191

DEtErmination of Fluorin€ in Eighty International Geochemical REfErmcc Sampks by Proton InducEd Gamma Ray Emission SpEctromEtry (PIGE)

Iwan ROELANDTS

Geology, P e t r o l o g y and Geochemis t ry , U n i v e r s i t y o f L i s g e , B4000 S a r t Ti lman, L i s g e , Belgium

Guy R O R A Y E , Georges WEBER* and Jeanne-Pari e DELBROIJCK

Exper imen ta l Nuc lea r P h y s i c s , U n i v e r s i t y o f L i s g e , B4000 S a r t Ti lman, L i s g e , Belgium

Fluorine content has been determined non des- tructively in e!ghty international peochemical reference samples (GRS) including rocks, so i l s , sediments, minerals a n d ores, by p r o t o n induced gamna ray emission spectrometry (PIGE) using the nuclear reaction 'OF(p ,py) l60. Under our operating conditions, the detection l imit i s around 25 ppn. Our analytical resul ts are compared w i t h the me- sently preferred values when available or w i t h other pub1 i shed data. The general agreewent between th is work and reported values i s reasona- bly good. The present paper includes resul ts on several GRS for which existing d a t a are rather scarce or even inexistant.

The d e t e r m i n a t i o n of f l u o r i n e i n geochemica l samples i s one of t he most d i f f i c u l t a n a l y t i c a l problems. L a r g e amounts of f l u o r i n e are ma in ly a n a l y s e d by g r a v i m e t r i c o r t i t r a t i o n p r o c e d u r e s . Fo r t r a c e amounts , t h e most common t e c h n i q u e s i n c l u d e : DC emiss ion s p e c t r o g r a p h y (l), t i t r a t i o n ( 2 ) , spec t ropho tomet ry ( 3 ) and f l u o r i d e ion-elec- t r o d e ( 4 ) . D e s t r u c t i v e a c t i v a t i o n a n a l y s i s methods u s i n g t h e r m a l ( 5 ) or f a s t (6 ) n e u t r o n s , and nho- t o n s ( 7 ) have been employed. These r e q u i r e cons i - d e r a b l e chemica l m a n i p u l a t i o n : comple t e d i s s o l u - t i o n of t h e sample, s e p a r a t i o n of t h e f l u o r i n e from p o s s i b l e i n t e r f e r e n c e s ( p r e c i p i t a t i o n , d i s - t i l l a t i o n , ion-exchange, s o l v e n t e x t r a c t i o n , pyro- h y d r o l y s i s ) . A l l t h e s e p r o c e d u r e s are complex and v e r y time-consuming, t h a t restricts t h e h a n d l i n g o f l a r g e numbers o f samples t h a t are o f t e n encoun- t e r e d i n geochemical i n v e s t i g a t i o n s . S e v e r a l i n s - t r u m e n t a l t e c h n i q u e s have a l s o been d e s c r i b e d in the l i t e r a t u r e e.p. X-Ray f l u o r e s c e n c e (a), mass s p e c t r o m e t r y (9), a c t i v a t i o n a n a l y s i s w i t h f a s t (10) o r e p i t h e r m a l (11) n e u t r o n s , p a r t i c l e induced

* Research A s s o c i a t e o f t h e N a t i o n a l Fund f o r S c i e n t l f i c Resea rch (Belgium).

gamma r a y e m i s s i o n (PIGE) (12 ) . Very few a n a l y t i - c a l t e c h n i q u e s a re c a p a b l e of p roduc ing u s e f u l d a t a a t c o n c e n t r a t i o n levels below 100 ppm i n s i l i c a t e r o c k s .

The PIGE method used h e r e i s based on t h e n u c l e a r r e a c t i o n ' 9F(p , ay ) ' eO . The i d e a o f apply- ing t h i s t e c h n i q u e t o t h e d e t e r m j n a t i o n of f l u o r i n e is n o t new. Fiowever, o n l y a l i m i t e d number of l a b o r a t o r i e s are equipped t o pe r fo rm a n a l y s i s of f l u o r i n e by t h i s t echn ique . As f a r as i t c a n h e a s c e r t a i n e d , o n l y f o u r p a p e r s have r e p o r t e d p r o t o n bombardment t o d e t e r m i n e F l u o r i n e i n s e v e n USGS and one CRPG r e f e r e n c e samples (12- 15) . In t h i s method, no d i s s o l u t i o n and s e p a r a t i o n s t e p s are r e q u i r e d , no l o s s of f l u o r i n e hy vola- t i l i s a t i o n i s t o b e t a k e n i n t o a c c o u n t .

