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Neutron Activation DEtErmination of Twenty-one TracE Elements , Including Rare - Earths, in Two ANRT GEochEmical RefErencc Samples : Diorite DR-N And GranitE GS-N

IWAN ROELANDTS

Geology, Petrology and Geochemistry University of LiPge, Sart-Tilman par LiSge 1, Belgium

Results for tventy-one truce ezements obtained by nsutror, act ivat ion analysis and high resolution Ge(Li) y-rag spectrometry i n two standard reference rocks -Diori te DR-N and Granite GS-N - distr ibuted by the Asso- c ia t ion Nationale de la Recherche Technique (ANRTI are presented.

There is no longer any need to stress the importance of geochemical reference sam- ples (GRS) in analytical geochemistry. The large number and variety of GRS (1.2) avail- able today bear eloquent witness to their growing importance. For silicate analysis, more than forty GRS are available. They cover a wide range of silicate rocks and minerals and most of them are well characterized for their content of major and minor elements; as such, these GRS are extremely useful for assessing the accuracy of bulk analyses during routine operation and during the development of new procedures. A s regards the trace ele- ments, the situation is much less optimistic, in particular, for elements which occur nor- mally in concentration levels less than 10 to 20 ppm and for elements which are diffi- cultly accessible to "comonl' methods of trace analysis such as atomic absorption, optical emission, and X-ray fluorescence spectrometry.

Under these circumstances, one prac- tical way of promoting trace analysis i: by contributing analytical data on such difficult trace elements by appropriate methods of ana- lysis. Without being a universal method, neu- tron activation analysis (NAA) is well adapted for trace element analysis, as it offers mul- tielement capacity, high sensitivity, and freedom from contamination by chemical re- agents. The purpose of this paper is to pre- sent our results on twenty-one trace elements including eight rare earth elements ( R E E ) , obtained by NAA in two GRS: Diorite DR-N (3) and Granite GS-N ( 4 ) . These two samples repre- sent two important categories of silicate rocks; another reason for choosing them is that they have been prepared in large amounts.

ANALYTICAL PROCEDURE

The analytical procedure employed has been described elsewhere ( 5 ) and is out- lined here very briefly:

-Epithermal neutron irradiation (2 days), followed by a non-destructive analysis

-Thermal neutron irradiation ( I day), fol- lowed by an instrumental analysis

-Thermal neutron irradiation (7 days), f o l - lowed by a radiochemical analysis.

The principle of radiochemical group separation is as follows. After an oxidant alkaline fusion of the irradiated sample and a leaching by water, we obtain two fractions:

-An insoluble hydroxide residue: Sc, Fe, Sr, Ba, REE, ...

-A supernatant liquid: Cr, Zn, Rb, C s , ... The hydroxide fraction is dissolved in 9M HCL and passed through an anion exchange column where the iron and cobalt are retained. The scandium and the REE contained in the eluate are separated by a tri-n-butyl phosphate ex- traction. The organic phase contains the scan- dium; the aqueous phase, the REE.

Table 1. Concentration used for BCR-1 standard (PPm).

