Platinum group minerals in podiform chromitites of the Bou Azzer ophiolite, Anti Atlas, Central Morocco     

M. El Ghorfi  F. Melcher  T. Oberthür  A. E. Boukhari  L. Maacha  A. Maddi  M. Mhaili 《Mineralogy and Petrology》2008,92(1-2):59-80

Summary The Neoproterozoic Bou Azzer ophiolite complex hosts numerous, small lenticular bodies of massive and disseminated chromite. Metallurgical-grade high-Mg and high-Cr spinels (cores with 48–62 wt% Cr₂O₃) reveal complex alteration patterns of successive Cr and Mn enrichment and loss of Al towards the rims, while the Mg# ratios [(Mg/(Mg + Fe²⁺)] remain almost constant. Concentration patterns of platinum-group elements are typical for ophiolitic chromitite poor in sulfides, with predominance of the IPGE, variable Rh, and low Pt and Pd. The most abundant platinum-group mineral is Rh-bearing laurite that occurs either included in spinel or in silicate matrix, whereas Os-Ir-Ru alloy is always included in spinel. Laurite inclusions reveal complex intergrowth textures with Rh-Ru-Pt rich alloy, and with Rh-rich sulfide. Most laurites display trends to sulfur-poor compositions leading to local formation of very fine-grained Ru-Os-Ir alloy phases. Ni-Co-Fe sulfides, arsenides and sulfarsenides devoid of PGE are associated with the alteration of chromite. Textural position and chemical composition of the base metal inclusions, as well as comparison of alteration features between chromite and accessory chromian spinel in the Co-Ni-As ores of the Bou Azzer ophiolite indicate a close connection. It is suggested that hydrothermal fluids percolated through the marginal zones of the ophiolite belt during greenschist facies metamorphism and deposited Ni-Co-Fe arsenides, sulfarsenides and minor sulfides as accessories within altered chromitites, and also in structurally favourable zones as Ni-Co-As ores. Author’s address: Dr. Frank Melcher, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany  相似文献   

National flood discharge mapping in Austria   总被引：5，自引：0，他引：5  

Ralf Merz  Günter Blöschl  Günter Humer 《Natural Hazards》2008,46(1):53-72

This article presents the approach and the results of a study in which 30, 100 and 200 year return period flood discharges were estimated for 26,000 km of Austrian streams. Three guiding principles were adopted: combination of automatic methods and manual assessments by hydrologists to allow speedy processing and account for the local hydrological situation; combination of various sources of information including flood peak samples, rainfall data, runoff coefficients and historical flood data; and involvement of the Hydrographic Services to increase the accuracy and enhance the acceptance of results. The flood discharges for ungauged catchments were estimated by the Top-kriging approach with manual adjustment to the local flood characteristics. The adopted combination approach proved to be very efficient both in terms of the project time required and in terms of the accuracy and acceptability of the estimated flood discharges of given return periods.  相似文献   

The role of the volatile phase for REE and Y fractionation in low-silica carbonate magmas: implications from natural carbonatites, Namibia     

B. Bühn 《Mineralogy and Petrology》2008,92(3-4):453-470

Summary Two bimodal carbonatite complexes in Namibia of Cretaceous age are explored as to the presence and composition of a coexisting carbonatitic fluid. The Kalkfeld and Ondurakorume complexes contain both Ca- and Mg/Fe-carbonatites, composed of calcite alone or calcite with ferroan dolomite, fluorapatite and strontianite. The major element evolution in the bulk rocks from s?vites to beforsites is due to crystallization of calcite and fluorapatite. All carbonatites show a negative Y anomaly in normalised REE plots. Fractionation is accompanied by successively lower HREE contents between Tb and Yb, expressed by the ratios Nd/Ho and Ho/Lu. The evolution of this downward-facing hump goes along with decreasing Y contents in bulk rocks and minerals. All this requires an additional phase coexisting with the carbonate liquid during fractionation. Comparison between the bulk rocks and the expelled fluid shows that the latter had preferentially accumulated the HREE and Y. Further evidence for this process are hydrothermal, HREE, Y-rich fluorites in other carbonatite complexes which reflect the composition of the expelled fluid. The high strength of fluoride complexes suggests that fluoride complexing in the carbonatitic fluid is the process responsible for extracting HREE and Y from the carbonatite magma, leaving fractionated carbonatite rocks depleted in these elements. The geochemical evolution of carbonatite magmas along fractionation has therefore to be considered in a melt-mineral-fluid system. Correspondence: B. Bühn, Instituto de Geociências, Universidade de Brasilia, Campus Universitário Darcy Ribeiro, Brasilia 70910-900, Brazil  相似文献   

