Home – Home – Jornals – Russian Geology and Geophysics 2016 number 4

Based on results of study of fluid inclusions, we have established the specific fluid regime of formation of the Kalguty Mo-W(Be) deposit (Gorny Altai). Using classical thermobarogeochemistry (cryo- and thermometry) and modern microprobing methods (Raman spectroscopy and LA-ICP-MS), we studied fluid inclusions in samples of quartz of quartz-wolframite veins (ore formation stage I), specific “quartz core” (quartz lens), and pyrite-chalcopyrite-molybdenite paragenesis (ore formation stage II). The results of study show that the quartz-wolframite veins of the Kalguty deposit formed with the participation of reduced W-Sb-bearing fluids with a salt content of up to 5.9 wt.%. Their gas phase consisted of CO2, N2, and CH4. Formation of pyrite-chalcopyrite-molybdenite mineralization involved oxidized hot (530-420 ºC) fluids with the average salt content of 9.3 wt.%. Their gas phase was of high density (up to 0.55) and consisted of CO2, N2, and H2S. The pressure of the mineral-forming environment varied from 50 to 25 MPa. The fluids contained Cu, Mo, Bi, and S. The productive greisen-vein Mo-W(Be) mineralization of the Kalguty deposit resulted from the superposition of greisen molybdenite-chalcopyrite mineralization on parageneses of earlier formed quartz-wolframite veins. Oxidized metal-bearing fluids that formed the Mo mineralization of the Kalguty deposit have high contents of S and are geochemical analogs of magmatic metal-bearing ore-forming fluids of the Central Aldan porphyry Cu-Au-Mo deposits, which are genetically related to alkaline massifs. This suggests the significant influence of the mantle source on the formation of the Kalguty rare-metal ore-magmatic system. The same is evidenced from the sulfur isotope composition of chalcopyrite, molybdenite, and pyrite from ore parageneses, falling in the narrow range of δ34S‰ from -1.2 to +2.9 corresponding to the isotope composition of mantle sulfur.

Having applied methods of comprehensive melt inclusion studies, we have elucidated the formation conditions for one of the largest apatite deposits in the Maimecha-Kotui province, located in the exocontact zone of the Magan alkaline ultramafic carbonatite massif, in apoquartzite fenite-aegirinites. We examined the most P-enriched exocontact nepheline-containing aegirinites and ijolite veins in them. In veined ijiolite, primary silicate-salt melt inclusions in nepheline and syngenetic primary silicate, alkali sulfate-carbonate, and carbonate melt inclusions in apatite were found. Primary alkali sulfate-carbonate melt inclusions were also identified in apatite from exocontact nepheline-containing aegirinites. Detailed analysis of the inclusions has shown that nepheline of the apatite-containing ijolite veins crystallized at 1100-1120 ºC from homogeneous nephelinite melt, which was enriched in SO3, Cl, CO2, and H2O and locally contaminated with quartz sandstones and quartzites. At lower temperatures (either at the final stages of nepheline crystallization or at the early stages of apatite formation), the melt was already heterogeneous (probably, because of immiscibility) and consisted of more Si-saturated, alkali sulfate-carbonate, and carbonate fractions. Apatite crystallized mainly from separated alkali sulfate-carbonate melts: at 1080-980 ºC in veined ijolites and at 940-760 ºC in aegirinites. Alkali sulfate-carbonate melts in veined ijolites were enriched in SO3 but depleted in P as compared with those in aegirinites. At the final stage, apatite crystallized from P-poor carbonate melts.

