P O S I V A O Y

FI -27160 OLKILUOTO, F INLAND

Tel +358-2-8372 31

Fax +358-2-8372 3709

V. Juhan i O ja l a

Pas i E i l u

Per t t i Tu runen

Arto Ju lkunen

Seppo Gehör

August 2007

Work ing Repor t 2007 -64

The Use of Gamma Spectrometryin Mapping Alteration Zones in Olkiluoto

August 2007

Base maps: ©National Land Survey, permission 41/MYY/07

Working Reports contain information on work in progress

or pending completion.

The conclusions and viewpoints presented in the report

are those of author(s) and do not necessarily

coincide with those of Posiva.

V. Juhan i O ja la , Per t t i Turunen

Geo log ica l Su rvey o f F in l and , Rovan iem i

Pas i E i l u

Geo log ica l Su rvey o f F in l and , Espoo

Arto Ju lkunen

Ast rock Oy , Sodanky lä

Seppo Gehör

K iv i t i e to Oy , Ou lu

Work ing Report 2007 -64

The Use of Gamma Spectrometryin Mapping Alteration Zones in Olkiluoto

ABSTRACT

In the Olkiluoto site, a detailed gammaspectrometry log from the drill hole OL-KR27

was used to estimate the concentrations of K, Th and U. The gamma spectrometry

results, lithological variations, and kaolinite and illite alteration visually mapped from

the drill hole were compared. The result indicate that the Th/K ratio correlates best with

lithology and that, in most cases, the changes in the ratio indicate lithological contacts

and rising or falling trends of Th/K ratio with some peaks have some correlation with

the kaolinite-illite alteration. From the result it is suggested that that very variable Th/K

ratio is a reasonably good indicator of alteration zones even in the migmatic gneiss area

in the Olkiluoto site.

Gammaspektrometriamittaukset muuttumisvyöhykkeiden kartoittamisessa Olkiluodossa

TIIVISTELMÄ

Olkiluodon tutkimusreikä OL-KR27:n detalji gammaspektrometrimittauksen perusteella

on arvioitu K, Th ja U pitoisuudet. Mittaustuloksia verrattiin visuaalisesti kartoitettuun

kivilajivaihteluun sekä kaoliini- ja illiittimuuttumisiin. Tulosten perusteella näyttää, että

Th/K suhde korreloi selvimmin kivilajien kanssa ja selvä muutos suhteessa indikoi

kivilajikontaktia. Nousevat ja laskevat trendit, joissa on mukana korkeita piikkejä,

korreloivat osittain kaoliini-illiittimuuttumisen kanssa. Tulokset viittaavat siihen, että

hyvin vaihteleva Th/K suhde on kohtuullisen hyvä muuttumisen indikaattori jopa

Olkiluodon alueen kaltaisella migmatiitti-gneissialueella.

1

TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

1. INTRODUCTION .................................................................................................... 2

2. OL-KR27 ALTERATION AND GAMMA SPECTROMETRY ................................... 4 2.1 Visual inspection of the graphic alteration logs and gamma spectrometry ..... 4 2.2 Gamma spectroscopy and alteration components.......................................... 9

2.2.1. Kaolinite-illite alteration ........................................................................... 9 2.2.2. Lithogical control ................................................................................... 15

3. CONCLUSIONS.................................................................................................... 22

REFERENCES ............................................................................................................. 23

2

1. INTRODUCTION

The use of gamma spectrometry to determine concentrations of elemental potassium,

regardless of the associated potassium mineral species, enables alteration mapping in a

wide range of geological settings. For example, potassic alteration is commonly

associated with many types of volcanic-associated massive sulphide base metal and

gold deposits (Franklin, 1996; Poulsen and Hannington, 1996). Potassium feldspar

alteration has been documented as a regional alteration product at volcanic associated

base metal deposits in the Bergelagen district, Sweden (Lagerblad and Gorbatschev,

1985) and in the Mount Read volcanics, Tasmania (Crawford et al, 1992). Potassium

alteration (in a form of sericite or biotite) is also typical to orogenic gold deposits (Eilu

and Groves, 2001, Goldfarb et al., 2001).

