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Distribution of rare earths among component minerals of bruderheim chondrite
EARTH AND PLANETARY SCIENCE LETTERS 2 (1967) 344-348. NORTH-HOLLAND PUBL. COMP., AMSTERDAM
D I S T R I B U T I O N OF RARE EARTHS A M O N G C O M P O N E N T MINERALS OF BRUDERHEIM CHONDRITE M a s a t a k e HONDA a n d M a s a k o SHIMA
Institute for Solid State Physics, University of Tokyo, Tokyo, Japan Received 3 April 1967
The distribution of r a r e e a r t h e l e m e n t s was studied among component m i n e r a l s in an ordinary chondrite, B r u d e r h e i m . F o r this purpose a wet fractional phase separation method was applied to a powd e r e d sample of B r u d e r h e i m . Eleven m e m b e r s of this group of e l e m e n t s in the fractionated samples were d e t e r m i n e d m a s s - s p e c t r o m e t r i c a l l y and by neutron activation, without individual chemical separation. Most of the e l e m e n t s were found to be concentrated in the phosphate fraction which was isolated mainly in EDTA solution. On the other hand, p r a c t i c a l l y all of Eu and an important part of Yb were found in the HCl-insoluble silicate fraction. This r e s u l t may indicate a lower oxidation level of the system in which the m i n e r a l s were formed.
1. I N T R O D U C T I O N In c o s m o c h e m i c a l s t u d i e s a n u m b e r of r a r e elements has recently been determined in chond r i t i c p r i m e v a l m a t e r i a l s [1]. C u r r e n t l y it i s a l s o r e a l i z e d t h a t i t i s u s e f u l to k n o w t h e d i s t r i b u t i o n of t h e m i n o r c o n s t i t u e n t s a m o n g t h e c o m p o nent minerals forming a chondrite assembly. Such knowledge will not only be helpful in understanding the conditions under which a meteorite w a s f o r m e d , b u t w i l l a l s o b e u s e f u l in d e t e c t i n g any minute effect caused by nuclear disintegrat i o n o r n u c l e a r r e a c t i o n w h i c h t o o k p l a c e in t h e extraterrestrial materials. For this purpose a clear-cut phase separation technique is indispensable. Although some extensive studies have been performed along with some particular investigations [2-6], we still have only fragmentary data in this field. We have already examined t h e d i s t r i b u t i o n of a l k a l i a n d a l k a l i n e e a r t h s i n s o m e o r d i n a r y c h o n d r i t e s a n d in a n e n s t a t i t e c h o n d r i t e , a n d h a v e s t u d i e d t h e a p p l i c a t i o n of t h e p h a s e f r a c t i o n a t i o n i n d e t e r m i n i n g t h e a g e of t h e s e c h o n d r i t e s b y t h e R b - S r m e t h o d [7]. In t h i s p a p e r we r e p o r t s o m e p r e l i m i n a r y r e sults concerning rare earth elements distributed in an olivine-hypersthene chondrite, Bruderh e l m . S i n c e v e r y e a r l y d a y s t h e i m p o r t a n c e of t h e r o l e s of r a r e e a r t h s h a s b e e n r e a l i z e d i n g e o c h e m i c a l a n d c o s m o c h e m i c a l s t u d i e s [8]. T h e b e h a v i o r of r a r e - e a r t h group elements was exp e c t e d to b e u n i q u e in m e t e o r i t e s w h i c h h a d b e e n formed under different conditions from terres-
trial rocks [9-16]. A systematic fractionation s c h e m e b y a w e t m e t h o d w a s a p p l i e d to s e p a r a t e the phosphate, sulfide and main silicate phases using a powdered sample.
2. E X P E R I M E N T A L
2.1. Phase separation The method applied for phase separation by a fractional dissolution technique was described in o u r p r e c e d i n g p a p e r s [7]. In t h e p r e s e n t w o r k w e used a total meteorite and the same fractions d e r i v e d f r o m t h e n o n - m a g n e t i c p a r t of t h e m e t e orite which were employed for the Rb-Sr age det e r m i n a t i o n [18]. T h e y w e r e E D T A ( m a i n l y p h o s p h a t e ) , B r 2 ( t r o i l i t e ) , 1N-HC1 ( o l i v i n e ) , 6 N - H C 1 ( r e m a i n d e r of o l i v i n e ) a n d H F (HC1 i n s o l u b l e p o lymerized silicates) fractions. The sample sizes w e r e 1 - 2 g of t h e t o t a l m e t e o r i t e . 2.2. Neutron activation analysis A s i n g l e p i e c e of t o t a l m e t e o r i t e , d r i e d s a m p l e s of s e p a r a t e d f r a c t i o n s a n d r e f e r e n c e s a m p l e s w e r e i r r a d i a t e d i n t h e T r i g a III ( G e n e r a l Atomics) type reactor at the Atomic Power Research Laboratory, St. P a u l ' s U n i v e r s i t y . T h e irradiation was done in the rotating specimen r a c k f o r 2 - 3 w e e k s u s i n g a flux of a b o u t 1012 n / cm2/sec. After the irradiation the samples were diss o l v e d w i t h HNO 3 o r H F + H C 1 0 4 m i x t u r e . A r a d i o c h e m i c a l s e p a r a t i o n w a s d e s i g n e d to i s o l a t e
DISTRIBUTION OF RARE EARTHS the rare-earth g r o u p a s a w h o l e , a n d a l s o to s i m u l t a n e o u s l y d e t e r m i n e Sc a n d o t h e r s . C a r r i e r s of L a , Sc, B a a n d o t h e r s e a c h i n t h e o r d e r of 10 m g w e r e a d d e d to t h e s a m p l e s . T h e s o l u t i o n s w e r e m a d e u p to 8M HC1 a n d w e r e p a s s e d through a 10-20 ml anion exchange column. With 8M HC1 r a r e e a r t h s a n d o t h e r s w e r e r e c o v e r e d in the effluents. Rare earths were separated from others using a 20-50 ml cation exchange c o l u m n . A f t e r e l u t i o n of o t h e r c a t i o n s w i t h 8 c o l u m n v o l u m e s of 2N-HC1, 4 c o l u m n v o l u m e s of 6 N - H C 1 w e r e u s e d to r e c o v e r t h e r a r e e a r t h g r o u p , Sc a n d B a . A n a l t e r n a t e s e l e c t i v e e l u t i o n was also achieved by using 2M ammonium acet a t e . T h e a c e t a t e c o u l d e l u t e r a r e e a r t h s a n d Sc i n t h e f i r s t c o l u m n v o l u m e of t h e e f f l u e n t s l e a v ing Ba and many others in the cation exchange column. Lanthanum hydroxide and the oxalate precipitations were carried out successively.
