Saturation of groundwaters with respect to minerals of the host rocks

Calculations of the saturation of groundwaters with respect to minerals of the rocks hosting these waters indicate that most of the analyzed groundwaters were saturates with respect to calcite, dolomite, and quartz. Brines of chloride-calcic composition were determined to be saturated with respect to calcite, whereas brines of chloride-sodic composition are saturated with respect to dolomite and quartz. The solution was simultaneously saturated with respect to six minerals for the association ankerite-calcite-dolomite-pyrite-quartz-strontianite. An increase in the number of minerals with respect to which solution is saturated is correlated with an increase in the diversity of types of groundwaters and an increase in the runoff rate. The paper proposes possible avenues for searches for relations between hydrogeological and geochemical parameters that make it possible to adapt the thermodynamic models to real geological-hydrogeological conditions. The research was centered on the testing of groundwaters for their saturation with respect to minerals of the rocks hosting these waters. This parameter plays a significant part in forming the geochemical type of natural waters because it reflects the crystallization of a mineral from a solution and, consequently, the removal of an element from the aqueous solution.     

Evidence for short term changes in the intensity and spectrum of hard X-rays from Cyg X-1

The paper presents experimental evidence for the existence of fast intensity fluctuations with time scales of the order of a minute in the X-ray emission from Cyg X-1 at energies greater than 29 keV. Spectral variations over time intervals of 20–25 min are also observed in the same energy range. Whereas, similar intensity and spectral fluctuations have been reported earlier at lower energies the observations presented here is the first evidence for the existence of similar fluctuations at high energies.     

A New Protocol for the Astrometric Follow-up of Near Earth Asteroids

A new protocol was devised to improve the efficiency of astrometric follow-up observations of Near Earth Asteroids for the accurate determination of their orbits. It was implemented in the activities of the Spaceguard Central Node (SCN, a facility of the Spaceguard Foundation, established with the support of the European Space Agency) in the form of a Priority List. Here we describe this protocol and results obtained during five years of activity (2000–2004).     

Stellar α Elements Abundance Gradient in M33

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the present study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. The determination of atmospheric parameters is based on analyses of silicon ionisation balance. Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy. We compare our results with the abundances expected from studies of HII regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nature and significance of the Neoproterozoic Sturtian–Marinoan Boundary,Northern Adelaide Geosyncline,South Australia

The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.     

Gold–quartz deposits of the Zhdaninsky ore–placer cluster,eastern Yakutia: Structural control and formation conditions

Gold deposits and occurrences small in reserves and high in Au grade conventionally determine the line of prospecting in terrigenous sequences of the Verkhoyansk–Kolyma region. In this paper, the geological structure of such gold objects is considered with the example of the deposits and prospects making up the Zhdaninsky ore–placer cluster in the Republic of Sakha (Yakuia). From lithological, structural, and mineralogical–geochemical data, the formation conditions of ore-bearing complexes are specified, the geological evolution history of the northern Ol’chan Zone of the Kular–Nera Belt is reconstructed, and the zonal distribution of mineralization within the ore–placer cluster is revealed. The structural–compositional complexes were formed in the following succession: (1) sedimentation at the shelf of the passive margin accompanied by synsedimentation deformations; (2) metagenesis of sediments and the development of bedding-plane intraformational detachments of collision stage D₁ under conditions of tangential compression and accompanied by the formation of carbon dioxide–aqueous metamorphic fluid at a temperature of 300°C and under a pressure of 1.4 kbar; (3) folding and faulting of orogenic stage D₂ with the formation of synkinematic magmatic bodies, metasomatic alteration, and Au-bearig mineral assemblages. Small Au-bearing objects with veined mineralization and high Au grade are localized in structures of stage D₂ transverse to bedding-plane schistosity S₁. They form at the collision stage above intraformational detachment surfaces and are controlled by shear structures of the orogenic stage with misalignment of these deformations. The ore zoning is determined by the distribution of Co and Ni minerals and by variations in the anionic composition of ore (S, As, Sb).     

Power spectrum of geomagneticK p-index detected at Misallat magnetic station

TheK _p-indices measured at Misallat station [ø = 29°45 N; = 30°54 E] during the period 1958–1989, have been compared with the data of two geomagnetic stations; one of them has similar longitude as Misallat and the second has almost similar latitude. The spectra of daily and hourly data of the three stations are compared together to define the latitude and longitude-effects on the detected periodicities. Daily periodicities ofK _p-index activities at the values 32.7, 21.2, 12.9, 11.6 and 9.2 days have been obtained to be common in the spectra of the three stations. The existence of 5-days periodicity in these stations has also been detected.