Ferromanganese crusts from submarine volcanoes of backarc basins as a new genetic type of gallium deposits

Study of the material composition of Fe-Mn crusts from submarine rises in the central part of the Sea of Japan, with modern precision methods applied, has yielded a high (up to 854 g/t) concentration of gallium contained in sorbed form. The new data obtained have allowed a new genetic type of gallium deposits—hydrothermal-sedimentary—to be distinguished.     

利用大地电磁资料对玄武岩成像的可行性

The magnetotelluric （MT） method has been among the favorite supporting tools for seismic imaging of sub-salt and sub-basalt targets. In this paper we present an example from Kachchh, India （where basaltic rocks overlie Mesozoic sedimentary rocks）, and discuss the feasibility of using MT method as an exploration tool in this geological setting. Our results highlight the difference in magnetotelluric response caused by the thin intrabasalt layering. The key issue addressed in this paper is what MT can and cannot provide in such geological settings. First, we compute apparent resistivity and phase response curves using representative resistivity-depth models and borehole data from the study area. Later, we compare these results to assess the plausibility of using MT to image the sub-volcanic sediments at Kachchh. Finally, we substantiate our discussion through one-dimensional inversion of the field observed MT data from this region that exhibits poor sensitivity of MT for thin basalt layers.     

The geochemistry of steam hydrothermal occurrences in the Koshelev volcanic massif,southern Kamchatka

New data are presented on the geochemistry of thermal waters in the Koshelev volcanic massif in southern Kamchatka. We discuss the conditions for the generation of thermal waters, possible variants of thermal and deep-seated material supply for the Koshelev hydrothermal system, and propose a conceptual model for the system.     

Using UCODE_2005 and PHREEQC to determine thermodynamic constants from experimental data

This article presents a method for estimating chemical thermodynamic constants from experimental data using the two computer programs UCODE_2005 and PHREEQC. As an example, the conditional stability constant for lead (Pb) complexation by a remediation agent (carboxymethyl-beta-cyclodextrin) is estimated, but the method can be applied to estimate other thermodynamic parameters such as sorption constants and degradation rate constants. Advantages of this technique include estimation of uncertainties associated with estimated parameters, evaluation of information content of observations, statistical evaluation of the appropriateness of the conceptual model, and statistical-based comparison of different models.     

Gzhelian fusulinids first discovered in central Iran

Gzhelian deposits established in Iran for the first time are described. They rest with a considerable hiatus on the Moscovian deposits constituting, along with Asselian strata, an integral carbonate succession of the Zaladu Formation in eastern Iran. The Zaladu Formation is correlative with the Vazhnan Formation of the Abadeh region (central Iran) and the Dorud Formation of the Elburz (Alborz) Mountains. An assemblage of Gzhelian fusulinids from the studied section is well comparable with the assemblage of the Ultradaixina bosbytauensis Zone distinguished in the uppermost Gzhelian of the Darvaz, Fergana, the Southern Urals, Donetsk Basin, and Carnic Alps. Two new species of the genus Schellwienia (Sch. anarakensis and Sch. stocklini) are described. Gzhelian and Asselian fusulinids found in the section are figured in two paleontological plates.     

Identification of buried sinkholes using refraction tomography at Ft. Campbell Army Airfield,Kentucky

Karst aquifers are highly susceptible to contamination, with numerous points of entry for contaminants through recharge features such as sinkholes, swallow holes and solutionally enlarged fractures. These recharge features may be filled or obscured at the surface, requiring the use of geophysical or remote sensing techniques for their identification. This study uses seismic refraction data collected at the Ft. Campbell Army Airfield (CAAF), Kentucky, USA, to test the hypothesis that refraction tomography is a useful tool for imaging bedrock depressions beneath thick overburden (greater than 20 m of unconsolidated sediment). Southeast of the main taxiway of CAAF seismic velocity tomograms imaged a bedrock low, possibly a closed depression, at a depth of 25 m that had been earlier identified through delay-time analysis of the same refraction data. Tomography suggests the bedrock low is about 250-m wide by 10-m deep at its widest point. High rates of contaminant vapor extraction over the western extension of this feature suggest a high concentration of contaminants above, and within, this filled bedrock low, the base of which may contain solutionally enlarged fractures (i.e. karst conduits) that could funnel these contaminants to the upper or lower bedrock aquifers. This study thus demonstrates the viability of seismic refraction tomography as a tool for identification of filled sinkholes and bedrock depressions in karst areas.     

Thermobarometry of the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway

The Bleikvassli massive sulfide ore deposit is hosted by Proterozoic pelitic, quartzofeldspathic, and amphibolitic rocks of the Uppermost Allochthon of the Scandinavian Caledonides. Staurolite-garnet-biotite and kyanite-staurolite-biotite assemblages indicate that metamorphism reached the kyanite zone of the amphibolite facies. Geothermobarometry was conducted on rocks in and around the deposit using a variety of silicate and sulfide calibrations. Temperature determinations are most reliant on the garnet-biotite exchange reaction, with analyses obtained from 259 garnet rims and adjacent biotite. Results from nine calibrations of the garnet-biotite geothermometer are considered, but compositional limitations of many calibrations involving high Ca and Mn contents in garnet and Al^VI and Ti in biotite make many of the coexisting mineral pairs unsuitable. Average temperatures calculated from the two calibrations that most closely address the garnet-biotite compositions observed at Bleikvassli are 584 °C ± 49 °C and 570 °C ± 40 °C. The application of two calibrations of the garnet-staurolite geothermometer on a limited number of samples yields 581 °C ± 2 °C and 589 °C ± 12 °C, assuming a _H2O=0.84, based upon calculations of the modal proportions of gaseous species. Pressure determinations are less constrained. Phengite and plagioclase-biotite-garnet-muscovite geobarometers give average pressures of approximately 5.0 kbar and 8.5 ± 1.2 kbar, respectively. Pressures obtained from the sphalerite-hexagonal pyrrhotite-pyrite barometer average 7.7 ± 1.0 kbar. In consideration of these results, the peak metamorphic conditions at the Bleikvassli deposit are estimated to be 580 °C and 8 kbar. Received: 18 June 1997 / Accepted: 14 May 1998     

The Néel transition and magnetic properties of terrestrial,synthetic, and lunar ilmenites

The magnetic susceptibility of a terrestrial, synthetic and lunar ilmenite specimen has been measured from 4 to 300 K. All specimens had a single Néel temperature transition which ranged from 56 to 57.7 K. In one case the powdered specimen was partially aligned in the magnetic field prior to the susceptibility measurements and the Néel transition was observed to shift to 60 K indicating magnetic anisotropy. A study of several magnetic parameters calculated from the experimental data showed gross impurities in the terrestrial specimen, single-domain to multi-domain metallic iron in the synthetic specimen, and a small amount of superparamagnetic metallic iron in the lunar sample. No multidomain iron was observed in the lunar ilmenite. The results of electron spin resonance measurements were also in general agreement with these findings. Because of the absence of Fe³⁺ compared to most terrestrial samples it is suggested that the anisotropic magnetic parameters be determined on lunar ilmenite when a large enough single crystal becomes available.