Chemical composition of Luna 20 rocks and soil and Apollo 16 soils

The abundances of 24 major, minor and trace elements have been measured by INAA in Luna 20 metaigneous rocks 22006,1 and 22007,1, breccia 22004 and soil 22001,9 and in Apollo 16 soils 62281, 66041 and 66081. An additional 12 trace meteoritic and non-meteoritic elements have also been determined in 22001 and 62281 soils by RNAA. The bulk compositions of L 20 and Ap 16 rocks and soils show close similarity between the two highland sites. There are appreciable differences in bulk compositions between the L 20 highland and the L 16 mare site (120 km apart), suggesting little intermixing of rocks and soils from either site. Luna 20 rocks 22006 and 22007 are nearly identical in chemical composition to Ap 16 metaigneous rocks 61156 and 66095. Luna 20 rocks are feldspathic and are similar to low K-type Fra Mauro basalts. Such rocks and anorthositic gabbros appear to be the major components in highland soils. Luna 20 soil can be distinguished from Ap 16 soils by lower abundances of Al₂O₃, CaO and large ion lithophilic elements. Luna 20 breccia 22004 probably is compacted soil. All L 20 samples show negative Eu anomalies with $\text{Sm}\text{Eu}$ ratios of 5.8, 7.2, 3.9 and 3.3 for rocks 22006, 22007, breccia 22004 and soil 22001, respectively. Norite-KREEP is insignificant, ≤1 per cent, at the L 20 highland site. The derivation of the L 20 soil may be explained by ≈33 per cent of L 20 metaigneous rocks and ≈ 65 per cent anorthositic gabbroic breccia rocks like 15418 (with a positive Eu anomaly) and ≈ 2 per cent meteoritic contributions. Interelement correlations observed previously for maria are also found in highland samples. Luna 20 and Ap 16 soils are low in alkalis. Both soils show an apparent Cd-Zn rich component similar to that observed at the mare sites and high 11 abundances relative to mare sites. The Ap 16 (62281) soil contains a fractionated meteoritic component (probably ancient) of ≈ 1.5 per cent in addition to ≈ 1.9 per cent Cl like material. Luna 20 soil may simply contain 1.9 per cent Cl equivalent.     

Investigation and simulation of metallic spherules from lunar soils

Metallic spherules selected from the Apollo 11, 12, 14, 15 and 16 sites were studied by optical techniques as well as the electron probe and scanning electron microscope. In addition, metallic spherules of similar composition were produced experimentally. The structure of the metallic lunar spherules indicates an origin by solidification of molten globules of metal. The experimentally produced spherules have external morphologies, metallographic structures and solidification rates (7 × 10² to 10⁶ ° C/sec) similar to the lunar spherules which have rapidly solidified. The majority of the lunar spherules are, however, either more slowly cooled or have been reheated in place with the lunar fragmental rocks, glass or soil. The heavy meteorite bombardment of the highlands is strongly reflected by the evidence of reheating and/or slow cooling of a majority of Apollo 14 and 16 spherules.The metallic spherules are probably produced from both lunar and meteoritic sources. Impact processes cause localized shock melting of metallic (and non-metallic) constituents at metal-sulfide phase interfaces in surface rocks and in the meteoritic projectile. The major source of metallic spherules is the metal phase present in the lunar rocks and soil. The large variation in spherule bulk compositions is attributed to the different meteoritic projectiles bombarding the Moon, metal phases of differing compositions in the lunar soils and rocks and to the experimental results which indicate that high S, high P alloys form two immiscible liquids when melted.     

