1. I. J. Ferguson, A. Krakowka, B. Cook, and J. Young University of Manitoba, Manitoba, Canada Electrical and magnetic properties of the Duport gold deposit, western Ontario, Canada

2. Deposit location: Cameron Island, Shoal Lake, Northwest Ontario 1. INTRODUCTION

3. Deposit history Deposit discovered in 1896 and mined for gold several times Drilling indicates along-strike extent of >1000 m and depth >500 m Estimated reserves 1.8 Mt (proven to inferred) grading ~12 g/t Au In-depth geological study by P.M. Smith (1987) 2005 airborne geophysical survey by Halo Resources

4. Objectives of this study: Define small-scale ground magnetic and ground EM responses on Cameron Island Use ground responses to relate airborne geophysics to smaller-scale geological features

5. Modified from Percival (2000) Modified from Ayer et al. (1991) 2. GEOLOGICAL BACKGROUND ● Western Wabigoon spr. ● Lake of the Woods Greenstone Belt

6. Modified from Smith (1986) Snowshoe Lake Batholith Stevens Island Diorite

7. Modified from Melquist (2005) Modified from Smith (1986) Stevens Island Diorite Duport Deformation Zone

8. Gold emplacement Mineralization was syn- to late-tectonic. Prograde amphibolite facies metamorphism in aureole of Snowshoe Lake batholith and subsequent retograde metamorphism caused by large volumes of high temperature fluid enriched in CO 2 and H 2 O in the deformation zone. Gold mineralization associated with sulphidation, silicification, biotization, and carbonatization. Precipitation of gold from bisulphide complexes was possibly related to iron content in host rocks.

9. (a) Airborne geophysical survey 1. DIGHEM: 2743 km 2. Azimuth 123 o 3. Line-spacing 50 m 4. Sampling 10 Hz (3.3 m) 5. Sensor clearance ~30 m 3. GEOPHYSICAL SURVEYS Modified from Garrie (2005)

14. (b) Ground geophysical surveys

17. (c) Core susceptibility measurements

18. (a) Modelling magnetic responses Modelling using POTENT ● Blocks 1,2: induced-dominant (k=0.1, 0.7 SI) ● Blocks 3,5: remanent-dominant ( J=23, 7 A/m, reversed ) ● Blocks 4,6: either 4. MODELLING AND INTEGRATION

19. 1. Conductive responses dominantly in quadrature 2. Magnetic responses dominantly in in-phase 3. HCP, VCP magnetic in-phase responses have opp. sign 4. HCP magnetic in-phase response positive (z<<r) EM31 Modelling Modelling using EMIGMA

20. (b) Magnetic signature in southeast of Cameron I. ● Surface samples k=0.065 SI ● Magnetic modelling Modelling: 0.1 SI ● EM31 in-phase anomalies HCP +ve, VCP –ve, k=0.3 SI ● HEM 900 Hz in-phase HCP –ve k=0.04 SI

21. ● Susceptibility of core samples: Schistose basalt k=0.2 SI Brecc. basalt k<0.05-0.1 SI ● Magnetic modelling Schistose basalt k=0.7 Brecc. basalt J~10 A/m ● EM anomalies: Negligible EM in-phase anomalies (c) Magnetic signature in northwest of Cameron I.

22. (d) Electrical conductivity ● EM31 Quadrature  =20-100 mS.m -1 In-phase HCP +ve, VCP +ve  = 300-400 mS.m -1 2. TEM For 100x20m plate:  =0.11 ms  400 mS.m -1 3. HEM Integrated response All frequencies In-phase and quadrature

23. 5. GEOLOGICAL INTERPRETATION Mafic intrusive rock (Stevens Island diorite) ● Induction-dominant magnetization due to magnetite ● Petrographic analysis: up to 5% mt on grain boundaries and disseminated in clinopyroxene pseudomorphs Plane-polarized lightReflected light

24. Schistose basalt ● Induction-dominant magnetization due to magnetite ● Petrographic analysis: up to 5-15% mt, typically fine- grained, and evenly distributed Plane-polarized lightCross-polarized light

25. Brecciated and sulphidized basalt Plane-polarized lightReflected light ● Remanent-dominant magnetization due to pyrrhotite ● Petrographic analysis: <3% mt, up to 10% sulphides

26. Magnetic susceptibility Modified from Clark & Emerson (1991) Geophysical responses Petrographic analyses

27. Koenigsberger ratio (qualitative) Modified from Clark & Emerson (1991)

28. Electrical conductivity Petrographic analyses Geophysical responses

29. 6. GEOPHYSICAL MODEL (CONCLUSIONS) Regional controls on mineralization Airborne magnetics ● Location of Snowshoe Lake batholith ● Zones of enhanced (secondary?) magnetite ● Defines deformation zones including Duport Def. Zone ● With filtering identifies some narrower geological units Airborne EM ● L ocation and integrated conductance of zones containing significant sulphidization ● Broader zones of induced magnetization

30. Local controls on mineralization Determination of physical properties Ground magnetics ● Location and width of lithological units and alteration facies ● Discrimination of remanent and induced magnetization and estimates of k and J Ground EM (EM31 and TEM) ● Location, width, and conductivity of sulphidized zones ● Relationship between conductive and magnetic zones ● Integrated conductance of these zones (TEM) ● Zones of induced magnetization, estimates of k Core Susceptibilty ● Relationship of alteration facies and lithology ● Definitive estimates of k ● Link between geology and geophysical responses

31. ACKNOWLEDGMENTS ● HALO RESOURCES ● Manitoba Geological Survey ● Petros Eikon and Geophysical Software Solutions ● KEGS Foundation