Aspects of conservation in the excavation site of the Athribis temple in Egypt     

Hans Leisen  Esther von Plehwe-Leisen  Christina Verbeek  Christine Jürgens  Sabine Krause 《Environmental Geology》2008,56(3-4):689-697

  相似文献   

Die Windverhältnisse im Davoser Hochtal     

M. Schüepp  Ch. Urfer 《Theoretical and Applied Climatology》1962,12(2):337-349

Zusammenfassung Die Davoser Windverh?ltnisse werden in ihrem tages- und jahreszeitlichen Ablauf sowie in ihrer Abh?ngigkeit von verschiedenen typischen Wetterlagen untersucht. Neben den ungest?rten Sch?nwetterlagen mit ihrem ausgepr?gten Talwind, der wie der Malojawind talabw?rts weht, werden die F?hnstr?mung aus Südwest und die Nordoststr?mung bei Staulagen und Bise kurz besprochen. Gegenüber dem benachbarten Dischmatal zeigt sich ein sp?terer Beginn des Talwindes bei Sch?nwetterlagen, w?hrend im Vergleich zu anderen T?lern, z. B. zum Wallis, ein früheres und schw?cheres nachmitt?gliches Windmaximum auftritt.

---

Summary The wind at Davos is analysed in his diurnal and annual variation and in the depence on the different weather types. The fair and undisturbed weather shows a typical valley breeze during the day, but not in the normal direction towards the higher part of the valley, but downstream, similar to the Malojawind in the Engadine. The opposite wind direction, from southwest, characterises the foehn-situation. Northeasterly winds develop in the case of higher pressure north of the Alps (e. g. in situations of barrage). The valley-breeze begins later than in the adjacent Dischma Valley, but it is weaker and reaches the highest intensity earlier than in other valleys, as e. g. in the Valais.

---

Résumé Les vents de Davos sont analysés selon leurs variations diurnes et annuelles et selon des types de temps caractéristiques. La situation de beau temps montre un vent de vallée assez accentué, soufflant du haut en bas, donc dans une direction anormale, mais analogue au vent de la Maloja en Engadine. En cas de ?foehn? le vent souffle du sud-ouest tandis qu'un vent du nord-est se manifeste par situations de surpression au nord des Alpes. Le vent de vallée se met à souffler plus tard à Davos que dans la vallée de Dischma toute proche. Il y atteint par contre sa vitesse maximale plus t?t que les vents correspondants d'autres vallées p. ex. du Valais. Le maximum y est cependant moins élevé.

---

---

Mit 6 Textabbildungen

---

Herrn Dr.W. M?rikofer zu seinem 70. Geburtstag gewidmet.  相似文献   

Neue ZnS-Polytypen (9R, 12R und 21R) in mesozoischen Sedimenten NW-Deutschlands     

Dozent Dr. Siegfried Haussühl  Dozent Dr. German Müller 《Contributions to Mineralogy and Petrology》1963,9(1):28-39

Summary Argillaceous sediments of jurassic and lower cretaceous age in NW-Germany contain in several localities authigenous ZnS-polytypes. The crystals with a maximum height of 2 mm exhibit hexagonal-pyramidal and trigonal-pyramidal habit.With X-ray rotation and precession technique the following polytypes could be identified: Sphalerite (3 R = 3 C) 211, 411, 6H 9R, 12R, 15R and 21R.The 9 R-, 12 R- and 21 R-polytypes have not until now been described elsewhere.The structures of the new polytypes were determined as 9R=(21), 12R=(13) and 21R=(3112).Oriented intergrowths of R- and H-polytypes were frequently observed. From the intergrowth-phenomena arguments for the environmental conditions of formation can be deducted.[/p]  相似文献   

