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

Deposit location: Cameron Island,

Shoal Lake, Northwest Ontario

1. INTRODUCTION

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

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

Modified from Percival (2000)Modified from Ayer et al. (1991)

2. GEOLOGICAL BACKGROUND

● Western Wabigoon spr.● Lake of the Woods Greenstone Belt

Modified from Smith (1986)

SnowshoeLake Batholith

StevensIslandDiorite

Modified from Melquist (2005) Modified from Smith (1986)

StevensIslandDiorite

Duport Deformation Zone

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.

(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

3. GEOPHYSICAL SURVEYS

Modified from Garrie (2005)

(b) Ground geophysical surveys

(c) Core susceptibilitymeasurements

(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

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

(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

● 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.

(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 ms400 mS.m-1

3. HEM

Integrated response All frequencies In-phase and quadrature

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 light Reflected light

Schistose basalt

● Induction-dominant magnetization due to magnetite● Petrographic analysis: up to 5-15% mt, typically fine- grained, and evenly distributed

Plane-polarized light Cross-polarized light

Brecciated and sulphidized basalt

Plane-polarized light Reflected light

● Remanent-dominant magnetization due to pyrrhotite● Petrographic analysis: <3% mt, up to 10% sulphides

Magnetic susceptibility

Modified from Clark & Emerson (1991)

Geop

hysic

al re

sp

on

ses

Petrographic analyses

Koenigsberger ratio (qualitative)

Modified from Clark & Emerson (1991)

Electrical conductivity

Petrographic analyses

Geop

hysic

al re

sp

on

ses

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

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

ACKNOWLEDGMENTS

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