Generation of unsaturated and aromatic hydrocarbons by thermal alteration of young kerogen

Monounsaturated, monoaromatic and polyaromatic hydrocarbons generated by artificial thermal alteration of young marine (Tanner basin, offshore California) kerogen were studied by computerized GC-MS. Their relative amounts changed with temperature (150–410°C) and time (5–120 hr) of heating as follows: Monounsaturates → Monoaromatics → Polyaromatics. Distribution of alkyl homologs of phenanthrene also changed with increasing degree of thermal alteration. These results are in agreement with those observed for crude oils and shales.     

Surface alteration of arsenopyrite (FeAsS) by Thiobacillus ferrooxidans

The surface of arsenopyrite was characterized after acidic, oxidative leaching in the presence of the bacterial species Thiobacillus ferrooxidans. Polished single-crystal grains of arsenopyrite were reacted for 1, 2, and 3 weeks with T. ferrooxidans suspended in a solution (pH 2.3) of essential salts (MgSO₄·7H₂O, [NH₄]₂SO₄, KH₂PO₄, and KCl). Abiotic control experiments were conducted in identical solutions. Reaction between arsenopyrite and T. ferrooxidans in the essential salts solution produced a uniform solid FePO₄ overlayer (∼0.2 μm thick) on the arsenopyrite surface within 1 week. The overlayer was detected visually by scanning electron microscopy (SEM) and chemically by X-ray photoelectron spectroscopy (XPS). It could not be distinguished by energy-dispersive X-ray analyses. No overlayer formed in the abiotic control. The uniform thickness and lateral continuity of the overlayer suggest an inorganic origin promoted by bacterial production of Fe³⁺. Iron released from arsenopyrite was oxidized by bacteria and subsequently precipitated with PO₄³⁻ (from the essential salts), forming ferric phosphate. After 2 and 3 weeks, SEM images revealed a roughened arsenopyrite surface, and XPS depth profiles indicated a progressively thicker phosphate overlayer and continued oxidation, diffusion, and dissolution of arsenopyrite beneath the overlayer. After only 1 week, the cells were isolated from the arsenopyrite surface by the uniform overlayer. Therefore, bacteria need not be attached to arsenopyrite to promote rapid reaction, and the mechanism of alteration at the arsenopyrite surface must have been inorganic. Because the delicate overlayer did not prevent continued alteration of arsenopyrite, FePO₄ may not be an effective barrier to oxidation in the tailings environment. The FePO₄ coating has likely formed in other experiments using these bacteria but was not detected because analytical techniques were not sufficiently surface sensitive to identify a separate, compositionally distinct overlayer. Some previous experimental results thus may be misleading or inapplicable to the tailings environment.     

Characterization of uraninite nanoparticles produced by Shewanella oneidensis MR-1

The reduction of uranium(VI) by Shewanella oneidensis MR-1 was studied to examine the effects of bioreduction kinetics and background electrolyte on the physical properties and reactivity to re-oxidation of the biogenic uraninite, UO_2(s). Bioreduction experiments were conducted with uranyl acetate as the electron acceptor and sodium lactate as the electron donor under resting cell conditions in a 30 mM NaHCO₃ buffer, and in a PIPES-buffered artificial groundwater (PBAGW). MR-1 was cultured in batch mode in a defined minimal medium with a specified air-to-medium volume ratio such that electron acceptor (O₂) limiting conditions were reached just when cells were harvested for subsequent experiments. The rate of U(VI) bioreduction was manipulated by varying the cell density and the incubation temperature (1.0 × 10⁸ cell ml⁻¹ at 20 °C or 2.0 × 10⁸ cell ml⁻¹ at 37 °C) to generate U(IV) solids at “fast” and “slow” rates in the two different buffers. The presence of Ca in PBAGW buffer altered U(VI) speciation and solubility, and significantly decreased U(VI) bioreduction kinetics. High resolution transmission electron microscopy was used to measure uraninite particle size distributions produced under the four different conditions. The most common primary particle size was 2.9-3.0 nm regardless of U(VI) bioreduction rate or background electrolyte. Extended X-ray absorption fine-structure spectroscopy was also used to estimate uraninite particle size and was consistent with TEM results. The reactivity of the biogenic uraninite products with dissolved oxygen was tested, and neither U(VI) bioreduction rate nor background electrolyte had any statistical effect on oxidation rates. With MR-1, uraninite particle size was not controlled by the bioreduction rate of U(VI) or the background electrolyte. These results for MR-1, where U(VI) bioreduction rate had no discernible effect on uraninite particle size or oxidation rate, contrast with our recent research with Shewanella putrefaciens CN32, where U(VI) bioreduction rate strongly influenced both uraninite particle size and oxidation rate. These two studies with Shewanella species can be viewed as consistent if one assumes that particle size controls oxidation rates, so the similar uraninite particle sizes produced by MR-1 regardless of U(VI) bioreduction rate would result in similar oxidation rates. Factors that might explain why U(VI) bioreduction rate was an important control on uraninite particle size for CN32 but not for MR-1 are discussed.     

