Minor and trace elements in some meteoritic minerals

Geoohlmiea et Cosrno~h~ca Acta, 1973, Vol. 37. pp. 1435 to 1456. Pergamon Press. Printediu Em-them Ireland

Minor and trace elements in some meteoritic minerals RALPH Department

0.

ALLEN,

JR.

of Chemistry, University of Virginia, ~ll&rlottesv~e,

Virginia 22903, U.S.A.

and BRIAN MASON Smithsonitan Institution, (Received 20 June 1972;

TVashington, D.C. 20560, U.S.A.

accepted in revised form

30 November 1972)

J&&a&--The mineral phases including olivine, orthopyroxene, clinopyroxene, troilite, nickeliron, plagioclase, chromite and the phosphates were separated from seveml meteorites. These were a hype~thene chondrite (~odoc), a bronzite chondrite (GuarelLa),an enstatite chondrite (Khairpur), and two eucrites (Haraiya and Hooro County); diopside was separated from the Nakhltb achondrite. The purified minerals were analyzed for trace and minor elements by spark source mass spectrometry and instrumental neutron activation analysis. On the meteorites examined our results show that Co, Ni, Cu, Ge, AS, Ru, Rh, Pd, Sn, Sb, W, Re, OS, Ir, Pt and Au are entirely or almost entirely siderophile; Na, Rb, Sr, Y, Ba and the rare earth elements lithophile; Se chalcophile. The transition elements SC, Ti, V, Cr and Mn are lithophile in most stony meteorites, but show chalcophiie affmities in the enstatite chondrites (and enstatite achondrites), as do Zn, Zr and Nb. In the ordinary chondrites Ga shows both lithophile and siderophile affinities, but becomes entirely siderophile in the enst~tite chondrites. molybdenum and tellurium show strong siderophile and weaker chalcophile affinity. The lithophile elements are distributed among the minerals according to the orystallochemical factors, the most effective controlling factor being ionic size. INTEODUOTION THE LARGE amount of reliable analytical

data on elemental abundances in meteorites was recently compiled in MASON (1971). Despite the information available on trace elements in different types of meteorites, relatively little is known about the distribution of these elements among the individual mineral phases. Good mineral separations aredifficult to make because of the small amounts of material available and the generally fine-grained nature of meteorites. The chondrites are of special interest since they represent the least fractionated and most primitive group of meteorites, and have abundances for many trace elements comparable to solar abundances. The achondrites are important because they seem to represent the products of some type of igneous differentiation, and show notable analogies to some lunar rocks. Although many investigators have measured a few mineral separates for particular elements, few have looked at the systematics of distributions of many elements in each mineral or phase of an individual meteorite. VILCSEK and WLNKE (1965) and SHIMA and HONDA (1967) used selective leaching techniques to conduct such a study. MASON and GRAHAM (1970) reported on the trace elements measured by spark source mass spectrometry in minerals from the two hypersthene chondrites Modoc and St. Severin. ALLEN (1970) analyzed mineral separates from the h~ersthene chondrite Bruderheim by multi-eIement radiochemical neutron activation analysis. This work has been extended using both neutron activation analysis and spark source mass spectrometry. The minerals 1435

from the bronzite ehondrite Guareiia and the enstatite chondrite Khairpur were examined and those from the hypersthene ohondrite Modoc were re-analyzed, The chondrites were selected because their recry&allized nature (petrographic class 6 of VAN Sclac~us and WOOD, 1967) was favora,bXefor mineral sepsrations, and because their examination would extend this type of detailed investigation to two importal& chondrite classes. In addition, the major minerals from two eucrites fIIaraiya and Noore country and diopside from the Xakhla achondrite were studied. Chemical and mineralogical compositions of the analyzed meteorites are given in Table f . Table 1. ChemicttI and mineralogical compositions of analysod meteorites (in weight per cent) 1 Fe xi

fs-68 1‘30

CO

043

FeS 8i0, TiO, +%O, Cr,O, Fe0 Mnu xgo CaO hia@ Iv %Qs c! To&I Qlivine U~h5~~~ene ~l~n~~~~~x%n~ Plagioolase

6.46 39.29 0.12 2.49 0.55 14.98 o-33 24=78 l-62 0.93 o-10 o-30 0.18 IO@17 46 23 4 10

Chromite Phosphate

0.8 O-7

Troilite Metal

7 8

2

3

16.30 l”74 O-09 5.48 36.74 0.12 2.04 0.65 10.24 0.32 2344 1*60 0.90 0.09 0.27 0.02 100~09 35 26

14-8 1.22 0.02 10.74 43.66 (0.01 2-42 0.19 o-30
4 fO

0.8 0.6 6 18

9

4 O-82 4&*16 O-32 15%7 0.44 15*02 0.31 8.41 11‘08 0.45 o-09 tO@W 51 45

5 0.25 tO*Of

0.27 48.30 0.67 Il.92 0.33 19*95 043 6-96 9.57 0,37 0.03 to.05 99G% 61 34

-

0.7 -

0.5: -

IO 16

O-8 -

0.3 0.3

1. Modoo, MASOX and T?TxlE,1967. 2. Cuare%+ JAHXSSV~CWand &&SON, 1969 (tot&l inchxdes II@ - &X5), 3. I%hairpur,Eeoss s$& 1967 (Fe includes 8i O&Z, P Q-11,and FeS includes Xxx O-19,Ca @34, Ti 0.07, Cr o.os). 4. Moore County, H&W and ZEKDEEWW, 194% 5. Haraiya, Jarosewich, unpublished (total includes El’,0 - 0.11, E&O + 0.60).