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T h e r e c o v e r y of t h i s g r o u p a s a w h o l e w a s e s t i m a t e d f r o m t h e w e i g h t of L a 2 0 3. The gamma-ray spectra were observed by conventional devices. By a successive peeling operation (subtraction) using their standard samples and also by the decay measurements extended over three months, more than seven elements could be detected. The following gamma-ray emitters induced by (n,7) reactions were observed. Their photo peaks, the energy indic a t e d i n t h e u n i t of M e V i n p a r e n t h e s e s , were u s e d f o r t h e e s t i m a t i o n s of r e s p e c t i v e n u c l i d e s at an appropriate cooling time. They were 140La ( 0 . 4 3 - 4 9 ) , 1 4 1 C e (0.145), 147Nd (0.09), 1 5 3 S m (0.103), 1 5 2 E u (0.122; 0.34), 1 6 0 T b (0.30; 0.9), 166Ho (0.08), 175Yb (0.40) a n d 1 7 7 L u (0.208). T h e r e l i a b i l i t i e s of t h e d a t a a r e n a t u r a l l y widely different from each other. Less reliable d a t a w e r e i n d i c a t e d b y t h e i r p r e s e n t a t i o n s . A1-
Table 1 Distribution of r a r e e a r t h s in the fractions of B r u d e r h e i m chondrite (unit: ~ g / g total meteorite). Non-magnetic fraction * Fraction (solvent)
Phosphate (EDTA)
Ferrous sulfide (Br2)
Orthosilicate (1N-HC1)
(6N-HC1)
Polysilicate
(HF)
Sum of all fractions
Total meteorite
L i t e r a t u r e [1] average chondrite
Rare earths By m a s s s p e c t r o m e t r y
0.63 0.47 0.154 0.0087 0.23 0.22
0.10 (0.40) 0.17 0.055 0.0032 0.078 0.088
0.118
0.036
La
Ce Nd Sm Eu Gd Dy Er Yb
0.011 0.02 0.02 0.004 0.0010 0.004 0.005 0.002 0.007
>0.002 0.02 0.009 0.003 0.0008 0.001 0.005
0.08 0.19 0.13 0.042 0.076 0.048 0.061 0.060 0.091
0.35
(O.Ol)
(o.o3)
0.07 (o.o7)
0.6 1.4
0.07 0.005 0.02 (0.03) 0.02 0.005
0.002 (0.006) (0.002)
0.003 (o.oo3) (o.ool)
0.005 (0.001)
0.006 (0.001)
0.07 o.12 o.oo8 (o.o3) O.ll o .009
0.30 0.14 0.07 (0.16) 0.21
0.34
1.25 0.79 0.26 0.090 0.36 0.37
1.1 0.61
0.26
0.20
0.23 0.08 0.34 0.34 0.24
By neutron activation La
Ce Nd Sm Eu Tb Ho Yb Lu
0.36 0.9 0.5 0.15 0.01 0.04 (o.1) 0.07 0.02
0.2
0.038
1.4 0.28 0.13 0.06
0.22 0.034
0.052 0.08 0.035
O t h e r e l e m e n t s **
P Sr Sc Mg Fe
520 0.23 (O.O4) 440 860
250 0.30 (0.1) 470 2300
58 0.07 (o.2) 68000 65000
1 0.03 (o.5) 83 750
15
9.5 (7) 47OOO 27000
* L e s s reliable data a r e put into p a r e n t h e s e s . ** These data a r e quoted f r o m a p r e v i o u s r e p o r t [18] except for Sc.
860 10.1 (8) 116000 102 000
10.5
1050 11 8
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M. HONDA and M. SHIMA 100 EDTA
50
°
i
'
r
;
Br,
EDTA
\/ A
20
m 5
La ' Ce ' P'r 1~d Pm ' S'm Eu' Gd T'b Dy ' Ho ' E 'r T m Y'b Lu' Z > mmAe
OAO
Fig. 1. Relative abundances of r a r e e a r t h e l e m e n t s found in the fractionated components of the B r u d e r h e i m meteorite plotted as a function of atomic number. The plots indicated with the solvents, EDTA, B r 2 and HF, correspond to the phosphate, f e r r o u s sulfide and HCl-insoluble silicate fractions, respectively. Content of E r in the total m e teorite was a s s u m e d to be 0.33 ppm which was e s t i m a t e d by an interpolation of other data by r e f e r r i n g to the l i t e r a t u r e [9]. though the individual determination was generally l e s s a c c u r a t e t h a n t h a t of m a s s s p e c t r o m e t r y , the composite spectra apparently demonstrated a n y d i f f e r e n c e in t h e c o m p o s i t i o n s of t h e s a m ples.
ever available the values obtained by this analys i s w e r e a d o p t e d e x c e p t f o r a few d a t a of L a a n d Ce.
