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Electrical and Magnetic Properties of Duport Gold Deposit, Ontario, Canada

This study investigates the electrical and magnetic properties of the Duport gold deposit in western Ontario, Canada. It examines the geological background, geophysical surveys, and modeling to better understand the mineralization processes. The study concludes with a geophysical model and insights into the regional and local controls on mineralization.

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Electrical and Magnetic Properties of Duport Gold Deposit, Ontario, Canada

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

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

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

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

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

  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 CO2 and H2O 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. 3. GEOPHYSICAL SURVEYS (a) Airborne geophysical survey 1. DIGHEM: 2743 km 2. Azimuth 123o 3. Line-spacing 50 m 4. Sampling 10 Hz (3.3 m) 5. Sensor clearance ~30 m Modified from Garrie (2005)

  10. (b) Ground geophysical surveys

  11. (c) Core susceptibility measurements

  12. 4. MODELLING AND INTEGRATION (a) Modelling magnetic responses ● 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 Modelling using POTENT

  13. EM31 Modelling Modelling using EMIGMA 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)

  14. (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

  15. (c) Magnetic signature in northwest of Cameron I. ● 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

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

  17. Plane-polarized light Reflected light 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

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

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

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

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

  22. Electrical conductivity Geophysical responses Petrographic analyses

  23. 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 • ● Location and integrated conductance of zones containing significant sulphidization • ● Broader zones of induced magnetization

  24. 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

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

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