Mimw~Eaepuratio~, The teohniq~ze of mine& separations ww that described by &$&ON and GRAEAM (1970). titer crushing, the -200 +- 325 mesh fraction was sedimented in water ta remove dnE&and mot&l particles extracted w&h a hand magnet. l%?Wy liq&s @xEx$,-tons and clerici soi~t~o~s) and the Frarxitz Is~~~a~~c arbor mre used to separ&e the minerals. The final plagioclase, pyroxene and ohromite fractions were treated with hot RCX

Minor and trace elements

in some meteoritic

minerals

1437

The purity of the mineral separates was evaluated by microto remove acid-soluble impurities. scopic examination. Purities were mostly 99 per cent, except for the metal phases, which contained some attached silicates and were only about 95 per cent pure. The Modoc diopside analysed by activation analysis was about 90 per cent pure, the remainder being largely orthopyroxene. Trace element andysis. The samples were analyzed both by spark source mass spectrometry (SSMS) and instrumental neutron activation analysis (INAA). The two techniques are quite complementary and in addition, allow checks on the analysis even with comparatively small samples. Sample sizes of less than 250 mg were convenient for INAA and 20-50 mg for SSMS. Some elements were not measured in all phases because of the specific compositions of the individual minerals, which gave rise to interferences with both techniques. Spark source mass spectrometry. The general analytical procedure was that of TAYLOR (1965). The A.E.I. MS 7 mass spectrograph in the Dept. of Geophysics and Geochemistry at the Australian National University was used. The ion source was a pulsed R.F. spark passed between two electrodes which were pressed from a 50-50 mixture of sample powder and a graphite/Lu,O, mix. The 50 ppm by weight Lu,O, was the internal standard for the analysis. The sample was finely ground in an agate mortar before mixing with the graphite in a mechanical shaker. Standard geochemical standards (G-l and W-l) were mixed in the same manner. The ions produced were doubly focused and the mass spectrum recorded photographically on an Ilford Q2 photoplate. Fifteen exposures measured in units of charge were taken on each plate. The conditions of the R.F. discharge spark were kept constant and the ion beam was attenuated for an exposure range of l-1000 by use of an electrical ‘chopping’ device. This avoided changing the relative sensitivities for elements due to changes in the sparking conditions. The intensity of the lines on the photographic plates were read on a Jarral-Ash microphotometer and the calculations made as described by TAYLOR (1971). The accuracy of the analysis depends upon the values accepted for the geochemical standards used for calibration, and upon the purity of the mineral separates. The precision was on the order of 520 per cent. Weighed samples and standards were sealed in Instrumeratal neutron activation analysis. polyethylene vials for irradiation. Two types of standards were used, one being liquids containing known concentrations of one or more elements of interest, and the other the USGS standard rock BCR-1. The latter acted as a check on the procedure, and for several elements was the primary standard. A sequential irradiation procedure similar to that used by WAKITA et al. (1970) was used, with all irradiations made in the core of the University of Virginia Nuclear, Reactor facility. Following a 1 minute irradiation at a flux of ~5 x 10” neutron cm-2 set-l Na and Mn activities were measured. The same sample was then irradiated for 1 hour at a flux of ~2 x lOi neutron cm+ se@. Samples were transferred to clean polyethylene vials and counted the day after irradiation, although the Mn and Na activities were the dominant features of the spectrum. Additional counts were made about 3 days, 7-10 days, and 30-40 days after irradiation. All y-ray spectrometry was on one of two lithium-drifted germanium (one with a FWHM resolution of 2.2 KeV and 8.5 per cent efficiency relative to a 3 x 3 NaI for the 1330 KeV y ray for Co60 and the other a resolution of 2.5 KeV and 5.6 per cent efficiency) detectors, each feeding The concentrations into one half of the memory of a 4096 channel analyzer (KICKSORT-706). were calculated using the standard monitors. Corrections for flux inhomogeneity in the reactor were made on the basis of the specific activities of iron wires wrapped around each sample tube. The uncertainties vary from element to element and are based on counting statistics, which arc usually the controlling factor in the precision. RESULTS

The analytical results are summarized in Tables 2 and 3. The SSMS data are expressed to one or two significant figures, although the precision is of the order of &SO per cent. In order to make the tables more legible, the propagated uncertainties based 011 counting statistics for the neutron activation analysis data are omitted, and the numbers rounded off to the nearest significant figure. Included for reference are

198 270 120

10 70; 25 50

l.o%* 0.5 %* 0.48 %§

Modoc GuareGa Khairpur Moore Co. Haraiya

Modoc Guareiia Khairpur Moore Co. Haraiya

Modoc Guareiia Khairpur Moore Co. Haraiya

Modoc Guarefia Khairpur Moore Co. Haraiya

Modoc Guareiia Khairpur Moore Co. Haraiyo

Ti

V

Cr

Mn

co

tl

7 2

7 20


1 f

0.3; 1

Modoc Guareiia Khairpur Moore Co. Haraiya

SC

100

6-O; 7 6.1; 7 2

34; 25 47; 7

93; 58 6.7; 36 12

3820; 36OOt 3660; 3400t

2200; soot 3900; SOOT 470

100 2

40

1ooot 11oot 20

12-l; IO 6.9; 9 17

Orthopyx

3660; 3600-t 3320; 33oot

600; 350 160; 200

9 40

100 90

5.1; 3 4.9; 4

Olivine

6-O; 6 6.1; 9

7.4; 3 3.1; 3

6000; 7000j6100; 7400t

1820; 2000t 1960; 2100t

3000; 2200t 2200; 19oot

28

45

1

0.5 %; 0.8 %f

0.6%t

37% 37%

0.4 %t
1.7 %t l-3 %I-

2 3.1; 3

Chromite

0.7; I 2 0.4; 1 0.5; f

< 300t 130 20 80 290


12 9

140 74 3900; 4100t 6500; 4soot

19 6

12

<200t 90 7 35 < 2OOf

6 1.7; 3 2 1.8; 9 1.3; 12

Feldspar

130

1soot 21oot

2400t 26OOt

35; 34 55; 40

96; 40 46; 37

Clinopyx

(Figures in ppm unless otherwise indicated)

150 100; 90 11oog

290; 140 195; 330 7500$

4 8 >O.l%

50 IO 6700f

0.5; 8 0.3; 9 13

Troilite

Table 2. Analyses of mineral separates.

Metal

Meteorite

Element

620

580

340 320

5

44 3.3

Phosphate

800* 900* 200* 3/l 3 ‘i I/

2600 2500* 1900* 2400* 3300*

3800” 3soo* 2100* 3000* 2300t

100 70 80

80 70

700* 700” 700” 2000” 3600*

10.811 2411 26/l

8.2II 8

Bulk

Minor and trace elements in some meteoritic minerals

1439

Modoo Guareiia Khairpur Moore Co. Haraiya

Modoo Guarefia Khairpur Moore Co. Haraiya

Zr

B&

<3

{JSCHMITTet al. (1972).

type,

Metal

IP\‘AA results in ordinary and Haraiya. * From Table 1. t Microprobe analysis. $ Moss et aE. (1907). $ KEIL (1968).

Meteorite

2. (Con&.)

Element

Table

6


o-5

<3 5

Olivine

SSMS results in italics;


2

3 3 23

Troilite

clinopyroxene

3

6

2

6 7 4

Orthopyx

is diopside

3 I

G

10

29

14

50

110

Clinopyx

in Xodoc

2

5 3

Chromite

and Gunrena,

42 40 36 140; 48 100; 72

7 5 5 2 2

Feldspar

pigeonitc

II

21 30

5 5

22 39

8 7

Bulk

in Moore County

650

Phosphate

F P

E

If

E

?