3. R E S U L T A N D DISCUSSION 2.3. Mass-spectrometric dilution analysis A n a l i q u o t of t h e f r a c t i o n s w a s s p i k e d w i t h a m i x t u r e of e n r i c h e d i s o t o p e s , 1 3 8 L a , 142Ce, 143Nd, 147Sm, 151Eu, 157Gd, 164Dy, 1 7 0 E r a n d 171Yb. T h e c h e m i c a l s e p a r a t i o n w a s p e r f o r m e d in an almost identical manner with the neutron a c t i v a t i o n m e t h o d . T h e s t e p f o r r e m o v a l of B a f r o m r a r e e a r t h s s e e m e d to b e u s e f u l . T h e m i x t u r e of r a r e e a r t h s w a s p l a c e d o n two s i d e f i l a m e n t s of a t u n g s t e n t r i p l e f i l a m e n t i o n s o u r c e . The AEI MS-5 type mass spectrometer (R = 30 cm) was used with an electron multiplier. Alt h o u g h t h e f r a c t i o n a l e v a p o r a t i o n of t h e e l e m e n t s on t h e f i l a m e n t s w a s u s e f u l to e l i m i n a t e t h e i r mutual interferences, it was a time-consuming work, and quite often the correction term reached a considerable level. The most serious interferences w e r e u s u a l l y c a u s e d b y B a O +, B a O 2 +, a n d m o n o - i s o t o p i c r a r e - e a r t h p e a k s . On t h e w h o l e i t w a s r e l a t i v e l y d i f f i c u l t to e s t i m a t e the heavier elements. In s p i t e of s e v e r a l d i f f i c u l t i e s , g e n e r a l l y m o r e r e l i a b l e d a t a ( n o r m a l l y b e t t e r t h a n +10~0 e r r o r ) c o u l d b e o b t a i n e d b y t h i s m e t h o d [16, 17]. W h e r -
T h e c o n t e n t s of a b o u t e l e v e n r a r e - e a r t h e l e m e n t s d e t e r m i n e d i n f i v e f r a c t i o n s of B r u d e r helm are tabulated in table 1 with some other data for comparison. Fig. 1 i l l u s t r a t e s t h r e e m a j o r p a t t e r n s of t h e r e l a t i v e a b u n d a n c e s f o u n d in the EDTA, Br 2 and HF fractions. A remarkable difference in their relative abundances between the EDTA (or Br2) and HF fractions may be very impressive at first inspection. Except f o r E u a n d Yb, 60% of a l l r a r e e a r t h s w e r e equally recovered in the EDTA fraction, which d i s s o l v e d o n l y a m a j o r p a r t of c a l c i u m p h o s p h a t e . On a v e r a g e 23% of t h i s g r o u p w a s a l s o found in the next bromine soluble ferrous sulfide fraction. And the composition was fairly parallel w i t h t h a t of t h e f i r s t f r a c t i o n . A c c o r d i n g to t h e mass spectrometry, Ce in the Br 2 fraction was m e a s u r e d to b e a b o u t 50% h i g h e r t h a n a n a v e r a g e v a l u e of t h e o t h e r r a r e e a r t h s . T h i s f i g u r e m a y n o t b e a c c u r a t e b e c a u s e a d o s e of t h e s p i k e u s e d in this measurement w a s t o o low. In f a c t two composite gamma-ray s p e c t r a of t h e B r 2 a n d EDTA samples have shown practically identical
DISTRIBUTION OF RARE EARTHS pictures throughout the counting period. The s e c o n d g r o u p m a y o n l y b e a t t r i b u t e d to t h e r e s i d u a l p a r t of r a r e e a r t h s a s s o c i a t e d w i t h t h e p h o s p h a t e l o c a t e d b e t w e e n t h e g r a i n s of s u l f i d e a n d s i l i c a t e m i n e r a l s . T h e a m o u n t s of p h o s p h o rus recovered in both fractions may support this i n t e r p r e t a t i o n . In f a c t 61% of t o t a l p h o s p h a t e in the non-magnetic fraction was recovered in the E D T A f r a c t i o n a n d 29% i n t h e B r 2 f r a c t i o n . A l t h o u g h t h i s m a y not n e c e s s a r i l y mean that the rare-earth group must be tightly associated with the calcium phosphate or that it forms a minor readily soluble proper mineral in this chondrite, an important correlation between rare earths a n d t h e p h o s p h a t e s e e m s to o f f e r a n a t t r a c t i v e viewpoint. The magnesium-ferrous-orthosilicate fraction w h i c h w a s d i s s o l v e d i n d i l u t e HC1 d i d not s e e m to c o n t a i n a n y s i g n i f i c a n t p a r t of t h i s g r o u p . O n l y a b o u t 1% of e a c h e l e m e n t w a s r e c o v e r e d i n t h i s f r a c t i o n a n d a s h a p e of t h e p a t t e r n w a s n o t c l e a r b e c a u s e of t h e e x t r e m e l y low a b u n d a n c e s . N o n e of t h e a c i d i n s o l u b l e s i l i c a t e s o r o t h e r m i n o r minerals such as chromite or titanate would either be responsible as an important host mine r a l of r a r e e a r t h s i n t h i s m e t e o r i t e e x c e p t f o r Eu. O t h e r r a r e e a r t h s , w h i c h a r e c o o r d i n a t e d with oxygen atoms normally in t h e i r M (III) s t a t e s , w e r e f o u n d to b e d i s t r i b u t e d i n t h i s f r a c t i o n o n l y a t t h e l e v e l of 16% of t h e t o t a l e x c e p t f o r Yb a n d Lu. B y t h e n e u t r o n a c t i v a t i o n m e t h o d C e w a s m e a s u r e d to b e o u t s t a n d i n g l y low b y a f a c t o r of a b o u t 3. C e r i u m i n t h e s a m p l e , h o w ever, could possibly be differentiated from the c a r r i e r L a in t h e c o u r s e of t h e c h e m i c a l p r o c e s s . It w a s p r e s u m a b l y c a u s e d b y o x i d a t i o n w i t h p e r c h l o r i c a c i d to t h e t e t r a v a l e n t s t a t e . As far as we have observed in this preliminary work, the elements which are relatively s t a b l e i n t h e i r M (II) s t a t e s , s u c h a s E u , s e e m to be preferentially accepted in the negative sites of p o l y m e r i z e d , s i l i c a t e s , o r m o s t p r o b a b l y of alumino-silicates. S u c h d e v i a t i n g b e h a v i o r of E u h a s o c c a s i o n a l l y b e e n p o i n t e d o u t to b e s i g n i f i c a n t e v e n i n t e r r e s t r i a l m a t e r i a l s [8, 12, 13, 19]. In t h e s i l i c a t e r o c k s a h i g h t e m p e r a t u r e m i g h t h e l p to k e e p E u a t l e a s t p a r t i a l l y i n t h e d i v a l e n t state even under a relatively higher oxygen partial pressure in the system. The divalent rare earth may be associated with alkaline earths such as Sr which has a similar ionic radius as E u 2+, a n d s t r o n t i u m i s c o m b i n e d m a i n l y i n f e l d s p a r s [17]. In t h e E D T A f r a c t i o n we f o u n d t h a t t h e o n l y 5% of t o t a l S r w a s t a k e n i n t o c a l c i u m p h o s p h a t e a n d 95% i n t h e HC1 i n s o l u b l e p a r t [18]. A s m a l l p e a k o r v a l l e y a t Yb i l l u s t r a t e d i n fig. 1
