THE MULTIFRACTAL CHARACTER OF LINEAMENT DENSITY ON THE KOLA PENINSULA

Analysis of data on the lineament network of the Kola Peninsula obtained through interpretation of space images at different scales provides an indication of the multifractality of lineament densities and the possibility of the geologic interpretation of the spectrum of fractal dimensions. The invariance of the distribution of densities of images of the lineament network at small and large scales reveals the scaling properties of these structural elements, and objectively reflects the heterogeneity of the geologic medium.     

Probable Endogenic Origin of Conglomerate-type Rocks on the Southeastern Coast of the White Sea

The southeastern coast of the White Sea and Kii Island incorporates outcrops of conglomerate-type rocks similar to boulder dikes filling tensile fractures in the early Precambrian basement of the platform. They are related to the southwestern flank of the Onega Graben representing the southeastern segment of the Onega–Kandalaksha paleorift. Genesis of these conglomerate-type rocks, previously considered sedimentary ones, is problematic. Special study of the cement of these rocks revealed that it has probably an endogenic nature. It is dominated by carbonate material replacing ultramafic volcanic glass. Carbonatization and analcime mineralization took place at the regressive stage of cement formation within a temperature range of 450–550°C with active release of H₂O- and CO₂-saturated fluids. Data on the isotopic composition (¹³C and ¹⁸O) for carbonate material of cement from the brecciated rocks testify that the carbonatization was related to input of deep-seated carbon dioxide under subsurface environment. The studies carried out allow us to suppose that these rocks were formed as a result of consolidation of solid–gaseous suspensions inside fractures in the crystalline basement. Penetration of fluidized material along them produced dike-shaped bodies. Such rocks are recently called fluidizates. The sources of solid–gaseous suspension fluxes were basic magmas with a high content of volatiles. Discharge of gases from the magmas was caused by their decompression due to the appearance of tensile zones in lithosphere during rifting.     

Rb-Sr study of Au-Ag Shkol'noe deposit (Kurama Mountains, north Tadjikistan): age of mineralization and time scale of hydrothermal processes

The epithermal Au-Ag Shkol'noe deposit is located in the Kandjol ore field, Kurama Mountains. This region is a part of the east-west trending Late Hercynian Bel'tau-Kurama volcanic belt, an Andean-style collisional margin. The deposit comprises a number of quartz-carbonate veins hosted by the syn-subductional Middle Carboniferous Karamazar granodiorites. The Au-Ag mineralization is considered to be the result of the earliest hydrothermal event in the region. The Rb-Sr isochron age 296.3 ± 1.3 Ma and an initial ⁸⁷Sr/⁸⁶Sr₀=0.7071 ± 2 ratio were obtained for an adularia-sericite-quartz-calcite sample from Au-Ag mineralization. The ⁸⁷Sr/⁸⁶Sr ratio range from 0.70645 ± 10 to 0.70741 ± 10 was obtained for the calcites from the earlier and later mineral assemblages. The Rb-Sr age is interpreted as a real geological age of the Au-Ag mineralization. It corresponds to the initial stage of the Late Carboniferous – Early Permian collision following the main syn-subduction stage of Bel'tau-Kurama volcanic belt evolution. The comparison of the Rb-Sr age with previously obtained ⁴⁰Ar-³⁹Ar and K-Ar data for adularia from the Au-Ag mineralization implies that gangue minerals of the Shkol'noe deposit bears the fingerprint of at least three events in its history. They are (1) Au-Ag mineralization at 296.3 ± 1.3 Ma; and (2) two subsequent thermal pulses at 277 ± 4 and 263–267 ± 8 Ma. The minimum time scale for the hydrothermal activity within the Shkol'noe deposit is thus approximately 30 million years. A general uniformity of the strontium source during the hydrothermal processes within the Au-Ag Shkol'noe deposit (⁸⁷Sr/⁸⁶Sr₀=0.70645 ± 10 to 0.70741 ± 10) is suggested as well as within the Bel'tau-Kurama belt (⁸⁷Sr/⁸⁶Sr₀=0.7051–0.707). The slight shift into a higher strontium isotope composition of the hydrothermal minerals of the Shkol'noe deposit in comparison with other deposits and rocks of the Bel'tau-Kurama belt may be ascribed to the contribution of relatively radiogenic strontium from the Karamazar-type granitoids. The mobilization of low radiogenic strontium during propylitic alteration of diabase dikes emplaced after the Au-Ag mineralization could be responsible for comparatively low ⁸⁷Sr/⁸⁶Sr ratios in some of the latest post-dike carbonates. Received: 4 August 1998 / Accepted: 25 August 1998     

Complex Isotopic and Hydrogeochemical Studies of Groundwater in the Kirov Region

Uranium-isotopic and multi-element hydrogeochemical methods are used to assess the natural pollution of fresh groundwater in horizons under development due to a modern intrusion of hypogene water with increased boron and fluorine contents in zones of old tectonic dislocations. The total index of the abovestandard (>MAC) pollution of groundwater in the region of the city of Kirov (the Kirov area) reaches 15. To reduce the effect of natural groundwater pollutants on the health of population, it is recommended that the groundwater intake should be regulated, purifiers should be used, and prospects revealed by the isotopic-and-hydrogeochemical data should be explored. The feasibility of modeling the groundwater formation and tracing the neotectonic dislocations in geological platforms is shown.