Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts

A series of high temperature experiments was undertaken to study partitioning of several highly siderophile elements (HSE; Ru, Rh, Pd, Re, Os, Ir, Pt and Au) between Cr-rich spinel, olivine, pyroxene and silicate melt. Runs were carried out on a Hawaiian ankaramite, a synthetic eucrite basalt, and a DiAn eutectic melt, at one bar, 19 kbar, and 20 kbar, respectively, in the temperature range of 1200 to 1300°C, at oxygen fugacities between the nickel-nickel oxide (NNO) and hematite-magnetite (HM) oxygen buffers. High oxygen fugacities were used to suppress the formation of HSE-rich “nuggets” in the silicate melts. The resulting oxide and silicate crystals (<100 μm) were analyzed using both SIMS and LA-ICP-MS, with a spatial resolution of 15 to 50 μm. Rhenium, Au and Pd were all found to be incompatible in Cr-rich spinel (D_Re^sp/melt = 0.0012-0.21, D_Au^sp/melt = 0.076, D_Pd^sp/melt = 0.14), whereas Rh, Ru and Ir were all found to be highly compatible (D_Rh^sp/melt = 41-530, D_Ru^sp/melt = 76-1143, D_Ir^sp/melt = 5-22000). Rhenium, Pd, Au and Ru were all found to be incompatible in olivine (D_Re^oliv/melt = 0.017-0.073, D_Pd^oliv/melt = 0.12, D_Au^oliv/melt = 0.12, D_Ru^oliv/melt = 0.23), Re is incompatible in orthopyroxene and clinopyroxene (D_Re^opx/melt = 0.013, D_Re^cpx/melt = 0.18-0.21), and Pt is compatible in clinopyroxene (D_Pt^cpx/melt = 1.5). The results are compared to and combined with previous work on HSE partitioning among spinel-structured oxides, and applied to some natural magmatic suites to demonstrate consistency.     

Anthropogenic transformations of the Arctic ecosystem of Lake Imandra: Tendencies for recovery after long period of pollution

Transformation of an Arctic aquatic ecosystem (a case study of Lake Imandra) under the impact of a mining industrial complex is considered. Water chemical composition and the ecosystem’s structural components (phyto- and zooplankton, zoobenthos, and ichthiofauna) are analyzed for the following periods: the preindustrial background (reference) conditions, industrial development of mineral resources and strong anthropogenic impact, industrial recession and decreased anthropogenic impact, and stabilization. The main regularities of the aquatic ecosystem successions under the conditions of anthropogenic loads and their decrease are established.     

Global features of sea-level pressure distribution in April and July associated with contrasting situations of Indian summer monsoon

Global sea-level pressure distribution has been analysed for the months of April and July for 5 years of contrasting situations of Indian summer monsoon, comprising of two drought years (1972 and 1974), a flood year (1975) and two normal monsoon years (1970 and 1973). Mean monthly sea-level pressure data at about 400 stations have been used in the study. Prominent features of pressure departures from long-term normals have also been noted. It is observed that the month of April shows more prominent contrasting features than July. In April, the high pressure centres over USSR and the North Pacific move considerably eastward during poor monsoon years, while a breakaway cell of Icelandic Low goes deep south. Both the high pressure areas over south Indian Ocean and Australia are stronger in good monsoon years. In July, the subtropical high pressure zone over the southern Indian Ocean is stronger and the Australian high is more eastward, in good monsoon years.     

Ge-bearing coals of the Luzanovka Graben, Pavlovka brown coal deposit, southern Primorye

Results of the study of a new Ge-bearing area of the Pavlovka brown coal deposit are presented. Ge is accumulated in bed III₂ lying at the bottom of the Late Paleogene-Early Neogene coal-bearing sequence adjacent to the Middle Paleozoic granite basement. The Ge content in coals and coal-bearing rocks varies in different sections from 10 to 200–250 ppm, reaching up to 500–600 ppm in the highest-grade lower part of the bed. The metalliferous area reveals a geochemical zoning: complex Ge-Mo-W anomalies subsequently grades along the depth and strike into Mo-W and W anomalies. Orebodies, like those at many Ge-bearing coal deposits, are concentric in plan and dome-shaped in cross-section. Coals in their central parts, in addition to Ge, W, and Mo, are enriched in U, As, Be, Ag, and Au. Distribution of Ge and other trace elements in the metalliferous sequence and products of gravity separation of Ge-bearing coals is studied. These data indicate that most elements (W, Mo, U, As, Be) concentrated like Ge in the Ge-bearing bed relative to background values are restricted to the organic matter of coals. The electron microscopic study shows that Ge-bearing coals contain native metals and intermetallic compounds in association with carbonates, sulfides, and halogenides. Coal inclusions in the metalliferous and barren areas of the molasse section strongly differ in contents of Ge and associated trace elements. Ge was accumulated in the coals in the course of the interaction of ascending metalliferous solutions with organic matter of the buried peat bogs in Late Miocene. The solutions were presumably represented by N₂-bearing thermal waters (contaminated by volcanogenic CO₂) that are typical of granite terranes.     