347
w a s e q u a l l y n o n - p r o m i n e n t a s t h a t of E u n o r w e l l established yet by the direct comparisons with the closest neighbour elements. When we could take this behavior seriously, a rare-earth group w o u l d b e u s e f u l a s a s e t of i n d i c a t o r s f o r a n e f fective oxidation level, oxygen partial pressure a n d t e m p e r a t u r e , of t h e s y s t e m i n w h i c h m i n e r a l s w e r e c r y s t a l l i z e d . In t h e m e t e o r i t e t h e p o t e n t i a l h a d to b e f a i r l y l o w e r , a s s u g g e s t e d b y t h e p r e s e n c e of m e t a l l i c i r o n , t h a n t h e t e r r e s trial media. As far as the present data are conc e r n e d , no a p p r e c i a b l e s m o o t h f r a c t i o n a t i o n e f f e c t due to a g r a d u a l t e n d e n c y of l a n t h a n i d e c o n t r a c t i o n c o u l d b e o b s e r v e d in a n y o n e of t h e c o m p o n e n t s [12, 14, 15]. Practically the same distribution patterns as described above were observed in the HCl-solub l e a n d H C l - i n s o l u b l e f r a c t i o n s of t h e L e e d y c h o n d r i t e . O t h e r t y p e s of c h o n d r i t e s a n d a c h o n d r i t e s s h o u l d a l s o b e s t u d i e d . So f a r w e h a v e found that an enstatite chondrite, Abee, contained l o w e r a b u n d a n c e s of r a r e e a r t h s i n t h e s i l i c a t e p h a s e w i t h o u t a n y a p p r e c i a b l e e n r i c h m e n t of Eu. In t h i s m e t e o r i t e , h o w e v e r , o n l y h a l f of t h e t o t a l strontium was found in the acid-insoluble silic a t e p h a s e [18].
ACKNOWLEDGEMENTS T h e a u t h o r s a r e i n d e b t e d to D r s . A. M a s u d a a n d Y. M a t s u i f o r t h e d i s c u s s i o n s i n t h e p r o b l e m s of n a t u r a l d i s t r i b u t i o n s of r a r e e a r t h s . T h e mass spectrometry and the neutron activation w e r e p e r f o r m e d w i t h t h e h e l p of M i s s S. T a k e u c h i a n d M i s s K. H o r i e , r e s p e c t i v e l y , to w h o m t h e a u t h o r s ' t h a n k s a r e due. T h e y w o u l d a l s o l i k e to t h a n k P r o f e s s o r R. E. F o l i n s b e e , A l b e r t a , C a n ada, for offering us the Bruderheim meteorite sample. REFERENCES [1] H . C . U r e y , A review of atomic abundances in chondrites and the origin of m e t e o r i t e s , Rev. Geophys. 2 (1964) 1. [2] E . V i l c s e k and H.W'~tnke, Ein V e r f a h r e n z u r get r e n n t e n Untersuchung d e r einzelnen M i n e r a l b e standteile von Steinmeteoriten mittels s p e z i f i s c h e r Lbsungsmittel, Z. Naturforsch. 20a (1965) 1282. [3] H. Hintenberger, E . V i l c s e k and H. v~r~fnke, Zur F r a g e d e r Diffusionsverluste von radiogenen und spallogenen Edelgasen aus Steinmeteoriten, Z. Nat u r f o r s c h . 19a (1964) 219. [4] R. Hintenberger, E. Vilcsek and H. W~nke, ~Jber die Isotopenzusammensetzung und ilber den Sitz d e r leichten Uredelgase in Steinmeteoriten, Z. Naturforsch. 20a (1965) 939.
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M. HONDA and M. SHIMA
[5] F. B e g e m a n n , E . V i l c s e k and H.W'~inke, Die P r o d u k t i o n s r a t e n von C1-36 und A r - 3 9 in M e t a l l - und S t e i n p h a s e d e s C h o n d r i t e n L e e d e y , Z. N a t u r f o r s c h . 21a (1966) 110. [6] C . M . M e r r i h u e , E x c e s s x e n o n 129 in c h o n d r u l e s f r o m the B r u d e r h e i m m e t e o r i t e , J. G e o p h y s . R e s . 68 (1963) 325. [7] M. S h i m a a n d M. Honda, D i s t r i b u t i o n and i s o t o p i c c o m p o s i t i o n of l i t h i u m in s t o n e m e t e o r i t e s , Geoc h e m . J. 1 (1966) 27. [8] E . M i n a m i , Gehalte an s e l t e n e n E r d e n in e u r o p l i i s c h e n und j a p a n i s c h e n T o n s c h i e f e r n , N a c h r . G e s . W i s s . GSttingen, M a t h . - p h y s . KI., IV, N . F . L . 1 (1935) 155. [9] R . A . S c h m i t t et al., A b u n d a n c e s of the f o u r t e e n r a r e e a r t h e l e m e n t s , s c a n d i u m , and y t t r i u m in m e t e o r i t i c and t e r r e s t r i a l m a t t e r , C-eochim. C o s m o c h i m . A c t a 27 (1963) 577. [10] R. A. S c h m i t t et a l . , R a r e e a r t h , y t t r i u m and s c a n d i u m a b u n d a n c e s in m e t e o r i t i c and t e r r e s t r i a l m a t t e r II, G e o c h i m . C o s m o c h i m . A c t a 28 (1964) 67. [11] L . A . H a s k i n et al., M e t e o r i t i c , s o l a r and t e r r e s trial rare earth distributions, Phys. Chem. Earth 7 (1966) 169. [12] C. D. C o r y e l l , J . W . C h a s e and J. W. W i n c h e s t e r , A p r o c e d u r e f o r g e o c h e m i c a l i n t e r p r e t a t i o n of t e r r e s t r i a l r a r e e a r t h a b u n d a n c e p a t t e r n s , J. Geop h y s . R e s . 68 (1963) 559.