‘z

;

II

Sm

Modoc

Nd

Nakhla

Modoc Guarefia Moore Co. Haraiya

Nakhla

Guareiia Moore Co. Haraiya

Modoc Guareiia Moore Co. Haraiya Nakhla

Pr

0.26 0.20

0.10 0.16

0.4 0.7

2.1 2-2

Modoc Guarefia Moore Co.

Ce

Haraiya Nakhle

0.15 0.20

1.2 1.0

Modoc Guareiia Moore Co. Haraiya Nakhls

Orthopyroxene

La

Olivine

earth abundances

Meteorite

3. Rare

Element

Table

I.3

0.3 0.3 0.40 0.19 0.31

1.3 0.9 I.4

1.1

1.30;

0.75;

0.51 0.36

I.0 0.7 1.3

0.82 1.8

1.2 1.5 2.91;-/%5

3.3; 1-l; 1.1; 2.7; 1.2;

2.48t 0.95

0.34;

0.30

0.25 0.38; 0.46t

tl

<0.3 0.47 0.22

1.0; 1.0 4.5; 3.9 2.0; 2.1

0.7; 0.6 1.8; 1.7 0.9; 1.4

1.6; 0.5 0.5; 0.3 0.34 0.65; 0.25 0.40; 0.32

in ppm

Feldspar

separates,

Clinopyroxene

in mineral

27 21

65 9

17

80

120

0.5; 0.34* 0.6

51 29

0*73*

1.9

0.24; 0.20” 0.30 0.938t

2.81.f 5.0 3.18**

0.63”

0.13* 0.4 0.43 1.2 0.67%.

1.7; 1.5* 1.5 3.0; 3.08? 6.1 6*2*

2.5 1*57*

1.0

Bulk

Phosphate

RALPH 0. ALLEN, JR. and &SIAN MASON

Modoc Guarefia Haraiya Nakhla

Lu


0.09 0.04

0.03 0.03

0.17 0.20

INAA results in ordinary type, SSMS results in italics; County and Haraiya. * SCHMITTet al. (1964). t SCHNETZLER and PHILPOTTS(1969).

Modoc GLlEUX&a Moore Co. Haraiya Nakhla

Y-h

clinopyroxene

0.03 0.04

0.20 0.14; o.osat 0.36; 0.22

18 24

0.044*

0.04; 0.036* 0.06

0,21*

0.18; 0.15* 0.34 1.087

is diopside in Modoc, Guareiia and Nakhla, pigeonite in Moore

0.52 0.13

0.21

1.4 0.91 1.5; 1.8 2.5; I.0 0.76

x444

RALPH 0. ALLEN, JR. and BRIAN MASON

concentrations for the bulk meteorites. In general, when an element was analyzed by both techniques, the results were in good agreement. An obvious advantage of the SSMS technique is the determination of more elements, while for some elements the INAA data are inherently more precise. The data are discussed element by element in the following sections. Sodium. This is a minor element in meteorites; it averages O-7 per cent in the ordinary chondrites and 0.3per cent in the eucrites. Practically all of it is combined in plagioclase, which in the ordinary chondrites has a mean composition of Ab,, (VAN SCHMUS and RIBBE, 1968) with an Na content of 7.3 per cent, and in the eucrites has a mean composition of about Ab,, (DUKE and SILVER, 1967) with an Na content of 0.8 per cent. Whitlockite usually contains about 2.2 per cent, Na, but since this mineral never exceeds 0.5 per cent of a meteorite, its contribution to the total sodium is negligible. Meteoritic diopside contains minor amounts of this element; microprobe analyses of diopside in Modoc and Guarefia gave 4200 ppm in each, a figure consistent with the average of 6400 ppm recorded by BUNCH et al. (1970) for diopside in silicate inclusions in irons. Orthopyroxene contains much less Na than diopside, microprobe analyses giving 700 ppm for this element in Modoc o~hop~oxene, and 500 ppm in this mineral from Guarena. Pigeonite in the eucrites is uniformly low in Na, 380 ppm in this mineral from &Ioore County and 520 ppm in this mineral from Haraiya. Figures for the other meteoritic minerals are not given in Table 1, because the presence of trace amounts of feldspar in the mineral separates renders the analytical results unreliable. GOLES (197 1) records an apparent Na content of 50 ppm in olivine from pallasites, but remarks that this figure may be affected by interferences in the method. In stony meteorites the only common chlorine-bearing mineral is Chlorine. chlorapatite, which probably accounts for most of the chlorine recorded in bulk analyses. The presence of lawrencite, (Fe, Ni)Cl,, has been suggested from the rapid appearance of brown rusty spots on freshly broken surfaces, but this is diflicult to prove ; however, KEIL (1968) has provided microprobe evidence for inclusions of lawrencite in metal and troilite in the enstatite chondrite Indarch. We have found significant amounts of chlorine in metal and troilite separates by SSMS analysis, as follows (ppm) :

Metal Troilite

Modoc

Guarefia

Khairpur

74 13

90 30

II0 160

Chlorine was not detected in olivine separates; in the remaining separates the use of HCl during separation introduced possible contamination, &can&urn. Both INAA and SSMS results are available for most of the mineral separates. The figures are generally consistent, except for troilite and for plagioclase from Moore County and Haraiya, for which the SSMS results are an order of magnitude higher; possible some unidentified interference has enhanced these results. However, GOLES (1971) reported 8.4 ppm in troilite from the M&Kinney chondrite. As has been observed in terrestrial rocks, scandium is concentrated in pyroxenes, with a marked preference for clinopyroxene over orthopyroxene. GOLES (1971)

