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Helmke, P. A.

Publications and source records attributed to Helmke, P. A..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Reflectivity and other physicochemical properties of Mn-substituted goethites and hematites

Goethite-bearing samples with values of Mn(s) (Mn/(Mn+Fe) mole fraction) up to 0.206 were synthesized by precipitation from alkaline solution. Samples with Mn(s) less than or equal 0.061 were single-phase Mn-goethites: samples with higher Mn(s) values contained another Mn-bearing phase (probably jacobsite). Mn-hematites were prepared by dehydroxylation of corresponding Mn-goethites at 500 C. Orthorhombic a and b unit cell dimensions of Mn-goethites changed in a linear manner with Mn(s), but not at rates predicted by the Vegrad law. Hexagonal unit cell dimensions of Mn-hematites did not vary with Mn(s). Moessbauer parameters isomer shift (IS), quadrupole splitting (QS), and hyperfine field (B(sub hf)) were measured at 293 and 15 K. For all single-phase Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061), magnetic splitting was observed at both temperatures. At 293 K, small but systematic decreases in B(sub hf) were observed with increasing Mn substitution; IS and QS were not dependent on Mn(s). Mn substitution strongly lowered the Morin transition temperature of hematite. At 15 K, the Morin transition was not present for Mn(s) greater than 0.020(4). The saturation magnetization of Mn-goethites and Mn-hematites (Mn(s) less than or equal 0.061) was the expected zero (within error) for antiferromagnetic goethite and for hematites obtained from dehydroxylation of goethites. Mn-geothites with Mn(s) greater than 0.061 were magnetic because of the presence of strongly magnetic jacobsite. For reflectivity spectra, bands resulting from MN(3+) were centered near 454 and 596 nm for Mn-goethites and near 545 and 700 nm for Mn-hematites. There is evidence for a approximately 700 nm band in spectral data for Martian bright regions, but association of it with Mn(3+) is not a unique interpretation. Comparison of laboratory and Martian spectral data implies that Mn(s) less than 0.032 for the Mn(3+) content of Martian hematites.

Vempati, R. K.↗
NASA NTRS1973

Major and trace elements in igneous rocks from Apollo 15.

The concentrations of major and trace elements have been determined in igneous rocks from Apollo 15. All materials analyzed have typical depletions of Eu except for minerals separated from sample 15085. Four samples have concentrations of trace elements that are similar to those of KREEP. The samples of mare basalt from Apollo 15 have higher concentrations of FeO, MgO, Mn, and Cr and lower concentrations of CaO, Na2O, K2O, and rare-earth elements (REE) as compared to the samples of mare basalt from Apollos 11, 12, and 14. The samples can be divided into two groups on the basis of their normative compositions. One group is quartz normative and has low concentrations of FeO while the other is olivine normative and has high concentrations of FeO. The trace element data indicate that the samples of olivine normative basalt could be from different portions of a single lava flow.

Helmke, P. A.↗
NASA NTRS1973

Rare earths, other trace elements and iron in Luna 20 samples.

The results of the analysis by neutron activation of six samples from the Luna 20 mission and one sample of less than 1 mm fines from Apollo 16 are reported. The concentrations of the rare-earth elements (REE) in the samples of fines from Luna 20 and Apollo 16 are less than those found for corresponding materials from the mare areas but a negative Eu anomaly is still present. The concentrations of the REE in fines from Luna 20 are only about two-thirds as great as in the sample of Apollo 16 fines, but the concentration of Co, Sc and Cr are greater by factors ranging from 1.5 to 2.3.

Helmke, P. A.↗
NASA NTRS1973

Trace elements in fines from the Apollo 15 deep drill.

Samples of fines from the bottom of the Apollo 15 deep drill core and from each junction between the six 42.5-cm long segments of the drill stem were analyzed for Ag, Co, Cr, Cs, Cu, Ga, Hf, Rb, Sc, and Zn by neutron activation. The most striking feature of the results is the absence of significant variations in concentration for any element throughout the depth of the drill sample and despite the considerable stratigraphy of the cored material. The presence of a significant amount of KREEP material is indicated.

Helmke, P. A.↗
NASA NTRS1973

Major and trace element abundances in samples from the lunar highlands

Analyses for major elements, REE, Co, Cr, Cs, Ga, Hf, Ni, Rb, Sc, and Zn have been done on samples of Apollo 16 rocks 60025, 60335, 64455, 65015, 67075, and 67629 and on fines 60601, 61221, 61241, 64501, 65701, 67601, and 69941. FeO, Na2O, REE, Co, Cr, Hf, and Sc have been determined in four 4-5 mg chips from 65015 and 20 individual, 2.5-9.5 mg fragments from 65702. It appears that trace element characteristics of small fragments are similar to those of larger rocks. No simple mixing relationship was found among KREEP basalts, VHA basalts, anorthosites, fines, and meteorites. Balances could not be simultaneously achieved for Al2O3 and LIL elements, using analyzed samples as end members for mixing models. Most samples analyzed have negative Eu anomalies, in contrast to the positive anomalies expected for plagioclase cumulates. Most samples may be derived from LIL-rich liquids that flowed into highland valleys.

Haskin, L. A.↗
NASA NTRS1972

Rare earths and other trace elements in Luna 16 soil.

An analysis has been made of four small samples of material brought to earth by the Luna 16 mission, with the aim to determine rare earths and other trace elements in these samples. The analytical results are tabulated, and the rare earth abundances are compared with the average for chondrites. A comparison is also made with the results of similar analyses of Apollo samples.

Helmke, P. A.↗
NASA NTRS1972

Rare earths and other trace elements in Apollo 14 samples.

REE and other trace elements have been determined in igneous rocks 14053, 14072, and 14310, in breccias 14063 and 14313, and in fines 14163. All materials analyzed have typical depletions of Eu except for feldspar fragments from the breccias and igneous fragments from 14063. Igneous rocks 14072 and 14053 have REE concentrations very similar to Apollo 12 basalts; 14310 has the highest REE concentrations yet observed for a large fragment of lunar basalt. The effects of crystallization of a basaltic liquid as a closed system on the concentrations of Sm and Eu in feldspar are considered. Small anorthositic fragments may have originated by simple crystallization from very highly differentiated basalt (KREEP) or by closed-system crystallization in a less differentiated starting material. Application of independent models of igneous differentiation to Sm and Eu in massive anorthosite 15415 and to Sm and Eu in lunar basalts suggests a common starting material with a ratio of concentrations of Sm and Eu about the same as that in chondrites and with concentrations of those elements about 15 times enriched over chondrites.

Helmke, P. A.↗