[13] J. W. C h a s e , J . W . W i n c h e s t e r and C . D . C o r y e l l , L a n t h a n u m , e u r o p i u m , and d y p r o s i u m d i s t r i b u t i o n s in i g n e o u s r o c k s and m i n e r a l s , J. G e o p h y s . R e s . 68 (1963) 567. [14] Y. M a t s u i and A. M a s u d a , On the v a r i a t i o n in r e l a tive a b u n d a n c e s of r a r e e a r t h e l e m e n t s a m o n g m e t e o r i t e s , i g n e o u s r o c k s , and s e d i m e n t s , G e o c h i m . C o s m o c h i m . A c t a 27 (1963) 547. [15] A. M a s u d a and Y. M a t s u i , The d i f f e r e n c e in l a n t h a nide a b u n d a n c e p a t t e r n b e t w e e n the c r u s t and the c h o n d r i t e and i t s p o s s i b l e m e a n i n g to t h e g e n e s i s of c r u s t and m a n t l e , G e o c h i m . C o s m o c h i m . Acta 30 (1966) 239. [16] A. M a s u d a , L a n t h a n i d e s in b a s a l t s of J a p a n with t h r e e d i s t i n c t t y p e s , G e o c h e m . J. 1 (1966) 11. [17] J. A. P h i l p o t t s , C . C . S c h n e t z l e r and H.H. T h o m a s , R a r e e a r t h and b a r i u m a b u n d a n c e s in the B u n u n u H o w a r d i t e , E a r t h P l a n e t . Sci. L e t t e r s 2 (1967) 19. [18] M. S h i m a and M. Honda, D e t e r m i n a t i o n of r u b i d i u m - s t r o n t i u m a g e of e h o n d r i t e s u s i n g t h e i r s e p a r a t e d c o m p o n e n t s , E a r t h P l a n e t . Sci. L e t t e r s 2 (1967) 337. [19] D. G. Towell e t a l . , R a r e e a r t h d i s t r i b u t i o n in s o m e r o c k s and a s s o c i a t e d m i n e r a l s of the b a t h o l i t h of S o u t h e r n C a l i f o r n i a , J. G e o p h y s . R e s . 70 (1965) 3485.
D I S T R I B U T I O N OF RARE EARTHS A M O N G C O M P O N E N T MINERALS OF BRUDERHEIM CHONDRITE M a s a t a k e HONDA a n d M a s a k o SHIMA
Institute for Solid State Physics, University of Tokyo, Tokyo, Japan Received 3 April 1967
The distribution of r a r e e a r t h e l e m e n t s was studied among component m i n e r a l s in an ordinary chondrite, B r u d e r h e i m . F o r this purpose a wet fractional phase separation method was applied to a powd e r e d sample of B r u d e r h e i m . Eleven m e m b e r s of this group of e l e m e n t s in the fractionated samples were d e t e r m i n e d m a s s - s p e c t r o m e t r i c a l l y and by neutron activation, without individual chemical separation. Most of the e l e m e n t s were found to be concentrated in the phosphate fraction which was isolated mainly in EDTA solution. On the other hand, p r a c t i c a l l y all of Eu and an important part of Yb were found in the HCl-insoluble silicate fraction. This r e s u l t may indicate a lower oxidation level of the system in which the m i n e r a l s were formed.
1. I N T R O D U C T I O N In c o s m o c h e m i c a l s t u d i e s a n u m b e r of r a r e elements has recently been determined in chond r i t i c p r i m e v a l m a t e r i a l s [1]. C u r r e n t l y it i s a l s o r e a l i z e d t h a t i t i s u s e f u l to k n o w t h e d i s t r i b u t i o n of t h e m i n o r c o n s t i t u e n t s a m o n g t h e c o m p o nent minerals forming a chondrite assembly. Such knowledge will not only be helpful in understanding the conditions under which a meteorite w a s f o r m e d , b u t w i l l a l s o b e u s e f u l in d e t e c t i n g any minute effect caused by nuclear disintegrat i o n o r n u c l e a r r e a c t i o n w h i c h t o o k p l a c e in t h e extraterrestrial materials. For this purpose a clear-cut phase separation technique is indispensable. Although some extensive studies have been performed along with some particular investigations [2-6], we still have only fragmentary data in this field. We have already examined t h e d i s t r i b u t i o n of a l k a l i a n d a l k a l i n e e a r t h s i n s o m e o r d i n a r y c h o n d r i t e s a n d in a n e n s t a t i t e c h o n d r i t e , a n d h a v e s t u d i e d t h e a p p l i c a t i o n of t h e p h a s e f r a c t i o n a t i o n i n d e t e r m i n i n g t h e a g e of t h e s e c h o n d r i t e s b y t h e R b - S r m e t h o d [7]. In t h i s p a p e r we r e p o r t s o m e p r e l i m i n a r y r e sults concerning rare earth elements distributed in an olivine-hypersthene chondrite, Bruderh e l m . S i n c e v e r y e a r l y d a y s t h e i m p o r t a n c e of t h e r o l e s of r a r e e a r t h s h a s b e e n r e a l i z e d i n g e o c h e m i c a l a n d c o s m o c h e m i c a l s t u d i e s [8]. T h e b e h a v i o r of r a r e - e a r t h group elements was exp e c t e d to b e u n i q u e in m e t e o r i t e s w h i c h h a d b e e n formed under different conditions from terres-
trial rocks [9-16]. A systematic fractionation s c h e m e b y a w e t m e t h o d w a s a p p l i e d to s e p a r a t e the phosphate, sulfide and main silicate phases using a powdered sample.
