gamma ray spectrometry theory and...

R. B. K. Shives, President, GamX Inc., www.gamx.ca

Gamma Ray Spectrometry: Mineral Exploration, Environment, Health and Safety Minerals North Conference April 26, 2017

Gamma Ray Spectrometry:Exploration, Environment, Health and Safety

R. Shives, GamX Inc.

Minerals North ConferencePrince George Conference and Civic Centre, April 26, 2017



Talk GoalsNot too technical, and with a geological focus

What are gamma rays?

How do we measure them?

How do they help us?

Bottom Line:For more than 50 years, gamma ray spectrometry has been used to map rocks/soils, find hydrocarbon and mineral deposits/mines, monitor environmental hazards, detect radioactive sources.



Very Basic Principles



Radioactivity is “everywhere”…Our universe …

our planet …

our bodies …

… are RADIOACTIVE

There is nowhere on Earth that you can not find naturally occurring radioactivity.

We can measure it in the air, water, rocks, soil, buildings and bodies.

http://www.solarviews.com/cap/ds/ngc4414.htm



What is Natural Radioactivity?

electrons

Atom

protons

neutrons

nucleus

α Alpha:

- a few cm in air, stopped by 1 layer skin

β Beta:

- several cm in air, stopped by several layers skin

5

When a nucleus has an excess of either protons or neutrons …..

Ɣ Gamma:

- 100’s m in air, can go right through your body

No good for geological“remote detection” purposes

No good for geological“remote detection” purposes

THAT works !

…. it is UNSTABLE.“Something has to go” ….



Radioactivity is part of theElectromagnetic Radiation

Spectrum …..

We use the high energy gamma ray part of the spectrum to map rocks,find ore, detect related environmental andhealth concerns.

6https://en.wikipedia.org/wiki/Electromagnetic_spectrum

ELF,VLF Planes, Ships, Subs

AMradio

PlanesShipsSubs

SWRadio

TVFM

radio

MicroWavesRadar

InfraredLight

VisibleLight

UVLight

X-rays

GammaRays

Low Frequency - Long Wavelength - Low Energy

High Frequency - Short Wavelength - High Energy

AM Radio

FM Radio

Visible Light

UV Light

X-ray

Gamma Rays



What are the radioactive element concentrations in rocks?

Source: Table 2, Radioelement concentrations in different classes of rocks (Killeen, 1979)

7

Potassium (%) Uranium (ppm) Thorium (ppm)



Rock Class K (%) U (ppm) Th (ppm)

Felsic 0.1 – 8 0.01 – 30 0.1 – 250

Mafic 0.02 – 3 0.01 – 6 0.03 – 15

Ultramafic 0 – 1 0 – 1.6 0 – 8

Sedimentary 0.01 – 10 0.1 – 80 0.2 – 350

Metamorphic 0.01 - 6 0.1 – 150 0.1 - 100

More simply…..

Low

Medium

High

Variable

8



How do we measure gamma rays?

Ground Spectrometers Airborne Spectrometer systems

Borehole Spectrometer systems

http://mountsopris.com/items/32gr-slim-natural-gamma-probe/



Schematic diagram of gamma ray detector

Anode

10

Detector

Flash of Light Amplified pulse

Photomultiplier Tube

200

300

400

500

600

700

800

900

1000v

1100v

1200v

How does a gamma ray detector work?

Output voltage is proportional to the gamma ray energy.A spectrometer sorts the energies.



11

What does a gamma ray spectrum look like?

Potassium

Uranium Thorium



AIRBORNE GAMMA RAY SPECTROMETRY

12

Spectra

Detector

Gamma Rays (K,U,Th)

Spectrometer(sorts K,U,Th energies)

MapsData

Speed

Altitude

GPS

MAG, EM



Calibration ensures accurate results

Concrete calibration pads contain known concentrations of K, U, Thand a blank. The spectrometer sorts the different gamma ray energies into a spectrum, which we use to calibrate the system.

13

Ground Spectrometers Airborne Spectrometers



Calibration: Airborne Spectrometers

Ottawa River

Aircraft loops over strip and water, at several altitudes.

A calibrated groundspectrometer is used to determine the ground concentrations of K, U and Th.

A boat is used allow measurements over the water.

14

Ottawa Calibration Strip



Ground and airborne spectrometers are calibrated using “flat” source geometry.

Departures from that can create false anomalies.We must consider this when we interpret our

data!

15



Ground spectrometer source concept

DetectorAIR

ROCK

The “field of view” for a ground spectrometer on a flat, uniform bedrock source can be depicted as a series of bowl-shapes, such that about 90% of the signal emanates from a 1 m diameter by 30 cm deep volume of rock.

0 10 20 30cm

30 cm

1 metre



Ground Spectrometry – GOOD Source Geometry

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Excellent geometry, uniform geology within the detector’s “sensitive volume”.

Large boulder, valid reading, but relationship to bedrock difficult to determine.

Large boulder, adequate geometry, and very close to source bedrock.

Excellent geometry, reading at least 1 m from edge of outcrop, behind operator.



