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Ontario Geological Survey 2015. Ground gravity survey, residual of the Bouguer anomaly, central Simcoe County area; Ontario Geological Survey, Map 82 771, scale 1:50 000.

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82 771

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RESIDUAL BOUGUER GRAVITY GRID

© Queen's Printer for Ontario, 2015.

2 km01 km

NTS References: 31 D/4, 5, 12; 41 A/1, 8, 9

Location map 1 cm equals 15 km

GPS ACQUISITION

Rapid real-time kinematic surveying using dual-frequency GPSreceivers.

Instrumentation: Leica® Viva® GS15 (3 units)Five (5) SmartNet™ RTK base stations surrounding the projectarea were used.RTK GPS surveying from 5 geodetic points (673117,28U131R, 65U9504, 84U123 and M053009; NaturalResources Canada) were used in areas with poor SmartNet™RTK coverage.

Average precision: 1.0 cm horizontally and 2 cm verticallyfor all units.

Re-occupied stations: 5.5% of the stations were repeatedwith an average repeat of 1.0 cm and a standard deviationof 1.75 cm.

GRAVITY ACQUISITION

Instrumentation:Type: Scintrex® CG-5 Autograv™ (2 units)Reading resolution: 0.001 mGal

Calibration: As a quality check, the instrument scale factor foreach of the 2 gravity meters was confirmed against theCanadian Gravity Standardization Network (CGSN).

Tie-in: The gravity survey is tied to CGSN gravity base stationDuntroon 9023-1991, located in central Simcoe County area,Ontario. One secondary base station #9999 was establishedusing the ABABA sequence. The average absolute drift forthe base tie-in was 0.027 mGal.

Survey drift: The average absolute drifts per loop for the 2gravity meters during production were 0.055 and 0.024 mGalafter tidal and instrument height corrections.

Re-occupied stations: 5.2% of the stations were repeated withan average repeat of 0.008 mGal and a standard deviationof 0.015 mGal. Based on these statistics, typical reading erroris estimated to be 0.015 mGal (maximum 0.039 mGal).Typical error on the Bouguer values is estimated to be betterthan 0.026 mGal.

SURVEY SPECIFICATIONS

Survey dates and details:September 30 to November 5, 2014: Geodetic tie-in, gravitymeter calibrations, base station establishment and readingof 4380 stations.

Nominal station separation: 100 m and 200 m.

CO-ORDINATE SYSTEM

Projection: Universal Transverse MercatorDatum: NAD83 CSRSCentral meridian: 81°00' W (UTM zone 17N)Central scale factor: 0.9996False easting: 500 000 mFalse northing: 0 mEllipsoid: WGS84Geoid model: HTv2.0

SURVEY PARAMETERS

DESCRIPTIVE NOTES

Introduction

The data on this map represent new ground gravity measure-ments. Data from a total of 4380 stations were collected duringthe fall of 2014. The data were processed and checked byAbitibi Geophysics Inc. All station locations are indicated on themap by symbols.

Data Reduction

The raw gravity observations were processed according to thestandards set forth by the International Gravity StandardizationNetwork 1971 (IGSN71) and the Geodetic Reference System1967 (GRS67), see Woollard 1979. This included the applicationof standard Earth tide, instrumental drift, latitude, free air andBouguer corrections. A density of 2.40 g/cm³ was used for theBouguer correction. Near zone terrain corrections were appliedto the Bouguer gravity out to a distance of 50 m from the gravitystations. The near zone correction was derived from fieldobservations of ground slope and calculated using Hammer's(Hammer 1939) formula for zones B and C.

Residual Anomaly Map

The residual anomaly field was calculated by subtracting theregional gravity field from the Bouguer or (reduced observed)gravity values. The regional field was estimated by upwardcontinued at height of 5.0 km of the Bouguer values. This surfacewas then subtracted from the Bouguer anomaly to create theresidual anomaly.

Scale 1:50 000

GROUND GRAVITY SURVEY

Residual of the Bouguer Anomaly

MAP 82 771

Ontario Geological Survey

This map is published with the permission of the Director,Ontario Geological Survey.

STATION LOCATIONS

Gravity stations

CREDITS

Data acquisition, data compilation and map production byAbitibi Geophysics Inc., Val-d’Or, Quebec.

Base maps and map surrounds by the Ministry of NorthernDevelopment and Mines, Sudbury, Ontario.

Contract management, base maps and map surrounds by theMinistry of Northern Development and Mines, Sudbury, Ontario.

Quality assurance and quality control by Desmond Rainsford,Ontario Geological Survey, Sudbury, Ontario.

Every possible effort has been made to ensure the accuracy ofthe information presented; however, the Ministry of NorthernDevelopment and Mines does not assume liability for any errorsthat may occur. Users should verify critical information.

Corresponding digital data for this survey are available from thefollowing Ontario Geological Survey publication:

Ontario Geological Survey 2015. Ontario geophysical surveys,ground gravity data, grid and point data (ASCII and Geosoft®formats) and vector data, central Simcoe County area; OntarioGeological Survey, Geophysical Data Set 1080.

Issued 2015.

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

Ontario Geological Survey 2015. Ground gravity survey, residualof the Bouguer anomaly, central Simcoe County area; OntarioGeological Survey, Map 82 771, scale 1:50 000.

SOURCES OF INFORMATION

Base map information derived from the Land Information OntarioData Warehouse, Land Information Ontario, Ministry of NaturalResources and Forestry, scale 1:20 000.

DEM information derived from 10 m DEM 2.0 grids from LandInformation Ontario, Ministry of Natural Resources and Forestry.

Magnetic declination for the centre of the map area wasapproximately 10°17.6' W in 2015.

1

Users of OGS products are encouraged to contact thoseAboriginal communities whose traditional territories may belocated in the mineral exploration area to discuss their project.

LEGEND

RESIDUAL BOUGUER GRAVITY CONTOURS

0.2 mGal contour

1 mGal contour Gravity

5 mGal contour

depression

REFERENCES

Hammer, S. 1939. Terrain corrections for gravimeter stations;Geophysics, v.4, p.184-194.

Woollard, G.P. 1979. The new gravity system—changes ininternational gravity base values and anomaly values;Geophysics, v.44, p.1352-1366.

milligal(mGal)