H i t h e r t o s i x p a p e r s d e a l i n g w i t h t h e d e t e r n i - n a t i o n o f f l u o r i n e in i n t e r n a t i o n a l geochemical r e f e r e n c e samples (GRS) have been p u b l i s h e d i n t h i s J o u r n a l (16-2.). In t h e p r e s e n t work e i g h t y GRS i s s u e d by d i f f e r e n t o r g a n i s a t i o n s i n t h e world (USGS, CRPG, ANRT, YINTEK, G C J , CCRKP, CT, NBS) and c o n t a i n i n g wide ly v a r y i n g c o n t e n t s o f f l u o r i n e w e r e a n a l y s e d by t h e PIGF method. They i n c l u d e i g n e o u s , metamorphic and s e d i m e n t a r y s i l i ca tes , c a r b o n a t e s , p h o s p h a t e s , m i n e r a l s , s o i l s and ores. A l l t h e s e r e f e r e n c e materials a r e of g r e a t v a l u e n o t o n l y t o s i l i c a t e a n a l y s t s bu t a l s o t o s o i l s c i e n t i s t s , e n v i r o n m e n t a l i s t s , a g r i c u l t u r a l che- m i s t s . . . F o r many of these samples , t h e p u b l i s h e d r e s u l t s f o r f l u o r i n e a re s t i l l v e r y scarce. Our d a t a f o r some of t h e samples a re t h e f i r s t t o be publ€shed.

EYPERIMEl!TAL

The PIGE method, f u l l d e t a i l s o f which w i l l e l s e w h e r e may be b r i e f l y o u t l i n e d as b e p u b l i s h e d

f ollnws.

Geostamlards Newsletter, Vol. 9, N o 2 , 08zto6re 1985, p . 197 2 19"

192

Samples f o r a n a l y s i s a r e made from a mixture of 9 p a r t s of powdered sample and 1 p a r t of pure g r a p h i t e SP-1C powder (Union Carb ide) . The mixture i s thoroughly ground and i n t i m a t e l y mixed i n a n a g a t e mortar b e f o r e p e l l e t i n g under 4 T p r e s s u r e .

S y n t h e t i c s t a n d a r d s are prepared in t h e same way by us ing pure q u a r t z (Merck) a s t h e m a t r i x and varying s u i t a b l e amounts of sodium f l u o r i d e , and n ix ing wi th 102 g r a p h i t e by weight .

The P I G E system, used i n t h i s s tudy i s s i m i - lar t o t h a t descr ibed p r e v i o u s l y ( 2 2 ) . The 3-MeV Van de Graaff a c c e l e r a t o r (HVEC) of t h e Experi- mental Nuclear Phys ics I n s t i t u t e ( U n i v e r s i t y of Liege) i s used as a source of pro tons t o bombard t h e g e o l o g i c a l m a t e r i a l s . For each run, s i x t e e n p e l l e t s a r e mounted onto an aluminum t a r g e t l a d d e r and i r r a d i a t e d under vacuue w i t h a 500 nA, 1.5 MeV i n c i d e n t proton beam. The beam s p o t a r e a is about 20 m m z . I n c o n t r a s t with o t h e r i n v e s t i g a t o r s , working with Ge(Li ) , t h e d e t e c t o r used f o r t h i s s tudy i s a 3" x 3" NaI ( T l ) gamma probe ( A E / E = 7% FHHM).

F l u o r i n e i s analysed us ing 7.12 MeV gamna r a y from ( 6 0 . Samples a r e counted f o r a n accumulated charge of 1 mC. The p u l s e h e i g h t a n a l y s i s was per- formed with a IN90 ( I n t e r t e c h n i q u e ) mul t ichannel a n a l y s e r . The i n t e g r a t e d s i g n a l is p r o p o r t i o n a l t o t h e f l u o r i n e conten t of t h e g e o l o g i c a l sample. Background c o r r e c t i o n s a r e a p p l i e d throughout .