Dicarboxylic acids generated by thermal alteration of kerogen and humic acids

Significant amounts (up to 2% of organic geopolymers) of low molecular weight (LMW) dicarboxylic acids (C₂–C₁₀) have been detected during thermal alteration (270°C, 2 h) of kerogens and humic acids isolated from young or ancient lithified sediments. Their distribution is characterized by predominance of oxalic acid followed by succinic, fumaric and methylsuccinic acids. These acids are probably released by the breakdown of macromolecular structures, which have incorporated biogenic organic compounds, including diacids, during early diagenesis in sediments. Because of their reactivity, LMW diacids may play the following geochemically important roles under natural conditions: (1) the diacids dissolve carbonates and clay minerals to increase porosity and permeability, which enhances migration of oils and gas generated from catagenesis of kerogen dispersed in shale, and (2) the diacids may form organo-metal complexes, which are important for mobilization, transport and accumulation of trace metals in sedimentary basins.     

Characterization of the manganese oxide produced by pseudomonas putida strain MnB1

Manganese oxides form typically in natural aqueous environments via Mn(II) oxidation catalyzed by microorganisms, primarily bacteria, but little is known about the structure of the incipient solid-phase products. The Mn oxide produced by a Pseudomonas species representative of soils and freshwaters was characterized as to composition, average Mn oxidation number, and N₂ specific surface area. Electron microscopy, X-ray diffraction, and X-ray absorption near edge structure spectroscopy were applied to complement the physicochemical data with morphological and structural information. A series of synthetic Mn oxides also was analyzed by the same methods to gain better comparative understanding of the structure of the biogenic oxide. The latter was found to be a poorly crystalline layer type Mn(IV) oxide with hexagonal symmetry, significant negative structural charge arising from cation vacancies, and a relatively small number of randomly stacked octahedral sheets per particle. Its properties were comparable to those of δ-MnO₂ (vernadite) and a poorly crystalline hexagonal birnessite (“acid birnessite”) synthesized by reduction of permanganate with HCl, but they were very different from those of crystalline triclinic birnessite. Overall, the structure and composition of the Mn oxide produced by P. putida were similar to what has been reported for other freshly precipitated Mn oxides in natural weathering environments, yielding further support to the predominance of biological oxidation as the pathway for Mn oxide formation. Despite variations in the degree of sheet stacking and Mn(III) content, all poorly crystalline oxides studied showed hexagonal symmetry. Thus, there is a need to distinguish layer type Mn oxides with structures similar to those of natural birnessites from the synthetic triclinic variety. We propose designating the unit cell symmetry as an addition to the current nomenclature for these minerals.     