Airborne: The effect of source geometry on count rateTerrain clearance (h) is determined by radar altimeter, and is the same

value for each case below

There are no reliable automated corrections for these effects (many have tried), so keep this in mind when interpreting data.

Normal count rate High count rate Low count rate



RADON in our environment can interfere with the measured gamma ray signal.

19



Precipitation effects on the uranium window (caused by Radon)

SnowRain

Wait 12 hours after ground-soaking rainfall to take gamma ray readings.Otherwise, false U estimates will result.

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• Potassium is a major element, Uranium is a mobile trace element, Thorium is a relatively immobile trace element

Airborne Gamma Ray Surveys: Basic Concepts

• Geophysical instrumentation, but 100% geochemical application

• “Top foot of surface” technique, so understand the surface.

21



(Handheld, backpack, vehicle, borehole)

(Helicopter or fixed wing)For geological uses,

gamma ray spectrometryis really about CHEMISTRY

Gamma rays emanate naturallyfrom K, U and Th in all rocks.

A spectrometer measures them.

Different rock types have different signatures, so we can map geology using the method.

Mineralizing systems alter the normal rock signature, so we can detect and map alteration.



Gamma Ray Spectrometry Applications



Flight line spacing affects MAPS (but not the profile data)

24

250 m

1000 m

500 m

2000 m



Beware! Absolute values not created equal!

Mount Milligan (the Mountain)• well exposed barren granitic bedrock

Mount Milligan Mine (the Deposits)• large porphyry Cu-Au deposits• poorly exposed, covered with till and glacial outwash

25

Potassium Map



Radioactive element ratios

Dutch CreekFormation

KitchenerFormation

CrestonFormation

B. eTh/K ratio

Dutch CreekFormation

KitchenerFormation

CrestonFormation

Less influenced by source variations, can provide better mapping guides than the individual elements can.

Above, east-west POTASSIUM trend (left) relates to south-facing slopes, notto the mapped, north-south trending geology, indicated.But the RATIO map (right) relates better to the mapped geology.

K eTh/K

26



Case HistoriesThere are hundreds!

We’ll look at just a few….



28

TERNARY (K-eU-eTh) Map of Canada

eU

eTh

K

Ternary maps enhance relative variations. Here, major geological domains are obvious.

The method can also define local anomalies at property scales.



LOW eTh/K ratio anomalies are caused by K alteration associated

with all known porphyry-Cu occurrences in the

Iron Mask area.

(Afton Mine, Ajax Mine, >20 other prospects)

eTho

rium/P

otass

ium

Baseline

315 o L 0

L 250

WL500 WL 7

50 WL 10

00 W

Afton Open Pit

BEATON CLAIMS

Copper King

Hilltop

Maxine

PothookOpen

Pit

AjaxWestPit

AjaxEastPit

Buddha

Ford Kimberly

Makaoo

PythonGalaxy

Iron Mask

Rainbow #2

Reg-Byr

Fargo

Phil

Joker

CrescentOpen

Pit Big Onion

Tailings

km0 5

N

29

Ironmask Area Cu Porphyries, Kamloops Area, BC

eTh/K

IronmaskBatholith:

Alkalic Porphyry (Cu-Mo) Deposits,

Afton, BC



Afton Survey Stacked Profiles, from 2 flight lines

30

eTh/K

eUeTh

eTh

K

MAG

Ajax West Mine Afton Mine

Neither K nor eTh show anomalies, but the eTh/K ratio DOES!



Toodoggone SurveyAfton Survey Stacked Profiles from 2 flight lines

31

Potassium (%)Alteration AND felsic rocks



32

Toodoggone Survey

Thorium/PotassiumLows map epithermal

alteration (NOT felsic rocks)



33

Improvedbedrock

geologicalmapping

Improved surficialgeological mapping

+

+

+ =

Potassium

OriginalGeology

MagneticTotal Field

RevisedGeology

Loam

Sand

Sand

Clay

Clay ??

3 km

Loam

Sand

Sand

Clay

Clay ??



34

Pilley’s Island, NF

K anomalies overlie K-alteredZones near Spencer’s Dock and Chess’s Dome

Felsic-dominated, bimodal VHMSDacitic flows host mineralization

Airborne EM has refined targets

Volcanic hosted massive sulphides – Cu, Pb, Zn, Ag



35

Unaltered pillow basalts

Pilley’s Island, NF

Volcanic hosted massive sulphides – Cu, Pb, Zn, Ag

Altered pillow basalts



36

K %

eTh/K

Epithermal Au, Ag (Cu, Pb, Zn, Hg, Sb)



• Small (0.4 km2), intrudes felsic gneisses• No carb. outcrops; fenitic aureole• Detected 1977 by AGRS: Th-rich glacial

dispersal train with many carb. boulders• 2 DDHs confirmed its presence

Allan Lake, OntarioCarbonatites/Fenites

Airborne “Stacked Profile”High eTh, Low K, eU, flat Mag

Ankerite-siderite carbonatite REEs in synchesite-bastnaesite, apatite

High Th, Zn, Ce, La, Nb, YP, Ba, Cu, Pb, Mo, Co

Ref: Ford, K.L., Delabio, R.N.W. and Rencz, A.N. 1988. Geological, geophysical and geochemical studies around the Allan Lake carbonatite, Algonquin Park, Ontario. Journal of Geochemical Exploration volume 30, pp.99-121