Mtior &nd trace elements in some meteoritic minerals

1445

commented that the amount of scandium he found in three chondrite pyroxenes only accounted for about half the scandium in these meteorites; however, his figures indicate that he was analysing orthopyroxene, and the diopside in these meteorites would account for much of the remaining scandium. Titanium. This element has been detected in all phases. The largest coneentrations in silicate minerals are for clinopyroxenes (at about 0.2 per cent) for both The orthopyroxenes of hypersthene and bronzite chondrites and achondrites. chondrites contain on the order of 0.1per cent, but the enstatite from Khairpur is much lower (20ppm). In the enstatite chondrites this element shows a remarkable change from lithophile to chalcophile behavior, as in Khairpur, where high Ti values were measured in the troilite. Analyses of troilites from enstatite achondrites indicate even higher Ti concentrations than in Khairpur [Norton County troilite, 4.1 per cent Ti (KEIL and FEEDRIKSSON, 1963); Khor Temiki troilite, 10 per cent Ti (KEIL, f969)]. In sharp contrast the troilite from four ordinary chondrites analyzed by Moss et at. (2967) contained 100-400ppm Ti, and we found from 10-50ppm in troilite from Guarefia and Xtodoc. Olivine and plagioclsse are low in Ti, and some of the results obtained may be somewhat too high, because of possible contamination wit.h chromite. Meteoritic chromite contains l-2 per cent Ti, and a slight contamination with this mineral will introduce appreciable amounts of this element. ~~~~~~u~~, In meteorites this element probably is present largely or entirely in the trivalent st,ate, and as a result it shows a close geochemical coherence with BUNCH et al. (1967) showed that most of the vanadium in the ordinary chromium. chondrites is contained in the chromite, and our measurements confirm this. In Khairpur vanadium is chalcophile, evidently accompanying chromium in daubreelite. The troilite from H, L and LL chondrites contain only on the order of 5 ppm V, in the same range as the troilite from the bronzite ehondrite Cullison (13ppm, NICHIPORUI~and CHO~OS, 1969). The pyroxenes contain small amounts of vanadium (40-130 ppm) with the exception of enstatite from the enstatite chondrites and achondrites, where the concentrations are much lower. Chronzium. In most meteorites chromium is highly concentrated in chromite, and t.he difficulty of completely eliminating tiny inclusions of this mineral renders the results for this element in separated minerals somewhat d~~bious and potentially too high. On this account microprobe data are preferred where available. Among the silicate minerals chromium is highest in clinopyroxenes, with lower concentrations in the orthopyroxenes. The figures for olivine are similar to those given by GOLES (1971) for olivine from pallasites. In Khairpur and other enstatite chondrites and enstatite achondrites, chrolnium is chalcophile, being present at about the 1 per cent level in troilite and as daubreelite; in these meteorites the orthopyroxene is notably depleted in chromium relative to the ordinary chondrites, as was shown by REID and COHEN (1967). Manganese. This minor element is lithophile in most meteorites, but becomes chaleophile in the enstatite chondrites and enstatite achondrites. It is geochemieally coherent with ferrous iron, and shows its greatest concentration in chromite; however, most of the Mn in the ordinary chondrites is contained in the abundant ferromagnesian silicates oIivine and orthopyroxene, in approximately equal concentration. Diopside contains less Mn than coexisting orthopyroxene, but in the

1446

RALPH 0. f&LEN,

JR.

and BRZAN

&~&ON

eucrites the clinopyroxencs are somewhat enriched in this element. Plagioclaso is notably low in Mn, and some of the figures given may be somewhat high through contamination with other minerats. In troilite from ordinary chondrites, Mn is 100-200ppm, but in the enstatite chondrites and onstatite chondrites, troilite contains about O-1 per cent, and alabandite, (Mn, Pe)S, may also be present; in these meteorites the pyroxene is notably depleted in this element, as is shown by our data for Khairpur, which is in agreement with the more extensive results of KEIL (1968) and REID and COHEN (1967). ~o~~Z~. This strongly siderophilic element is found at concentrations of about 0.4-1.0 per cent in the metal of chondrites, which is similar to the levels in iron meteorites (MOORE, 1971). The figure of 0.02 per cent in the bulk analysis of Khairpur (Table 1)seems erroneously low, and is inconsistent with 0.48 per cent in the metal phase determined by KEIL (1968). Practically all the Co in an enstatite or ordinary chondrite is in the metal phase, but it can be measured in the ferromagnesian silicates, being more concentrated in the olivine than in the pyroxenes; it is also present in troilite, at 10-100 ppm. 1Vickel. This element is geochemically similar to Co. The H group and enstatite chondrites contain more Ni than the L and LL group ordinary chondrites, but the concentration of Ni in the metal phase varies in the opposite sense, reflecting dilution of Ni-rich taenite by Ni-poor kamacite. LL-6 St. Severin contains 26.8 per cent Ni in the metal phase; L-6 Modoc, 14.9 per cent; L-6 Bruderheim 13.4 per cent (ALLEN, 1970); H-6 Guarefia 9.7 per cent; and E-6 Khairpur 6.9 per cent. Nickel is present in troilite at about the 0.1 per cent level. NICHIPORUK and CHODOS (1959) reported 0.017-6.61 per cent Ni in sulfide nodules from meteorites, but their high Ni values were due to the presence of nickel-iron. Our measurements show Ni in chondritic olivine at 100-200 ppm, and at lower concentrations in the coexisting pyroxenes. The Ni determinations in olivines from stony-irons by iMAsoN and GRAHAM (1970) and BUSECK and GOLDSTEIN (1969) fall in the range of 34110 ppm. copper. HEY and EASTON (1968)have studied the distribution of this element in chondrites and find that it is concentrated in the nickel-iron, especially in taenite. In addition, small and sporadic grains of native copper are not uncommon in chondrites. The figures in Table 2 confirm the concentration in the metal phase; the high concentrations in Guarefia chromite and Khairpur troilite may possibly be due to GOLES (1971) found less Cu in chromite from two inclusions of native copper. hyperthene chondrites (5-12 ppm) and a pallasite (22 ppm) than we found in the Guareiia chromite (200 ppm). The Cu concentrations in the sulfide phases seem to all be less than 220 ppm (except Goles’ report of L-4 k&Kinney 580 ppm), ~dicating slight chalcophilic tendencies. The silicate phases contain little Cu; the figures for Haraiya pyroxene and plagioclase are anomalously high and indicate contamination. The olivine in the stony-irons (1-7 ppm Cu, including 6 samples by GOLES, 1971) seems to be a little lower than the olivine from chondrites (8-19 ppm). Zinc. This element is detectable in all the separated minerals, although it is predominately found in the silicates, as indicated by NISXXIMURA and SANDELL (1964). As for several other elements, in the enstatite chondrites the concentrations of Zn is lower in the pyroxene and substantially higher in the troilite, indicating chalcophile

