51

Iodine Content of Some GEochemical ReferencE Samples

R . FUGE AND C.C. JOHNSON

Geology Department, U n i v e r s i t y Col lege o f Wales, Aberystwyth, Dyfed SY23 3DB, United Kingdom

18 geochemical reference samples have been cmalysed for iodine using an automated photo- metr ic method. Few comparative values are available i n the l i t e ra ture but of the s i x that are maiZable four show good agreement wi th the data reported. In a l l but one case the values obtained are Less than 0.3 ppm, the exception being a bauxite (B.C.S. 395) with 8 .8 ppm I .

Since t h e e a r l y 1960's t h e r e has been a c o n s i d e r a b l e re-awakening of i n t e r e s t i n iod ine geochemistry. Much of t h i s i n t e r e s t has been concerned with iod ine i n m e t e o r i t e s where it has been found t o be a s t r o n g l y deple ted element i n o r d i n a r y c h o n d r i t e s (I). I n a d d i t i o n , i n t e r e s t h a s grown i n t h e d i s t r i b u t i o n o f iod ine i n igneous rocks and minera ls ( 2 , 3 ) . However, f e w d a t a f o r t h e i o d i n e c o n t e n t s of geochemical r e f e r e n c e samples a r e a v a i l a b l e i n t h e l i t e - r a t u r e .

The a u t h o r s have developed a r a p i d and s e n s i t i v e method for t h e de te rmina t ion o f i o d i n e i n geochemical samples ( 4 ) . The method o f a n a l y s i s is an automated photometr ic method based on t h e c a t a l y t i c a c t i o n o f i o d i n e on t h e r e a c t i o n between A s 3 + and Ce4+ ( i . e . t h e Sandell-Kol t h o f f r e a c t i o n , 5 ) , fo l lowing a l k a l i f u s i o n . The p r e c i s i o n of t h e method is such t h a t samples c o n t a i n i n g 0.22 ppm and 4.46 ppm I can be determined wi th c o e f f i c i e n t s of v a r i a t i o n o f 26% and 5% r e s p e c t i v e l y . The d e t e c t i o n l i m i t of t h e method is 0 .04 ppm.

RESULTS AND DISCUSSION

The r e s u l t s ob ta ined i n t h i s s t u d y , t o g e t h e r with a v a i l a b l e publ i shed v a l u e s , a r e l i s t e d i n Table 1. I t can be seen from t h i s compi la t ion that only s i x comparat ive v a l u e s a r e a v a i l a b l e and o f t h e s e , f o u r are i n f a i r l y good agreement wi th va lues quoted i n t h e p r e s e n t s t u d y . The comparat ive d a t a l i s t e d f o r t h e U.S.G.S. samples were obta ined by neut ron a c t i v a t i o n a n a l y s i s .

Apart from B.C .S . Bauxi te 395, a l l t h e i o d i n e va lues o b t a i n e d are low ( < 0.3 ppm). There

Table 1. Iodine in geochemical reference samples

I content Comparative Ref. (PP) values . - -. _-

I1.S.G.S.

C.S.G.S.

:I. S .G. s ~

IJ. B .G.S . U.S.C.S.

U.S.G.S.

c .R .P .G.

C.Y.P.G.

C.H.P.G. C.H.P.G. C.L.A.S. C.A.A.S. Tnnzmia

B.C.S. S.C.S. B.C.S.

R.C.S. B.C.S.

Grani te G 2 Cranodior i te GSP-1

Andesi t e AGV-1

Sasal t BCR-1 P e r i d o t i t.e PCC-1 h l n i t e IYIXS-1

GritniTe GA

Gr,mite GA Basalt HR Iron Mica Sulphide Ore

Syenite 1 Tonal i te T-1 Dolomite 368 Ew.?si te j C 9

B a n i i t e 395 Sad8 feldspar 375 Potash feldspar 376

n.d.*

0.11

0.23

0.19 0.26

0.14 0.70f'

0.15

0.m

0.06

0.12 0.24

0.25

0.18

0.04

8.8

0.70 0.22

0.15 (7) 0.06 ( I )

-. . __--.

* n.d. = not detec ted * * l?ie autkrs would l i k e t o poin t Out that i n the Case of this sample

a previously quoted r e s u l t (8) of 0.04 ypn vaB i n error.

appears t o be a l a c k of r e f e r e n c e samples which might have a high i o d i n e c o n t e n t , such as o r g a n i c - r i c h sediments ( 9 ) . The a u t h o r s would welcome t h e o p p o r t u n i t y o f a n a l y s i n g such refe- rence samples i f they are a v a i l a b l e .

RESUME

18 echantil lons geochimiques de refCrence ont e t6 analyses pour leur teneur en iodure avec une methode photometrique automatisee. Peu de donnees pour comparaison sont disponibles mais parmi les six donnees disponibles, quatre sont en accord avec nos valeurs. Sauf dans u n cas, tous les resul ta ts obtenus sont inferieurs a 0.3 ppm, l'exception e t a n t une bauxite (B.C.S. 395) avec 8.8 ppm I .

c.Orturdudr Fkmkttrr, V o 2 . 3, N o I , A v r i L 1979, p . 51 d 5 2

5 2

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