- b 7 5

36.2

I1 .h

a.95

4 . 1 2

4 6 . 6

U.63

10.7

130

11.91

~~~~~

(1) Bet. 6; !b) R e f . 8 ; ( c ) Ref. 9 .

Geostandards Nrmkttw, V o l . I , N o I, Janvier 7977, p . 7 d 3

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The yields of the chemical separa- tions are determined by a reactivation tech- nique. The radioactivity measurements are per- formed by means of a high resolution Ge (Li) detector.

The USGS reference sample basalt BCR-I ( 6 ) was used as the multielement compa- rative standard for these activation pro- cedures. This sample has been well studied for its trace element content during the re- cent campaigns on the analysis of lunar mate- rials and has thus become an exceptionally valuable reference sample for trace elements. The values adopted for BCR-I in our work are presented in Table 1 . The DR-N and GS-N sam- ples were analyzed during routine work with no special attention.

Table 2. Comparison o f NAA data on t r a c e e l e - ments i n D i o r i t e DR-N.

Data from 1973 report on 7 Elements This Diorite DR-N (Ref. 3)

(PW) paper Cha' Jaf' Dale' Bra' RVs AV'

BE 400 co 32.6 Cr 32.0 cs 6.13 Hf 2.6 Rb 73.6 Sb 0.41 SC 26.2 Sr 40 I ?a 0.64 Th 4.63 U 1.69 Zn I05

La 19.7 Ce 49 Nd 25.7 sm 5.18 E" 1.57 Tb 0.87 Yb 2.63 L" 0.37

292 22

5.8 2.4 80

310 0.52 5.6 1.4

20 46 39 24 25 3.4 3.4 1.55 1.43 0.61 0.8

2.7 n.65

380 32 33 35

45 b,6.8.9,20

75

36 31 32.32 400

1

22 5.12.5 1.1.3

I50

12

4.8

Table 3 . Comparison o f NAA data on t r a c e e le - ments i n Granite GS-N.

Data from 1974 report On Granite GS-N (Ref. 6) Elements This

( p p d paper Jdf' Pal' VSGS' W* AV'

Ba co CT

cs Hf Rb

Sb

sc

sr Ta Th U

Zn

1414 1338 66.5 54 56.4 41 5.34 8 0.57 5.0 5.3 0.19

179 213 0.50 0.31 6.77 6.4

605 529 2.55 1.67 2.79 43.9 43.25 8.i 4.1 25 36

1440 1380 b2.6 bS 49 55

5.5 b

5.9 I86 I90 0.6 7.19 5

570 2.74

40.7 16

48 57

La 70.5 81 100

Ce 145 I28 141 Nd 52.4 46 49 sm 7.83 9.3 B" 1.70 1.5 1.79 1.5

Tb 0.68 0.60 0.64 Yb 0.96 I .67 I .6 L" 0. I6 0.21 0.22

' - RM resultm; A m l p t - II.Jaftra=ic; * AMly8C - 8 . h l ; Am- lyst - J.J.Sarr sad 1.J.ScluWrtI. unpub1ish.d rtwlts from USCS; ' W - Propoaed value: ' AV - In th. absuta of PV, available ovm-lUA data.

.. - ' - ' IM resu~ts ; Ref. 10. Analyst - H.Jaffreric; Am1y.r - I.A. Dale; ' h l y o t - C.Branche; ' RV - Recownded Value; ' AV - In the ab- lance of RV, available rc.m-NM data.

RESULTS AND DISCUSSION

Our NAA values for Diorite DR-N and Granite GS-N are presented respectively in Tables 2 and 3 and are compared with published NAA results. Due to the paucity of published NAA results, a critical examination of these data is not possible. However, it is seen that in the case of six elements (Ba, Co, Cr, Rb, Sr, Zn) for which reconmended or proposed va- lues are available, our results stand a favo- rable comparison. In the case of the other elements, in particular for REE, the 2 or 3 sets of NAA results show remarkable consis- tency. Another approach to judge our results is to plot a normalized REE concentration for DR-N and GS-N (Fig.1). This procedure consists of taking the ratio of each REE content in the studied material to the average content of the same element in chondrite meteorites

1 La C. m yn EU l b Yb LU

11 Alarnic numbif

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F igure 1. Chondrite-normal i z e d patterns f o r D i o r i t e DR-N and Granite GS-N.

(values taken from Haskin et a1 -Ref. 7) and plotting it against the atomic number of the elements. It is generally admitted that a smooth curve, except for Ce and Eu, is a good criterion of the determination of REE.

ACKNOWLEDGEMENTS

The work was carried out while the author was a guest at the Mineralogisk Geo- logisk Museum, University of Oslo, Norway. He thanks J.A.Dons and A.O.Brunfelt for allow- ing him to use their Ge (Li) detector.

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The Fonds National de la Recherche Scientifique and the Fondation Paul Michot are gratefully acknowledged for financial sup- port.

REFERENCES

( I ) F.J. Plnnaaon (1974) Reference samples for the earth sciences, Geochimica et Cosmochimica Acta, 38 : 1731-1744.

(2 ) S . Ahbey (1975) Studies in "standard samples" of silicate rocks and minerals, part 4 : 1974 edition of "usable" values, Geological Survey of Canada, paper 74-41: 23n.

( 3 ) H.de la Roche et K.Govindaraju ( 1 9 7 3 ) Rapport (1972) sur quatre standards geochimiques de l'hssocaition Nationale de la Recherche Technique : Diorite DR-N, Serpentine US-N, Bauxite BX-N, et Dis- thene DT-N, Bulletin de la SociBtO Fraqaise de COra- mique, 100 : 49-75.

( 4 ) H.de la Roche et K. Govindaraju (1976) Xouveaux &talons g6ochimiques : Granite GS-Y et Feld- spath FK-N, Analusis, 4 : 347-372.

( 5 ) 1.Roelandts (1975) Contribution au dosage par activation neutronique des terres rares et d'autres elements en trace dans les roches magmatiques, ThBse. Universit6 de Lilge.

(6) F.J.Flanagan (1973) 1972 Values for International Geochemical referenre samples, Geochemica et Cosmochimica Acta, 37 : 1189- 1200.

(7) L.A.Haskin, P.A.Helmke, T.P.Paster, and R.O.Allen (1971) Rare earths in meteoritic, terrestrial, gnd lunar mit- ter. In "Activation analysis in geochemistry and cosmo- chemistry", 201-218. Ed : A.O.Brunfelt and E.Steinnes, Oslo.

( 8 ) A.O.Brunfelt and E.Steinnes (1971) A neutron activation scheme developed for the deter- mination of 42 elements in lunar material, Talanta, 18 : 1197-1208.

(9 ) G.Del Fiore, J.M.Peters, and 1.Roelandts (1974) Precise determination of uranium in rocks and minerals by neutron activation analysis using 1331 fission pro- duct, Chemical Geology, 13 : 309-319.

(10) B.Chayla, H.Jaffrezic, et J.L.Joron (1973) Analyse par activation dans les neutrons Spithermiques. Application 5 la determination d'iliments en traces dans lea roches, comptes rendus de l'acadhie des Sci- ences, Paris, 277 : D 277-275.