Minor and trace elements in some meteoritic minerals

1447

behavior in these meteorites. KEIL (1968) reports 800 ppm Zn in the troilite and In chondritic troilite, NISHIMURA and 1500 ppm Zn in daubreelite from Khairpur. SANDELI, (1964) report 10 & 5 ppm Zn, similar to our figures. Chromite sometimes shows high Zn concentrations, as in Guarefia and St. Severin (1800 ppm; MASON and GRAHAM, 1970). Gallium. This element is particularly important in elucidating groups of possibly In the ordinary chondrites like Guarefia, Ga is genetically related iron meteorites. concentrated in the metal phase, the chromite, and the plagioclase (probably substituting for Al in the latter mineral). In the enstatite chondrites like Khairpur, the Ga has lost its lithophile character (being only 1 ppm in plagioclase) and is almost entirely in the metal phase. The plagioclase in the eucrites is notably lower in Ga than the feldspar from ordinary chondrites. Germanium. Unlike Ga, the Ge is almost entirely in the metal phase. In Guarena the metal contained 60 ppm Ge, and in Khairpur the concentration was 100 ppm. Moss et al. (1967) reported 123 ppm Ge in Khairpur metal, 122 ppm in Barwell and 127 ppm in Ohuma metal phases (the latter two are hypersthene chondrites). This, in conjunction with data from POUCHI? and SMALES (1967), suggests no significant difference between Ge concentrations in the metal of enstatite and ordinary chondrites. Troilite from Khairpur and Guarefia contained about 2 ppm Ge, which is somewhat less than has been recorded in sulfide nodules from irons (LOVERTNQ, 1957; SHIMA, 1964). Arsenic. Like Ge, this element is almost entirely siderophile. It was detected only in the metal phases, as follows: Modoc, 25 ppm ; Guareiia, 8 ppm, Khairpur, 11 ppm. In the metal from a composite of H and L group chondrites ONISHI and SANDELL (1955) found ll-13ppm As. Arsenic was not detected (< 1 ppm) in SSMS analyses of troilite, although ONISHI and SANDELL (1955) recorded 8-l 1 ppm As is a troilite composite. Selenium. This element is chalcophile in meteorites, as it is terrestrially. The concentrations in the troilite from two ordinary chondrites (Guareiia and Modoc) were in the 100-140 ppm range. KIESL and HECHT (1969) found 52 ppm in troilite from the L-group chondrite Mocs and a range of 130-300 ppm in troilite from three iron meteorites. Rubidium. Plagioclase is the only mineral in which this element was detected. The Guarefia plagioclase analysed by INAA gave 52 ppm, and by SSMS 22 ppm ; the latter figure is more consistent with the 29 ppm reported by WASSERBUR~ et a.1. (1969). The sodic plagioclase from Modoc contains 28 ppm, St. Severin 5 ppm, and Winona 12 ppm (MASON and GRAHAM, 1970). The total Rb content of St. Severin (- 0.7 ppm; GOPALAN and WETHERILL, 1969) is notably low in comparison to other chondrites. The calcic plagioclase from the Haraiya achondrite contains substantially less Rb (O-25 ppm) than the sodic feldspars from chondrites. Strontium. This element is also concentrated in the plagioclase, although pyroxenes contain appreciable amounts. The olivine contains less Sr than the pyroxenes and this may be due in part to contamination. Other minor phases have been reported to contain Sr. The whitlockite from St. Severin was reported to contain 30 ppm Sr by PAPANASTASSIOUand WASSERBUR~ (1969) and 62 ppm Sr by MASON and GRAHAM (1970). The latter authors also reported 87 ppm Sr in the phosphate 3

1448

RALPH

0. ALLEN,

JR. and BRIAN MASON

(chlorapatite) from Modoc. WASSERBUR~ et al. (1970) found 53 ppm Sr in Guareiia phosphate, Both Guarefia and Khairpur contain some Sr in the troilite. J’ttrium. MASON and GRAHAM (1970) showed that this element is highly concentrated in the phosphate minerals of chondrites at 160-210 ppm. Compared to this, only trace amounts are found in the other minerals. In Khairpur, which contains no phosphate mineral, the concentration of this element in the other minerals is similar to the Guarefia minerals. Niobium. Data on the distribution of this element in meteoritic minerals have recently been presented by GRAHAM and MASON (1972). In Khairpur it appears to be concentrated in the troilite (1.6 ppm), suggesting that under the highly reducing conditions of the enstatite chondrites this element develops chalcophile affinity. Molybdenum. This element was detected by SSMS in the metal and troilite Lack of standards prevented precise phases of Modoc, Guarefia and Khairpur. evaluation of the amounts present, but the metal contains 5-10 ppm and the troilite about one-third this amount. These figures are consistent with the data of KTJRODA and SANDELL (1954), although their results are generally somewhat higher. Ruthenium, rhodium and palladium. These elements were detected in spectra of the metal phases only, their concentration being of the order of l-5 ppm. Tin and antimony. These elements were detected in spectra of the metal phases only; tin is present at about 2 ppm, antimony at 0.5-l ppm. Tellurium. This element was detected in both metal and troilite, the concentration in the metal (l-2 ppm) being about three times that in the troilite. Barium. Most of the barium in stony meteorites is contained in the feldspar, Comparison with the chondritic with a little in the phosphates and pyroxenes. plagioclases indicates that the more calcic plagioclases from the two eucrites are richer in Ba. SCHNETZLERand PHILPOTTS (1969) found - 70 ppm Ba in plagioclase fractions and N 4.5 ppm in pyroxene fractions from Moore County and another eucrite Juvinas. The achondrites have higher and more variable Ba contents than the ordinary chondrites (SCHNETZLER, 1970). The troilite in Khairpur contains significantly more Ba than that in Guarefia or other ordinary chondrites, suggesting that this element develops chalcophile tendencies under highly reducing conditions. Rare Earth Elements (Lanthanides). These non-volatile lithophilic elements have nearly the same relative abundances in all types of chondrites and most achondrites. Our data are given in Table 3. Because the relative as well as the absolute abundances are important, the concentrations in the various minerals are normalized to a chondrite composite (HASKIN et al., 1968) and plotted versus atomic number in Figs. 1-4. In the Ca-rich achondrites the REE are found in clinopyroxene and plagioclase; among these meteorites the eucrites and howardites comprise a sequence with relative REE abundances like chondrites but with 3 to 17 times the absolute abundances. They are considered to be products of igneous differentiation. The pyroxene REE concentrations in Haraiya are somewhat higher and the plagioclase concentrations slightly lower than in Moore County. The results are in agreement with the suggestion by SCHNETZLERand PHILPOTTS (1969) that Ca-rich achondrites are a result of closed system hypabyssal or extrusive crystallization. The smaller negative slope and smaller Eu anomaly in the Haraiya plagioclase resemble the data for the eucrite Juvinas (SCHNETZLERand PHILPOTTS, 1969). Both of these eucrites contain relatively

Minor and trace elements in some meteoritic mineraIs

Eruderheim

o.,I IA

Ce

Pr

Nd

Pm Sm Eu

Gd Tb

Dy

Ho Er

Tm Yb

Lu

Fig. 1. Rare earth element distribution in meteoritic pyroxenes normalized to chondrite average. Clinopyroxenes are from the eucrites Juvinas (SCHNETZLER and PHILPOTTS, 1969), Moore County and Haraiya, the nakhlite Nakhla, the H-6 chondrite Guarega and the L-6 chondrite Modoc. The o~hop~oxenes are hypersthene from the L-6 chondritea Bruderheim (ALLEN, 1970) and Modoc and bronzite from H-6 chondrite Guam&a.