2. E X P E R I M E N T A L
2.1. Phase separation The method applied for phase separation by a fractional dissolution technique was described in o u r p r e c e d i n g p a p e r s [7]. In t h e p r e s e n t w o r k w e used a total meteorite and the same fractions d e r i v e d f r o m t h e n o n - m a g n e t i c p a r t of t h e m e t e orite which were employed for the Rb-Sr age det e r m i n a t i o n [18]. T h e y w e r e E D T A ( m a i n l y p h o s p h a t e ) , B r 2 ( t r o i l i t e ) , 1N-HC1 ( o l i v i n e ) , 6 N - H C 1 ( r e m a i n d e r of o l i v i n e ) a n d H F (HC1 i n s o l u b l e p o lymerized silicates) fractions. The sample sizes w e r e 1 - 2 g of t h e t o t a l m e t e o r i t e . 2.2. Neutron activation analysis A s i n g l e p i e c e of t o t a l m e t e o r i t e , d r i e d s a m p l e s of s e p a r a t e d f r a c t i o n s a n d r e f e r e n c e s a m p l e s w e r e i r r a d i a t e d i n t h e T r i g a III ( G e n e r a l Atomics) type reactor at the Atomic Power Research Laboratory, St. P a u l ' s U n i v e r s i t y . T h e irradiation was done in the rotating specimen r a c k f o r 2 - 3 w e e k s u s i n g a flux of a b o u t 1012 n / cm2/sec. After the irradiation the samples were diss o l v e d w i t h HNO 3 o r H F + H C 1 0 4 m i x t u r e . A r a d i o c h e m i c a l s e p a r a t i o n w a s d e s i g n e d to i s o l a t e
DISTRIBUTION OF RARE EARTHS the rare-earth g r o u p a s a w h o l e , a n d a l s o to s i m u l t a n e o u s l y d e t e r m i n e Sc a n d o t h e r s . C a r r i e r s of L a , Sc, B a a n d o t h e r s e a c h i n t h e o r d e r of 10 m g w e r e a d d e d to t h e s a m p l e s . T h e s o l u t i o n s w e r e m a d e u p to 8M HC1 a n d w e r e p a s s e d through a 10-20 ml anion exchange column. With 8M HC1 r a r e e a r t h s a n d o t h e r s w e r e r e c o v e r e d in the effluents. Rare earths were separated from others using a 20-50 ml cation exchange c o l u m n . A f t e r e l u t i o n of o t h e r c a t i o n s w i t h 8 c o l u m n v o l u m e s of 2N-HC1, 4 c o l u m n v o l u m e s of 6 N - H C 1 w e r e u s e d to r e c o v e r t h e r a r e e a r t h g r o u p , Sc a n d B a . A n a l t e r n a t e s e l e c t i v e e l u t i o n was also achieved by using 2M ammonium acet a t e . T h e a c e t a t e c o u l d e l u t e r a r e e a r t h s a n d Sc i n t h e f i r s t c o l u m n v o l u m e of t h e e f f l u e n t s l e a v ing Ba and many others in the cation exchange column. Lanthanum hydroxide and the oxalate precipitations were carried out successively.
345
T h e r e c o v e r y of t h i s g r o u p a s a w h o l e w a s e s t i m a t e d f r o m t h e w e i g h t of L a 2 0 3. The gamma-ray spectra were observed by conventional devices. By a successive peeling operation (subtraction) using their standard samples and also by the decay measurements extended over three months, more than seven elements could be detected. The following gamma-ray emitters induced by (n,7) reactions were observed. Their photo peaks, the energy indic a t e d i n t h e u n i t of M e V i n p a r e n t h e s e s , were u s e d f o r t h e e s t i m a t i o n s of r e s p e c t i v e n u c l i d e s at an appropriate cooling time. They were 140La ( 0 . 4 3 - 4 9 ) , 1 4 1 C e (0.145), 147Nd (0.09), 1 5 3 S m (0.103), 1 5 2 E u (0.122; 0.34), 1 6 0 T b (0.30; 0.9), 166Ho (0.08), 175Yb (0.40) a n d 1 7 7 L u (0.208). T h e r e l i a b i l i t i e s of t h e d a t a a r e n a t u r a l l y widely different from each other. Less reliable d a t a w e r e i n d i c a t e d b y t h e i r p r e s e n t a t i o n s . A1-
Table 1 Distribution of r a r e e a r t h s in the fractions of B r u d e r h e i m chondrite (unit: ~ g / g total meteorite). Non-magnetic fraction * Fraction (solvent)
Phosphate (EDTA)
Ferrous sulfide (Br2)
Orthosilicate (1N-HC1)
(6N-HC1)
Polysilicate
(HF)
Sum of all fractions
Total meteorite
L i t e r a t u r e [1] average chondrite
Rare earths By m a s s s p e c t r o m e t r y
0.63 0.47 0.154 0.0087 0.23 0.22
0.10 (0.40) 0.17 0.055 0.0032 0.078 0.088
0.118
0.036
La
Ce Nd Sm Eu Gd Dy Er Yb
0.011 0.02 0.02 0.004 0.0010 0.004 0.005 0.002 0.007
>0.002 0.02 0.009 0.003 0.0008 0.001 0.005
0.08 0.19 0.13 0.042 0.076 0.048 0.061 0.060 0.091
0.35
(O.Ol)
(o.o3)
0.07 (o.o7)
0.6 1.4
0.07 0.005 0.02 (0.03) 0.02 0.005
0.002 (0.006) (0.002)
0.003 (o.oo3) (o.ool)
0.005 (0.001)
0.006 (0.001)
0.07 o.12 o.oo8 (o.o3) O.ll o .009
0.30 0.14 0.07 (0.16) 0.21
0.34
1.25 0.79 0.26 0.090 0.36 0.37
1.1 0.61
0.26
0.20
0.23 0.08 0.34 0.34 0.24
By neutron activation La
Ce Nd Sm Eu Tb Ho Yb Lu
0.36 0.9 0.5 0.15 0.01 0.04 (o.1) 0.07 0.02
0.2
0.038
1.4 0.28 0.13 0.06
0.22 0.034
0.052 0.08 0.035
O t h e r e l e m e n t s **
P Sr Sc Mg Fe
520 0.23 (O.O4) 440 860
250 0.30 (0.1) 470 2300
58 0.07 (o.2) 68000 65000
1 0.03 (o.5) 83 750
15
9.5 (7) 47OOO 27000
* L e s s reliable data a r e put into p a r e n t h e s e s . ** These data a r e quoted f r o m a p r e v i o u s r e p o r t [18] except for Sc.