P.ESllLTS ANC DISCUSSION

Under our o p e r a t i n g c o n d i t i o n s , t h e lower l i m i t of d e t e c t i o n has been c a l c u l a t e d as t h e amount which g i v e s a n e t i n t e n s i t y equal t o t h r e e times t h e s tandard count ing e r r o r of t h e back- ground i n t e n s i t y and found t o be equal t o 25 p p ~ of f l u o r i n e .

The p r e c i s i o n of t h e method has been estima- t e d from some r e p l i c a t e de te rmina t ions on samples o f varying composi t ion. The r e l a t i v e s tandard d e v i a t i o n i s 10% a t 100 ppm f l u o r i n e c o n t e n t , 6% a t 1000 ppm f l u o r i n e c o n t e n t and 3% a t 1% f l u o r i n e conten t . These va lues i n c l u d e a l l e r r o r s a r i s i n g i n our a n a l y s e s (count ing e r r o r s , homogeneity of t h e samples.. . )

To e v a i u a t e t h e g e n e r a l v a l i d i t y of t h e pre- s e n t method f o r t h e de te rmina t ion of f l u o r i n e , e ighty GRS have been ana lysed as r o u t i n e samples. These GRS powders were used as rece ived from t h e producers . Our a n a l y t i c a l r e s u l t s on t h e s e samples ( i n ppn except where o t h e r w i s e i n d i c a t e d ) a re g iven i n Tables 1 t o 6 and compared w i t h t h e es t i - mates quoted in previous compi la t ions whenever a v a i l a b l e a s w e l l a s means by groups of a n a l y t i c a l methods. Our va lues f o r most samples a r e from s i n g l e de te rmina t ions . Comparison with l i t e r a t u r e i s sometimes d i f f i c u l t because of t h e p a u c i t y of t h e f l u o r i n e d a t a o r t h e enormous spread of t h e repor ted r e s u l t s obtained by t h e v a r i o u s a n a l y t i -

c a l methods. An i n s p e c t i o n of t h e s e t a b l e s shows t h a t f o r a m a j o r i t y of cases car 1 - d u e s f a l l w i t h i n t h e range o f compiled d a t a and compare favorably w i t h t h o s e p r e v i o u s l y publ ished. How- e v e r , s e v e r a l d i s c r e p a n c i e s do e x i s t . Each t a b l e i s b r i e f l y d i s c u s s e d below.

Table 1

F l u o r i n e d a t a on e i g h t o l d e r (G-1 t o PCC-1) USGS rock s t a n d a r d s (USGS I, 11) and s i x USGS-AES geochemical e x p l o r a t i o n r e f e r e n c e samples (GXR-1 t o GXR-6) have been r e c e n t l y c o l l e c t e d i n two compi la t ions by Gladney e t a l . (23, 25). Consensus v a l u e s have been based on c o l o r i m e t r y (COLOR) and f l u o r i d e ion e l e c t r o d e ( ISE) f o r USGS I , I1 and on TSE f o r GXR samples. For t h e remaining USGS samples, r e c e n t compi la t ions by S t e c h e r (21) (USGS 111) and Flanagan ( 2 4 ) (USGS IV) were used. In s t r i k i n g c o n t r a s t w i t h t h e t w o f i r s t genera- t i o n s , the q u a n t i t y of a n a l y t i c a l d a t a r e p o r t e d f o r t h e s e new series is comparat ively s m a l l , and l a r g e u n c e r t a i n t i e s e x i s t among t h e a v a i l a b l e con- c e n t r a t i o n r e s u l t s . With the except ions of G-1 and GXR-1, t h e f l u o r i n e v a l u e s obta ined i n t h e present work f a l l w i t h i n t h e quoted ranges and a g r e e in most i n s t a n c e s w i t h t h o s e compi la t ions by approxi- mately t e n percent . For G-1, t h e c o a r s e g r a i n s i z e has been o f t e n noted i n t h e l i t e r a t u r e as a source of t h e s c a t t e r of t h e i n d i v i d u a l r e s u l t s . Indeed, t h e r e p o r t e d v a l u e s obta ined by t h e v a r i o u s analy- t i c a l methods range from 70 t o 920 ppm.

