GDS 1024b 45 +25 40 27



Appendix Table A-2. Bamaji–Vickers supergrid, 2003.


(metres)

Continuation Height

(metres)


Order of Merging

Bamaji–Fry lakes area 120 −90 40 1 Pickle Lake area 120 −90 40 2 Vickers area 30 0 40 3 Gitche Lake area

GDS 1013 GDS 1012b GDS 1106bd—Revised GDS 1206—Revision 1 45 −15 20 4

Appendix Table A-3. Dryden supergrid, 1999.


(metres)

Continuation Height

(metres)


Order of Merging

Dryden area EDS 1016 120 −75 40 1 Manitou–Stormy lakes area EDS 1019 45 0 40 2 Sioux Lookout area EDS 1023 45 0 40 3 Sturgeon Lake–Savant Lake area EDS 1033 45 0 40 4

Note: The 1999 Dryden supergrid, rather than the 2003 Stormy Lake supergrid, was used to create the updated Stormy Lake supergrid.

Appendix Table A-4. Fort Hope–James Bay–Attawapiskat supergrid, 2003.


(metres)

Continuation Height

(metres)


Order of Merging

Attawapiskat area 80 0 40 and 80 1 Albany River–James Bay area 80 0 80 2 Kenogami River area 65 +15 50 3 Nagagami–Squirrel–Wakashi rivers area

GDS 1211b GDS 1209—Revised GDS 1227 GDS 1225 56 +24 40 4

Albany–Atikameg–Attawapiskat rivers area GDS 1212 80 0 40 and 80 5 Kapiskau River east area 100 −20 50 6 Fort Hope area

GDS 1214—Revised GDS 1109b 75 +5 40 7

Note: The updated Fort Hope–James Bay–Attawapiskat supergrid was not built on the 2003 version, but was recreated from scratch.

Appendix Table A-5. Schreiber supergrid, 2003.


(metres)

Continuation Height

(metres)


Order of Merging

Schreiber area 30 +15 40 1 Geco–Manitouwadge area 45 0 30 2 Hemlo area

GDS 1104b—Revised GDS 1205b—Revised GDS 1207—Revised 55 −10 20 3



Appendix B. Grid Archive Definition The gridded data are provided in 2 formats:

• *.gxf Geosoft® uncompressed ASCII grid exchange format (revision 3.0) • *.grd Geosoft® Oasis montaj™ uncompressed binary grid file

All grids are UTM projected to NAD83, with a grid cell size of 40 m × 40 m. The UTM zones are shown for each supergrid. The grids are summarized as follows:

• Abitibi_magsup83.gxf/.grd Abitibi supergrid of the GSC-levelled magnetic field in nT (UTM zone 17N)

• Abitibi_2VDsup83.gxf/.grd Abitibi supergrid of the calculated second vertical derivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 17N)

• Bamaji-Vickers_magsup83.gxf/.grd Bamaji–Vickers supergrid of the GSC-levelled magnetic field in nT (UTM zone 15N)

• Bamaji-Vickers_2VDsup83.gxf/.grd Bamaji–Vickers supergrid of the calculated second verticalderivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 15N)

• FtHope-JamesBay_magsup83.gxf/.grd Fort Hope–James Bay–Attawapiskat supergrid of the GSC-levelled magnetic field in nT (UTM zone 16N)

• FtHope-JamesBay_2VDsup83.gxf/.grd Fort Hope–James Bay–Attawapiskat supergrid of thecalculated second vertical derivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 16N)

• Quetico_magsup83.gxf/.grd Quetico supergrid of the GSC-levelled magnetic field in nT (UTM zone 16N)

• Quetico_2VDsup83.gxf/.grd Quetico supergrid of the calculated second vertical derivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 16N)

• RedLake-Stormy_magsup83.gxf/.grd Red Lake–Stormy supergrid of the GSC-levelled magneticfield in nT (UTM zone 15N)

• RedLake-Stormy_2VDsup83.gxf/.grd Red Lake–Stormy supergrid of the calculated second verticalderivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 15N)

• Schreiber_magsup83.gxf/.grd Schreiber supergrid of the GSC-levelled magnetic field in nT (UTM zone 16N)

• Schreiber_2VDsup83.gxf/.grd Schreiber supergrid of the calculated second vertical derivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 16N)

• SE_Ont_magsup83.gxf/.grd Southeast Ontario supergrid of the GSC-levelled magnetic field in nT (UTM zone 18N)

• SE_Ont_2VDsup83.gxf/.grd Southeast Ontario supergrid of the calculated second vertical derivative of the GSC-levelled magnetic field in nT/m2 (UTM zone 18N)

Documents

Ontario Airborne Geophysical Surveys Magnetic Supergrids