Untersuehungen an den Sedimenten der Tongrube von Willershausen     

Dr. Necip Güven 《Contributions to Mineralogy and Petrology》1963,9(1):40-64

Zusammenfassung Nach der Profilaufnahme sind die Sedimente der Tongrube der Ziegelei von Willershausen in zwei Gruppen einzuteilen : A. Die unteren hellen Schichten, B. die oberen dunklen Schichten.Die unteren hellen Schichten bestehen aus Sandsteinen, Sanden, tonigen Sanden und Grobtonen, welche Quarz, Feldspäte und Glimmer als Hauptminerale und in geringeren Mengen Illit, Chlorit und manchmal Montmorillonit füren. Als Schwerminerale dieser Sande und Sandsteine treten der Häufigkeit nach Apatit, Zirkon, Granat, Anatas, Rutil, Turmalin und Opakminerale auf.Die oberen dunklen Schichten bestehen hauptsächlich aus mm-rhythmisch geschichteten Tonen mit Einschaltung einzelner Mergelbänke und toniger Sandschichten. Dioktaedrischer Illit ist das häufigste Tonmineral, dann folgen Chlorit und in geringeren Mengen in feinen Fraktionen Montmorillonit. Die Chlorit-Reflexe verschwinden bereits bei Erhitzung auf 450° C. Chemisch handelt es sich um die dem Pennin naheliegenden Diabantite.Die Unterschiede in Beschaffenheit und Menge der Quarze, Feldspäte und Glimmer, die unterschiedliche Verteilung der Schwerminerale sprechen dafür, daß die hellen Schichten wahrscheinlich zum Mesozoikum, vielleicht zum Buntsandstein gehören.Von der Mathematisch-Naturwissenschaftlichen Fakultät der Georg-August-Universität zu Göttingen genehmigte Dissertation.  相似文献   

Buchbesprechungen     

F. Steinhauser  W. Mörikofer  K. Cehak  W. Müller 《Theoretical and Applied Climatology》1965,13(4):558-568

Ohne Zusammenfassung  相似文献   

Underwater sounds near a fuel receiving facility in western Hong Kong: relevance to dolphins   总被引：1，自引：0，他引：1  

Würsig B  Greene CR 《Marine environmental research》2002,54(2):129-145

Western Hong Kong is home to two species of marine mammals: Indo-Pacific humpbacked dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides). Both are threatened in many parts of their range in southeast Asia [for example, International Biological Research Institute Reports 9 (1997), 41; Asian Marine Biology 14 (1997) 111]. In 1998, when the new Hong Kong International Airport opened in western Hong Kong, small tankers (about 100 m long, cargo capacity about 6300 metric tons) began delivering fuel to the Aviation Fuel Receiving Facility (AFRF) just off Sha Chau Island, north of the airport. Calibrated sound recordings were taken over a 4-day period from a quiet, anchored boat at distances 80-2000 m from aviation fuel delivery activities at the AFRF. From the recordings, 143 sections were selected for analysis. Narrowband spectral densities on the sound pressures were computed, and one-third octave band levels were derived for center frequencies from 10 to 16,000 Hz. Broadband levels, viz. 10-20,000 Hz. were also computed. The results showed that the Sha Chau area is normally noisy underwater, with the lowest broadband levels measured corresponding to those expected during a storm at sea (sea state 6). This background noise is believed to come largely from heavy vessel traffic in the Urmston Road to the north and east of Sha Chau and from vessels in the Pearl River Estuary to the West. The sound levels from the AFRF tankers are comparable to the levels measured from similar- and smaller-sized supply vessels supporting offshore oil exploration. The strongest sounds recorded were from a tanker leaving the AFRF at distance 100 m from the hydrophone, for which the one-third octave band level at 100 Hz was 141 dB re 1 microPa (spectrum level 127 dB re 1 microPa2/Hz) and the 10-20,000 Hz broadband level was 146 dB. At distances of 100 m or more and frequencies above 300 Hz, the one-third octave band levels were less than 130 dB (spectrum level 111 dB re 1 microPa2/Hz) and decreased with increasing frequency and distance. At distances greater than about 500 m, AFRF-associated sounds were negligible, masked by the generally high noise level of the area and attenuated by poor transmission in the very shallow water (<10 m). Because it is believed that humpbacked dolphins and finless porpoises are not very sensitive to sounds below 300 Hz, the Airport Authority Hong Kong (AA) stipulated that dedicated terminal vessels not radiate underwater sounds at spectrum levels greater than 110 dB re 1 microPa2/Hz at frequencies above 300 Hz and distances greater than 300 m. The spectrum levels at 300 Hz and higher frequencies of sounds from the tankers arriving, departing, or off-loading at AFRF were less than 110 dB re 1 microPa2/Hz even at distances of 200 m or less. The AA stipulation was met. However, it is presently unknown whether the generally strong noise levels of western Hong Kong inhibit acoustically based feeding and communication, or result in increased stress or permanent shifts in hearing thresholds.  相似文献   

Response of the barrier island coastal region of southwestern Nigeria to climate and non-climate forcing     

IB Danladi  M Gül  E Ateş 《African Journal of Marine Science》2020,42(1):43-51

Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise.  相似文献