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© Ministry of Mines and

Northern Development Minerals and Mines Division

Ontario O N T A R I O G E O L O G r C A L S U R V E Y

G E O P H Y S I C A L / G E O C H E M I C A L S E R I E S

MAP 81262

TASHOTA-GERALDTON-LONGLAC AREA

Airborne Electromagnetic Survey Total Intensity Magnetic Survey

DISTRICT OF THUNDER BAY « o o yr Z

Scale: 1:20 000 O

M e t r e s 500 9 1 Kilometre ^ I 1 I 1 t 1 I - ^

M i l e 1/4 0 1/2 M i l * (D

NTS References: 521/8,521/9.42L/5,42U12 ODM-GSC Aeromagnetic Map: 960G,970G,2i3iG,2i38G, ODM-Geological Compilation Map: 2102

•1989 Queens Printer for Ontario Printed in Ontario, Canada

S12 ) S^iW B I Z 6 1 ^ l a w 81263 B1264 | |Z65 B^^fc J l £ * 7 JBaprf SraMl ifttDTO 8 1 ^ 1 , ^ ^ - ^ ' ' ^

W M * B 1 S » f e »l'277 8<27a B1B7», « 4 S B 0 - V ' ^ -VftS' f^TW 1' J f c ^ /

B PJjIjrp"'' ^Zs 81290 tl29^ -ai Bi j ' ' " ' ! ]t^^ ^^^'^''^'^V'T" ^ ' -"^-^^^Z^

B1 OT. ^61305 S roA Bww' aiaoe B I ^ 8 I 3 ^ 'waw in?io B i j f 1(1^ * « i 3 '/ s '^ ' j ' 8^3i7 j

I - , ai .IB e"iiT9- "alaio- W^*- " 1 3 2 ^ ^)?^ 4^ ^ "^F" 0' ^ I

jj|Lb4' « f ^ 1^ *** jb?? r^^^v. ' - y ^ Tdm — ^J / ^ ;f ^^^

Index Map ^ o . ^ p . o 20 ^ 0 kriomelres

LEGEND

L E C T R O M A G N E T I C A N O M A L Y S Y M B O L S

omaly Conduc tance Classi f icat ion

0 > 32 Siemens ^ 16 - 32 Siemens A N O M A L Y L E T T E R ^ I ^ IN-PHASE R E S P O N S E (ppm)

Q 8 - 1 6 Siemens ^ P P ^ ^ ^ ^ ^ D E P T H (m) 3 5 1 7 Q U A D R A T U R E R E S P O N S E (ppm)

(J 4 - 8 Siemens 0 2 - 4 Siemens

O 1 - 2 Siemens f'^y < 1 siemen

^ very weak conductor (quadrature anomaly only) ^ jg^ frequency anomalies are distinguished from low

n r i i l tura! Rp<innnc;p frequency anomalies by plotting an aster isk(*) in the U cultural r e s p o n s e epparent depth quadrant of tha anomaly symbol

(1 siemen in SI units = 1 mho)

MAGNETIC CONTOURS 500 n l Contour ^ ^ ^ ^ ^ ^ ^ 50 nT Contour iQnT Contour

Magnetic depression CZ^~^ (1 Gamma = 1 nanoTesIa in SI units) Mean magnetometer sensor alt i tude 45 metres Mean electromagnet ic sensor altitude 30 metres Mean fl ight line spacing 200 metres Fl ight l ines 12630<-p—_

' 5460 '

1000 p 1 1 1 1

A E R O D A T H E M S Y S T E M R E S P O N S E ^ / .p" ^

V E R T I C A L H A L F - P L A N E <f ^-3" ^ ^

a: / ^ „ ^ < ^ / / \ / /

I >>/ / / / / v / / " ' -

^^^UU/ A// i / / / y / \ / / / f - F tequen ty ( H i l

.r / / \ w , , 1 10 100 1000

IN-PHASE RESPONSE (ppm}

DESCRIPTIVE NOTES ? helicopter is equipped with the Aerodat Electromagnetic System which measures in-phase and quadrature com lents at tour frequencies, employing two vertical coaxial coil pairs operating at 935 and 4600 Hz and two coplana I pairs operating at 4175 Hz and 32 kHz. The EM data are sampled at 0.1 second intervals employing a O.lsec j time constant. In Addition to bedrock conductors, the helicopter electromagnetic system responds to conduc ! overburden and near-surface horizontal conducting layers. Discrimination of conductors is based upon the rati( in-phase to quadrature responses, variation of response with frequency, magnetic correlation, and variation o smaiy shape of the two coil configurations together with conductor pattern and topography. Conductance anc Mh estimates are determined, assuming a vertical half-plane model in free-space, at 935 Hz (signal to noise per ting) where conductive overburden effects are minimal. In addition, a more representative value is achieved a )wer (requency since a larger portion of a conductor is energized. Other peripheral information (e.g. 60 Hz monito j Radar Altimeter) is recorded. The response diagram in the legend is derived from the model results presentet Figure 3.3.2 on page 60 in Ghosh (1972). e aeromagnetic total fiekj contours are generated from digitally recorded data from an Aerodat/Scintrex High Sen vity Optically Pumped Cesium Magnetometer and the sampling interval is 0.2 seconds. The magnetic data an corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data and (ii) intei lated onto a regular 0.25 cm grid at the map scale of 1 20 000 using a cubic spline technique. No correction ha an made for the regional vanation ol the earth's magnetic field. 3y(edis SR-3 radar navigation system is used for both navigation and flight path recovery. The aircraft posilioi jerived several times per second to a relative accuracy ot less than 10 metres. Absolute positional accuracy a I presented data with respect to the photomosaic base maps should generally be within 25 metres.

— INTERPRETATION REFERENCES — losh, M.K. 1972: Interpretation of Airborne EM Measurements Based on Thin Sheet Models; unpublished Ph. C esis, University of Toronto

CREDIT la compilation and drafting were done by Aerodat Limited, Toronto, Ontario. June to December 1988. Th^ Dtomosaic base maps were prepared by Herdes and Herdes Consultants, Toronto, using Ontario Ministry of Naturs sources 1:15 840 aerial photographs which were controlled by reference to 1:50 000 topographic maps publishei Energy. Mines and Resources, Ottawa,

ery possible effort has been made to ensure the accuracy of the information presented on this map, howevei J Ontario Ministry of Northern Development and Mines does not assume any liability for errors that occur. User ly wish to verify the analog records on file for a limited time at the Resident Regional Geologist's office nearest tt ip area

The Survey was funded by the Ontario Government Northern Development Fund.

is map is published with the permission of V G Milne, Director, Ontario Geological Survey, ignetlc declination in the area was approximately 3''27'W in November 1988. lued 1989. ormation from this publication may be quoted if credit is given. It is recommended that relerence be made in th lowing form: JTARIO GEOLOGICAL SURVEY 19 Airbornfi Flficlromagnetic and Total Intensity Magnetic Survey. Tashola-Geraldton-Longlac Area. District c

Thunder Bay by Aerodat Limited for the Ontario Geological Survey. Geophys/cal/Geochemical Series Map 8126; Scale 1:20 000 Survey and Compilation, June to December 1988,

lOTE: A set of 1:31 680 scale maps showing topography, flight lines and electromagnetic results ac­companies this set of maps and is available free of charge with the purchase of this set of maps.