Chemistry and surface morphology of soil particles from Luna 20 LRL sample 22003

Six siliceous glass spheres, five siliceous glass-bonded agglutinates and one breccia fragment from Luna 20 LRL sample number 22003 were analyzed by optical microscope, scanning electron microscope, scanning electron microprobe and energy-dispersive techniques. The data suggest that most of the glass spheres were probably derived locally by meteoritic impact processes and that most craters on their surfaces may have occurred from impacts of relatively high velocity particles in the impact-produced debris cloud while the glass sphere was at elevated temperatures. This is suggested by the nature of the craters, the partially buried fragments of plagioclase surrounded by radiating fractures and by the apparent absence of craters on the glass surfaces of the glass-bonded agglutinates. One glass sphere has a surface suggestive of a complex multiple impact origin involving liquid siliceous material and numerous siliceous spherules from 0.1 μm to 1 μm in diameter that may have formed from vaporization and condensation processes possibly in a relatively large scale meteoritic impact event.The surfaces of the siliceous glass spheres have several different types of materials. Concentration of metallic iron spherules on the surfaces of the glass spheres is generally lower than for similar Apollo 11 and 12 glass spheres. This is consistent with reduction processes being of primary importance in the formation of this metallic iron. Surface material composed only of Ca, C and O₂, possibly CaCO₃, is probably derived from carbonaceous chondrites. Splashes of material rich in Ca, Al, Fe, K and Cl occur. The origin of the relatively low temperature chlorine-bearing melt is unknown but it may be related to vaporization and condensation processes, possibly volcanic in nature, or possibly to partial fusion of components of carbonaceous chondrites. Siliceous surface material rich in potassium may represent either fused splash material of granitic composition or material enriched by vaporization and condensation processes.     

Siderophile-rich particles in the melt rocks at the E. Clearwater impact structure,Quebec: Their characteristics and relationship to the impacting body

The composition of the sampled melt rocks at the 22 km diameter E. Clearwater impact structure indicates the presence of ～8% C-1 material. The meteoritic component is fractionated with refractory siderophiles, up to 30 times C-1 abundances, concentrated in ten to hundred micron-sized, magnetic particles. These particles consist of the Ni-sulphide, millerite, and what is assumed to be a mixture of refractory silicates and magnetite with grain sizes of <1 μm. The larger particles have a core-rim structure with millerite and occasionally very minor galena and possibly pentlandite in the core. An origin as a combination of altered meteoritic metal and condensed meteoritic silicate is favored for the origin of the siderophile-rich particles. If 8% meteoritic material is taken as the average meteoritic contamination in the melt, then the E. Clearwater projectile may have impacted with a velocity of 17 km s^?1. Peak shock pressures would have been of the order of 300 GPa, sufficient to vaporize the silicate component but only melt the metal component of the projectile. As the meteoritic material was being driven down into vaporized/ melted target rocks during the initial stages of impact, the melted Fe, Ni metal underwent oxidation, Fe was removed, and meteoritic silicate material recondensed on the cooler, essentially Ni metal. As cavity excavation proceeded, these Ni metal, silicate-oxide particles were incorporated in the melt, their refractory nature prevented thermal digestion and sulphur in the melt reacted with the metal to produce millerite on final equilibration. If this hypothesis is correct, it suggests that the E. Clearwater projectile was a C-2 or C-3 chondrite, both of which are compatible with the trace element composition of the melt rocks. Clearwater Lake is a twin impact structure formed by an asteroid pair. It is still not clear, however, what type of projectile formed the 32 km diameter western structure, where the surface melt rocks contain no identifiable meteoritic signature.     

Siderophile-rich particles in the melt rocks at the E. Clearwater impact structure,Quebec: Their characteristics and relationship to the impacting body