On the in situ aqueous alteration of soils on Mars

Early (>3 Gy) wetter climate conditions on Mars have been proposed, and it is thus likely that pedogenic processes have occurred there at some point in the past. Soil and rock chemistry of the Martian landing sites were evaluated to test the hypothesis that in situ aqueous alteration and downward movement of solutes have been among the processes that have transformed these portions of the Mars regolith. A geochemical mass balance shows that Martian soils at three landing sites have lost significant quantities of major rock-forming elements and have gained elements that are likely present as soluble ions. The loss of elements is interpreted to have occurred during an earlier stage(s) of weathering that may have been accompanied by the downward transport of weathering products, and the salts are interpreted to be emplaced later in a drier Mars history. Chemical differences exist among the sites, indicating regional differences in soil composition. Shallow soil profile excavations at Gusev crater are consistent with late stage downward migration of salts, implying the presence of small amounts of liquid water even in relatively recent Martian history. While the mechanisms for chemical weathering and salt additions on Mars remain unclear, the soil chemistry appears to record a decline in leaching efficiency. A deep sedimentary exposure at Endurance crater contains complex depth profiles of SO₄, Cl, and Br, trends generally consistent with downward aqueous transport accompanied by drying. While no model for the origin of Martian soils can be fully constrained with the currently available data, a pedogenic origin is consistent with observed Martian geology and geochemistry, and provides a testable hypothesis that can be evaluated with present and future data from the Mars surface.     

Classification and thermal history of petroleum based on light hydrocarbons

Classifications of oils and kerogens are described. Two indices are employed, termed the Heptane and IsoheptaneValues, based on analyses of gasoline-range hydrocarbons. The indices assess degree of paraffinicity. and allow the definition of four types of oil: normal, mature, supermature, and biodegraded. The values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type. Aliphatic and aromatic kerogens are definable. Only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group (41%) in the sample set. This group was evidently generated at subsurface temperatures of the order of 138°–149°C, (280°–300°F) defined under specific conditions of burial history. It is suggested that all other petroleums are transformation products of normal oils.     

Formation of meteorite hydrocarbons from thermal decomposition of siderite (FeCO3)

Thermal decomposition of siderite has been proposed as a source of magnetite in martian meteorites. Laboratory experiments were conducted to evaluate the possibility that this process might also result in abiotic synthesis of organic compounds. Siderite decomposition in the presence of water vapor at 300°C generated a variety of organic products dominated by alkylated and hydroxylated aromatic compounds. The results suggest that formation of magnetite by thermal decomposition of siderite on the precursor rock of the martian meteorite ALH84001 would have been accompanied by formation of organic compounds and may represent a source of extraterrestrial organic matter in the meteorite and on Mars. The results also suggest that thermal decomposition of siderite during metamorphism could account for some of the reduced carbon observed in metasedimentary rocks from the early Earth.     

Experimental hearths and the thermal alteration of Caliche on the Southern High Plains

Throughout the Holocene, caliche has been a ubiquitous technological resource for the people of the Southern High Plains. Archaeological sites on the Southern High Plains often contain thermal features that appear to utilize caliche nodules in various cultural processes. These processes usually involve some degree of thermal dynamic alteration to the caliche, identified in the archaeological record as fire‐scorched or blackened nodules. Previous studies of the pyrodynamic properties of caliche have focused on quantification of color and fracture patterns within a laboratory setting, without direct involvement of cultural processes or problems associated with thermal features. Thermal alteration variables of caliche are examined from an actualistic perspective, utilizing previously excavated basin feature geometry and local caliche outcrops. Results indicate that sustained, intense heating of caliche (above 204°C) causes significant, but variable, structural transformations at the specimen level. The experimental use of shallow basin hearths demonstrates that hearth structures were easily capable of achieving and sustaining temperatures that would result in the physical alteration of individual caliche nodules, defined here as hearthstones. The broader implications of this study suggest that the interpretation of archaeological hearthstone assemblages should reflect variability, as observed during this experiment. © 2005 Wiley Periodicals, Inc.     