We studied the distribution and modes of occurrence of the main (Au and Ag) and major associated elements indicating mineralization (Hg, Sb, As, Pb, Zn, and Cu) in samples of loose sediments fr om lithochemical sediment streams of Au-Ag zones at the Dukat deposit. The major mineral and nonmineral modes of occurrence of elements indicating Au-Ag mineralization have been detected with POLAM-312 and POLAR-3 ore microscopes and by X-ray electron probe microanalysis with Superprobe 733 and JXA 8200 (JEOL, Tokyo, Japan) microprobes. The distribution and modes of occurrence of ore elements in the loose (alluvial) sediments of streams draining the Au-Ag zones are closely related to the ore composition. As in the ores, the main elements indicating mineralization are Au and Ag, while the major associated elements are Hg, Sb, As, Cu, Pb, and Zn. Gold in alluvial sediments occurs as electrum, fine (dispersed, ultradispersed, and colloid-dispersed) particles, and the so-called “bound” (predominantly with sulfides) invisible Au (sorption component and its derivates). Silver occurs not only as hypergene forms, microinclusions, and ultrasized particles but also in native form and as partly preserved sulfides and sulfosalts. The other elements (Hg, Sb, As, Pb, Zn, and Cu) are observed as secondary minerals of complex composition and differently preserved corroded fragments of pyrite, chalcopyrite, galena, and sphalerite grains, dominated by oxides and hydroxides (mainly those of iron). Salts and water-soluble sulfates of Fe, Cu, Pb, and Zn are less widespread. In study of the conditions of sediment stream formation in cryolithogenesis zones, wh ere physical weathering is regarded as the major process, chemical factors (first of all, chemisorption) should also be taken into account. This is proven by the enrichment of “fine” loose material in Au, Ag, and ore elements in general. The high percentage of mobile forms of elements, which are easily leached out by ordinary acids, in ores and aureoles, together with the widespread occurrence of clay minerals and hydroxides, has a significant influence on chemisorption. For example, the portion of fine and “bound” Au, the element considered to be the least prone to chemical weathering, reaches 50-60% in the riverbed sediments of the stream head. Native Au (electrum) makes up 40-50%. The material is diluted during its transport. As Au content decreases, the portion of fine and “bound” Au in the sediment stream increases to 95%. Evidently, these two Au forms are predominant in streams as compared with ores. The modes of occurrence of elements indicating Au-Ag mineralization in secondary environments, as in primary ones, serve as an effective criterion for assessment of the potential of geochemical anomalies detected in sediment streams. They are a reliable indicator of ore associations, which is of practical significance. We think that modes of occurrence can sometimes be used to estimate the erosion level of drained zones and sites (i.e., to predict mineralization to depth). This criterion can be successfully applied at all stages of geochemical study of ore-bearing areas, from the prediction of the potential of anomalies detected in sediment streams in poorly studied areas to the detailed exploration of known ore objects.

Clinopyroxene binary solid solutions in the systems diopside-hedenbergite, diopside-aegirine, and hedenbergite-aegirine have been synthesized. Based on data from X-ray diffraction studies, the unit-cell parameters of these solid solutions have been refined, and their concentration dependences have been established. These clinopyroxene series are near-ideal continuous solid solutions. The partition of Mg and Fe between the diopside-hedenbergite binary solid solutions and biotite of the phlogopite-annite series was studied by the method of cation exchange equilibria at 650 and 750 ºC and 2 kbar. The application of KF solution as a reaction medium permitted achieving equilibrium in a considerably shorter time and from its both sides. The partition of Mg and Fe is near-ideal within the experimental error. The experimental results were compared with results of calculations based on literature data on the thermodynamic properties of pure end-members.

A study of triobite distribution allowed a biostratigraphic subdivision of the Kuonamka Formation section exposed in the middle reaches of the Olenek River (18 km downstream of the village of Olenek). Through detailed description of the section, a biostratigraphic subdivision down to the level of biozones and faunal beds was performed. These are beds with Calodiscus-Triangulaspis annio , Delgadella ultima-Bergeroniellus expansus Zone, Lermontovia dzevanovskii-Neopagetina orbiculata Zone, Anabaraspis Zone, Cheiruroides arcticus-Pagetia horrida Zone, Kounamkites Zone, Triplagnostus gibbus Zone, and beds with Tomagnostus fissus-Paradoxides sacheri . These biostratigraphic subdivisions were correlated with regional zones of the Siberian Platform. The study also provides analysis of trilobite assemblages from the Lower/Middle Cambrian boundary interval, which was identified in the studied section and other previously described sections (Nekekit, Molodo, Boroulakh Rivers). In the studied section, the base of the Middle Cambrian is defined by the FAD of Cheiruroides arcticus , i.e., at the base of the Cheiruroides arcticus-Pagetia horrida Zone. This level correlates with a presumed lower boundary of Stage 5 of a new International Stratigraphic Chart for the Cambrian System.

The study presents a summary of the latest data on ostracod microfaunas from Middle-Upper Holocene lacustrine deposits of southern West Siberia collected from lakes Malye Chany, Bol’shaya Lozhka, Beloe, and paleolake Chicha. A total of 28 ostracod species were identified. The identified ostracod assemblages reveal local variations in the lake ecosystems as well as general trends, which can be correlated with both regional and global climate changes. A cooling episode during the second half of the Subboreal is marked by the transition from a warm-water mesohaline assemblage to cold-water candonid ostracods at ca. 3.4 cal ka BP. The widespread occurrence of mesopolythermophilic ostracod species at 1.9-0.6 cal ka BP indicates the end of cooling and lowering of lake-water level. From 0.6 cal ka BP to present, the ostracod assemblages area characterized by the high specific diversity, which is probably an indication of the increased variability of aquatic ecosystems due to fluctuations in salinity and water levels of the lakes. Climate changes identified by ostracod assemblages are consistent with the climatic trend constrained by early palynological studies.

