Mixing and gangue dispersion in flotation machine pulps

Tracer experiments using quartz in sized ranges to simulate gangue minerals provide information on how impeller speed, air rate, and particle size determine the concentration of gangue in the uppermost pulp layers. Tests with and without a froth will contribute towards an understanding of the selective action of the froth column.Results indicate that the laboratory machine-operating conditions required for flotation coincide with a hydrodynamic region which is responsible for fine-gangue transfer from the pulp into the froth column by elutriation and entrainment process acting in the pulp, thus compromising the selective action of the flotation process itself.Topics are suggested requiring further investigation and mention is made of machine design features to which attention should be paid in attempting to reduce gangue transfer from pulp to froth.     

Black material on mineral inclusions and in internal fracture planes in diamond

The black material observed on the surface of crystalline inclusions in diamond and also in adjacent internal fracture planes has been classified as a result of a preliminary examination of several hundred diamonds from Sierra Leone, Ghana, and South Africa (particularly the Premier Mine), as well as diamond slices of unknown origin, followed by a detailed examination of some 100 diamonds. X-ray, electron diffraction, and qualitative electron microprobe techniques were used in identifying this material as graphite, pyrrhotite and pentlandite. The possible origins of these minerals are discussed.     

The partial fusion of peridotite

In a study of the origin of basalt magma, peridotite has been partially fused and the composition of the liquid phases determined. Peridotite was chosen because it is thought to be the most likely material of the upper mantle. Geological evidence suggests that the upper mantle is not of basaltic composition and eclogitic mineralogy but that it is of ultrabasic composition. Although under some conditions an ultrabasic mantle may be within the field of eclogite stability, the comparative rarity of high-pressure phases such as garnet in ultrabasic nodules suggests that normal basalts are derived from non-eclogitic regions. The peridotite composition selected for experimental work was that of average peridotite (Nockolds). Charges of the synthetic peridotite were held at constant temperature (±1/2°C) in a non-oxidising atmosphere for one week. After quenching, the glass was extracted and analysed. The glass content varied from 4% at 1250°C to 26% at 1355°C. Its composition ranged from a basalt more or less saturated in normative silica at a temperature of 1310°C (15% fusion) and below, to picrite basalt at higher temperatures. The results confirm the general assumption that basalts can be the product of the partial fusion of peridotite. To date, the experimental work has been under anhydrous conditions at atmospheric pressure.     

Tension fractures and boudinage oblique to the maximum extension direction: an analogy with lüders' bands

A study has been made of the orientation of boudin necklines and extension fractures with respect to the maximum extension direction X determined by infilling fibre growth. Several localities, within the Variscan belt of Western Europe, the Pyrenees and the Alps, have been investigated in detail. It has been generally accepted that boudinage and extension fracturing occur perpendicular to X in the rock at the time of their formation; however, we have shown that is not the case: boudin necklines and extension fractures occur at an angle between 45°–90° to X, with the most frequent orientations between 65°–70° and 80°–85°. Angles of exactly 90° are rare.In order to explain · this obliquity, an analogy is made with the phenomenon of Lüders' bands (localised regions of plastic deformation) developed in thin metal plates under tensile testing. Because the thickness of a layer is negligible compared with its lateral extent, we will only be concerned here with the case of thin metal plates.     

Natural partial melting of syenite blocks from Ascension Island

Blocks of coarse-grained syenite included in a trachyandesite lava flow on Ascension Island exhibit features attributable to partial melting. The liquid so formed has been quenched to a glass and the chemical variation of the glass is considered to depend on the amount of melting, the mineralogy and modal proportions of each block — especially the presence or absence of quartz — and the chemical composition of the minerals subjected to melting. Partial melting of quartz-syenites such as these could have produced magmas of composition similar to that of the comendites and granites found on Ascension but differences in major element and minor element chemistry between the glass and the comendites and granites suggest otherwise.     

Isotopic composition of lead and strontium in lavas and coarse-grained blocks from Ascension Island,South Atlantic

New Sr and Pb isotope data are presented for a selection of lavas and associated coarse-grained blocks from Ascension Island. K-Ar dates for the lavas range up to1.5±0.2Ma. Initial⁸⁷Sr/⁸⁶Sr ratios are consistent with earlier measurements and for most rocks are ca. 0.7029, but range up to 0.7135 in the case of the most evolved lavas and blocks. Pb isotope data are also consistent with earlier measurements, but the Pb in two gabbroic blocks is less radiogenic than Pb in the other rocks. It is suggested that these gabbroic blocks crystallized from a magma of tholeiitic composition whose source was similar to that of mid-oceanic ridge basalt whereas the lavas and other blocks crystallized from mildly alkaline magmas derived from a source further from the crest of the Mid-Atlantic Ridge. The high⁸⁷Sr/⁸⁶Sr ratios result from contamination of the most silicic magma by radiogenic Sr from pelagic sediments. These data and their interpretation are consistent with the petrological and geochemical observations that the granite blocks are the coarse-grained equivalents of the volcanic suite [11] and not fragments of relict continental material [2,3].     

Isotopic composition of lead and strontium in lavas and coarse-grained blocks from Ascension Island,South Atlantic—an addendum

Natural marokite (CaMn₂O₄) has been studied at high pressures and temperatures using a diamond-anvil press coupled with laser heating in the pressure range 100–250 kbar. A mixture of marokite, CaMnO₃ (perovskite) and MnO (rocksalt) has been observed in all runs in the above pressure range by X-ray diffraction study of the quenched samples. It was interpreted that marokite disproportionates into the mixture CaMnO₃ (perovskite) + MnO (rocksalt) at pressures below 100 kbar. A general comparison of the molar volume for all known compounds having the marokite-related structures (including CaFe₂O₄ and CaTi₂O₄) with those for a mixture of perovskite plus rocksalt structures suggested that the mixture is more stable than the marokite-related structures at high pressures, as confirmed by the present experimental result. The CaFe₂O₄-modification of common nepheline (NaAlSiO₄) is also suggested to be unstable relative to the component oxides of α-NaAlO₂ + SiO₂ (stishovite) at high pressures.     

Characteristics of southern California atmospheric rivers

Theoretical and Applied Climatology - Atmospheric rivers (ARs) are channels of high water vapor flux that transport moisture from low to higher latitudes on synoptic timescales. In areas of...