Rock relationships in the Mogok metamorphic belt, Tatkon to Mandalay, central Myanmar

The Mogok metamorphic belt (MMB), over 1450 km long and up to 40 km wide, consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the Western margin of the Shan Plateau in central Myanmar and continuing northwards to the eastern Himalayan syntaxis. Exposures in quarries allow correlation of Palaeozoic meta-sedimentary, early Mesozoic meta-igneous and late Mesozoic intrusive rocks within a 230 km long northerly-trending segment of the MMB, from Tatkon to Kyanigan north of Mandalay, and with the Mogok gemstone district 100 km to the northeast. Relationships among the metamorphic and intrusive rocks, with sparse published radiometric age controls, indicate at least two metamorphic events, one before and one after the intrusion of Late Jurassic to early Cretaceous calc-alkaline rocks. These relationships can be explained by either of two possible tectonic histories. One, constrained by correlation of mid-Permian limestones across Myanmar, requires early Permian and early Jurassic regional metamorphic events, prior to an early Tertiary metamorphism, in the western part of but within a Shan-Thai – western Myanmar block. The second, not compatible with a single laterally continuous Permian limestone, requires pre-Upper Jurassic regional metamorphism and orogenic gold mineralization in the Mergui Group and western Myanmar, early Cretaceous collision of an east-facing Mergui-western Myanmar island arc with the Shan Plateau, and early Tertiary metamorphism in the MMB related to reversal in tectonic polarity following the arc-Plateau collision.     

Delivery of transuranic elements by rain to the Mediterranean Sea

The concentrations of ²³⁸Pu, ^{239 + 240}Pu, ²⁴¹Am and ¹³⁷Cs were determined in rain samples collected at Monaco in the course of 1978–1979. Based on these data, the annual deliveries of these radionuclides to the Mediterranean by rain are computed to be 0.18 ± 0.01 pCim^?2 for ²³⁸Pu, 8.1 ± 0.1 pCim^?2 for ^{239 + 240}Pu, 0.58 ± 0.02 pCim^?2 for ²⁴¹Am and 351 ± 4 pCim^?2 for ¹³⁷Cs.Comparing the delivery data with the mixed layer inventories of ^{239 + 240}Pu and ²⁴¹Am in the Mediterranean, the upper limits of the mean residence time of these radionuclides in the mixed layer were estimated to be 12.3 yr for ^{239 + 240}pu and 2.9 yr for ²⁴¹Am. These values are consistent with the conclusion deduced from the vertical distribution pattern of these transuranic elements in the Mediterranean.Based on delivery values, the annual activity ratios for ${}^{238}\text{pu}{}^{\mathrm{239\; +\; 240}}\text{Pu}$, ${}^{241}\text{Am}{}^{\mathrm{239\; +\; 240}}\text{Pu}$ and ${}^{\mathrm{239\; +\; 240}}\text{pu}{}^{137}\text{Cs}$ are found to be 0,022, 0.072 and 0.023 respectively. The ${}^{238}\text{pu}{}^{\mathrm{239\; +\; 240}}\text{pu}$ and ${}^{\mathrm{239\; +\; 240}}\text{Pu}{}^{137}\text{Cs}$ activity ratios vary within relatively narrow ranges with time, while a much wider variation was observed for the ${}^{241}\text{Am}{}^{\mathrm{239\; +\; 240}}\text{Pu}$ activity ratio. The cause of the wider variation of the ${}^{241}\text{Am}{}^{\mathrm{239\; +\; 240}}\text{Pu}$ ratio may be related to the difference in the mean age of fallout brought down in different seasons.     