Dating of marine sediments and faunal remains they contain in stratotype and reference sections by the methods of infrared optically stimulated luminescence (IR-OSL) of K-feldspar, optically stimulated afterglow (OSA) of quartz, electron spin resonance (ESR), and ²³⁰Th/U provides new constraints on deposition in the Yenisei mouth during the Kazantsevo interglacial. The luminescence and U-Th ages in the 120-68 ka range and 93-70 ka ESR ages show that the deposition spanned the whole marine isotope stage (MIS) 5. The sediment structures and textures, grain sizes and mineralogy, and faunal records indicate tidal and shelf deposition environments. The sampled assemblages of marine mollusks comprise taxa that typically live in relatively shallow and warm water, as well as abundant subarctic and boreal species, including the Arctica islandica index species. The variations of faunal patterns, more likely, had facies rather than climatic controls, while the sediments were deposited during transgression, in a warm climate, when the area was ice-free.

We performed a chromato-mass-spectrometric study of the distribution of hopane hydrocarbons in the organic matter of Jurassic-Lower Cretaceous mudstones from wells drilled in the western Yenisei-Khatanga regional trough. A series of 25-norhopanes has been first identified; these hydrocarbons, often found in naphthides, are commonly related to biodegradation processes. We consider other hypotheses of formation of 25-norhopanes. Based on the examined distribution of rare rearranged hopanes, new biomarker parameters have been introduced, which ensure a more reliable estimation of the conditions of accumulation of organic matter in rocks and of its thermal maturity.

The contents and distribution of chalcophile elements in the Upper Jurassic-lower Lower Cretaceous Bazhenov Formation (black shales), West Siberian sea basin, are related to the composition of rocks, sedimentation rate, and redox conditions of sedimentation. The total content of chalcophile elements in the argillaceous-siliceous and argillaceous mudstones of normal sections (1360.7 and 498.4 ppm, respectively) is higher than the clarkes for black shales of this type, while that in the silty argillaceous mudstones of anomalous sections (186.7 ppm) corresponds to average contents for clays. On the other hand, the contents of Zn, Cu, As, Se, Cd, and In in the argillaceous-siliceous mudstones are above the clarkes, those of Pb, Ga, Ag, Hg, and Te are close to the clarkes, and the contents of Tl, Ge, Bi, and Sn are below the clarkes. In the argillaceous mudstones of normal sections, the first group of elements includes Zn, As, and Ga; the second, Cu, Pb, Sb, Tl, Ge, and Bi; and the third, Se, Ag, In, Sn, Hg, and Te. In the silty argillaceous mudstones of anomalous sections, the first group includes Ga, Ag, Ge, Bi, and Te(?); the second, Cu, As, Cd, Pb, and In; and the third, Zn, Se, Sb, and Hg. We have found that S, Cu, Zn, As, Ge, Se, Ag, Cd, In, Sb, and Hg are associated with pyrite and organic matter in the formation, whereas Ga, Sn, Pb, Bi, and Tl are mainly of terrigenous origin (which was earlier substantiated by Ya.E. Yudovich and M.P. Ketris for the first four elements) and are associated with clay material.

Combined geophysical and geochemical investigations of drainage streams from sulfide-containing waste dumps of the Novo-Urskoe deposit allow determining two directions of highly mineralized toxic solutions. Surface drainage stream flows over the natural slope of the valley. In addition, along the natural fault, vertical penetration of drainage solutions into groundwater occurs to a depth of 20 m. Based on geophysical-data interpretation, we assume that penetration of solutions into geologic environment leads to their dilution by groundwater, followed by a six-fold decrease in total mineralization.

The study updates the theory of tides by specifying latitude dependence of the gravimetric factor (amplitude factor δ) for diurnal and semidiurnal tidal waves in the oceanless elastic Earth. The strain of an elastic flattened gravitating sphere with latitude-dependent geopotential, density, and Lamй constants is described by a system of sixth-order ordinary differential equations. The elliptical sphere is presented as consisting of layers, with density and elasticity varying as a function of latitude along the sphere surface as mean radiuses of equidensity and equielasticity ellipsoids that cross this surface. Dissipation is taken into account as a logarithmic creep function. Integration of the derived equations allows avoiding the use of approximate methods. The predicted factors for degree 2 tides depend on latitude and increase from the equator to the pole by 0.12 to 0.18% for different reference Earth models. The obtained latitude dependences are compared with superconducting gravimeter (SG) data after including effects associated with the inertial and Coriolis forces, as well as dynamic resonance. The theoretical predictions and the observations show good fit, to hundredths of percent. The average δ factors predicted in this study for the PREM model are intermediate between those computed with the hydrostatic and nonhydrostatic tidal gravity models of Dehant, Defraigne, and Wahr (DDW/H and DDW/NH), while the estimates obtained with reference to the IASP91 model coincide with the DDW/NH results to the fifth decimal digit.