Characterization of solid bitumens originating from thermal chemical alteration and thermochemical sulfate reduction

Solid bitumen can arise from several reservoir processes acting on migrated petroleum. Insoluble solid organic residues can form by oxidative processes associated with thermochemical sulfate reduction (TSR) as well as by thermal chemical alteration (TCA) of petroleum. TCA may follow non-thermal processes, such as biodegradation and asphaltene precipitation, that produce viscous fluids enriched in polar compounds that are then altered into solid bitumens. It is difficult to distinguish solid bitumen formed by TCA from TSR since both processes occur under relatively high temperatures. The focus of the present work is to characterize solid bitumen samples associated with TSR- or TCA-processes using a combination of solid-state X-ray Photoelectron Spectroscopy (XPS), Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES), and ¹³C NMR. Naturally occurring solid bitumens from three locations, Nisku Formation, Brazeau River area (TSR-related); La Barge Field, Madison Formation (TSR-related); and, the Alaskan North Slope, Brooks Range (TCA-related), are compared to solid bitumens generated in laboratory simulations of TSR and TCA.The chemical nature of solid bitumens with respect to organic nitrogen and sulfur can be understood in terms of (1) the nature of hydrocarbon precursor molecules, (2) the mode of sulfur incorporation, and (3) their concentration during thermal stress. TSR-solid bitumen is highly aromatic, sulfur-rich, and nitrogen-poor. These heteroatom distributions are attributed to the ability of TSR to incorporate copious amounts of inorganic sulfur (S/C atomic ratio >0.035) into aromatic structures and to initial low levels of nitrogen in the unaltered petroleum. In contrast, TCA-solid bitumen is derived from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. TCA-bitumens from the Brooks Range have <75% aromatic carbon. TCA-bitumens exposed to greater thermal stress can have a higher aromaticity, like that observed in TSR-bitumens. Organic sulfur in TCA-organic solids remains relatively constant with increasing maturation (S/C atomic ratio <0.035) due to offsetting preservation and H₂S elimination reactions. Although S-XANES and ¹³C NMR provide information needed to understand changes in structure and reactivity that occur in the formation of petroleum solids, in some cases XPS analysis is sufficient to determine whether a solid bitumen is formed by TCA or TSR.     

Effects of thermal maturation on steroid hydrocarbons as determined by hydrous pyrolysis of Phosphoria Retort Shale

Hydrous pyrolysis experiments on the Phosphoria Retort Shale generate bitumen extracts and expelled oils that have steroid hydrocarbons with m/z 217-, 231-, and 253-mass Chromatographic distributions that are similar to those of bitumens and crude oils in the natural system. These experiments agree with the natural observations that diasteroid hydrocarbons increase relative to their regular counterparts with increasing thermal stress, while their C₂₇ through C₂₉ proportionality shows a slight enrichment in C₂₇. Relative concentrations of 20S to 20R configurations of 24-ethyl-14α,17α-cholestane show the expected increase with increasing thermal stress into the early part of the primary oil generation stage, but thereafter decrease with increasing thermal stress. If this reversal is found in high maturity sections of the natural system, the utility of this transformation as a maturity index will be limited. Triaromatic- to monoaromatic-steroid hydrocarbon concentrations increase with increasing thermal stress as observed in the natural system. Preferred migration of monoaromatic steroid hydrocarbons from bitumen extracts to expelled oils places considerable doubt on currently employed kinetic models for this aromatization reaction. As in the natural system, the experiments show relative concentrations of low-molecular weight- to high-molecular weight-triaromatic steroid hydrocarbons to increase with increasing thermal stress. Assuming a first-order reaction rate, the apparent activation energy and pre-exponential factor for this apparent side-chain cleavage reaction are 175.59 kJ mol⁻¹ and 2.82 × 10¹³ hr⁻¹, respectively. These kinetic parameters are geologically reasonable and are similar to those for the overall generation of expelled oil.     

Microbial mineralization and assimilation of black carbon: Dependency on degree of thermal alteration

Black carbon is degraded slowly in the environment and its formation can therefore be an effective sink for atmospheric CO₂. This study examined whether charcoal is assimilated by microorganisms or not and estimated the rate of mineralization depending on the degree of thermal alteration of the black carbon. Charcoals were produced at three different temperatures from homogeneously ¹⁴C labelled plant material and incubated in soil, and ¹⁴C in the evolved CO₂ and the microbial biomass was measured. Unlike parallel plant samples, CO₂ evolution from the charcoals showed no lag phase, but a period of faster CO₂ evolution for the first 5–8 days followed by a period of slow evolution. The mineralization of charcoal appeared to decrease with increasing temperature at which it was produced. This was also the case after the initial period of fast CO₂ evolution. With the techniques used, it was not possible to observe any microbial assimilation of charcoal, either because it did not occur, or because the methods used were not sufficiently sensitive. However, the lack of a lag phase in the CO₂ evolution from the charcoals is in line with earlier evidence that charcoal is initially oxidized at the surfaces by abiotic processes.     