The composition of the sampled melt rocks at the 22 km diameter E. Clearwater impact structure indicates the presence of 8% C-1 material. The meteoritic component is fractionated with refractory siderophiles, up to 30 times C-1 abundances, concentrated in ten to hundred micron-sized, magnetic particles. These particles consist of the Ni-sulphide, millerite, and what is assumed to be a mixture of refractory silicates and magnetite with grain sizes of <1 m. The larger particles have a core-rim structure with millerite and occasionally very minor galena and possibly pentlandite in the core. An origin as a combination of altered meteoritic metal and condensed meteoritic silicate is favored for the origin of the siderophile-rich particles. If 8% meteoritic material is taken as the average meteoritic contamination in the melt, then the E. Clearwater projectile may have impacted with a velocity of 17 km s^–1. Peak shock pressures would have been of the order of 300 GPa, sufficient to vaporize the silicate component but only melt the metal component of the projectile. As the meteoritic material was being driven down into vaporized/ melted target rocks during the initial stages of impact, the melted Fe, Ni metal underwent oxidation, Fe was removed, and meteoritic silicate material recondensed on the cooler, essentially Ni metal. As cavity excavation proceeded, these Ni metal, silicate-oxide particles were incorporated in the melt, their refractory nature prevented thermal digestion and sulphur in the melt reacted with the metal to produce millerite on final equilibration. If this hypothesis is correct, it suggests that the E. Clearwater projectile was a C-2 or C-3 chondrite, both of which are compatible with the trace element composition of the melt rocks. Clearwater Lake is a twin impact structure formed by an asteroid pair. It is still not clear, however, what type of projectile formed the 32 km diameter western structure, where the surface melt rocks contain no identifiable meteoritic signature.     

Major element compositions of Luna 20 glass particles

Major element analyses of nineteen Luna 20 glass particles indicate that most of the Luna 20 glasses have Al₂O₃ contents greater than 21 wt.% and compositions similar to Apollo 10 and Luna 20 rocks and soils. Three of the glass particles have low Al₂O₃ (< 13 wt.%) and high FeO (> 18 wt.%) contents and were probably derived from one of the adjacent maria. The low glass content of the Luna 20 soil indicates that it is relatively young or less mature than most mare soils that have been studied.     

青海东昆仑乌兰乌珠尔铜矿金属矿物特征及意义

通过详细的光、薄片研究,认为乌兰乌珠尔铜矿主要金属矿物有黄铁矿、黄铜矿、磁铁矿、磁黄铁矿、毒砂、闪锌矿、黑钨矿和锡石等.进一步通过金属矿物组合及其成分分析和流体包裹研究,推断乌兰乌珠尔铜矿的金属矿物主要是在高硫逸度较还原环境下形成的,其形成作用可划分为锡石-多金属和黄铜矿-多金属两个成矿阶段.结合乌兰乌珠尔区域地质和矿床地质的研究,确定该矿床为中高温热液Cu矿床.     

Petrology of some lithic fragments from Luna 20

Microscopic and electron microprobe studies were made of polished thin sections of part of a 30-mg sample of 250–500 μm lunar soil returned by Luna 20 from a point between Mare Fecunditatis and Mare Crisium. Very fine-grained lithic (crystalline) rock fragments, composing about one fifth of the total sample, have mineralogical compositions equivalent to various types of gabbro, anorthositic gabbro, gabbroic anorthosite and troctolite, with minor basalt. The textures now observed in these fragments are in large part metamorphic. Twentyseven electron microprobe analyses of minerals from these fragments are presented, including olivine, plagioclase, pyroxene, spinel, nickel-iron and a Zr-Ti-REE mineral possibly similar to ‘phase B’ of Lovering and Wark (1971). Analyses of seven melt inclusions and twenty-eight defocused beam analyses of lithic fragments are also given. Some of the fragments contain ‘gas’ inclusions which, along with the fine grain size, are believed to indicate final crystallization under low pressure near surface conditions. The almost complete absence of granophyric material in this sample raises the question of whether or not there are at least two distinct magmas for the plagioclase-rich terrae rocks from which this soil sample was derived in part.     

Radiation damage in Luna 20 soil

Micron-sized soil grains from the Luna 20 mission are the most lightly irradiated we have examined, in contrast to micron-sized grains from the Luna 16 soil, which are the most heavily irradiated. Radiation damage in micron-sized grains is inversely correlated with albedo of the soil. The absence of angular, amorphous grains in Luna 20 supports our previous contention that such grains in Luna 16 were produced by intense radiation damage.     