Chondrltes h

GuorePio(H-61 \

Fig. 2. Chondri~-normalized concentrations of rare earth elements in chondritio plagioclase. Results for Bruderheim (L-6) from ALLEN (1970), for Winona from &WON and &AHAM (1970). Results for Guareiia (H-6) are by INAA and the partial analysis of Khairpur (E-0) by SSMS.

I449

1450

L

’ La

“1 Ce

Pr

Nd

11 Pm Sm

* Eu

’

*

Gd

Tb

1”

Dy

Ho

*

Er

Tm

s

r

Yb

Lu

Fig. 3. ~hon~ite-no~al~ed eon~entrationsof rare earth elements in plagioclase from eucrites. Results for Juvinas are from SCRNETW;ER and PIXILPOTTS (1969).

“.!_.. La

ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Fig. 4. ~hon~ite-norm~~zed ~oneentr~tio~ of raze earth elements in phosphate _ miner& from meteorites. Results for Bruderheim (L-6) whitlockitefrom ALLEN (1970) and for St. Severin whitlockite from &WON and GRAHAM:(1970). fine-grained plagioclase. If Juvinas and Haraiya represent liquids which lost or gained hypersthene {~cE~~TzL~~ and PHILI?OTTS,1969), leaving the whole meteorite REE patterns unfkactionated the plagioclase and pyroxene concentrations represent closed-system competition. The plagioclase in Moore County is coarsely crystallized, possibly reflecting slower cooling of the latter. This meteorite has a positive Eu anomaly and probably is a cumulate, but the plagioclase does not appear to have been in equilibriunl with a eucrite melt. This may be due to post-accumulation competition between minerals, which would suggest that these minerals are zoned, and

Minor and trace elements in some meteoritic minerals

1461

may explain the slight differences between the concentrations we report and those observed by SCHNETZLERand PHILPOTTS (1969). The other Ca-rich achondrite analyzed was Nakhla, which has a fractionated REE pattern similar to terrestrial basalts (SCHMITTet al., 1964). The REE concentrations measured in the Nakhla diopside are lower than in the achondritic pigeonites The concentrations observed are similar to those predicted by using examined. diopside partition coefficients and a liquid enriched in REE by about an order of magnitude over chondrite levels. The much smaller negative Eu anomaly suggests less closed-system competition with plagioclase, which is present only in trace amounts. The phase which carries most of the light REE is unknown but plagioclase seems unlikely, since the diopside accounts for most, of the Eu in the meteorite, whereas in other meteorites most of the Eu is in the plagioclase. The fractionation trend of the whole meteorite data suggests that Nakhla was produced from the liquid phase resulting from partial melting or fractional crystallization of a material with relative chondritic REE abundances and a solid phase which preferentially concentrated the heavy REE, such as clinopyroxene. In the ordinary chondrites, which show very little relative fractionation of the REE, the phosphate minerals are the site of most of the REE except Eu, which is concentrated in the plagioclase, presumably due to its reduction from the +3 to +2 oxidation state. In the enstatite chondrite Khairpur, which contains no phosphate, our partial data for the plagioclase and troilite suggest that the REE are forced into other minerals when the phosphate is absent. In line with this, SHIMA and HONDA (1967), using selective leaching techniques, found substantial amounts of REE in the troilite of the enstatite chondrite Abee. The chondritic orthopyroxenes contain less REE and the patterns show less fractionation than the achondritic clinopyroxenes. The possible contamination of the separates with small amounts of phosphate may account; for the higher REE contents and lower Eu anomaly for the bronzite from Guarefia relative to the two hypersthenes from Modoc and Bruderheim (ALLEN, 1970). Using phenocryst/matrix partition coefficients (SCHNETZLER and PHILPOTTS, 1970), it is possible to generate the concentrations observed in the plagioclases, orthopyroxenes, and clinopyroxenes of the chondrites only if they had been in contact with a liquid where the REE were uniformly concentrated about an order of magnitude over the chondritic average. The negative Eu anomaly in the pyroxenes is not predicted using the phenocryst/matrix partition coefficient. It, might be expected that the Eu anomaly would be higher for the plagioclase of the reduced enstatit’e chondrite Khairpur, but it is lower than observed for the ordinary chondrii;es. The partition coefficients (SCHNETZLERand PHILPOTTS, 1970) for plagioclase indicate that the Eu anomaly should also increase as the percentage of anorthite decreases. The Ca-rich plagioclase from Haraiya has a Eu/“Eu3+” ratio (actual Eu concent’ration divided by the concentration predicted by a smooth curve between Sm and Gd concentrations) of about 6, which is somewhat higher than predicted from the terrestrial partition coefficients. In the Na-rich feldspars from Guarefia and Bruderheim (ALLEN, 1970) the Eu/“Eu3+” ratio is between 5 and 6, and much lower than expected on the basis of an extrapolation of the Eu anomaly versus the composition of the plagioclase (SCHNETZLER and PHILPOTTS, 1970). The REE concentrations in these two plagioclase samples are almost the same as found in

1452

RALPB: 0. Aram.

