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[en] Beaches are the main sources for economic heavy minerals (HM) like ilmenite rutile, monazite, zircon, garnet and sillimanite. The seasonal HM accumulations, colloquially called 'beach washings' are mined by IREL and KMML in Kerala and by IREL and several private enterprises in Tamil Nadu. These sediments are found to contain 85-90% THM. It is presumed that during the monsoon, the sea is agitated and the churning and spiralling action of water lifts HM-bearing sediments from the sea floor and transports in suspension and deposits on the beach berm, the backwash taking the relatively lighter part of the sediment load back into the sea. This process is thought to give rise to HM-enriched sand on the beach face and the swash plain. It is pertinent to understand the controls on these economically important and scientifically interesting processes. Beachface is the seaward section of a beach exposed to and shaped by the action of waves. The beach face is the zone of most active change. Berm is the terrace of a beach that has formed in the backshore, above the water level at high tide. Berms are commonly found on beaches that have fairly coarse sand and are the result of the deposition of material by low energy waves. On broad beaches there may be three or more sub-parallel berms, each formed under different wave conditions. Swash zone is defined as that part of the beach extending from a nearshore shallow depth to the limit of maximum inundation; is a relatively narrow region of great importance for the exchange of sediment between land and sea. Morphological processes such as storm-induced erosion, post-storm recovery, seasonal variation in foreshore shape, and evolution of rhythmic
[en] The microstructures of natural ilmenite found in Panzhihua district, China, were examined by high-resolution electron microscopy (HREM). The [anti 12anti 10] structural images showed clearly the (10anti 11) nonbasal twinning which seems to be coincident with the [anti 1012] rotation twinning. The superlattices with periodicities of 16.8 and 12.6 A, respectively, as well as the unit-cell twinning related to the ordering of (10anti 11) multiple twinnings were observed. The superlattice resulting from the ordering arrangement of (10anti 11) stacking faults related to the slip systems suggested by Heuer were also detected. Possible genetic aspects are considered. (orig.)
[en] Complete text of publication follows. More like one century the field-reversal hypothesis has been accepted to explain an origin of the reversed remanent magnetization (RM) of rocks. The experimental evidences and the theoretical principles do support the self-reversal origin of the RM of several rocks. The recent rhyodacites of the intermediate hematite-ilmenite (Hem-Ilm) composition posses the self-reversed origin of the thermoremanent magnetization (TRM) from localities: Mt. Haruna - Japan, Mt. Shasta - USA, Mt. St. Helen - USA (the self-reversal tendency of the TRM was proven by my results), the 1991 Pinatubo eruption and from three other localities from Philippines. From my study follows that also the titanomagnetite (Ti-Mt) is a source of the self-reversed PTRM in Haruna rhyodacite. I revealed an increase of the reversed intensity of the TRM of Haruna and Olongapo (Philippines) rhyodacite rocks down to -196 deg C. I can deduce, that an ordering of the magnetic ions in the crystalline lattice of the Hem-Ilm is the dominant phenomenon of this type of the self-reversal. The second type: The self-reversal of the chemical remanent magnetization (CRM) of rocks due to the reordering of the magnetic ions and so the reversal of spontaneous magnetization in the crystalline A and B sub-lattices of the ferrimagnetic Ti-Mt - Ti-Mgh solid solutions. My results of basalts from Slovak volcanic fields, Bohemian Massif, Syria and Nigeria have proven that the rocks containing the low-temperature oxidized phase carry the reversed CRM. The self-reversed PTRM was induced also in the artificially prepared basaltic samples and in the andesite and rhyolite samples from about 177 outcrops. The self-reversed CRM of oxidized continental and sub-marine basalts was revealed also by foreign authors. The third type: The self-reversal RM was revealed in highly-temperature oxidized basalts containing dominantly the Hem-Ilm -es of low Ilm content. No self-reversal RM (TRM or CRM) is present in the volcanic rocks containing either the pure magnetite or the Ti-rich Ti-Mt without the low-temperature oxidized phase.