The separate production of H2S from the thermal reaction of hydrocarbons with magnesium sulfate and sulfur: Implications for thermal sulfate reduction

The yields and stable C and H isotopic composition of gaseous products from the reactions of pure n-C₂₄ with (1) MgSO₄; and (2) elemental S in sealed Au-tubes at a series of temperatures over the range 220–600 °C were monitored to better resolve the reaction mechanisms. Hydrogen sulfide formation from thermochemical sulfate reduction (TSR) of n-C₂₄ with MgSO₄ was initiated at 431 °C, coincident with the evolution of C₂–C₅ hydrocarbons. Whereas the yields of H₂S increased progressively with pyrolysis temperature, the hydrocarbon yields decreased sharply above 490 °C due to subsequent S consumption. Ethane and propane were initially very ¹³C depleted, but became progressively heavier with pyrolysis temperature and were more ¹³C enriched than the values of a control treatment conducted on just n-C₂₄ above 475 °C. TSR of MgSO₄ also led to progressively higher concentrations of CO₂ showing relatively low δ¹³C values, possibly due to input of isotopically light CO₂ derived from gaseous hydrocarbon oxidation (e.g., more depleted CH₄).     

Carbonate and carbon isotopic evolution of groundwater contaminated by produced water brine with hydrocarbons

The major ionic and dissolved inorganic carbon (DIC) concentrations and the stable carbon isotope composition of DIC (δ¹³C_DIC) were measured in a freshwater aquifer contaminated by produced water brine with petroleum hydrocarbons. Our aim was to determine the effects of produced water brine contamination on the carbonate evolution of groundwater. The groundwater was characterized by three distinct anion facies: HCO₃⁻-rich, SO₄²⁻-rich and Cl⁻-rich. The HCO₃⁻-rich groundwater is undergoing closed system carbonate evolution from soil CO_2(g) and weathering of aquifer carbonates. The SO₄²⁻-rich groundwater evolves from gypsum induced dedolomitization and pyrite oxidation. The Cl⁻-rich groundwater is contaminated by produced water brine and undergoes common ion induced carbonate precipitation. The δ¹³C_DIC of the HCO₃⁻-rich groundwater was controlled by nearly equal contribution of carbon from soil CO_2(g) and the aquifer carbonates, such that the δ¹³C of carbon added to the groundwater was −11.6‰. In the SO₄²⁻-rich groundwater, gypsum induced dedolomitization increased the ¹³C such that the δ¹³C of carbon added to the groundwater was −9.4‰. In the produced water brine contaminated Cl⁻-rich groundwater, common ion induced precipitation of calcite depleted the ¹³C such that the δ¹³C of carbon added to the groundwater was −12.7‰. The results of this study demonstrate that produced water brine contamination of fresh groundwater in carbonate aquifers alters the carbonate and carbon isotopic evolution.     

Using GC-MS/Combustion/IRMS to determine the C/C ratios of individual hydrocarbons produced from the combustion of biomass materials--application to biomass burning