JR. and BRIANXASOW

Haraiya, despite the much higher bulk REE concentrations in the latter. This occurrence of similar Eu anomalies in the plagioclase from meteorites which crystallized under different oxidation conditions, and the negative Eu anomalies in the pyroxenes, suggests a closed system competition for Eu. The uniformity in the REE concentrations in chondrites suggests that the distribution of these elements among the minerals is due to the crystallization of a closed chemical system. H$&urn. As might be predicted, hafnium follows the pattern of zirconium, being detected only in those samples relatively rich in this element. MASONand GRAHAM (1970)recorded 18 ppm in Modoc phosphate and 4 ppm in Winona diopside; we found 0.9 ppm in pyroxene from Moore County, l-3 ppm in pyroxene from Haraiya, and 2.9 ppm in Modoc diopside. Tungsten, rhenium, platinum metals and gold. These elements were detected in spectra of the metal phases only. Suitable standards for evaluating the amounts were not available, but the results are consistent with the figures given for chondrite metal by other investigators : Re, 0.5 ppm (FOUGHTand &&ES, 1967); Ir, 2.8 ppm (NICHIPORUKand BROWN, 1965); Pt, 84ppm (NICHIPORTJK and BROWN, 1965); Au, 1.2 ppm (BAEDECKERand EHMANN,1965). DISCXSSIOX Two types of elemental fractionation are illustrated by the data: fractionation between the individual minerals in a specific meteorite, and fractionation between different groups of meteorites, as for example the different classes of chondrites, or between the chondrites and the achondrites. It has been well-established that most achondrites are strongly depleted in the siderophile elements, such as Ni, Co and others, in comparison with the chondrites. Within the different classes of chondrites, LARIMERand ANDERS(1967) have established a pattern of depletion for many minor and trace elements with respect to their abundances in Type I carbonaceous chondrites. The highly depleted elements are mainly volatile ones, most of which are present at very low concentrations in the ordinary chondrites and the eucrites. The chondrites we have investigated are all Type 6, well crystallized, and with the individual minerals having uniform composition throughout a specific meteorite. For the elements we measured, the only ones showing marked depletion (by a factor of 5 or more) relative to the Type I carbonaceous chondrites are Ga, Ge, Sn and Zn. For the other minor and trace elements and the major elements also, these meteorites are remarkably uniform in bulk composition, save for the variation in Fe, Ni, Co contents related to variation in the metal content. Relative to the chondrites, the eucrites are massively depleted (by factors of 10-100 or more) in Ni, Co, Cu and probably the other siderophile elements, in S and Se and in Rb ; they are enriched about five to ten-fold in some of the lithophile elements, notably Ca, AI, SC, Ti, Ba, Y and the rare earth elements. An investigation of this kind poses some significant questions. How are trace element distributions between minerals influenced by the conditions under which the meteorite was formed? Has there been post-formation equilibration or transfer of trace elements between minerals? Is the difference in concentration of a specific element in similar minerals from two different meteorites to be ascribed to (a) differences in bulk composition and conditions of crystallization, (b) differences in the

Minor and trace elements in some meteoritic minerals

1453

other minerals present, (c) compositional or crystallographic differences in the mineral in question ? The situation is a complex one, and the specific factors probably did not act independently. According to LARIMER and ANDERS (1967,19’iO), the abundances of most elements in chondrites were established by fractionation during the condensation of the solar nebula, and therefore predate the parent meteorite bodies. They believe that accretion of chondrites began when the temperature had dropped to about 600°K. Material first to accrete would be poorest in volatile trace elements, and, being situated in the innermost regions of the body, it would experience the most intense grade of thermal metamorphism, corresponding to the Type 6 meteorites of the Van Schmus-Wood classification. Subsequent layers would be progressively richer in trace elements and less metamorphosed, corresponding to Types 5 to 3. Presumably, separate parent bodies with different metal content and different degrees of oxidation are required to account for the different chondrite classes (E, H, L and LL). This theory seems to require a source region for the parent body or bodies of each class in which the accreting material was well mixed and broadly homogeneous both mineralogically and chemically, while at the same time being isolated from the source regions of the other chondrite classes. Especially significant in this regard are those accessory minerals that contain all or the major part of a minor or trace element, such as the phosphates with Y and the lanthanides, and chromite with Cr and V. Small variations in the percentages of these minerals in different parts of the parent body would lead to marked variations in the amounts of these elements in different meteorites of the same class. Such variations have not been observed, except for K and Rb in LL chondrites. It would appear that a uniform distribution of minor and trace elements within their host minerals was achieved during crystal growth within the solar nebula and prior to accretion. Among the ordinary (H, L and LL) chondrites the mineralogy is essentially uniform, although the relative amounts, and the composition of the ferromagnesian silicates, vary systematically between the classes. However, the enstatite chondrites stand in marked contrast. Olivine, a major phase in the ordinary chondrites, is absent or present only in traces; enstatite, essentially pure MgSiO,, is the dominant mineral, possibly accompanied by a little pigeonite or diopside; no phosphate is present, the phosphorus being combined as the phosphide schreibersite; and several normally lithophile elements, such as Ca, Ti, V, Cr and Mn, are now chalcophile, present in troilite or in other sulfides. However, in spite of the marked differences in mineralogy and geochemical affinity of many elements between the enstatite chondrites and the ordinary chondrites, the abundances of most of the minor and trace elements remain essentially unchanged. These elements either find appropriate sites in other minerals (i.e. Mn in sulfide phases rather than in ferromagnesian silicates), or are taken up in other ways (i.e. in the absence of a phosphate phase, the lanthanides are evidently accommodated at low concentration in the pyroxene and possibly troihte). Whon we turn to a comparison between the chondrites and the achondrites, specifically the two eucrites we have investigated, we are faced with a strong contrast in mineralogy and texture, and significant differences in bulk chemistry, both in major aad in minor and trace elements. Nevertheless, there are some remarkable