Trace elements in natural metallic iron from Disko Island,Greenland

The largest occurrence of natural metallic iron on Earth is on the island of Disko, Greenland. Metallic iron is found there in a variety of different types, from small metal particles in basalts to large meter-sized blocks. We have studied three different types of metallic iron: small metal spherules (< 300 m) in basaltic magma; larger metal grains (300 m-3 mm), often composed of aggregates of smaller particles, in similar host rocks; and massive iron lumps (up to several tons). Analytical data for 13 siderophile elements in samples from these three types are presented. All metals analysed have a distinctly crustal pattern of siderophile elements. High Co/Ni, Re/Ir or W/Ir ratios clearly demonstrate that a meteoritic origin for the metallic iron must be excluded. Since the Co/Ni and Re/Ir ratios are approximately chondritic in the upper mantle of the Earth, a mantle origin for the Disko metals can also be ruled out. This supports earlier petrological and geological evidence that the metallic iron was formed through reduction of basaltic magma by carbon derived from Tertiary shales and coals. Significant differences in absolute and relative abundances of siderophile elements occur among the three kinds of metals. The strongly siderophile elements (e.g. Ir, Re, Ni) increase in concentration from the small metal spherules through the larger grains to the massive iron lumps. The contents of less strongly siderophile elements (P, W, Ga) decrease in the same sequence. Evidence is presented that the small metal spherules are formed by in situ reduction. Larger iron metal grains and massive iron lumps are composed of small spherules, accumulated by gravitational settling in a magma reservoir. These metal cumulates have extracted highly siderophile elements from a larger volume of basaltic melt.Part of a Ph.D. thesis by W. Klöck     

Luna 20 soil: abundance of 17 trace elements

Luna 20 soil is remarkably similar to Apollo 16 soil, in its content of 17 mainly volatile or siderophile elements: Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl, U, and Zn. Like other highland soils, it seems to contain an ancient meteoritic component of fractionated, volatile-poor composition. The bulk soil has a high $\text{Tl}\text{Cs}$ ratio (9.4 × 10^?2), similar to that in Apollo 16 soils (5.4 × 10^?2), but higher than that in samples from other sites (1.1 × 10^?2). It is severely contaminated with Ag, Cd, Re, and Sb, judging from a comparison with a 1.7 mg soil breccia sample from the coarse fraction of the soil.     

The halogens in Luna 16 and Luna 20 soils

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.     

Foreign meteoritic material of howardites and polymict eucrites

Howardites and polymict eucrites are fragments of regolith breccias ejected from the surface of a differentiated (eucritic) parent body, perhaps, of the asteroid Vesta. The first data are presented demonstrating that howardites contain, along with foreign fragments of carbonaceous chondrites, also fragments of ordinary chondrites, enstatite meteorites, ureilites, and mesosiderites. The proportions of these types of foreign meteoritic fragments in howardites and polymict eucrites are the same as in the population of cosmic dust particles obtained from Antarctic and Greenland ice. The concentrations of siderophile elements in howardites and polymict eucrites are not correlated with the contents of foreign meteoritic particles. It is reasonable to believe that cosmogenic siderophile elements are concentrated in howardites and polymict eucrites mostly in submicrometer-sized particles that cannot be examined mineralogically. The analysis of the crater population of the asteroid Vesta indicates that the flux of chondritic material to the surface of this asteroid should have been three orders of magnitude higher than the modern meteoritic flux and have been comparable with the flux to the moon’s surface during its intense meteoritic bombardment. This provides support for the earlier idea about a higher meteoritic activity in the solar system as a whole at approximately 4 Ga. The lithification of the regolith (into regolith breccia) of the asteroid Vesta occurred then under the effect of thermal metamorphism in the blanket of crater ejecta. Thus, meteorite fragments included in howardites provide record of the qualitative composition of the ancient meteorite flux, which was analogous to that of the modern flux at the Earth surface.     

