Weissbergite (TlSbS2) and Avicennite (Tl2O3), Rare Thallium Minerals: First Findings in Yakutia

Geology of Ore Deposits - Rare thallium minerals, avicennite and weissbergite, were found for the first time within the karst zones of the Khokhoy field of the Verkhnyaya Amga gold area, South...     

GEOELECTRIC MODELS IN ENGINEERING GEOPHYSICS*

Man's engineering activities are concentrated on the uppermost part of the earth's crust which is called engineering-geologic zone. This zone is characterized by a significant spatialtemporal variation of the physical properties status of rocks, and saturating waters. This variation determines the specificity of geophysical and, particularly, geoelectrical investigations. Planning of geoelectric investigations in the engineering-geologic zone and their subsequent interpretation requires a priori) geologic-geophysical information on the main peculiarities of the engineering-geologic and hydrogeologic conditions in the region under investigation. This information serves as a basis for the creation of an initial geoelectric model of the section. Following field investigations the model is used in interpretation. Formalization of this a priori) model can be achieved by the solution of direct geoelectric problems. An additional geologic-geophysical information realized in the model of the medium allows to diminish the effect of the “principle of equivalence” by introducing flexible limitations in the section's parameters. Further geophysical observations as well as the correlations between geophysical and engineering-geologic parameters of the section permit the following step in the specification of the geolectric model and its approximation to the real medium. Next correction of this model is made upon accumulation of additional information. The solution of inverse problems with the utilization of computer programs permits specification of the model in the general iterational cycle of interpretation.     

Estimating the influence of seismic and meteorological factors on the accuracy of measurements by relative gravimeters

Continuous high-precision long-term gravity measurements are carried out at the geophysical observatory located in the experimental base of Vladimir State University. The long time series of gravity acceleration and its standard deviation are obtained. The factors responsible for the increases in the studied deviations are analyzed. The recommendations for improving the accuracy of relative gravity measurements are formulated.     

Geothermal asymmetry in transform faults of the equatorial Atlantic Ocean

Doklady Earth Sciences - Statistical analysis of heat flow values measured in transform faults of the equatorial part of the Atlantic Ocean has been performed. Owing to the calculation using the...     

Sr Isotope Composition of Mud Volcanic Waters in the Kerch–Taman Province

Doklady Earth Sciences - Waters at seventeen mud volcanoes of the Kerch–Taman province in the Northwestern Cis-Caucasus region have been analyzed for Sr isotope composition. The 87Sr/86Sr...     

Integrated geophysics and soil gas profiles as a tool to characterize active faults: the Amer fault example (Pyrenees, NE Spain)

The combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions. In this study, we carried out geochemical soil gas sampling (²²²Rn, ²²⁰Rn and CO₂), electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of Amer in the Spanish Pyrenees, where the presence of recent fractures is evident in the field. Data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects. Geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that: (1) endogene gases radon (²²²Rn) and carbon dioxide (CO₂) are released from the meta-sedimentary basement rocks across the main fractured zones with higher permeability values, while lower Cenozoic detrital sedimentary formations act as an impervious boundary; (2) sites with highest radon concentrations (52?kBq?m^?3) coincide with the zones in the Amer fault showing more recent geomorphic evidence of activity, and more specifically with those areas covered by thinner surficial formations; (3) the lowest ²²²Rn values (0.2?C0.4?kBq?m^?3) were recorded just on the master active fault plane. This pattern could be explained by a dilution effect resulting from high rates of soil CO₂ efflux (267?g?m^?2?day^?1); (4) soil thoron (²²⁰Rn) activity is maximum (143?kBq?m^?3) in areas with high surficial fracturing; (5) groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases. The agreement between the different data (geochemical, geophysical, and hydrogeological) and field observations (geology and geomorphology) leads us to propose a preliminary tectonic-gravitational model for the study area.     

Enthalpies in (Na,Ca)- and (K,Ca)-feldspar binaries: a high-temperature solution calorimetric study

A series of high structural state plagioclases (Ab-An) was crystallized from glasses. By exchanging Na for K in KCl melts, metastable K-plagioclases (Or-An) were prepared which possess the same structural state as the starting plagioclases. Both series were investigated at 980 K by lead borate solution calorimetry. Continuing the ideas of Carpenter and McConnell (1984) and Carpenter (1992a), the results can be interpreted as follows. In the high plagioclase series, the enthalpies of solution, jH_sol, reflect the schemes of Al,Si ordering: (1) analbite-like (C2/m) ordering in the An-poor region 0hX_AnА.2, (2) high albite-like (C1¥) ordering in intermediate plagioclases, and (3) anorthite-like (I1¥) ordering in the An-rich region 0.7AnБ. In regions 1 and 2, jH_sol decreases as a function of X_An, but increases in region 3 as a consequence of the C1¥MI1¥ ordering reaction. Therefore, it is not a mixing effect but a compositionally restricted ordering effect which causes the excess enthalpies, jH^ex, to be positive in the plagioclase binary as a whole. Neglecting the existence of phase transitions at X_An=0.2 and X_An=0.7, jH^ex can be approximated by a two-parameter Margules model yielding W^H_AnAb=14Dž kJ/mol and W^H_AbAn=40Dž kJ/mol. jH_sol values of I1¥ plagioclases (X_An>0.7) can be "corrected" for the C1¥MI1¥ ordering effect (Carpenter 1992a). When combining the corrected values with the jH_sol data which were actually measured on the C1¥ plagioclases (X_An<0.7), negative excess enthalpies are generated in the plagioclase binary. This may be expected when C1¥ ordering occurs relative to topochemically monoclinic reference states of analbite and hypothetical anorthite devoid of I1¥ order. The solution experiments on the K-plagioclases resulted in similar characteristics as those found for the plagioclases. However, in addition to the ordering effects observed in the plagioclase binary, volume mismatch effects contribute to jH^ex in the K-plagioclase series. jH^ex can be represented by a Margules model with W^H_AnOr=60ᆞ kJ/mol and W^H_OrAn=91ᆢ kJ/mol when the phase transitions at X_An=0.2 and X_An=0.7 are again neglected. The contribution of the volume mismatch effect to jH^ex is considerable, as appears from the large difference between the K-plagioclase and the plagioclase Margules parameters. Their difference corresponds to a practically symmetrical dependence of jH^ex_volmism on composition, with W^H_volmism=48ᆡ kJ/mol.