Geochemistry and mineralogy of platinum-group elements at Hartley Platinum Mine,Zimbabwe     

Thomas?OberthürEmail author  Thorolf?W.?Weiser  Lothar?Gast  Kari?Kojonen 《Mineralium Deposita》2003,38(3):327-343

The behaviour of platinum-group elements (PGE) in the exogenic cycle was examined in profiles of oxidized Main Sulfide Zone (MSZ) ores, in which the general metal distribution patterns of the pristine MSZ are grossly preserved. However, at similar Pt grades, significant proportions of Pd have been lost from the system. This indicates that Pd is more mobile than Pt and is dispersed in the supergene environment. Sperrylite and cooperite/braggite are stable in the oxidized MSZ. In contrast, the (Pt,Pd)-bismuthotellurides, common in pristine MSZ ores, have disintegrated, and ill-defined (Pt,Pd)-oxides or (Pt,Pd)-hydroxides have formed. The assemblage of detrital PGM present in the Makwiro River close to the Hartley Platinum Mine indicates further mineralogical changes. Sperrylite largely remains stable whereas most cooperite/braggite grains have been partly altered or completely destroyed. Grains of Pt-Fe alloy are ubiquitous in the alluvial sediments. Most likely, these grains are neo-formations that formed either from pre-existing, unstable PGM or via a solution stage under low-temperature conditions.  相似文献   

Particle Size Distribution and Gas-Particle Partition of Polycyclic Aromatic Hydrocarbons in Helsinki Urban Area     

Masahiko Shimmo  Karri Saarnio  Pasi Aalto  Kari Hartonen  Tuulia Hyötyläinen  Markku Kulmala  Marja-Liisa Riekkola 《Journal of Atmospheric Chemistry》2004,47(3):223-241

Ambient concentrations of polycyclic aromatic hydrocarbons (PAHs) were measured in Helsinki (Finland). Particle mass size distributions were obtained with a cascade impactor (12 stages) with glass fibre filters as substrates. Simultaneously with the impactor measurements, particulate and gaseous PAHs were collected on a quartz filter and XAD-2 adsorbent, respectively, for evaluation of gas-partition coefficients. Samples were analysed for PAHs by on-line coupled supercritical fluid extraction — liquid chromatography — gas chromatography — mass spectrometry. The impactor results showed that most of the PAHs in Helsinki urban area were concentrated in fine particles (<2.5 μm diameter) with unimode peak at about 1 μm. The results were comparable with the number distribution measured with a differential mobility particle sizer. Total amounts of PAHs (gas + particle) varied from 15 (acenaphthylene) to 1990 (fluorene) pg/m³. The PAHs lighter than 202 amu (pyrene and fluoranthene) were exclusively in gas phase, whereas those heavier than 202 amu were mostly associated with particles. A plot of the partition coefficients (logKp) versus the temperature dependent sub-cooled vapour pressures (logp _L ⁰ ) showed a gradient of −0.66, which deviated from equilibrium state (gradient = −1).  相似文献   

The tilt effect for Saturn's rings     

Larry W. Esposito  Kari Lumme 《Icarus》1977,31(1):157-167

Multiple-scattering computations are carried out to explain the variation of the observed brightness of the A and B rings of Saturn with declination of the Earth and Sun. These computations are performed by a doubling scheme for a homogeneous plane-parallel scattering medium. We test a range of choices for the phase function, albedo for single scattering, and optical depth of both the rings. Isotropic scattering and several other simple phase functions are ruled out, and we find that the phase function must be moderately peaked in both the forward and backward directions. The tilt effect can be explained by multiple scattering in a homogeneous layer, but, for ring B, this requires a single-scattering albedo in excess of 0.8. The brightest part of ring B must have an optical depth greater than 0.9. We find that the tilt effect for ring A can be reproduced by particles having the same properties as those in ring B with the optical depth for the A ring in the range 0.4 to 0.6.  相似文献   

Depositional history of peatland pines (Pinus sylvestris L.) in NW Enontekiö, Finnish Lapland: implications for Middle Holocene drought and temperature fluctuations     