Optical and chemical analysis of iron in Luna 20 plagioclase

The iron content of Luna 20 anorthitic plagioclase ranges from a few hundredths to a few tenths of a weight per cent from crystal to crystal. Rather than being related to the original composition of the parent magma or magmas, the optical and chemical properties of the iron appear to be caused by postcrystallization migration and exsolution.Oriented inclusions of iron alloy present as needle-like crystals are observed, and the host plagioclases are irregularly chemically zoned in iron. It is not known whether thermal metamorphism or another process of chemical reduction related to impact and shock is responsible for the observed phenomena. Postcrystallization effects may obscure evidence of the original oxidation state and iron concentration of these crystals.     

Comparison of the magnetic properties of glass from Luna 20 with similar properties of glass from the Apollo missions

Magnetic susceptibility measurements have been made on four glass spherules and fragments from the Luna 20 fines; two at 300°K and two from 300°K to 4°K. From these data the magnetic susceptibility extrapolated to infinite field, the magnetization at low fields and also the saturation magnetization at high fields, the Curie constant, the Weiss temperature, and the temperature-independent susceptibility were determined. Using a model previously proposed for the Apollo specimens, the Curie constant of the antiferromagnetic inclusions and a zero field splitting parameter were calculated for the same specimens. The data show the relatively low concentration of iron in all forms in these specimens. In addition, the Weiss temperature is lower than that measured for the Apollo specimens, and can be attributed almost entirely to the ligand field distortion about the Fe²⁺ ions in the glassy phase. The data further suggest that the Luna 20 specimens cooled more slowly than those of the Apollo missions, and that some of the antiferromagnetic inclusions in the glass may have crystallized from the glass during cooling.     

Visible and near-infra-red transmission and reflectance measurements of the Luna 20 soil

Visible and near-infra-red spectra of chemically analyzed grains of glass and minerals from the Luna 20 sample were compared with diffuse reflectance spectra of the bulk soil. As in the spectra of soil samples from other localities on the Moon, pyroxene contributes two broad absorption features near 1 μm and 2 μm. The soil has a high integral reflectance (or albedo) arising from plagioclase, which appears to be the dominant mineral in the lunar highlands. The Luna 20 soil curve is most similar to the reflectance curves of the non-rayed soils at Apollo 16, in agreement with the generally similar mineralogy of these samples. The average pyroxene composition in the Luna 20 soil, as determined from the absorption bands in the diffuse reflectance spectra, and analyses of single crystals, is more calcic than in the lithic fragments. Thus, the soil appears to have a few per cent of admixed material derived from mare basalts. Comparison of the soil spectrum with telescopic curves of nearby areas reveals a close similarity; however, the Luna 20 sample is slightly less mature than expected. Luna 20 may have sampled subsurface material that is fresher than the regional surface soil, or alternatively, the Luna 20 area may contain an admixture of relatively recently exposed material from a ray crater.     

Fractional Determination of Gold in Twenty Six Geological Reference Materials by Sequential Extraction with Graphite Furnace Atomic Absorption Spectrometry

A method is described to estimate the chemical form of gold (Au) in a variety of geological reference samples, combining a sequential extraction scheme with graphite furnace atomic absorption spectrometry, after extraction of Au as iodide or chloride with methyl isobutyl ketone. The fractions dissolved by sequential extraction are empirically defined as the exchangeable, amorphous, metallic, aqua regia-soluble and residual fractions. The amounts of Au in the amorphous fraction have been derived mainly from oxide or amorphous phases, and the chemical forms of Au are considered to be mostly amorphous and partly metallic. The metallic fraction of Au is likely to exist as submicroscopic grains of native metal which are relatively free from the rock-forming minerals, whereas the aqua regia-soluble or residual fraction of Au may be bound more intimately perhaps as inclusions or solid solutions of either native metal or electrum in most cases. Satisfactory agreement was observed between the sum of the Au values from exchangeable to residual fractions and the reported total Au values, except for a few samples which contained a large amount of reducing materials. Analytical results of Au for twenty six geological reference materials are tabulated, and geochemical and mineralogical features are discussed.     

