G.W. Reed

Determinations of concentrations of heavy elements in meteorites by activation analysis

Abstract Barium, mercury, thallium, lead, bismuth and uranium contents and isotopic composition of stone and the troilite phase of iron meteorites have been determined by neutron activation analysis. Two groups of chondrites were observed: the one containing enstatite and carbonaceous chondrites has orders of magnitude more of the chalcophilic elements studied than other chondrites. Barium and uranium do not show this variation. The lead in this group is primordial in its 208 204 isotopic composition as might be expected from the Pb/U ratio. Some of the nuclear and geochemical implications of the results are suggested.

HALOGENS IN CHONDRITES

Cl, Br and I contents in samples of the several classes of chondrites have been simultaneously measured by activation analysis. Auxiliary information derived from this work confirms U and Te concentrations and I/Te ratios reported in the literature. For the ordinary (bronzite and hypersthene), pigeonite, enstatite and carbonaceous chondrites the respective Cl contents are 4–90, 120, 516 and 280 ppm; the Br contents are 0·05–0·2, 2·0, 1·5–6·5 and 2·0–11·0 ppm and the I contents are 0·05–0·08, 0·16, 0·07–0·47 and 0·23–1·21 ppm. Cl and Br are positively correlated; most chondrites fall on correlation lines with Cl/Br weight ratios between 20 and 100. Br and I exhibit a simple correlation; most meteorites fall near a line with a Br/I weight ratio of about 1. Leaching experiments yielded results that supported these interhalogen relations, and also gave the degree of water solubility of the halogens: Cl < Br ~ I ~ Te. Abundances derived from the data support current thinking that the Type I carbonaceous chondrites have best retained a primordial complement of solar system matter. The astrophysical and meteoritic abundances of chlorine based on oxygen agree reasonably well, 22 vs. ~9 atom Cl104 atom 0; whereas the abundance based on Si differ greatly, 1·5 × 105 vs. 2800 atom Cl106 atom Si.

The uranium contents of iron meteorites

Abstract Seven iron meteorites and the iron phase of one pallasite have been examined for uranium content by neutron activation. The results are at the limit of detection by this method under the conditions used, but indicate a variable uranium content in the range 10 −12 to 10 −10 g/g. This agrees with the limits set by Reed and Turkevich (1955) in preliminary results of the application of neutron activation to this problem, and is more than a factor of 10 lower than previous determinations by other methods.

Interrelations Among Isotopically Anomalous Mercury Fractions from Meteorites and Possible Cosmological Inferences

The magnitudes of the mercury anomaly found in unequilibrated meteorites appear to fit a trend. The excesses in the ratios of mercury-202 to mercury-196 are related by simple multiplication factors. This periodicity may be interpreted in terms of the mode of production and ejection of the anomalous isotope from a stellar source.

Trace Elements and Accessory Minerals in Lunar Samples

Halogen contents similar to those in meteorites are reported in Apollo 11 samples. Concentrations of 0.6 to 13 parts mercury, 0.2 to 0.8 part uranium, 1 to 17 parts lithium, and 1 to 800 parts osmium per million and 0.5 to 1 percent chromium oxide by weight have been measured. In contrast to meteorites and terrestrial rocks a large mercury release below 110�C is observed. Some implications of these results are presented. Fluorapatite, quartz, tridymite, fayalite, and iron-rich, manganese-poor pyroxmangite, previously unreported, have been identified. The small amount of fluorapatite found does not account for the fluorine contents.

Fluorine in lunar samples - Implications concerning lunar fluorapatite.

Abstract The F contents of a number of Apollo 14 and 15 samples range from less than a ppm for anorthosite rock fragments to ~165 ppm for some soils and breccias. Apollo 15 soils tend to have lower F contents (50–70 ppm) than soils from other sites. In most cases samples were run simultaneously with W-1 in which F was determined to be 216 (±11) ppm. The F P 2 O 5 ratio is 0·032 ± 0·005 in soils and rocks. A correlation exists in soils between F, P 2 O 5 , and that fraction of the Cl which is insoluble in hot water. The F Cl r ratio in soils and rocks, though different, requires that the phosphate phase involved be fluorapatite; this is consistent with mineralogical observations. F, like Cl, is correlated with KREEP elements at all sites for which data are available.

Hg and Pt-metals in meteorite carbon-rich residues: suggestions for possible host phase for Hg

Abstract Carbon-rich and oxide residual phases have been isolated from Allende and Murchison by acid demineralization for the determination of their Hg, Pt-metal, Cr, Sc, Co and Fe contents. Experimental procedures used eliminated the possibility of exogenous and endogenous contaminant trace elements from coprecipitating with the residues. Large enrichments of Hg and Pt-metals were found in Allende but not in Murchison residues. Hg-release profiles from stepwise heating experiments suggest a sulfide as the host for Hg. Diffusion calculations for Hg based on these experiments indicate an activation energy of 7–8 kcal/mol, the same as that for Hg in troilite from an iron meteorite. This is further support for a sulfide host phase for Hg. Equilibration of Hg with this phase at ~900 K is indicated. Reasons why the Pt-metals are present in non-cosmic relative abundances are explored.

Surface-Related Mercury in Lunar Samples

Lunar samples contain mercury, which may be volatilized at lunar daytime temperatures. Such mercury may constitute part of the tenuous lunar atmosphere. If mercury can escape from the atmosphere by a nonthermal mechanism, an interior reservoir or exterior sources (such as meteorite infall or solar wind, or both) are required to replenish it. Core samples exhibit an increase in surface-related mercury with depth, which suggests that a cold trap exists below the surface. The orientation of rocks on the lunar surface may be inferred by differences in the amounts of surface-related mercury found on exterior and interior samples.

The halogens in Luna 16 and Luna 20 soils

Abstract Cl and P2U5 do not appear to exhibit the same correlation in soils from the Luna 20 and possibly the Luna 16 sites as they do in samples from the Apollo 11–15 sites. Nevertheless, the coherence between labile Cl and other KREEP-related elements is maintained.

Fluorine and other trace elements in lunar plagioclase concentrates

Abstract The F contents of plagioclase concentrates from Apollo 11 fines and an anorthosite inclusion from an Apollo 12 breccia are of the order of 100 ppm. This is very much lower than the ∼ 2500 ppm F found by Surveyor VII in soil of anorthositic composition at the crater Tycho. Thus it appears that there is a negligible admixture of this type of terra material at the Tranquillitatis and Procellarum landing sites. Apollo 14 soils from Fra Mauro are rich in plagioclase but contain no more F than the mare soils. In addition to F the contents of Br, Ba, U, Ru and Os were measured in the Apollo 11 and 12 plagioclase concentrates and in rock 12040 and core sample 10004.