For GXR-1, o u r v a l u e i s h igher t h a n t h e con- sensus v a l u e by approximately a f a c t o r o f 1 .5 . A p e l l e t w a s f i r s t ana lysed i n d u p l i c a t e (1962 ppm and 2000 ppm). To de te rmine whether t h e f l u o r i n e w a s d i s t r i b u t e d homogeneously among b o t t l e s , w e decided t o r e p e a t t h e experiment from a second b o t t l e (1941 ppm). There w a s no s i g n i f i c a n t d i f f e r e n c e i n t h e f l u o r i n e c o n t e n t between each b o t t l e . It i s known t h a t e lements such as aluminum and i r o n form s t r o n g complexes w i t h f l u o r i d e i n t h e s o l u t i o n and i n t e r f e r e w i t h i t s de termina t ion by ISE by reducing t h e f r e e f l u o r i d e . Perhaps t h e h i g h i r o n c o n c e n t r a t i o n of GXR-1 (25%) and a t o o low amount of masking a g e n t s are the explana t ions f o r t h e lower ISE value . There i s a need f o r addi- t i o n a l d a t a by independent methods b e f o r e t h e f l u o r i n e c o n t e n t i s w e l l e s t a b l i s h e d i n samples h igh i n i r o n . The u l t r a b a s i c rocks DTS-1 and PCC-1 c o n t a i n f l u o r i n e in amounts below o u r l i m i t of d e t e c t ion.

Our v a l u e s f o r W-1 and ZJ-2 are p r a c t i c a l l y s i m i l a r , which seems t o be e v i d e n t s i n c e t h e s e GRS were c o l l e c t e d from t h e same quarry.

For t h e remaining two USGS IV samples, i t Is not p o s s i b l e t o comment f u r t h e r on o u r r e s u l t s : more d a t a on t h e s e rocks are c l e a r l y d e s i r a b l e .

T a b l e 2

For t h e French GRS compi la t ions by Govin- d a r a j u have been used (26-33). Among t h e 18 samples ana lysed "working va lues" have been assi-

193

Table 1. Comparison o f dati! on reference samples from U.S. Geological Survey, USA

LITERATURE

Sample No Type

G-1 w - I AGV- 1 BCR-1 O T S - I G-2 GSP-1 PCC-1 BHVO-1 MAG-1 QLO-1 RGM-1 sco-I SDC- 1 SGR-1 STM-I BIR-1 ONC-1 w-2 GXR-1 GXR-2 GXR-3 GXR-4 c GXR-5 GXR-6

g r a n i t e diabase andesi t e b a s a l t dun i te g r a n i t e g r a n o d i o r i t e p e r i d o t i t e b a s a l t marine mud quar tz l a t i t e r h y o l i t e Cody shale mica s c h i s t shale syen i te b a s a l t diabase diabase jaspero id s o i l deposi t

s o i l s o i l

:opper m i l l - head

This work Proposed values

603 7 2 0 ~ 3 0 201 230240 41 7 420250

(25 1 226 514 480+40

1279 1260+90 3477 3600+300 425 12+7 379 370 796 800 220 265 306 345 a7 7 750 565 600

886 900 2368 I eon

27 59d 71 l l s d

205 1 80d

6.37% 8. 6+3. o

1961 1200~190 416 4302120

2686 2970+270 239 280~TlO 208 240270

Ref. I n d i v j d u a l Means by A n a l y t i c a l Techniques COLOR I S E

23 23 23 23 23 23 23 23 Z i 21 21 21 21 21 21 21 24 24 24 25 25 25 25 25 25

1400 650

2850 600 600

720+2e(3)

457555(7) 494?43(8)

9+9 (7)

248:50( 5 )

10+9( 3 ) 1 2 z 0 ~ 7 9 ( 10) 3604+167 (8)

3E3213 ( 3 ) 737 264(2)

749 587

1869 890 130(2)

334(2)

144+95( 3 ) 199T2)

Others

664' P IGE

408' P I G E 49Ib,47OC PIG€ 17' P IGE 1224'PIGE 4608+1409(4) OES 17'PTGE 500 CHEM 900 CHEM 200 CHEM 600 CHM 600 CHM 1100 CHEM 1700 CHEM 900 CHEM 37 5SMS 56 SSMS 164 SSMS

285" PIGE

The f i g u r g i n parentheses 1 ' 8 d i c a t e s the number o f balues. aRef.13; Ref.14; 'Ref.15; magnitude. Abbrev iat ions : CHEM : chemical methods, i n genera l ; C O L O R : c o l o r i m e t r y ; ISE : s p c c i f i c i o n e lec t rode ; MS : mass spectrometry; OES : (op t i ca l emission spectrometry; P I G € : p a r t j c l e induced gamma ray emission; SSMS : Spark source mass spectrometry; UU : u i i spec i f i ed method.