Geology of the High Sulfidation Copper Deposits,Monywa Mine,Myanmar

The 50 km² Monywa copper district lies near the Chindwin River within the northward continuation of the Sunda‐Andaman magmatic arc through western Myanmar. There are four deposits; Sabetaung, Sabetaung South, Kyisintaung, and the much larger Letpadaung 7 km to the southeast. Following exploration drilling which began in 1959, production of copper concentrates from a small open pit started at Sabetaung in 1983. Since 1997, when resources totaled 7 million tonnes contained copper in 2 billion tonnes ore, a heap leach–electro‐winning operation has produced over 400,000 t copper cathode from Sabetaung and Sabetaung South. Ore is hosted by mid‐Miocene andesite or dacite porphyry intrusions, and by early mid‐Miocene sandstone and overlying volcaniclastics including eruptive diatreme facies which the porphyries intrude. District‐wide rhyolite dykes and domes with marginal breccias probably post‐date andesite porphyries in the mine area and lack ore‐grade copper. Host rocks to mineralization are altered to phyllic and advanced argillic hydrothermal assemblages within an outer chlorite zone; hypogene alunite is most abundant at Letpadaung and Kyisintaung. Most mineralization is structurally‐controlled with digenite‐chalcocite in breccia dykes, in steeply dipping NE‐trending sheeted veins, and in stockwork and low‐angle sulfide veins. A high‐grade pipe at Sabetaung grades up to 30% Cu, and much of the ore at Sabetaung South is in a NE‐trending zone of mega‐breccia and stockworked sandstone. The hydrothermal alteration, together with replacement quartz, alunite and barite in breccia dykes and veins, the virtual absence of vein quartz, and the presence of chalcopyrite and bornite only as rare veins and as inclusions within the abundant pyrite, indicate that the deposits are high sulfidation. Regional uplift, resistance to erosion and leaching of the altered and mineralized rocks have resulted in porous limonite‐stained leached caps over 200 m thick forming the Letpadaung and Kyisintaung hills. The barren caps pass abruptly downwards at the water table into the highest grade ore at the top of the supergene enrichment zone, within which copper grade, supergene kaolinite and cubic alunite decrease, and pyrite increases with depth; in contrast, marcasite is mostly shallow. Much of the copper to depths exceeding 200 m below the water table occurs as supergene digenite‐chalcocite and minor covellite. Disseminated chalcocite is mostly near‐surface and hence almost certainly supergene. We infer that during prolonged uplift at all four deposits, oxidation of residual pyrite at the water table generated enough acid to leach all the copper from earlier supergene‐enriched ore; below the water table the resulting acid sulfate solutions partly replaced enargite, covellite, chalcopyrite, bornite and pyrite with supergene chalcocite. Undeformed upward‐fining cross‐bedded conglomerates and sands of the ancestral Chindwin River floodplain overlie the margins of the Sabetaung deposits, form a major aquifer up to 40 m thick, and are a potential host for exotic copper mineralization. A mid‐Miocene pluton is inferred to underlie the Monywa deposits, but the possibility of porphyry‐type mineralization within the district is at best highly speculative.     

Geochemische Trends in der Minette (Jura,Luxemburg/Lothringen)

Zusammenfassung Aus 19 Profilen der eisenoolith-führenden Minette (Toarcium-Aalenium), ihrem Liegenden (Toarcium) und Hangenden (Bajocium), sowie aus dem erzführenden Aalenium der Vorbergzone des Schwarzwaldes wurden an 1253 Proben folgende Elemente und der HCl/HNO₃ — unlösliche Rückstand ( SiO₂) bestimmt: Na, Mg, Al, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Fe²⁺, Co, Ni, Cu, Zn, As, Sr, Ba und Pb. Die Auswertung des umfangreichen Datenmaterials erfolgte mit Hilfe verschiedener multivariater statistischer Verfahren. Es zeichnen sich stratigraphische und regionale Trends ab, die im Zusammenhang mit der Genese der Lagerstätte diskutiert werden. Die Eisenooide sind in Latosolen auf dem Festland entstanden und wie bei Lagerstätten des Salzgitter-Typs als klastische Abtragungsprodukte lateritischer Verwitterungsdecken ins Meer verfrachtet worden. Auf einem ausgedehnten Schelfareal wurden die Erzkörner in flachem Wasser mehrfach umgelagert, sortiert und schließlich als marine Seife konzentriert. Auch andere mesozoisch-känozoische Lagerstätten des Minette-Typs sind wahrscheinlich auf diese Weise entstanden. Das Modell erklärt Herkunft und Transport des Eisens auf aktualistische Weise und steht im Einklang mit bekannten geochemischen Befunden, wonach sowohl in Lateriten als auch in Minette-Erzen die Elemente Al, Si, Ti, V, Cr, Mn und P als Begleiter des Eisens auftreten.