Samuli Helama  Hannu Herva  Joonas Uusitalo  Andy Moir  Kari Mielikäinen  Pekka Nöjd  Markku Oinonen  Raimo Sutinen 《Boreas: An International Journal of Quaternary Research》2023,52(3):427-439

High altitude and latitude findings of subfossil peatland pine trees were unearthed from the region of NW Finnish Lapland and dated by ¹⁴C and tree-ring methods. The depositional history of the trees illustrated two distinct peatland pine phases dated to Middle Holocene intervals 4900–4400 and 4100–3400 cal. a BC. It seems evident that both thermal and hydroclimatic fluctuations have played roles of varying importance in the establishment of this pine population and its demise. The presence of these pines, from a site ~60 km north of the coniferous timberline and conditions ~1 °C and 100 degree-days colder than those at the present-day timberline, concurs with previous studies demonstrating the association between the high-latitude summer-temperature cooling and circumpolar timberline retreat since the Middle Holocene due to Milankovitch forcing. On the other hand, the peatland pine recruitment was made possible by drier than present surface conditions during the previously reconstructed Middle Holocene drought anomaly (Hyvärinen-Alhonen event). Our data suggest this event was not continuous but reached its two-phase climax during the peatland pine phases, with an interruption of several centuries with moister surface conditions between 4400 and 4100 cal. a BC. The findings highlight the sensitivity of well-dated peatland tree assemblages in terms of recording past climatic evolution and events and the need for new collections from north and south Fennoscandia and the Baltic region, for more detailed analyses over extended time intervals and regions.  相似文献   

Holocene floristic diversity and richness in northeast Norway revealed by sedimentary ancient DNA (sedaDNA) and pollen     

Charlotte L. Clarke  Mary E. Edwards  Antony G. Brown  Ludovic Gielly  Youri Lammers  Peter D. Heintzman  Francisco Javier Ancin‐Murguzur  Kari‐Anne Brthen  Tomasz Goslar  Inger G. Alsos 《Boreas: An International Journal of Quaternary Research》2019,48(2):299-316

We present a Holocene record of floristic diversity and environmental change for the central Varanger Peninsula, Finnmark, based on ancient DNA extracted from the sediments of a small lake (sedaDNA). The record covers the period c. 10 700 to 3300 cal. a BP and is complemented by pollen data. Measures of species richness, sample evenness and beta diversity were calculated based on sedaDNA sampling intervals and 1000‐year time windows. We identified 101 vascular plant and 17 bryophyte taxa, a high proportion (86%) of which are still growing within the region today. The high species richness (>60 taxa) observed in the Early Holocene, including representatives from all important plant functional groups, shows that modern shrub‐tundra communities, and much of their species complement, were in place as early as c. 10 700 cal. a BP. We infer that postglacial colonization of the area occurred prior to the full Holocene, during the Pleistocene‐Holocene transition, Younger Dryas stadial or earlier. Abundant DNA of the extra‐limital aquatic plant Callitriche hermaphroditica suggests it expanded its range northward between c. 10 200 and 9600 cal. a BP, when summers were warmer than present. High values of Pinus DNA occur throughout the record, but we cannot say with certainty if they represent prior local presence; however, pollen influx values >500 grains cm^?2 a^?1 between c. 8000 and 7300 cal. a BP strongly suggest the presence of pine woodland during this period. As the site lies beyond the modern tree limit of pine, it is likely that this expansion also reflects a response to warmer Early Holocene summers.  相似文献   

Kimberlite emplacement and mantle sampling through time at A154N kimberlite volcano,Diavik Diamond Mine: lessons from the deep     

Moss  Stephen W.  Kobussen  Alan  Powell  William  Pollock  Kari 《Mineralogy and Petrology》2018,112(2):397-410

