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[en] An experiment for uranium sorption onto fresh and weathered biotites was performed. After centrifugation, concentrations of uranium in the supernatants were analyzed using ICP-MS, and biotite samples were investigated using XRD and SEM. With powdered biotites (<3 mm in size), we have conducted uranium sorption experiments about fresh and weathered biotites to obtain uranium sorption amounts in various pH conditions. The uranium sorption was not high at a low pH (e.g., pH 3), but increased with increasing pH. There were lower uranium sorption by the weathered biotites than by the fresh ones, and the difference was much larger at higher pH (e.g., pH 11). The lower sorption values of uranium by the weathered biotites may be caused by a change of mineral surfaces and a chemical behavior of surrounding dissolved elements. It seems that the uranium-mineral interaction has been diminished, especially, in the weathered biotite by a destruction and dissolution of preferential sorption sites on the mineral surfaces and by the colloidal formation from dissolved elements.
[en] Presence of Early Tertiary pyroclastic material (tephra) has been documented petrographically, for the first time, in the Mandi-Bilaspur Sector from Tileli area, Dharamsala basin of Himachal Pradesh. The tephra is reported from the red shale, identified as tuffaceous siltstone belonging to lower Dharamsala Formation that lies above the uraniferous sandstone body and occurs as thin layers of over 300m along the strike, close to the contact of lower and upper Dharamsala formations. The tuffaceous material shows crude but preferred orientation of minerals like biotite, muscovite, chlorite, clay, hematite and specularite. Various features indicating presence of tephra are, glass shards altered to clay but retaining 'U' shaped outline, spindle-shaped hematite with preferred orientation, spherical to sub-spherical clay and altered Fe oxide rich balls, clay groundmass with flow pattern, flaky minerals in association with clast depicting asymmetrical ramp structure. A zone of approximately 300 m length containing tuffaceous material has been established at Tileli overlying the uraniferous sandstone body. Identification of tephra at Tileli has significant implications as it enabled in demarcating the boundary between the upper and lower Dharamsala formations in central part of the basin in Bilaspur-Mandi Sector of HP Himalaya and also in guiding the uranium exploration programme in the lower Dharamsala Formation. (author)
[en] Data on replacement of host rock minerals by uranium minerals are given. It is shown that uranium minerals as well as minerals of other elements are often formed by replacement of host rock minerals. In this case phenomena of replacement are noted not only for high temperature but for medium and low temperature ore manifestations as well. Uranium usually migrates in hexavalent state as uranium silicate, alkali carbonate and other complexes. Decomposition of compleXes took place under interaction of uranium bearing solutions with host rock minerals which played the role of restorers and promoted uranium deposition as hardly soluble compounds-uranium minerals. Braunnerite uranitite and coffinite are usually attributed to corous blende, riebeckite, aegirite or biotite
[en] The fission track age of uranium-bearing veins in a biotite sample from Bancroft in Canada has been determined. The apparent age was corrected by measurements of track lengths of fossil- and induced-fission tracks in the samples. The corrected age of the veins is found to be 273 ± 20 Myr. A comparison of the fission track ages of the veins and of the bulk mica shows that the veins were formed before the rock had cooled to the fission-track retention (or ''closure'') temperature of ∼ 100 0C. (author)
[en] Complete text of publication follows. The Anisotropy of Magnetic Susceptibility (AMS) at room temperature has been used for decades as a means to gain further understanding of petrofabrics within granites. Hence, the orientation of the magnetic ellipsoid is used as a kinematic marker for the emplacement mechanism of granitic bodies. In order to secure a correct interpretation of AMS as a result of magmatic fabric, one factor must be considered: the carrier of the AMS. In the case of the paramagnetic Marimanha igneous body, the carrier of the magnetic fabric is biotite (Antolin et al., 2007), which represents 20-25 % vol. as seen in thin section. Five sites chosen from the five petrographic zonations of the plutonic body are further studied via image analyses of biotites and crystallographic preferred orientations (CPOs) of quartz. On one hand there will be an external control of the AMS with the image analyses of biotite and on the other, more information of the orientation of quartz grains provide new data about the behavior of crystals during emplacement. In addition, the relationship between paramagnetic and diamagnetic grains will be established. The image analyses followed two approaches, on one side, the orientation of the biotite is studied in three perpendicular thin sections and on the other, the basal planes of biotites are represented as lines, whose orientation is subsequently studied again in the same thin sections. The crystallographic orientations of quartz c-axes were measured using electron backscatter diffraction (EBSD) analyses. In addition, cooled samples (down to 77degK) are analyzed to obtain the LT-AMS and to compare with the AMS at room temperature. Preliminary results from this weakly oriented granitoid suggest that the paramagnetic mineral biotite is the carrier of the AMS at room and at low temperature. Image analyses seem to have different solutions for every site and do not correspond directly to AMS results. The orientation of quartz c-axes is different in the five sites. These results are discussed in terms of crystal orientation, rock composition and influence of the shape and degree of anisotropy of the orientation ellipsoid.
[en] New volcanogenic layers found in the Northern Appennines of Romagna at the Tortonian/Messinian transition have been dated. The Globorotalia suterae FAD yielded a date of 7.72±0.15 Ma (K/Ar on biotites). The boundary taken as the Globorotalia conomiozea FAD is closely predated by 7.33 Ma (K/Ar on biotite and 39Ar/40Ar on plagioclase). An age of 7.26±0.10 Ma for the boundary is suggested. There are appropriate conditions for placing here the related Global Stratotype Section and Point
[en] The larger plutonic bodies of the Stara Planina calc-alkali igneous association were subjected to K/Ar dating and ages were found falling into two intervals: one between 330 and 360 million years and the other between 240 and 260 million years. The formed interval is assumed to give the time of the intrusion of these bodies into the diabase-phyllitoid complex and partially in the Ordovician rocks, while the latter interval is thought to express the partial ''rejuvenation'' due to tectonic processes in the period from the end of the Carbonic to the beginning of the Mesozoic. (A.K.)
[en] The results of K/Ar dating are presented for 17 samples, taken in various locations, of the granitoid pluton of Muntele Mic in Romania. Age values were found in the range from 207 to 440 million years. (A.K.)