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HemloOntario

K eU eTh

Main Zone

K

eTh/K

Borehole Spectrometry

Barrenmicroclinephase

OreZone

• 3 properties - David Bell, Golden Giant, Page-Williams• 2900m strike length, 2500m down dip, 3 to 45m thick• reserves > 80 Mt 7.7 g/t Au (Mo, Ba Sb, As, Hg also present)

• post-metamorphic hydrothermal potassic alteration: <2 % K in unaltered 10 % K in altered, ore grade rocks

• eTh/K distinguish barren K in felsic volcanics or granites, from anomalous K related tomineralization

Archean shear hosted Au CRAPPY SLIDE AWARD!



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Mazenod Lake NWT

Geo

logy

LOULAKE

1

1

21

3

3 3

3

31

4

7

67

7

7

5

5

Sect

ion

B

A 1 km

116 50'

63 32'

63 34'

116 45'

LOU

LAKE

FAUL

T

LOULAKE

B

LOULAKE

B

1 km

LOULAKE

B

1 km 1 km

A B

DC

Lou Lake volcanic assemblage

Great Bear intrusions (1870-1840 Ma)

Giant quartz vein

Granite, granodiorite plutons

Granite; sodic, leucocratic

Monzonite, quartz monzonite

Quartz-feldspar porphyry

Rhyolite, rhyodacite flows,tuff, agglomerate, siltstone

Snare Group metasediments; argillite, siltstone, quartzite

Syntectonic intrusions (>1900 Ma); dacite, granodiorite, monzonite

SYMBOLS

Au-Co-Cu-Bi-W-As

UNCONFORMITY

Vein & disseminated

U veins

8

7

6

5

4

3

2

1

K% eTh/K

eU/eTh MAG

Felsic flows

Granite

Metaseds

Vein, disseminated Bi-Cu-Co-Au-As



40

Felsic volcanic rocks

Felsic volcanic rocks

km0 4

B

Porphyry Cu-Au-Mo

Casino DepositYukon Territory

K%

eTh/K

Deposit

Deposit



Ground spectrometry follow-up to airborne gamma ray survey. Two days of field work, 34 measurements.

Direct detection, distinguishing end-member (Mg-Ca) carbonatite phases bytheir differing concentrations of U and Th.

U is closely associated with Ta in pyrochlore, columbite

eU

eTh

British ColumbiaCarbonatite Sills, Dikes

K

eTh

Beforsite

BeforsiteSӧvite

Sӧvite

F.I.



42

Environmental/HealthAnd

EmergencyRadiological/Nuclear

Response



Proposed NewDevelopment

RADON LEVELIN HOMES

>800150 - 800<150

eURANIUM (ppm)200 m line spacing

(Bq/m )3

AGRS eU(ppm)

0 - 11 - 22 - 44 - 6> 6

<150Bq/m3

>150Bq/m3

>800Bq/m3

52.9% 47.1% 049.2% 50.8% 6.6%53.3% 46.7% 16.7%33.3% 66.7% 36.4%24.1%

U.S.E.P.A.

Guideline

HealthCanada

Guideline

65.9% 41.4%

Calciocarbonatite (sövite), dominated by whitish calcite, minor brownish pyrochlore is slightly uraniferous(Na,Ca)2Nb2O6(OH,F) - a niobium ore mineral & very mildly radioactive

blackish biotite mica + pyroxene or amphibole and minor blackish magnetite.

http://www1.newark.ohio-state.edu/Professional/OSU/Faculty/jstjohn/Carbonatites/Oka-Carbonatite.htm

Gamma ray surveysFor exploration andenvironment

Oka, Quebec



44

Port HopeOntario

RadioactiveLandfill

Sites

SubdivisionsPlaygrounds

??

This slide intentionally fuzzy!



45

Douglas PointNuclear

GeneratingStation

Bruce

Exposure RateuR/hr

0.75

1.00

0.00

0.50

1.25

1.50

1.75

Argon-41 plume Nuclear generating station

Douglas Point, Ontario



46

1978 Cosmos-954 satellitenuclear emergency response Great Slave Lake

Northwest Territory



47

GreatSlaveLake

HayRiver

DawsonLanding

FortResolution

Radioactivity FromCosmos 954 Debris

1.5 km

1978 Russian Cosmos-954 satellite



48

Lost Radioactive Sources, Dirty Bomb Stuff



49

NRCan Results ….

Near real-time paper output delivered less than 1 hour after surveying commenced

Incident commander (red cap) has maps in front of him ………..… to aid ground crew deployment.



Gamma rays are good for you!Gamma ray spectrometry helps geological

mapping, mineral exploration, environmental monitoring, health and security issues.

Conclusion:



Gamma Ray Spectrometry:Exploration, Environment, Health and Safety

Thank You!

gamma ray spectrometry theory and...

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