A. A. Giardini

Some petrological aspects of the Prairie Creek diamond-bearing kimberlite diatreme, Arkansas

Based on modal and chemical composition, the rocks of the Prairie Creek diatreme situated 4 km SSE of Murfreesboro, Pike County, Arkansas, are classified as micaceous kimberlite. The K-Ar isotopic analysis of phlogopite from this diatreme yielded an age of 106 ± 3 m.y. (Albian) which is in agreement with stratigraphic relations. Electron beam probe data on minerals from kimberlite breccia, one of the three textural types, are presented. The breccia is considered as the potential source of the diamonds that have been mined at the diatreme. It contains phenocrysts of olivine (Fo90–92) and serpentine pseudomorphs after olivine embedded in a groundmass of serpentine, minor calcite, chrome-diopside, phlogopite (Mg/Mg+Fe = 84.15%), perovskite, spinels, and pentlandite. Xenoliths of shales, sandstones, and mantle-derived ultramafic material are also present. Spinels are rich in Cr, Ti, and Fe and generally low in Al. Zoned spinels show enrichments in Ti and Fe towards their rims. A positive correlation between 100(Fe3++Ti)/(Cr+Al+Fe3++Ti) and 100 Mg/(Mg+Fe2+) ratios exists in these spinels and probably reflects an oxygen fugacity increase during magma crystallization. Occluded gases in diamonds and kimberlites corroborate the hypothesis that the parent magma of the Prairie Creek kimberlite was derived by partial melting of upper-mantle garnet lherzolite under volatile-rich conditions, primarily enriched in H2O and CO2.

Composition and volume of gas released by crushing coal from West Virginia, Kentucky and Alabama

Abstract Analyses of the composition and volume of gaseous inclusions in samples of coal from West Virginia, Alabama and Kentucky have been made at room temperature by mass spectrometric techniques. This was done by crushing the coal in the high-vacuum inlet system of a research mass spectrometer. The gases observed were composed of C, S, H, O, N, He and Ar atoms. Water was the most abundant gas; others were hydrogen, helium, methane, ammonia, methanol, ethanol, carbon monoxide, nitrogen, ethane, oxygen, hydrogen sulphide, argon and carbon dioxide. Gas compositions were found to be a function of the source of the coal. For example, over 6% of the gas from Alabama coal was methane, but West Virginia coal contained only 0.1% methane. The volume of gas also was a function of the coal source. Coal from Kentucky contained 2.3 cm 3 g −1 (STP), whereas coal from West Virginia contained 0.4 cm 3 g −1 .

Composition and volume of gas released by ‘melting’ coal from West Virginia and Alabama

Abstract Analyses of the composition and volume of gases released by ‘melting’ samples of coal from West Virginia and Alabama under vacuum have been made by mass spectrometric techniques. This was done by melting the coal in a quartz tube attached to the highvacuum inlet system of a research mass spectrometer. The gases observed were composed of C, S, H, O, N, He and Ar atoms. Hydrogen was the most abundant gas; others were helium, methane, ethylene, ethane, carbon monoxide, nitrogen, hydrogen sulphide, propane, argon, carbon dioxide and sulphur dioxide. Gas compositions were found to be a function of the source of the coal. For example, over 65% of the gas from Alabama coal was hydrogen, but West Virginia coal yielded only about 30% of hydrogen. All coals released about 100 cm 3 g −1 (STP) (about 2300 ft 3 (short ton) −1 ) of combustible gas. An additional observation was the fact that about 90% of the sulphur was physically separated from the coal in the vacuum melting process.