Table 2. Comparison of data on CRPG and ANRT samples, France

LITERATURE

Sample no Type

GA granite

GH granite

BR basalt

Mica-Fr b i o t i t e

Mica-Mg phlogopite

DR-N diorite

UB-N serpentine

tlX-N bauxite

DT-N dlsthene

VS-N glass standard G5-N granite t K-N feldspar

GL-0 glauconite AN-G anorthositc

BE-N basalt

MA-N granite

AL-I albite IF -6 i r o n farmetinn

This work

565

3886

1214

1 .68%

3.10"

491

89

855

110

25

1077

4 2 5

1929

93

1242

1.13%

d6

45

Working values

500

3500

1000

1.58

2.85

470

1050

120

1000

1.70

45

SO

Ref Individual Means by COLOR

26

26

26 27 l.ss+O.n&(a)

27

28 &DO

28

ztl

28

29

30

30

11

3 2 16Ol:Z)

32 890 1: 2 )

5 2 1.66+0.27(41

33

3>

Analytical 'lechniques ISE Others

439i2) 491+31(7)CHEM

3309(2)

1 O60( 2 )

l.60+o.01(4)

2.79+0.11(4)

49&+76(3,

9 3 ( 2 ) 808(2)

38

930b

1034+25(5)

1620b

1 5 4 ~ 7 2 ( 9 )

1057+168(121

1.62+0.22( 17 1 55225 ( 6 )

97285 ( 7 )

128(2)

3562+516(9)CHEM

881+272(l)CHEM

1 .71aPIGE 2.95(2)CHEM

513+112(4)CHEM

290 CHEM

1003+159(3)CHEM

116+159(3lCHEM

1 S17+16O( 3)CHEM

870 MS

1.30 MS

aRef. I 2

'Ref. 16

194

Table 3. Comparison of data on MINTEK samples, South Africa

LITERATURE Sample No Type This work Recomnended Ref. Individual Means by Analytical Techniques

values COLOR ISE Others

NIM-D NIM-G NIM-L NIM-N NIM-P NIM-S 5-7

5-8

s-9

5-1 0

s-11

5-1 2

5-1 3

S-14

5-15

S-16

S-17

s-18

S-19

s-2 0

dunite granite lujavrite norite pyroxene syenite kimberlite carbonatite

carbonaceous shale soil magnesite

sillimanite schist kinzingiet

stream sediment serpentine granite quartz dolerite

stream sediment stream sediment

* approximative value

425

4920

4783

35

44

146

1998

1143

1248

43

145

181 305

94

42

4.77%

4 2 5

238

102

134

11 MS 4200 34 429021 56 ( 3) 39532337(4) 4400 MS 4400 34 395 72350 ( 3 ) 4257+484(5) BOO0 MS

34 100 25

34 25052 59 ( 3 7 5 3 3 (4 1 10 MS 17151 84 ( 3) 3421 3(4 1 100 MS 34

34 18651 59 ( 3 ) 1 21227 ( 4 170 M5

4.40*

Table 4. Comparison o f data on CCRMP samples, Canada

LITERATURE Sample No Type This work Usable Ref Individual Means by Analytical Techniques

values COLOR I SE Others

S Y - I syenite 1532 35,36 1703+99(3) 1750* 594 uu SY-2 syenite 6047 5100 37-39 46405873(5) 49112203(9) 4900 MS

MRG-1 gabbro 272 250 37-39 29321 2 ( 3 ) 4462345 ( 9 ) 150 MS su- 1 sulphide ore 194 35,36 200

SY-3 syeni te 7295 6600 37-39 6296+1645(5) 6820+527(10) 7100(2) MS

*Ref 40

195

Table 5 . Comparison o f data on r e f e r e n c e samples f rom Geologica l Survey o f Japan