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Summary On 1253 samples of 19 vertical sections from the oolitic Minette ironstone (Toarcian — Aalenian, Luxemburg, Lorraine), its under- and overlying beds and from the aalenian oolitic ironstone of the Freiburg region, the following elements have been analysed: Na, Mg, Al, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Fe²⁺, Co, Ni, Cu, Zn, As, Sr, Ba, Pb and the insoluble residu in HCI/HNO₃. Data processing has been accomplished by different methods of multivariate statistics. The results show stratigraphical and regional trends which are discussed in connexion with the genesis of the ore deposit. We believe, that the iron oolites derive from latosols of continental areas. After erosion of the lateritic caprock the oolitic grains were transported into thes ea. The iron ore particles were then winnowed in shallow marine water to be finally concentrated as a marine placer — similar to the Lower Cretaceous iron ores of Salzgitter, Lower Saxony. Other mesozoic to cainozoic deposits of the Minette-type have probably been formed in the same manner. This model explains in a simple and actuogeological way the origin and transport of iron and is fully compatible with the wellknown occurence of the elements Al, Si, Ti, V, Cr, Mn and P, accompanying the iron in laterites as well as in Minette-type ores.

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Résumé Les éléments Na, Mg, Al, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Fe²⁺, Co, Ni, Cu, Zn, As, Sr, Ba, Pb et le résidu insoluble à HCl/HNO₃ ont été analysés sur 1253 échantillons, soit 19 coupes du minerai de fer oolithique toarcien — aalénien de la minette, de son mur et de son toit ainsi que des couches aaléniennes de la région de Fribourg. Le grand nombre des données a été traité à l'aide de méthodes différentes de la statistique multivariable. Il en résulte des tendances stratigraphiques et régionales qui sont discutées en rapport avec la genèse du minerai. Les oolithes ont pris naissance dans des sols latéritiques sur le continent et ont été transportées ensuite au cours de l'érosion comme produits détritiques dans la mer (comparable aux minerais du type Salzgitter). Sur un vaste shelf peu profond les grains de minerai ont été déplacés plusieurs fois pour Être enfin concentrés à la faÇon de placers marins. Pendant les temps mésozoiques et cénozoiques d'autres gÎtes oolithiques stratiformes du type minette se sont peut-Être formés de la mÊme manière. Ce modèle de formation explique de faÇon simple et actuelle la provenance et le mode de transport du fer et correspond avec des résultats géochimiques connus d'après lesquels des éléments Al, Si, Ti, V, Cr, Mn et P accompagnent le fer aussi bien dans des latérites que dans des minerais de fer du type minette.

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1253 19- ToarciumAalenium. (Toarcium) (Bajocium) Aafenium : Na, Mg, Al, , S, , , , V, Cr, Mn, Fe, Fe²⁺, , Ni, Cu, Zn, As, Sr, Pb , NCl/HNO₃, .. . . ; . — — , . , , , . - . , , . : Al, Si, , V, Cr, Mn, P

     

Sedimentationsabläufe im Atlas-Golf (Kreide Küstenbecken Marokko)

The Geological Institute of Bonn University since 1975 investigates in connection with DSDP/IPOD the Cretaceous of the Atlantic coastal basin in south-western Morocco. 30 main stratigraphic sections and numerous auxiliary ones were taken along several traverses, running along distances of 150 to 200 km in west-east direction. The recognized epicontinental facies-pattern along the traverse of the southern High Atlas mountain range depicts clearly, that we cut here the critical region of intertonguing marine, fine-clastic-carbonaceous sediments and continental detritic deposits. The littoral zone successively progrades with three major transgressions (Neocomian, Upper Aptian, Turonian) towards the African Continent. Sedimentation processes, stratigraphy, paleomagnetics, geochemistry, sedimentology and paleogeography are investigated, taking selected horizons on one hand and complete stratigraphic columns on the other. A new sedimentation model reflecting transgression and regression events in the Cretaceous “Atlas Gulf” show some probabilities of eustatic sea-level changes. There are similarities between the Atlas Gulf and other coastal basins on both sides of the Atlantic Ocean. There are certain relations between the sedimentary record of the proand regrading littoral zone on the continent and in the nearby deep sea deposits. There is an exciting coincidence between the stratigraphie succession of the downwarping Atlas Gulf and the sedimentary cover of the interior of Africa, especially the Mesozoic Sahara Basin.     

Geochemical element balance during tropical weathering. Hercynian Rheinisches Schiefergebirge (Germany): a case study

Introduction The Rheinisches Schiefergebirge, the northern,non metamorphic part of the Hercynian orogen in Middle Europe is one of the most excellent examples of a stable continental area, deeply weathered under a tropical to subtropical climate during upper Mesozoic and especially Paleogene periods.     

The emergence of multiplex dynamics between information provision ties and rescue collaboration ties: a longitudinal network analytic approach to flooding cases in Myanmar

Natural Hazards - In disaster response processes, collaborations among multiple organizations are vital for effective disaster management. This study examined how multiplex ties concerning...