Many alkaline and calc-alkaline porphyry Au-Cu (+/-Mo) deposits have extensive

potassic hydrothermal alteration halos (Schroeter, 1995), which vary mineralogically,

both laterally and vertically, with changes in pressure, temperature, eH, and pH during

magmatic, hypogene, and subsequent supergene processes. A well-established

alteration-mineralization potassic zoning sequence common to porphyry deposit has

been recognised by early explorers (eg. Lowell and Guilbert, 1970). The zoning may be

evident within a single deposit, ranging from a central, orthoclase and/or biotite core

(+/- sericite as fracture controlled and pervasive replacements) outwards through

successive phyllic (sericitic), argillic and propylitic zones. Although phyllic zones may

contain less bulk potassium gain than potassic cores, their peripheral distribution

commonly offers much larger targets for detection by gamma spectrometry.

As thorium enrichment generally does not accompany potassium during hydrothermal

alteration processes, Th/K ratios can provide distinction between potassium associated

with alteration and anomalies related to normal lithological variations (Galbraith and

Saunders, 1983). This important correlation of low a Th/K ratio with many alteration

processes is evident in countless studies worldwide.

In the Olkiluoto site, a detailed gammaspectrometry log is available from the drill hole

OL-KR27 (Fig. 1.). This report presents the observations done on the correlation of the

gamma spectrometry results and alteration visually mapped from the drill hole. Special

attention was paid to the correlation of kaolinite and illite alteration, which reduce the

geomechanical strength of the rock, and gamma spectrometry results.

3

Figure 1. Location of the drill hole OL-KR27 at the Olkiluoto site.

4

2. OL-KR27 ALTERATION AND GAMMA SPECTROMETRY

2.1 Visual inspection of the graphic alteration logs and gamma spectrometry

Kivitieto Oy geologist have logged the lithology and alteration in the drill hole OL-

KR27 in detail and Astrock Oy have measured the gamma ray radiation in the hole in

every 5 to 10 cm. The graphic log of the results is presented in Fig 2. The logs were also

available as Astrock’s Hyperdata logs for visual correlation of the gamma spectrometry

and geological logs to the digital image of the drill hole and core.

5

Figure 2. Graphic log of the Gammaspectrometry results and lithological and

alteration logging of the drill hole OL-KR27.

6

It is obvious from the graphic log that the gamma spectrometry values are very variable

at the measured 5 to 10 cm scale, as expected in gneissic and migmatitic rocks, and the

mapped clay or sericite alteration zones do not correlate directly with the calculated low

Th/K ratio. The lithological control seems to be the most important and some low Th/K

and peak U values correlate with pegmatites. However, when a moving average or

standard deviation of Th/K is calculated over one-metre moving intervals (Fig. 3a),

some patterns start to emerge in addition to the lithological control. Most of the mapped

kaolinite and illite alteration zones, and some of the strongest sericite alteration zones,

coincide with the zones of low Th/K or variable Th/K (high standard deviation).

Although many of the mapped alteration zones do not correlate with low Th/K,

graphical log suggests that at least very low Th/K values correlate with alteration, or

some change in rock composition, and the high Th/K standard deviation indicates

lithological contacts or changes in the alteration style or type. Overall, the where Th/K

is very variable seem to have a better correlation with the visually logged alteration

zones than just low Th/K (Figs. 3b and 3c).

7

Figure 3a. Graphic log of the Gammaspectrometry results and lithological and

alteration logging of the drill hole OL-KR27. A column of the standard deviation over

one metre added to the left side and main zones of low Th/K highlighted.

8

Figure 3b. Th/K variations compared with the visually logged kaolinite (green bars)

and illite alteration zones (blue bars) along the drill hole OL-KR27. Th/K variations are

shown as a grey scale image and the darker grey tones indicate larger variations of

Th/K values. Variations of Th/K are imaged by gridding the Th/K values in the xy-

space.

9

Figure 3c. Visually logged kaolinite (green bars) and illite alteration zones (blue bars) compared to the alteration zones (red) inferred from the Th/K ratios and its variability.

2.2 Gamma spectroscopy and alteration components

2.2.1. Kaolinite-illite alteration

Correlation of the kaolinite-illite alteration and total gamma radiation is not obvious in

histogram presentations (eg. Fig. 4). The correlation of the kaolinite-illite alteration

appears to be very poor also with calculated K, U and Th contents as shown in Figs 5 to

7. In all diagrams (histograms, box and whisker and ternary plot) the rocks logged to

belong in the kaolinite-illite alteration zones overlap with less altered zones. This is in

line with the observations from the graphic log inspection that there is enough variation

in the visually estimated alteration zones to mask changes in K, U or Th contents and to

use them directly to indicate alteration.