Simultaneous mass spectral detection and stable carbon isotope analysis was performed on individual indigenous n-alkanes isolated from single C₄ and C³ plant species and on a series of aliphatic and polycyclic aromatic hydrocarbons (PAH) produced from the combustion of these same biomass materials. The analysis technique used a combined gas chromatograph-mass spectrometer/combustion/isotope ratio mass spectrometer (GC-MS/C/IRMS). Precision (2σ) for replicate measurements of individual compounds in standard solutions using this novel configuration ranged between 0.2 and 0.5‰ for n-alkanes and 0.3 and 0.8‰ for PAH. Accuracy of the n-alkane measurements ranged between 0.1 and 0.4‰ and that of the PAH measurements ranged between 0.2 and 0.9‰. Replicate GC-MS/C/IRMS measurements on the combustion-derived n-alkene/alkane pairs were performed to within a precision of between 0.1 and 1.1‰ and the precision for the combustion PAH was similar to the standard PAH solution. No notable isotopic effects were observed when altering the temperature of the combustion process from 900 to 700°C, or as a result of the individual n-alkenes/alkanes partitioning between the gaseous and condensate fractions. Combustion-derived n-alkenes/alkanes ranged from C₁₁ to C₃₁, and the C₄-derived n-alkenes/alkanes were approx. 8‰ more enriched in ¹³C than the C₃-derived compounds. Both the C₄ and C₃-derived n-alkenes/alkanes (C₂₀-C₃₀) were isotopically similar to the indigenous n-alkanes and were 2-3‰ more depleted in ¹³C than the lower mol. wt (C₁₁₁₁-C₁₉) n-alkenes/alkanes, suggesting an independent origin for the lower mol. wt compounds. Combustion-generated C₄ and C₃-derived 2-, 3-, and 4-ring PAH were also isotopically distinct (Δδ = 10‰). Unlike the n-alkenes/alkanes, no compound-to-compound variations were observed between the low and high mol. wt PAH. This study demonstrates that the isotopic composition of original plant biomass material is mainly preserved in the aliphatic hydrocarbons and PAH generated by its combustion. Consequently, analyses of these compounds in sediments impacted by fire occurrences may provide useful information about paleo-fire activity that may help elucidate the impact biomass burning may have had and could have on climate-biosphere interactions.     

Modification of thermal and oxidative properties of biodiesel produced from vegetable oils

Trans esterification of three vegetable oils, sunflower oil, linseed oil and mixed oils as; sunflower-soyabean and olein were carried out using methanol, and potasium hydroxide as catalyst. The methyl esters of the corresponding oils were separated from the crude glycerol and characterized by physical-chemical methods to evaluate their thermal properties. This methods are determination of densities, cloud points, pour points, flash points, kinematic viscosities, hydrogen/carbon ratios, sulfur contents, ash contents and triglycerides. The physico-chemical characteristic of biodiesel treated with ozone showed improvement of pour point and flash point indicating higher degree of safety for fuel. Methyl esters mixed with their corresponding ozonated oil were subjected to comparison and evaluation for their thermal properties by the thermo gravimetric analysis differential thermal analysis from which the calculated heat of enthalpy and comparison with the heat of conventional diesel. The results showed that the oxygen content of biodiesel samples treated with ozone increased weight % and resulted in more extensive chemical reaction, promoted combustion characteristics and less carbon residue was produced. Gas chromatography appeared more suitable to address the problem of determining/verifying biodiesel methyl ester and showed that methyl ester content was impurity free. Ultra violet-detection was used for rapid quantization of triglycerols. From the analyses performed biodiesel treated with ozone modified the thermal and oxidative stability shown by the high combustion efficiency indicated by the high heat of enthalpy and reducing the emission of particulate matter.     

纳米镍/铁去除氯代烃影响因素的探讨

氯代烃是地下水中最常检出的有机污染物之一,传统的处理方法去除率很低。近年来随着铁还原技术的发展,纳米铁和纳米双金属也成为一个活跃的研究领域。利用批实验的研究方法以四氯乙烯(PCE)和四氯化碳(CT)为目标污染物,研究纳米镍/铁在去除PCE过程中的影响因素。实验结果表明,在碱性条件下,纳米Ni/Fe对PCE脱氯速率比在酸性和中性条件下脱氯速率更快;纳米Ni/Fe对初始浓度为6·51mg/L的PCE溶液脱氯速率是对初始浓度为20·56mg/L的PCE溶液脱氯速率的1·8倍;对于氯代程度相同的CT和PCE,对CT的脱氯速率明显快于对PCE。     

Geochemistry of rare-earth elements in thermal waters of Uzon-Geyzernaya hydrothermal system (Kamchatka)