The mechanisms of reduction of hexavalent chromium by green rust sodium sulphate: Formation of Cr-goethite

The molecular-level processes that control green rust sodium sulphate (GR_Na,SO4) reaction with chromate were studied using high-resolution techniques. Changes in solid morphology, structure and composition were observed with atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results suggest the following mechanisms: Chromate replaces sulphate in the GR interlayer and is reduced by Fe(II). Formation of sparingly soluble Cr(III)-solid blocks further chromate entry, but Cr(VI) reduction continues at the GR solid/solution interface. Electron transfer from the centre of the GR crystals to the surface facilitates rapid reaction. Less stable zones of the reacted GR_Na,SO4 dissolve and amorphous Cr(III),Fe(III)-solid forms. During equilibration, Cr-substituted goethite evolves in association with remaining GR_Na,SO4, fed by material from the amorphous phase and dissolving oxidised GR. In contrast, previous Cr(VI) experiments with the carbonate form of GR, GR_CO3, have suggested only reaction and deposition at the surface. From the perspective of environmental protection, these results have important implications. Goethite is sparingly soluble and the inclusion of Cr(III) as a solid-solution makes it even less soluble. Compared to Cr adsorbed at the surface of an Fe(III)-phase, Cr(III) incorporated in goethite is much less likely to be released back to groundwater.     

An integrated approach to investigate saline water intrusion and to identify the salinity sources in the Central Godavari delta, Andhra Pradesh, India

The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO ₄ ^?2 /Cl^?and Na⁺²/Cl^?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites.     

Some modifications of Stokes' formula that account for truncation and potential coefficient errors

 Stokes' formula from 1849 is still the basis for the gravimetric determination of the geoid. The modification of the formula, originating with Molodensky, aims at reducing the truncation error outside a spherical cap of integration. This goal is still prevalent among various modifications. In contrast to these approaches, some least-squares types of modification that aim at reducing the truncation error, as well as the error stemming from the potential coefficients, are demonstrated. The least-squares estimators are provided in the two cases that (1) Stokes' kernel is a priori modified (e.g. according to Molodensky's approach) and (2) Stokes' kernel is optimally modified to minimize the global mean square error. Meissl-type modifications are also studied. In addition, the use of a higher than second-degree reference field versus the original (Pizzetti-type) reference field is discussed, and it is concluded that the former choice of reference field implies increased computer labour to achieve the same result as with the original reference field. Received: 14 December 1998 / Accepted: 4 October 1999     

Geochronological constraints on the emplacement history of an anorthosite — rapakivi granite suite: U−Pb zircon and baddeleyite study of the Korosten complex,Ukraine

U–Pb zircon/baddeleyite ages obtained for the Korosten anorthosite-rapakivi granite complex, Ukrainian shield, suggest that different magmatic phases were emplaced during a period of ca. 30 million years as a series of distinct igneous episodes. The earliest 1789.1±2.0 Ma anorthosites were followed by 1781.3±3.2 Ma dykes of plagiogranite porphyries. The emplacement of a major rapakivi granite phase took place at 1767.4±2.2 Ma, and was followed by emplacement of layered intrusions of anorthosites, gabbronorites, diabases and ultrabasic rocks between 1761 and 1758 Ma. The minimum duration of magmatism of about 30 million years, the 6–15 million years interval between igneous pulses, and alternation of discrete episodes of basic and felsie magmatism are common features of major anorthositemangerite-charnockite-rapakivi granite complexes. Temporal distribution of igneous activity in the Korosten complex shows that the gabbro-anorthosites and the granites are not comagmatic, although they are possibly cogenetic, and that at least four portions of granitic and basic magmas were generated during a relatively long period of at least 30 million years. The time gap of about 20–25 million years between early basic and later and more voluminous granitic magmatism, characteristic of the Korosten pluton, Wiborg and Salmi batholiths, probably reflects the duration of extensional processes before the generation of large volumes of magma in the lower crust.