This work Working v a l u e s Ref Sample No Type

JG-la

JB-la

38-2

JB-3

JA-1

JGb-I

JR-1

JK-Z JP-I

g r a m d i n r i t e 459

b a s a l t 347

b a s a l t 90 120

b a s a l t 308

a n d e s i t e 196 170

gabbro 152

r h y o l i t e 949 1100

r h y o l i t e 1002

P e r i d o t i t e < 25

41

41

41

gned f o r 12 GRS. The comparison appears s a t i s f a c - t o r y . For AN-G and IF-G, our d a t a are lower than t h e p r e f e r r e d va lues by approximately 10 percent ; f o r t h e t e n o t h e r GRS, t h e s i t u a t i o n is i n v e r s e . I t is of i n t e r e s t t o n o t e t h a t o u r a n a l y t i c a l r e s u l t s f o r BR and BE-N a r e p r a c t i c a l l y i d e n t i c a l .

For t h e g l a s s s tandard , Govindaraju 's compi- l a t i o n (29) does not sugges t any f l u o r i n e va lue , a l though Jecko and Ravaine (16) r e p o r t e d a v a l u e of 930 ppm by ISE. A major disagreement is found wi th oiir a n a l y s i s : f l u o r i n e i n VS-N is near our d e t e c t i o n l i m i t . An explana t ion f o r t h i s severe discrepancy must await f u r t h e r s tudy.

U13-N, BX-N, DT-N, FK-N, and GL-0 may prove t o be v a l u a b l e GRS i n minera l and i n d u s t r i a l s t u d i e s . No acceptab le va lues have been ass igned f o r any of them. C r i t i c a l comparison of our r e s u l t s w i t h d a t a of o t h e r methods is imposs ib le in t h e s e cases because of t h e p a u c i t y of repor ted v a l u e s o r t h e a n a l y t i c a l d i s p e r s i o n .

Table 3

MINTEK ( former ly NIM) has prepared two sets of r e f e r e n c e m a t e r i a l s : t h e six "NIMROC" (NIM-D t o NIM-S) and f o u r t e e n a d d i t i o n a l "secondary re fe- rence sample : SAROC". Recommended va lues a r e o n l y g iven for NIII-G and NIM-L (34). Our v a l u e s a r e s y s t e m a t i c a l l y h igher t h a n t h e recommended v a l u e s , bu t they compare r a t h e r favorably w i t h t h o s e re- c e n t l y r e p o r t e d f o r NIM-G, NIM-L, NIM-N, NIM-P and NIPI-S by E s p r i t e t a l . ( 4 3 ) u s i n g f a s t neutron a c t i v a t i o n .

A s f a r as w e know, no informat ion has been publ ished on "SAROC" by t h e o r i g i n a t o r . However, i t is c l e a r t h a t t h e s e m a t e r i a l s have great poten- t i a l f o r f u t u r e u s e (e.g. sediments , s o i l s ...) bu+ much a n a l y t i c a l work remains t o be done...

Table 4

The f i r s t rock samples SY-1 and SU-1 have a l s o been included i n t h i s s tudy. Although they

are no longer a v a i l a b l e , many l a b o r a t o r i e s may s t i l l have t h e s e on hand. Furthermore, SU-1 compo- s i t i o n may b e very u s e f u l in t h e a n a l y s i s of su l - phide o r e s . I n a d d i t i o n t o t h e d a t a publ ished i n t h e compi la t ions ( 3 5 , 36), t w o o t h e r v a l u e s have been gleaned i n t h e l i t e r a t u r e f o r s y e n i t e SY-1 : 1750 ppm ISE (40) and 1590 ppn by COLOR (44). Our r e s u l t s are i n accordance w i t h t h o s e pre- v i o u s l y publ ished.

by

For t h e remaining t h r e e C C M rocks , compila- t i n s by Abbey (37-39) were used. The agreement is good even though our v a l u e s are s y s t e m a t i c a l l y somewhat h igher t h a n t h e u s a b l e va lues .