The Diavik Diamond Mine in the NWT of Canada has produced in excess of 100 million carats from 3 kimberlite pipes since mining commenced in 2002. Here, we present new findings from deep (>400 m below surface) mining, sampling and drilling work in the A154N kimberlite volcano that require a revision of previous geological and emplacement models and provide a window into how the sub-continental lithospheric mantle (SCLM) below Diavik was sampled by kimberlite magmas through time. Updated internal geological models feature two volcanic packages interpreted to represent two successive cycles of explosive eruption followed by active and passive sedimentation from a presumed crater-rim, both preceded and followed by intrusions of coherent kimberlite. Contact relationships apparent among the geological units allow for a sequential organization of as many as five temporally-discrete emplacement events. Representative populations of mantle minerals extracted from geological units corresponding to four of the emplacement events at A154N are analyzed for major and trace elements, and provide insights into the whether or not kimberlites randomly sample from the mantle. Two independent geothermometers using clinopyroxene and garnet data indicate similar source depths for clinopyroxenes and G9 garnets (130–160 km), and suggest deeper sampling with time for both clinopyroxene and garnets. Harzburgite is limited to 110–160 km, and appears more prevalent in early, low-volume events. Variable ratios of garnet parageneses from the same depth horizons suggest random sampling by passing magmas, but deeper garnet sampling through time suggests early preferential sampling of shallow/depleted SCLM. Evaluations of Ti, Zr, Y and Ga over the range of estimated depths support models of the SCLM underlying the central Slave terrane.

  相似文献   

Monitoring biological effects of pollution in the Baltic Sea: neglected--but still wanted?     

Lehtonen KK  Schiedek D 《Marine pollution bulletin》2006,53(8-9):377-386

In the Baltic Sea, studies regarding biological effects of contaminants are relatively few, partly due to political and economical reasons, specific hydrographic characteristics, and a strong eutrophication-targeted research focus during the past three decades. The development of a monitoring strategy concerning biological effects and its implementation into environmental monitoring programmes in the Baltic Sea is lagging behind the progress currently taking place in most of western and southern Europe. The pan-European project BEEP (Biological Effects of Environmental Pollution on Marine Coastal Ecosystems, 2001-2004) included the Baltic Sea as one of the target areas for the evaluation of a suite of biological effects indicators in European coastal waters. The main aims of the BEEP project are described and how the expected outcome for the Baltic Sea could provide the needed "baseline" information and expertise for a biological effect monitoring and contribute to harmonise environmental monitoring programmes within the EU.  相似文献   

Biochemical biomarkers in adult female perch (Perca fluviatilis) in a chronically polluted gradient in the Stockholm recipient (Sweden)     

Hansson T  Schiedek D  Lehtonen KK  Vuorinen PJ  Liewenborg B  Noaksson E  Tjärnlund U  Hanson M  Balk L 《Marine pollution bulletin》2006,53(8-9):451-468

A battery of biochemical biomarkers and the SigmaPCB concentration in adult female perch (Perca fluviatilis) verified an aquatic pollution gradient with the city of Stockholm (Sweden) as a point source of anthropogenic substances. The investigation included both an upstream gradient, 46 km westwards through Lake M?laren, and a downstream gradient, 84 km eastwards through the Stockholm archipelago. Besides the main gradient from Stockholm, there were strong indications of pollution coming from the Baltic Sea. The results indicated a severe pollution situation in central Stockholm, with poor health status of the perch, characterised by increased specific EROD activity in the liver, increased liver EROD somatic index, decreased AChE activity in the muscle, increased amount of DNA adducts in the liver, and a high concentration of biliary 1-pyrenol. In addition, laboratory exposure to common EROD inducers elicited an abnormal response, suggestive of chronic intoxication.  相似文献   

Palaeomagnetic cave stratigraphy of sediments from Hellemofjord, northern Norway     

Reidar Løvlie  Kari Lise Ellingsen  Stein-Erik Lauritzen 《Geophysical Journal International》1995,120(2):499-515

  相似文献   

Magma mixing and the generation of isotopically juvenile silicic magma at Yellowstone caldera inferred from coupling 238U–230Th ages with trace elements and Hf and O isotopes in zircon and Pb isotopes in sanidine     

Mark E. Stelten  Kari M. Cooper  Jorge A. Vazquez  Mary R. Reid  Gry H. Barfod  Josh Wimpenny  Qing-zhu Yin 《Contributions to Mineralogy and Petrology》2013,166(2):587-613

The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare ²³⁸U–²³⁰Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in ¹⁷⁶Hf/¹⁷⁷Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source.  相似文献