The Luna 20 lithic fragments,and the composition and origin of the lunar highlands

Luna 20 soil 22003,1 (250–500 μ) is similar to Apollo 16 soil 61501,47 (250–500 μ) in terms of the percentage of different types of particles. However, among the lithic fragments, the Apollo 16 sample contains a greater percentage of fragments with more than 70 wt. % modal plagioclase and a significantly greater proportion of KREEP-rich particles. Modal analyses of non-mare lithic fragments in Luna 20 and Apollo 11, 14, 15 and 16 indicate that the KREEP-poor highland regions (the bulk of the lunar terrae), though relatively feldspathic, are compositionally inhomogeneous, ranging in plagioclase content from approximately 35 to 100 wt. %. The average plagioclase content lies in the range 45–70 wt.%. Luna 20 pyroxene analyses cluster in two groups, one more magnesian than the other. The groups persist when pyroxene analyses from KREEP-poor noritic, troctolitic and anorthositic lithic fragments from Apollo 11, 14, 15 and 16 and Luna 20 are included. Olivine compositions mimic these pyroxene groups.Within each pyroxene group Cr₂O₃ and TiO₂ decrease as $\text{Fe}\text{(Fe + Mg)}$ increases, suggesting a relationship by fractional crystallization. The two groups suggest that at least two magma compositions were involved. To account for these observations we envisage a Moon-wide magma system in which initial accretionary heterogeneities were imperfectly erased by diffusion and convection. During the cooling of this magma system fractional crystallization was effected by the flotation of plagioclase and sinking of pyroxene, olivine and perhaps ilmenite. The endproduct was an upper layer enriched in plagioclase and a lower layer enriched in mafic silicates. KREEP-rich rocks, which are predominantly noritic in major element composition, may be mechanical mixtures of KREEP-poor norite and material residual after fractional crystallization of the surface magma system.     

A lunar differentiation model in light of new chemical data on Luna 20 and Apollo 16 soils

Fines from a Luna 20 soil sample and from three Apollo 16 deep drill core samples have been analyzed for major-minor element abundances by a combined, semi-micro atomic absorption spectrophotometric and colorimetric method. Both the major element and large ion lithophile trace element abundances in these soils, the first from interior highland sites, are greatly influenced by the very high normative plagioclase content, being distinctly richer in Al and Ca, and poorer in K, P, Cr, Mn, Fe, and Ti, than most bulk soil samples from previous lunar missions. The relatively large compositional variations in the Apollo 16 core can be ascribed almost entirely to decreasing plagioclase with increasing depth. The chemical composition of the Luna 20 soil indicates less plagioclase and less KREEP than in the Apollo 16 soils. A lunar differentiation model is presented in which is made the suggestion that KREEP is the result of a second fusion event in a lunar crust consisting of early feldspathic cumulates and primary aluminous ‘liquid’.     

The mineralogy and petrology of the Luna 20 soil sample

Fragments of igneous rocks, glasses and minerals comprise 25 per cent of the studied sample of the Luna 20 soil. Basalt fragments in the Luna 20 soil are similar to basalts from the mare regions of the Moon—in that they are characterized by the presence of iron-rich olivines and pyroxenes. On the basis of the FeO contents of plagioclases, it appears possible to distinguish between the plagioclase of the mare and highland regions of the Moon. Other igneous rock fragments are anorthosite, gabbroic anorthosite and anorthositic gabbro. The most abundant rock type (75 per cent of the sample) is microbreceia. One third of the fragments of microbreccia have undergone thermal metamorphism resulting in the homogenization of phases and the development of poikioblastic and hornfelsic textures. Excluding the basalt fragments, the dominant minerals in the Luna 20 soil are anorthite (An_93–98), magnesium-rich orthopyroxenes, intermediate clinopyroxenes and olivine (< Fa₅₀). Chemically, the Luna 20 and Apollo 16 soil samples are similar, but the Luna 20 soil is slightly depleted in aluminum and calcium and enriched in iron and magnesium relative to the Apollo 16 soils. The slight difference in bulk chemistry of the two soils may be a result of the presence of a minor amount of mare material in the Luna 20 soil and its apparent absence in the Apollo 16 soils.