ANALYSIS OF STRUCTURAL TRANSFORMATIONS IN NATURAL QUARTZITES UNDER THE INFLUENCE OF GAMMA IRRADIATION

Using the methods of IR spectroscopy, crystal-optical and XRD analysis the evolution of the structure of Ovruch deposit natural quartzites under the influence of γ-irradiation in the range of absorbed doses (Dabs =106…3.5107 Gy) has been researched. The elemental composition of natural quartzites was determined by the gamma activation method on a linear electron accelerator. It was found that as a result of irradiation the crystal structure of quartz, which forms the basis of quartzite, is improved due to radiation annealing of the defects in the initial structure. At the same time crystallization of amorphous silica, which fringes large grains of quartz, occurs with its transformation into fine-crystalline quartz. These processes do not lead to cracking in the quartzite rock. Obtained data indicates a high radiation resistance of the Ovruch deposit quartzites and confirms the prospects of using this geological formation as a natural barrier for the construction of radioactive waste long-term storage.

Black Agates from Paleoproterozoic Pillow Lavas (Onega Basin, Karelian Craton, NE Russia): Mineralogy and Proposed Origin

The present study provides the first detailed investigation of black agates occurring in volcanic rocks of the Zaonega Formation within the Onega Basin (Karelian Craton, Fennoscandian Shield). Three characteristic texture types of black agates were identified: monocentric concentrically zoning agates, polycentric spherulitic agates, and moss agates. The silica matrix of black agates is only composed of length-fast and zebraic chalcedony, micro- and macro-crystalline quartz, and quartzine. In addition to silica minerals, calcite, chlorite, feldspar, sulphides, and carbonaceous matter were also recognised. The black colour of agates is related to the presence of disseminated carbonaceous matter (CM) with a bulk content of less than 1 wt.%. Raman spectroscopy revealed that CM from black agates might be attributed to poorly ordered CM. The metamorphic temperature for CM from moss and spherulitic agates was determined to be close to 330 °C, whereas CM from concentrically zoning agates is characterised by a lower temperature, 264 °C. The potential source of CM in moss and spherulitic agates is associated with the hydrothermal fluids enriched in CM incorporated from underlaying carbon-bearing shungite rocks. The concentrically zoning agates contained heterogeneous CM originated both from the inter-pillow matrix and/or hydrothermal fluids.

Structural Changes in Silica Glass under the Action of Electron Beam Irradiation: The Effect of Irradiation Dose

Structural changes in silica glass, produced by electron irradiation, with electrons energies of 50 keV and doses of 5–80 mC/cm2 were studied by Raman spectroscopy in frequency ranges of 300–550 and of 700–1500 cm–1. It is shown that for irradiation doses less than 5 mC/cm2 the decrease of siloxane rings concentration in glass takes place. The further increase of dose results in the increase of siloxane rings concentration in glass network after irrsdiation. And for doses of more than 40 mC/cm2 the whole destruction of glass structure and its structural units takes place. The obtained results for silica glass were compared with similar results for crystalline quartz.

Výrazně zonální tetraedrit-tennantit z Kramolína, rudní revír Michalovy Hory (Česká republika)

The crystals of significantly zonal tetrahedrite-tennantite were found in the mine dump material of the Grubenwall 42 mine, Kramolín, the Michalovy Hory ore district, western Bohemia (Czech Republic). Tetrahedrite-tennantite forms layer of tetrahedral, partly corroded crystals up to 1 mm in size on a crust of crystalline quartz in association with chalcopyrite and cerussite. Individual zones in oscillatory zoned crystals are represented by three members of tetrahedrite group minerals - tetrahedrite-(Zn), tennantite-(Zn) and rare tennantite-(Fe). The observed range of AsSb-1 substitution is unusual within a single crystal and indicates high variability of the As/Sb ratio in the hydrothermal fluids.

Diatomaceous Earth: Characterization, thermal modification, and application

The diatomaceous earth (DE), collected from the Mariovo region in North Macedonia, was characterized and thermally modified. The material represents a sedimentary rock of biogenic origin, soft solid that can be easily disintegrated, with white to grayish color, with bulk density of 0.51–0.55 g/cm3, total porosity of 61–63%, and specific gravity of 2.25 g/cm3. The chemical composition is as follows: SiO2, 86.03; Al2O3, 3.01; Fe2O3, 2.89; MnO, 0.06; TiO2, 0.20; CaO, 0.76; MgO, 0.28; K2O, 0.69; Na2O, 0.19; P2O5, 0.15; and loss of ignition, 5.66 (wt%). The mineralogy of the raw DE is characterized by the predominant presence of amorphous phase, followed by crystalline quartz, muscovite, kaolinite, and feldspar. Significant changes in the opal phase are observed in the 1,000–1,200°C temperature region. At 1,100°C, the entire opal underwent solid–solid transition to cristobalite. Further ramp of the temperature (1,100–1,200°C) induced formation of mullite. Scanning electron microscopy (SEM) and transmission electron microscopy depict the presence of micro- and nanostructures with pores varying from 260 to 650 nm. SEM analysis further determined morphological changes in terms of the pore diameters shrinkage to 120–250 nm in comparison to the larger pores found in the initial material. The results from this investigation improve the understanding of mechanism of silica phase transition and the relevant phase alterations that took place in DE upon calcination temperatures from 500 to 1,200°C.

Diagenesis of Xing’anling Oil Reservoir in Sudeerte Area

In order to explore the types of diagenesis in Sudeerte area, through core and thin slice identification, it is clear that the Xing’anling oil layer is mainly affected by compaction, cementation, andrecrystallization. The compaction is mainly early compaction, late pressure dissolution is not obvious; cementation presents two forms of crystalline quartz and amorphous opal; recrystallization is manifested as the conversion process of opal t-ochalcedony quartz.