10

0 100 200 300 400 500 600

0

20

40

60

80

()

OLKR 27

Illite fracture

Kaolinite illite

Figure 4. Total gamma, kaolinite-illite fracture controlled alteration.

11

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

Illite fractureIllite kaoliniteOther

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0 5 10 15 20

0

0.01

0.02

0.03

0 5 10 15 20

0

0.01

0.02

0.03

0 5 10 15 20

0

0.01

0.02

0.03

K

U

Fre

qu

en

cy

F

requency

Figure 5a. Kaolinite-illite fracture controlled alteration, K and U histograms.

12

0 5 10 15 20K/Th

0

0.05

0.1

0.15F

req

ue

ncy

0 5 10 15 20K/Th

0

0.05

0.1

0.15

Fre

qu

en

cy

0 5 10 15 20K/Th

0

0.05

0.1

0.15

Fre

qu

en

cy

Illite fracture

Illite kaolinite

Other

Figure 5b. Kaolinite-illite fracture controlled alteration K/Th ratio.

13

0

10

20

30

K% U_ppm Th_ppm

0

10

20

30

40

K% U_ppm Th_ppm

0

10

20

30

40

50

K% U_ppm Th_ppm

Illite fracture

Illite kaolinite

Other

Figure 6a. Kaolinite-illite fracture controlled alteration box and whisker plots.

14

0

10

20

30

40

50

K% U_ppm Th_ppm

IlliteKaoliniteOther

Figure 6b. Pervasive kaolinite and illite alteration, box and whisker plots overlayed.

0 0.2 0.4 0.6 0.8 1

Potassium

1

0.8

0.6

0.4

0.2

0

Ura

niu

m

1

0.8

0.6

0.4

0.2

0

Thorium

OLKR 27

Illite fracture

Illite kaolinite

Other

Figure 7. Kaolinite-illite fracture controlled alteration on the K-U-Th diagram.

15

2.2.2. Lithogical control

Most of the rocks in the Olkiluoto site are various types migmatitic mica gneisses

(Posiva 2005). The high-grade gneisses and migmatites of Olkiluoto have been grouped

and classified initially on the basis of texture, migmatite structure and major mineral

composition, without any reference to the results of instrumental analyses. The

evaluation of these mesoscopic variables shows that the rocks fall into five major

classes: 1) migmatites MGN, VGN, 2) homogeneous grey gneisses TGG, 3)

homogeneous mica-bearing gneisses and quartzitic gneisses DGN, 4) amphibolites and

other mafic gneisses MFG and 5) granite pegmatites (PGGR). In addition, narrow

dolerite dyke cut the country rocks in places. The migmatites can be divided into three

subgroups in terms of their structural type: vein migmatites, dyke migmatites and mica

gneiss migmatites

On the ternary K-U-Th diagrams and histograms (Fig. 8 to 11) it can be seen that all

other rock types except PGGR overlap and their direct distinction on the basis of

gammaspectrometry is not possible. The higher U content of PGGR can in most cases

be used to distinguish it from the other rock types. However, the large spread of U

values (Fig. 9) suggests that there are different types of pegmatites. The distribution of

U (Fig. 9) and total radiation (Fig. 10) of more mafic rock MFG is slightly lower but

again, individual measurement is not diagnostic of rock type. Migmatites are by

definition heterogeneous rocks and spectrometry data are expected to be complex and

noisy. However, the data suggests that the slight changes in levels and ratios could be

used to detect the lithological contacts.

16

DGN MFG

MGN PGGR

TGG VGN

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

0 0.2 0.4 0.6 0.8 1

K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

Figure 8a. Rock types on the K-U-Th diagrams.

17

0 0.2 0.4 0.6 0.8 1K

1

0.8

0.6

0.4

0.2

0

U

1

0.8

0.6

0.4

0.2

0

Th

DGNMFGMGNPGGRTGGVGN

Figure 8b. KR27 classified rocks on the K-U-Th diagram.

18

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6 7 8 9 10

0

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6 7 8 9 10%

0

0.01

0.02

0.03

0.04

0.05

DGN

MFG

MGN

PGGR

TGG

VGN

Potassium

Figure 9. Potassium histogram.