T a b l e 5

For t h e samples analyeed h e r e , l i t t l e i n f o r - mation h a s appeared i n p r i n t . Only t h r e e "working va lues" are a v a i l a b l e (41) w i t h no informat ion on t h e i n d i v i d u a l r e s u l t s from which they were der i - ved. Our v a l u e s mani fes t good agreement w i t h t h e s e d a t a . For t h e six o t h e r samples, a s f a r as w e know, d a t a are f u r n i s h e d f o r the f i r s t t i m e .

Table 6

The composition of t h e samples considered i n t h i s t a b l e d i f f e r s g r e a t l y Prom t h e o t h e r s . They have been s e l e c t e d i n o r d e r t o v e r i f y t h e f e a s i b i - l i t y of t h e PIGE technique for o t h e r types of geo- l o g i c a l m a t e r i a l s such as phosphate and carbonate samples. Gladney e t a l . (42) have r e c e n t l y provi- ded a compi la t ion of a n a l y t i c a l d a t a on NBS refe- r e n c e materials. The consensus v a l u e f o r NBS 120a (phosphate rock) is equal t o 3.88% and is based on ISE. Our r e s u l t confirms t h i s value.

For t h e two A u s t r i a n carbonate rocks i ssued from t h e "Geotechnisches I n s t i t u t " (Vienna), as f a r as i t c a n be a s c e r t a i n e d , on ly ISE d a t a by T r o l l and Farzaneh (17) are a v a i l a b l e and no com- p i l a t i o n of a n a l y t i c a l d a t a h a s ever been publ ished. The ISE v a l u e f o r UI-EA-ADT (dolomite) is very similar t o our r e s u l t s , bu t f o r IU-EA-LLL- 1 ( l imes tone) , our p r e s e n t d a t a are h igher by approximately a f a c t o r of 2.5. More d a t a are needed t o assess which of t h e two va lues is t h e b e s t one.

Table 6. Comparison o f data on NBS (USA) and GI ( A u s t r i a 1 samples

Sample No Type This work Consensus value Ref. COLOR ISE ~~ ~~~

NBSl2Oa phosphate 4.04% 3.88 ? 0.09 42 3.8'

IU-EA-LLL-lC 1 imestone 227 IU-EA-ADTC dolomite 214

aRef 45 bRef ir 'Reference samples issued from Geotechnisches I n s t i t u t , Hien.

rock

91b 19lh

196

CONCLUSIONS

The observed accuracy, the acceptable preci- s i o n and the high s e n s i t i v i t y are su f f i c i ent ev i - dences t o show that the PIGE technique can be used i n place o f , or i n conjunction with, other analy- t i c a l methods to provide fluorine data i n a w i d e variety of geological materials, even i n parti- cularly "d i f f i cu l t" matrices. The present method is re la t ive ly rapid and convenient for routine analysis. I t does not involve chemical pre- treatment of the sample (no dissolution, no sepa- ration). I t I s non destructive; multiple analyses are therefore possible on a s ing le specimen. I t is €ree of spectral interference. I t is hoped that the investigation w i l l be useful for further work i n the determination of f luorine.

ACKNOWLEDGEMENTS

We acknowledge those who have supplied the geochemical reference samples analysed i n t h i s paper. We vers i t a i r e support.

Le f t i v e , dans

are indebted t o the Ins t i tu t Interuni- des Sciences NuclEaires for f inancia l

RESUME

uor a e t6 dose, par vo ie non destruc- k h a n t i 1 lons geochimi- quatre- v i n g t s

ques in te rna t ionaux de r6f6rence de roches, de sols, de sediments, de mineraux e t de miners is au moyen de l a spectrometr ie d'emission gamna i n d u i t e par protons ( P I G € ) su ivant l a reac t i on nucle- a i r e iQF(p,ay) 160. llans nos cond i t ions de t r a v a i l , l a l i m i t e de de tec t ion e s t d 'env i ron 25 ppm. Nos r e s u l t a t s analyt ioues sont compares avec l e s valeurs prefgrees wand e l l e s sont d ispon ib les ou avec l e s valeurs publ i6es dans l a l i t t i r a t u r e . En general, 1 'accord e s t sa t i s fa i san t . Ce t r a v a i l con t i en t de nouveaux r e s u l t a t s sur quelques 6ta- lons pour lesquels l e s donnees sont peu nombreuses ou inexistantes.

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