S. Jovanovic

196Hg and202Hg isotopic ratios in chondrites: revisited

Additional evidence for an isotopically anomalous Hg fraction in unequilibrated meteorites has been obtained using neutron activation to produce196Hg and202Hg followed by stepwise heating to extract the Hg. In the latest experiments Allende matrix samples released the anomalous Hg but various high-temperature inclusions did not. Nucleogenetic processes are suggested as the probable cause of the anomaly.

Hg isotopes on the moon and in achondrites

196Hg and 202Hg isotopes measured by neutron activation analysis have been found to have ratios differing from normal in some lunar and meteoritic matter. Some Hg fractions extracted by stepwise heating from several samples of Apollo-14 breccia 14305 and one sample of 14321 exhibit deviations from the normal isotopic ratio by ∼ 20–30%. Samples from three Antarctic basaltic achondrites contain 196Hg202Hg ratios that are lower than normal by factors of 2–4. The anomalies in these meteorites and the temperature fractions in which they occur are reproducible. The anomalous Hg occurs in a single but variable temperature fraction from 14305 samples but only in the 130°C fraction from the three achondrites; data on two of the Antarctic achondrites have been published. The amount of Hg in the fractions with anomalous ratios varied from 10% to ∼ 0.1 % in samples with total Hg of 2–200 ppb. The other 5 to 6 thermally extracted Hg fractions per sample have normal ratios. These fractions act as internal standards and thus serve to reduce uncertainties related to neutron flux variables and sample matrix effects. The anomalous Hg is found in samples from three possible parent bodies: the Moon, that of the shergottites and that of the eucrites. The final thermal evolution of the samples occurred over a time-span ranging from < l.3 to ⩾ 3.9 Ga ago. These facts present obstacles to understanding how this anomalous Hg was acquired; a possible explanation is periodic encounters of the solar system with a dense cloud of interstellar dust containing such Hg.

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.

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.

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.

Trace element profiles, notably Hg, from a preliminary study of the Apollo 15 deep-drill core

Abstract Previously reported results on Hg in Apollo 11, 12 and 14 and Luna 16 core and trench samples are interpreted in terms of the diurnal thermal pulse and layering processes. Apollo 15 deep-drill core samples from greater depths would not be expected to and do not respond to diurnal heating but the (labile) Hg profile reflects a layering process with little or no mixing and is in agreement with the extent of surface exposure that might be predicted on the basis of track studies by Phakey et al. Concentrations of Os, Ru and U in the deep-drill core samples are also reported.

Heavy element affinities in Apollo 17 samples

Abstract 204 Pb, Bi, Tl and Zn in samples from Apollo 17 exhibit relationships not found in samples from other sites. 204 Pb, Tl and Zn in residues remaining after dilute acid leaching are correlated with one another. Orange soil 74220, which is enriched in 204 Pb, Tl and Zn, is included in these relationships. In addition the submicron metallic phase generally associated with agglutinate formation is correlated with all three of these elements; this relationship has already been reported for 204 Pb in other samples. Thus, orange soil and agglutinates appear to be involved in concentrating heavy volatile metals. A process other than mixing is required to account for this. As a consequence of the isolation of the landing site by the surrounding massifs, local supply and recycling of volatile trace elements in soils may account for some of the interelement relations.

Lunar bulk sample trace element contents and kreep

The geochemical coherence between the labile element Cl and more refractory F, K, REE and P in lunar soils is utilized to gain insight into the evolution of the lunar samples studied.

History of Boulder 1 at Station 2, Apollo 17 based on trace element interrelationships

Correlations among the trace and minor element pairs Cl and Br, Cl and P2O5, and Ru and Os, present in parent igneous rocks, generally survived the processes of boulder breccia formation.Fractions of the Cl, Br, and Hg that are mobilized by water leaching and/or volatilization at moderate temperatures (⩽450°C) place constraints on the thermal history of Boulder 1 and its component breccias. Since, and possibly during, consolidation, the boulder has probably not been subjected to temperatures of ⩾450°C.The parent rocks of the Apollo 17 boulder and breccia samples studied could have been derived from two initial magmas. Boulder 1, Station 2 gray competent breccias 72255 and 72275 Clast #2 appear to be genetically unrelated to gray competent breccia and anorthositic material 72215, or to light friable breccia 72275; they do appear to be related to samples 72395 (Boulder 2) and 76315 (Station 6 boulder).Vapor clouds from apparently external sources permeated the source regions of the boulders.