Precisional analyses of the abundances of La, Ce, and major elements in thermal waters and rocks of the Uzon-Geyzernaya volcanotectonic depression, supplemented by published data on a number of modern high-temperature hydrothermal systems of Kamchatka and two other areas of the world, allowed defining genetically important patterns of rare-earth elements (REE) distribution. The La and Ce abundances positively correlate with silica contents both in fresh igneous rocks of the study areas and in the products formed by hydrothermal processes.All studied hydrothermal clays are enriched in La and Ce. The general enrichment trend is similar to the pattern of positive correlation between the La and Ce abundances. Geothermal waters display a strong relationship between REE enrichment and pH. Enhanced REE enrichment trend is observed in thermal waters with abundant SO₄^2 ? and K. The REE versus Cl and B diagrams show two individual fields reflecting the level of acidity-alkalinity of thermal waters. These data demonstrate that La and Ce concentrations in the products of modern hydrothermal systems (in fluids and secondary mineral phases) are governed by wallrock composition, anionic water composition, and pH/Eh-dependent adsorption processes.     

The Olduvai buffalo Pelorovis and the origin of Bos

The origin of the genus Bos is a debated issue. From ∼ 0.5 Ma until historic times, the genus is well known in the Eurasian large mammal assemblages, where it is represented by Bos primigenius. This species has a highly derived cranial anatomy that shows important morphological differences from other Plio-Pleistocene Eurasian genera of the tribe Bovini such as Leptobos, Bison, Proamphibos-Hemibos, and Bubalus. The oldest clear evidence of Bos is the skull fragment ASB-198-1 from the middle Pleistocene (∼ 0.6-0.8 Ma) site of Asbole (Lower Awash Valley, Ethiopia). The first appearance of Bos in Europe is at the site of Venosa-Notarchirico, Italy (∼ 0.5-0.6 Ma). Although the origin of Bos has traditionally been connected with Leptobos and Bison, after a detailed anatomical and morphometric study we propose here a different origin, connecting the middle Pleistocene Eurasian forms of B. primigenius with the African Late Pliocene and early Pleistocene large size member of the tribe Bovini Pelorovis sensu stricto. The dispersal of the Bos lineage in Western Europe during middle Pleistocene times seems to coincide with the arrival of the Acheulean tool technology in this continent.     

Metal contents of recent thermal waters, mineral precipitates and hydrothermal alteration in active geothermal fields, Kamchatka

All the Kamchatkan recent hydrothermal systems are restricted to two volcanic zones, Central Kamchatka of Late Miocene-Pliocene age and East Kamchatka, where several active volcanoes are located. Solutions from active hydrothermal systems commonly contain elements, including As, Sb, Hg, Li, Rb, Cs, B, Cu, Pb, Zn, Ag, Au,Sr and Ba, with the first seven predominating. Higher abundances of ore elements occur in active hydrothermal systems with solutions of sodium chloride composition. Those are the Kireunskaya, Dvukhyurtochnaya and Apapelskaya systems in the Central Kamchatka volcanic zone and the Uzon hydrothermal system in the East Kamchatka volcanic zone. The hydrothermal systems are restricted to structures having very long histories of evolution and which are characterized by contrasting types of magmatism. At present chemical precipitates and altered rocks with higher abundances of As, Sb and trace amounts of Au, Ag, Cu, Ph and Zn are forming in the discharge zones of these hydrothermal systems. Large zones of alterations (alunitic quartzites^* and argillites) with high abundances of As, Sb, Hg, Cu, Pb, Ga and Zr occur in the Central Kamchatka volcanic zone. Here zones of mineralization (cinnabar, realgar, stibnite, orpiment, pyrite, chalcopyrite, sphalerite, galena) occur also; native gold, native silver and gudmundite occur rarely.In the recent Uzon caldera hydrothermal system, As-Sb-Hg mineralization with bitumen and oils is now forming. The ore deposit is zoned, with the most abundant ore minerals being realgar, uzonite, alacranite, stibnite and pyrite. Cinnabar, orpiment, marcasite and native mercury occur occasionally, and single grains of native gold, native silver and native copper are present. At present a total of 7000 t As, 350 t Sb and 200 t Hg have been deposited in the mineralization zone at geochemical boundaries. The general geological and geochemical data suggest that at depth the As-Sb-Hg mineralization may change to gold-silver mineralization.