860 10.1 (8) 116000 102 000
10.5
1050 11 8
346
M. HONDA and M. SHIMA 100 EDTA
50
°
i
'
r
;
Br,
EDTA
\/ A
20
m 5
La ' Ce ' P'r 1~d Pm ' S'm Eu' Gd T'b Dy ' Ho ' E 'r T m Y'b Lu' Z > mmAe
OAO
Fig. 1. Relative abundances of r a r e e a r t h e l e m e n t s found in the fractionated components of the B r u d e r h e i m meteorite plotted as a function of atomic number. The plots indicated with the solvents, EDTA, B r 2 and HF, correspond to the phosphate, f e r r o u s sulfide and HCl-insoluble silicate fractions, respectively. Content of E r in the total m e teorite was a s s u m e d to be 0.33 ppm which was e s t i m a t e d by an interpolation of other data by r e f e r r i n g to the l i t e r a t u r e [9]. though the individual determination was generally l e s s a c c u r a t e t h a n t h a t of m a s s s p e c t r o m e t r y , the composite spectra apparently demonstrated a n y d i f f e r e n c e in t h e c o m p o s i t i o n s of t h e s a m ples.
ever available the values obtained by this analys i s w e r e a d o p t e d e x c e p t f o r a few d a t a of L a a n d Ce.
3. R E S U L T A N D DISCUSSION 2.3. Mass-spectrometric dilution analysis A n a l i q u o t of t h e f r a c t i o n s w a s s p i k e d w i t h a m i x t u r e of e n r i c h e d i s o t o p e s , 1 3 8 L a , 142Ce, 143Nd, 147Sm, 151Eu, 157Gd, 164Dy, 1 7 0 E r a n d 171Yb. T h e c h e m i c a l s e p a r a t i o n w a s p e r f o r m e d in an almost identical manner with the neutron a c t i v a t i o n m e t h o d . T h e s t e p f o r r e m o v a l of B a f r o m r a r e e a r t h s s e e m e d to b e u s e f u l . T h e m i x t u r e of r a r e e a r t h s w a s p l a c e d o n two s i d e f i l a m e n t s of a t u n g s t e n t r i p l e f i l a m e n t i o n s o u r c e . The AEI MS-5 type mass spectrometer (R = 30 cm) was used with an electron multiplier. Alt h o u g h t h e f r a c t i o n a l e v a p o r a t i o n of t h e e l e m e n t s on t h e f i l a m e n t s w a s u s e f u l to e l i m i n a t e t h e i r mutual interferences, it was a time-consuming work, and quite often the correction term reached a considerable level. The most serious interferences w e r e u s u a l l y c a u s e d b y B a O +, B a O 2 +, a n d m o n o - i s o t o p i c r a r e - e a r t h p e a k s . On t h e w h o l e i t w a s r e l a t i v e l y d i f f i c u l t to e s t i m a t e the heavier elements. In s p i t e of s e v e r a l d i f f i c u l t i e s , g e n e r a l l y m o r e r e l i a b l e d a t a ( n o r m a l l y b e t t e r t h a n +10~0 e r r o r ) c o u l d b e o b t a i n e d b y t h i s m e t h o d [16, 17]. W h e r -
T h e c o n t e n t s of a b o u t e l e v e n r a r e - e a r t h e l e m e n t s d e t e r m i n e d i n f i v e f r a c t i o n s of B r u d e r helm are tabulated in table 1 with some other data for comparison. Fig. 1 i l l u s t r a t e s t h r e e m a j o r p a t t e r n s of t h e r e l a t i v e a b u n d a n c e s f o u n d in the EDTA, Br 2 and HF fractions. A remarkable difference in their relative abundances between the EDTA (or Br2) and HF fractions may be very impressive at first inspection. Except f o r E u a n d Yb, 60% of a l l r a r e e a r t h s w e r e equally recovered in the EDTA fraction, which d i s s o l v e d o n l y a m a j o r p a r t of c a l c i u m p h o s p h a t e . On a v e r a g e 23% of t h i s g r o u p w a s a l s o found in the next bromine soluble ferrous sulfide fraction. And the composition was fairly parallel w i t h t h a t of t h e f i r s t f r a c t i o n . A c c o r d i n g to t h e mass spectrometry, Ce in the Br 2 fraction was m e a s u r e d to b e a b o u t 50% h i g h e r t h a n a n a v e r a g e v a l u e of t h e o t h e r r a r e e a r t h s . T h i s f i g u r e m a y n o t b e a c c u r a t e b e c a u s e a d o s e of t h e s p i k e u s e d in this measurement w a s t o o low. In f a c t two composite gamma-ray s p e c t r a of t h e B r 2 a n d EDTA samples have shown practically identical
DISTRIBUTION OF RARE EARTHS pictures throughout the counting period. The s e c o n d g r o u p m a y o n l y b e a t t r i b u t e d to t h e r e s i d u a l p a r t of r a r e e a r t h s a s s o c i a t e d w i t h t h e p h o s p h a t e l o c a t e d b e t w e e n t h e g r a i n s of s u l f i d e a n d s i l i c a t e m i n e r a l s . T h e a m o u n t s of p h o s p h o rus recovered in both fractions may support this i n t e r p r e t a t i o n . In f a c t 61% of t o t a l p h o s p h a t e in the non-magnetic fraction was recovered in the E D T A f r a c t i o n a n d 29% i n t h e B r 2 f r a c t i o n . A l t h o u g h t h i s m a y not n e c e s s a r i l y mean that the rare-earth group must be tightly associated with the calcium phosphate or that it forms a minor readily soluble proper mineral in this chondrite, an important correlation between rare earths a n d t h e p h o s p h a t e s e e m s to o f f e r a n a t t r a c t i v e viewpoint. The magnesium-ferrous-orthosilicate fraction w h i c h w a s d i s s o l v e d i n d i l u t e HC1 d i d not s e e m to c o n t a i n a n y s i g n i f i c a n t p a r t of t h i s g r o u p . O n l y a b o u t 1% of e a c h e l e m e n t w a s r e c o v e r e d i n t h i s f r a c t i o n a n d a s h a p e of t h e p a t t e r n w a s n o t c l e a r b e c a u s e of t h e e x t r e m e l y low a b u