1454

RALPH 0. ALLEN, JR. and BRIAN MASON

analogies (such as the constant Ca/AI ratio, discussed by AHRENS, 1970), and the abundances of many of the major, minor, and trace elements are relatively uniform (within a factor of 2) between the chondrites and the eucrites. The most notable difference is the much increased concentration in the eucrites of refractory lithophile elements such as Ti, Sr, Y, Zr, Ba and the lanthanides, similar to that observed in the lunar rocks. In texture the unbrecciated eucrites show unequivocal evidence of magmatic crystallization, and this has led many investigators to devise schemes for deriving the eucrites and other achondritic meteorites by the melting and magmatic differentiation of material of chondritic composit,ion. For example, MASON (1967) showed that a body of chondritic composition, if melted and fractionally crystallized, could result in the production of pallasite (39 per cent), hypersthene achondrite (46 per cent), and eucrite (15 per cent); the balance for major elements was remarkably close, except for Na, much of the chondritic Na being unaccounted for in the differentiates. The situation is more complex, however, for the minor and trace elements. As pointed out above, the eucrites are strongly depleted in the siderophile elements. This is a consequence of the almost total absence of nickel-iron in these meteorites, and can be explained by the separation of a metallic liquid at an early The lithopile elements present a more intriguing problem. stage of differentiation. In the eucrites the lanthanides are contained in the pyroxene and plagioclase, whereas in the ordinary chondrites they are contained in the phosphate minerals. Phosphorus is a minor element in the chondrites, whereas it is a trace element in the eucrites, and no phosphate minerals have been recorded in them. Thus, to derive the eucrites from the ordinary chondrites, some procedure must be devised to remove the phosphorus and to redistribute the lanthanides in the pyroxene and plagioclase of the eucrites. Removal of phosphorus by reduction and formation of the phosphide schreibersite is conceivable; however, relative to the chondrites, the eucrites are oxidized rather than reduced, having a considerably higher FeO-MgO ratio. Nevertheless, the degree of enrichment of the lanthanides in the eucrites, approximately ten-fold with respect to the chondrites, and uniform throughout the series La-Lu, is consistent with the mass relationship of 15 per cent eucritic material derived by differentiation from chondritic parent material; the pallasitic differentiate would contain practically no lanthanides, and the hypersthene achondrite differentiate relatively little. It is significant that most of the eucrites show no bulk Eu anomaly, the positive anomaly in plagioclase being exactly cancelled by the negative anomaly in the pyroxene. The lack of any fractionation of the lanthanides between the chondrites and the eucrites, plus the distribution of these elements between the minerals as compared to measured partition coefficients strongly suggests a ‘closed-system’ differentiation process. A&nowledgewaenta--One of us (B. M.) is indebted to the Smithsonian Research Foundation for financial assistance which enabled him to make the spark-source spectrometric analyses at the Australian National University and to Dr. S. R. TAYLORfor the use of the equipment and much valuable advice; some of his research was supported by NASA grant NGR-09-015-170. The neutron activation analyses were supported by NASA grant NGR-43-005-176, which is gratefully acknowledged. Funds for part of the y-ray spectrometry equipment were provided by a NSF Center of Excellence grant to the University of Virginia.

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REFZRENCES &r&ENS I,. H. (1970) The composition of stony meteorites (IX). Abundance trends of the refractory elements in chondrites, basaltic achondritesand Apollo 11 fines. Earth Plan&. A%% L&t. 10, 1-6. AT,LENR. 0. (1970) Multi-element neutron activation analysis: development and application to trace element study of the Bruderheim chondrite. Ph.D. Thesis, University of Wisconsin. BA,EDECI~ER P. A. and EHMYA.NN W. D. (1965) The distributionof some noble metals in meteorites and natural materials. aeochim. Cosmochim. Acta 29, 329-342. RTJ~~JCH 7‘. E., KEIL K. and SNETSINUER K. G. (1967) Chromitc composition in relation to chemistry and texture of ordinary chondrites. ~e~c~~rn.Cosmo~h~m.Acta 31, 1569-1582. BCTXCH T. E., KEIL K. and OLSENE. (1970) Mineralogy and petrology of silicate inclusions in iron meteorites. Codrib. ~%!lineral. Petrol. 25, 297-340. I%USECK P. R. and GOLDSTEIN J. I. (1969) Olivine compositions and cooling rates of pallasitio meteorites. Bull. Oeol. Sot. Amer. 80, 2142-2158. DUKE M. B. and SILVERL. T. (1967) Petrology of eucritcs, howardites and mesosiderites. &o&m. ComMtchim. Acta 31, 1637-1666. Fouc~i K. F. and &ALES A. A. (1967) Distrib~ltionof trace elements in chondritic meteoritc~s. Chem. @eoE.2, 105-133. GOLESG. G. (1971) Sodium; potassium; scandium; chromium; manganese; copper; rubidium. In Ha&book of Elemental dbundancesiraikfeteorites (editor B. Mason), pp. 109-114; 149-170: 175-180; 193-208; 229-234; 285-296. Gordon & Breach. GOPALANK, and WETHERILLG. W. (1969) Rubidium-strontium age of amphoterite (LL) chondrites. J. Cfeophys. Bee. P&4349-4358. GRAHAMA. L. and &or*- B. (1972) Niobium in meteorites. aeoch~m. Co~moch~m. Acta 38, 917-922. HA~EIN L. A., HASKINM. A., FREY F. A. and WILDE= T. R. (1968) Relative and absolute terrestrial abundances of the rare earths. In Origin and Disttibution of the h’lements (editor L. H. Ahrens), pp. 889-912. Pergamon. HESS H. H. and HENDERSONE. P. (1949) The Moore County meteorite: a further study with comment on its primordial environment. Amer. Mined. 34,494-507. HEY M. IX and EASTONA. J. (1968) Copper in various phases of several oli~.ine-hypersthene and olivin+bronzite chondrites. MinePal. Mug. 36, 855-858. J~nos~wrc~ E. and &SON B. (1969) Chemiaal analysis with notes on one mesosiderite and seven chondrites. Geochim.Cosmochim. dcta 33, 41 l-416. KEIL K. (1968) Mineralogicaland chemicalrelationshipsamong enstatite chondrites. J. aeophy,?. Res. 73, 6945-6976. KEIL K. (1969) Ti ~stribution in enstatite chondrites and a&o&rites and its bearing on their origin. Earth Planet. Sci. Lett. 7, 243-248. KEIL K. and FREDRIKSSON K. (1963) Electron microprobe analysis of some rare minerals in the Norton County achondrite. Geochim. Cosmochim. Acta 27, 939-947. KIESLW. and HECHTF. (1969) Meteoritesand the high-temperatureorigin of terrestrialplanets. In Meteorite Research (editor P. M. Millman), pp. 67-74. Reidel. KURODAP. K. and SANDELLE. B. (1954) Geochemistry of molybdenum. QLeochim.Cosnochim. Acta 6, 35-63. LARIMER,5. W. and AM)ERS, E. (1967) Chemical fractionations in meteorites II. Abundance patterns and their interpretation. aeochim. Cosmochim. Acta 31, 1239-1270. LAFUMER J. W. and ANDE~SE. (1970) Chemicalfractionationsin meteorites III. Major element fractionations in chondrites. aeoehim. Cosmochim. Acta 34, 367-387. LOVERIN~J. F. (1957) Pressures and temperatures within a typical parent meteorite body. aeochim. Cosmochim. Acta 12, 253-261. MASON 13. (1967) Meteo~tss. Amer. Sei. 55, 429-455. MASON11. (1971) Hadbook of~~e~~t~l Abundances in Meteorites. Gordon & Breach. MASON13. and GRAHAM,4. L. (1970) Minor and trace elements in meteoritic minerals. Smithson. Contrib. Earth Sci. 3, l--17.

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RALPH 0. -N,

JR. and BR~K WON

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