[en] The feasibility studies of magnetic concentration of the Campo Alegre de Lourdes ore were carried out, trying to obtain a maximum recovery of vanadium. As a consequence of the complex nature of the ore, mainly due to the presence of ilmenite as a exolutions in the interior of hematite/martite particles, it was not possible to separate the hematite-ilmenite eficiently, wich would be necessary for obtaining a high grade vanadium concentrate with low titanium content. (author)
[pt]Foram avaliadas as possibilidades de concentracao magnetica do minerio de Campo Alegre de Lourdes, visando principalmente a maxima recuperacao do vanadio. Verificou-se que devido a natureza complexa do minerio, principalmente em funcao da presenca de ilmenita na forma de exolucoes no interior dos graos de hematita/martita, nao foi possivel realizar-se uma eficiente separacao hematita-ilmenita, o que seria fundamental para obter-se um concentrado com alto teor de vanadio e baixo teor de titanio. (autor)
[en] The most important and strategic minerals in the Egyptian beach sands are monazite, zircon, rutile and ilmenite. Due to their importance, several flowsheets were designed for their separation economically. Electrostatic separation plays an important role in most of these flowsheets depending on the main differences between them concerning their electrical conductivity. This paper describes the design of a cell for the measurement of the electrical conductivities of these minerals. It also establishes a quantitative relationship between the electrical conductivity and the behaviour of these minerals during their electrical separation. A computer program was written to facilitate the calculation of the slope of the discharge curve from which the electrical conductivity or the reciprocal resistivity. Relaxation time and the data correlation coefficient for the tested minerals are obtained. For all the tests performed, the correlation coefficient value was found to be better than 99%. In general the electrical conductivity was shown to be a function of both temperature and grain size. It was found also that the presence of iron staining on the surface of monazite grains and inclusions in the zircon grains alters noticeably the bulk conductivity of the tested minerals
[en] The magnetic phase transition and magnetocaloric properties of both mineral and synthetic melanostibite Mn2FeSbO6 with ilmenite-type structure have been studied. Mn2FeSbO6 orders ferrimagnetically below 270 K and is found to undergo a second-order magnetic phase transition. The associated magnetic entropy change was found to be 1.7 J/kg K for the mineral and 1.8 J/kg K for the synthetic melanostibite for 5 T field change. For the synthetic Mn2FeSbO6 the adiabatic temperature change was estimated from magnetic- and specific heat measurements and amounts to 0.2 K in 1 T field change. Perspectives of the functional properties of Mn2FeSbO6-based materials are discussed. -- Highlights: ► The magnetic phase transition of both mineral and synthetic melanostibite is studied. ► Mn2FeSbO6 exhibits an ilmenite-type structure with alternating layers of Mn and Fe/Sb. ► Mn2FeSbO6 undergoes a second-order magnetic phase transition close to room temperature. ► The magnetocaloric properties of this ferrimagnetic system are investigated
[en] Complete text of publication follows. Three selected basalt flow units from the Xitle volcano (2000-year-old, Basin of Mexico) are used to study the vertical variation of anisotropy of magnetic susceptibility (AMS) to examine their possible relationship with magnetic mineralogy, flow strain and general dynamic flow behavior of lava flows. Selected profiles are 4.8, 5.0 and 6.6 m thick and are located at different positions inside the flows; the thickest one is at the flow border. Sampling was performed at intervals from 12 to 20 cm. Number of specimens was 42, 75 and 36, respectively. Measurements were performed with a KLY2 and a Minisep instruments, a comparative analysis with selected specimens was performed with both instruments. Jelinek statistic was applied, as well as density distribution analysis for determining maximum distribution areas of principal directions. Hysteresis curves, Curie temperatures and some ore microscopy analysis indicate that magnetic mineralogy is dominated by Ti-poor titanomagnetite and that large ilmenite grains are also present, their sizes increasing towards the flow center. The k1 (maximum AMS axis) means broadly parallel the local geologically inferred flow direction, their inclinations point toward flow source. The respective k3 (minimum AMS axis) means reveal near horizontal main foliations (at least in 2 sites) defining dominant AMS ellipsoids dipping against flow. The density distribution analysis show that k3 individual directions have two maximums peaks; one of these peaks corresponding to a foliation dipping against the flow direction and the other one towards it, lying the k3 means among the two maximum peaks. A detailed analysis of the vertical variations of the AMS ellipsoids allowed identifying several zone-layers in the flow units, each one characterized with a particular AMS pattern. The lower layer in all cases shows ellipsoids dipping against flow; meanwhile the upper layer usually presents AMS ellipsoids dipping in favor of flow direction or dipping both against and favor of flow (site at flow border). Significant bottom most and topmost horizons and in cases thin middle layers show transversal ellipsoids, suggesting that all these layers and horizons have a rheological origin.