n d a n c e s . N o n e of t h e a c i d i n s o l u b l e s i l i c a t e s o r o t h e r m i n o r minerals such as chromite or titanate would either be responsible as an important host mine r a l of r a r e e a r t h s i n t h i s m e t e o r i t e e x c e p t f o r Eu. O t h e r r a r e e a r t h s , w h i c h a r e c o o r d i n a t e d with oxygen atoms normally in t h e i r M (III) s t a t e s , w e r e f o u n d to b e d i s t r i b u t e d i n t h i s f r a c t i o n o n l y a t t h e l e v e l of 16% of t h e t o t a l e x c e p t f o r Yb a n d Lu. B y t h e n e u t r o n a c t i v a t i o n m e t h o d C e w a s m e a s u r e d to b e o u t s t a n d i n g l y low b y a f a c t o r of a b o u t 3. C e r i u m i n t h e s a m p l e , h o w ever, could possibly be differentiated from the c a r r i e r L a in t h e c o u r s e of t h e c h e m i c a l p r o c e s s . It w a s p r e s u m a b l y c a u s e d b y o x i d a t i o n w i t h p e r c h l o r i c a c i d to t h e t e t r a v a l e n t s t a t e . As far as we have observed in this preliminary work, the elements which are relatively s t a b l e i n t h e i r M (II) s t a t e s , s u c h a s E u , s e e m to be preferentially accepted in the negative sites of p o l y m e r i z e d , s i l i c a t e s , o r m o s t p r o b a b l y of alumino-silicates. S u c h d e v i a t i n g b e h a v i o r of E u h a s o c c a s i o n a l l y b e e n p o i n t e d o u t to b e s i g n i f i c a n t e v e n i n t e r r e s t r i a l m a t e r i a l s [8, 12, 13, 19]. In t h e s i l i c a t e r o c k s a h i g h t e m p e r a t u r e m i g h t h e l p to k e e p E u a t l e a s t p a r t i a l l y i n t h e d i v a l e n t state even under a relatively higher oxygen partial pressure in the system. The divalent rare earth may be associated with alkaline earths such as Sr which has a similar ionic radius as E u 2+, a n d s t r o n t i u m i s c o m b i n e d m a i n l y i n f e l d s p a r s [17]. In t h e E D T A f r a c t i o n we f o u n d t h a t t h e o n l y 5% of t o t a l S r w a s t a k e n i n t o c a l c i u m p h o s p h a t e a n d 95% i n t h e HC1 i n s o l u b l e p a r t [18]. A s m a l l p e a k o r v a l l e y a t Yb i l l u s t r a t e d i n fig. 1
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w a s e q u a l l y n o n - p r o m i n e n t a s t h a t of E u n o r w e l l established yet by the direct comparisons with the closest neighbour elements. When we could take this behavior seriously, a rare-earth group w o u l d b e u s e f u l a s a s e t of i n d i c a t o r s f o r a n e f fective oxidation level, oxygen partial pressure a n d t e m p e r a t u r e , of t h e s y s t e m i n w h i c h m i n e r a l s w e r e c r y s t a l l i z e d . In t h e m e t e o r i t e t h e p o t e n t i a l h a d to b e f a i r l y l o w e r , a s s u g g e s t e d b y t h e p r e s e n c e of m e t a l l i c i r o n , t h a n t h e t e r r e s trial media. As far as the present data are conc e r n e d , no a p p r e c i a b l e s m o o t h f r a c t i o n a t i o n e f f e c t due to a g r a d u a l t e n d e n c y of l a n t h a n i d e c o n t r a c t i o n c o u l d b e o b s e r v e d in a n y o n e of t h e c o m p o n e n t s [12, 14, 15]. Practically the same distribution patterns as described above were observed in the HCl-solub l e a n d H C l - i n s o l u b l e f r a c t i o n s of t h e L e e d y c h o n d r i t e . O t h e r t y p e s of c h o n d r i t e s a n d a c h o n d r i t e s s h o u l d a l s o b e s t u d i e d . So f a r w e h a v e found that an enstatite chondrite, Abee, contained l o w e r a b u n d a n c e s of r a r e e a r t h s i n t h e s i l i c a t e p h a s e w i t h o u t a n y a p p r e c i a b l e e n r i c h m e n t of Eu. In t h i s m e t e o r i t e , h o w e v e r , o n l y h a l f of t h e t o t a l strontium was found in the acid-insoluble silic a t e p h a s e [18].
ACKNOWLEDGEMENTS T h e a u t h o r s a r e i n d e b t e d to D r s . A. M a s u d a a n d Y. M a t s u i f o r t h e d i s c u s s i o n s i n t h e p r o b l e m s of n a t u r a l d i s t r i b u t i o n s of r a r e e a r t h s . T h e mass spectrometry and the neutron activation w e r e p e r f o r m e d w i t h t h e h e l p of M i s s S. T a k e u c h i a n d M i s s K. H o r i e , r e s p e c t i v e l y , to w h o m t h e a u t h o r s ' t h a n k s a r e due. T h e y w o u l d a l s o l i k e to t h a n k P r o f e s s o r R. E. F o l i n s b e e , A l b e r t a , C a n ada, for offering us the Bruderheim meteorite sample. REFERENCES [1] H . C . U r e y , A review of atomic abundances in chondrites and the origin of m e t e o r i t e s , Rev. Geophys. 2 (1964) 1. [2] E . V i l c s e k and H.W'~tnke, Ein V e r f a h r e n z u r get r e n n t e n Untersuchung d e r einzelnen M i n e r a l b e standteile von Steinmeteoriten mittels s p e z i f i s c h e r Lbsungsmittel, Z. Naturforsch. 20a (1965) 1282. [3] H. Hintenberger, E . V i l c s e k and H. v~r~fnke, Zur F r a g e d e r Diffusionsverluste von radiogenen und spallogenen Edelgasen aus Steinmeteoriten, Z. Nat u r f o r s c h . 19a (1964) 219. [4] R. Hintenberger, E. Vilcsek and H. W~nke, ~Jber die Isotopenzusammensetzung und ilber den Sitz d e r leichten Uredelgase in Steinmeteoriten, Z. Naturforsch. 20a (1965) 939.
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