19

0 2 4 6 8 10 12 14 16 18 20

0

0.01

0.02

0.03

0.04

0.05

0 2 4 6 8 10 12 14 16 18 20

0

0.01

0.02

0.03

0.04

0.05

0 2 4 6 8 10 12 14 16 18 20

0

0.01

0.02

0.03

0.04

0.05

0 2 4 6 8 10 12 14 16 18 20

0

0.01

0.02

0.03

0.04

0.05

0 2 4 6 8 10 12 14 16 18 20

0

0.01

0.02

0.03

0.04

0.05

0 2 4 6 8 10 12 14 16 18 20ppm

0

0.01

0.02

0.03

0.04

0.05

DGN

MFG

MGN

PGGR

TGG

VGN

Uranium

Figure 10. Uranium histograms.

20

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

0 1 2 3 4 5 6 7 8 9 10

0

0.05

0.1

0.15

0.2

0 1 2 3 4 5 6 7 8 9 10%

0

0.05

0.1

0.15

0.2

DGN

MFG

MGN

PGGR

TGG

VGN

Thorium

Figure 11. Thorium histograms.

21

0 10 20 30 40 50 60 70 80

0

0.05

0.1

0 10 20 30 40 50 60 70 80

0

0.05

0.1

0 10 20 30 40 50 60 70 80

0

0.05

0.1

0 10 20 30 40 50 60 70 80

0

0.05

0.1

0 10 20 30 40 50 60 70 80

0

0.05

0.1

0 10 20 30 40 50 60 70 80

0

0.05

0.1

DGN

MFG

MGN

PGGR

TGG

VGN

Total gamma

Figure 12. Total gamma histograms classified by rock types.

22

3. CONCLUSIONS

From the available lithological and alteration logging and gamma spectrometry results

from the drill hole OL-KR27 it can be concluded that:

Th/K ratio correlates well with lithology and abrupt changes in most cases

indicate lithological contacts rather than alteration

there are two pegmatite populations

K/U/Th-peak values do not directly correlate with alteration

very low Th/K ratio indicates alteration or pegmatite

some rising or falling trends of Th/K ratio with some peaks have a weak

correlation with kaolinite-illite alteration

very variable Th/K ratio is a reasonably good indicator of alteration zones

23

REFERENCES

Crawford, A.J., Corbett, K.D. and Everard, J.L., 1992 Geochemistry of the Cambrian

volcanic-hosted massive sulfide-rich Mount Read volcanics, Tasmania, and some

tectonic implications. Economic Geology. v.87, p.597-619.

Eilu, P. and Groves, D.I. 2001 Primary alteration and geochemical dispersion haloes of

Archaean orogenic gold deposits in the Yilgarn Craton: the pre-weathering scenario.

Geochemistry: Exploration, Environment, Analysis, v. 1, p. 183–200.

Franklin, J.M., 1996 Volcanic-associated massive sulphide base metals; in Geology of

Canadian Mineral Deposit Types, (ed.) O.R. Eckstrand, W.D. Sinclair and R.I Thorpe;

Geological Survey of Canada, Geology of Canada, no. 8, p. 158-183.

Galbraith, J.H. and Saunders, D.F., 1983 Rock classification by characteristics of aerial

gamma ray measurements; Journal of Geochemical Exploration, v. 18, p. 49-73.

Goldfarb, R.J. Groves, D.I. and Gardoll, S. 2001. Orogenic gold and geologic time: a

global synthesis. Ore Geology Reviews v 18, p.1–75

Hoover, D.B., and Pierce, A.A., 1990 Annotated bibliography of gamma-ray methods

applied to gold exploration; United States Geological Survey Open File Report 90-203.

Lagerblad, B. and Gorbatschev, R., 1985 Hydrothermal alteration as a control of

regional geochemistry and ore formation in the central Baltic Shield; Geologische

lunschau, v. 74, p.33-49.

Lowell, J.D. and Guilbert, J.M., 1970 Lateral and vertical alteration-mineralization

zoning in porphyry ore deposits; Economic Geology, v. 65, p. 373-408.

Posiva 2005 Olkiluoto Site Description 2004. POSIVA report 2005-03. pp. 444.

Poulsen, K.H. and Hannington, M.D., 1996 Volcanic-associated massive sulphide gold;

in Geology of Canadian Mineral Deposit Types, (ed.) O.R. Eckstrand, W.D. Sinclair

and R.I Thorpe; Geological Survey of Canada, Geology of Canada, no. 8, p. 183-196.

Schroeter, T.G., 1995 Porphyry deposits of the northwestern cordillera of North

America; Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 46,

pp. 888.