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In the Chindwin Basin in northern Burma, there is a system of five Pleistocene terraces in which gold placers with low concentrations of platinum-group minerals (PGM) occur. Samples were taken from four sites in the Chindwin Basin and one from near an ophiolite occurrence on the northeast side of the Chindwin Basin; they were studied under the microscope, with a scanning electron microscope, and an electron microprobe. The main minerals were Pt-Fe and Os-Ir-Ru alloys, usually in a ratio between 2 and 5. In most cases, the shape of the grains allowed a quick distinction between the two types. Sperrylite, laurite, irarsite, cooperite, tulameenite, and isomertieite occur infrequently as individual mineral grains and sometimes as inclusions in the alloy grains. Braggite, platarsite, hollingworthite, bowieite, keithconnite, cuproiridsite, malanite, stibiopalladinite, geversite, kashinite, several unnamed PGM, and Fe, Ni, and Cu sulfides were observed as inclusions, mainly in the Pt-Fe alloys and also to a lesser extent in the Os-Ir-Ru alloys. Lamellar and myrmekite-like intergrowths, oriented exsolution lamellae, and idiomorphic inclusions of sulfides in the alloys indicate a magmatic origin of the PGM. The origin of the PGM is assumed to be ophiolites in northern Burma. A continual decrease in mean grain size occurred during transport.
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Platingruppenminerale in quartären Goldseifen im oberen Chindwingebiet in Nord-Burma
Zusammenfassung Im Gebiet des Chindwin Basin in Nordburma ist ein System von fünf pleistozänen Terrassen ausgebildet, in denen Goldseifen mit geringen Anteilen an PGM auftreten.PGM-Konzentrate von vier Vorkommen des Chindwin Basin und eine weitere Probe aus der Nähe eines Ophiolithvorkommens im Nordosten des Chindwin Basin wurden mit optischer Mikroskopie, Rasterelektronenmikroskopie und Mikrosonde untersucht.Hauptmineralien sind Pt-Fe-Legierungen und Os-Ir-Ru-Legierungen in einem Verhältnis von 2: 1 bis 5: 1. Ihre Morphologie kugeliger oder plattiger, teilweise idiomorpher Körner erlaubt in den meisten Fällen eine rasche Identifizierung der beiden Typen. Sehr selten treten als Einzelminerale, aber auch als Einschlüsse in Legierungen, Sperrylith, Laurit, Irarsit, Cooperit, Tulameenit und Isomertieit auf. Braggit, Platarsit, Hollingworthit, Bowieit, Keithconnit, Cuproiridsit, Malanit, Stibiopalladinit, Geversit, Kaschinit, einige unbekannte PGM und Fe-, Ni- und Cu-Sulfide wurden nr als Einschlüsse, hauptsächlich in Pt-Fe-Legierungen, weniger in Os-Ir-Ru-Legierungen, beobachtet.Lamellare und myrmekitische Verwachsungen, orientierte Entmischungen und idiomorphe Einschlüsse von Sulfiden in Legierungen weisen auf eine magmatische Entstehung der PGM hin. Die Herkunft der PGM wird in Ophiolithen Nordburmas vermutet. Beim Transport hat eine kontinuierliche Abnahme der mittleren Korngrösse stattgefunden.
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Rock relationships in the Mogok metamorphic belt, Tatkon to Mandalay, central Myanmar 总被引：5，自引：0，他引：5
A.H.G. Mitchell Myint Thein Htay Kyaw Min Htun Myint Naing Win Thura Oo Tin Hlaing 《Journal of Asian Earth Sciences》2007,29(5-6):891-910
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. 相似文献
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Myanmar is located in Southeast Asia within the Mekong River Basin. The estimated annual surface and groundwater potentials are 1 081 km3 and 494 km3, respectively. Based on geological conditions, 11 different types of aquifers have been classified in Myanmar. The recent alluvial formation, Irrawaddy formation, Upper Pegu Group and Plateau limestone formation are the major water-bearing geologic formations of the country. In Myanmar, 89% of the groundwater is used for agriculture, approximately 8% is used for domestic consumption, and 3% is used for industrial purposes. Climate change projections for Myanmar from 2001 to 2100 predict general increases in temperature, clear-sky days, rainfall variability and flooding risks and a greater occurrence and intensity of extreme weather events across the country. Additional technology and investments are required to achieve groundwater resource security in response to climate changes. In addition, methods of ensuring the sustainability of groundwater resources must be implemented via collaborations with other countries and international sources. 相似文献
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General characteristics of macrobenthos of the muddy sediments of the subtidal (19–24 m) zone in Nha Trang Bay (South Vietnam) were described based on the survey performed in April–May 2002. The mean abundance of organisms was 637 ind/m2 and the mean biomass was 2.3 g/m2. Sixty-seven macrobenthic species were found during the study. The main structural features of the macrobenthos were high species diversity, low species recurrence, and high eveness of the species structure with the absence of clearly manifested dominants. The number of species encountered regularly increased with the increase in the total area sampled from 210 to 5000 cm2, though the relation did not reach saturation. The similarities and differences between the macrobenthos structures in Nha Trang Bay and those in some tropical and boreal soft-bottom communities are discussed. 相似文献
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Andrew H. G. Mitchell Win Myint Kyi Lynn Myint Thein Htay Maw Oo Thein Zaw 《Resource Geology》2011,61(1):1-29
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. 相似文献
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Nyein N. Sint Kotaro Yonezu Thomas Tindell May T. Aye Htay Win Akira Imai Koichiro Watanabe 《Resource Geology》2019,69(1):85-106
The Shwe Min Bon Cu–Au skarn deposit lies within one of the largest Au–Cu belts in Myanmar. The deposit is situated along the Shan scarp zone, which marks the boundary between the Myanmar central basin to the west and the Shan plateau to the east. The Shwe Min Bon deposit comprises skarn‐type metasomatic alteration, and the Cu–Au mineralization occurs along the contact face between the Nwabangyi Dolomite and Shweminbon Formation and the Cretaceous dioritic rocks. The metasomatic process resulted in pro‐ and retrograde mineral assemblages in exoskarn. Hydrothermal activities in the Shwe Min Bon deposit are classified into prograde, retrograde stage I, and retrograde stage II. The prograde skarn is classified into a proximal garnet skarn with minor clinopyroxene and a distal wollastonite skarn. Chlorite, epidote, and tremolite–actinolite were formed during the retrograde stage I. Cu–Au mineralization mainly occurred in retrograde stage I, which was characterized by moderate temperatures (260–320 °C) and fluid with a moderate salinity (5.0–6.0% NaCl equiv.). Low temperature (180–200 °C) and low salinity (2.0–3.0% NaCl equiv.) were responsible for retrograde stage II. Au mineralization is mainly associated with chalcopyrite and tennantite in retrograde stage I and with tellurobismuthite in retrograde stage II. 相似文献
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Abstract. Gold mineralization at Kyaukpahto occurs as a stockworks/dissemination style with localized breccia zones in silicified sandstones of the Male Formation (Eocene). The mineralization appears to be closely associated with NNE-SSW trending extensional faults probably related directly to the dextral movement of the Sagaing Fault system. Intense silicifica-tion associated with sericitization, argillic alteration and decalcification is recognized in the Kyaukpahto gold deposit. The important ore minerals associated with the gold mineralization are pyrite, arsenopyrite and chalcopyrite with minor amounts of other sulfides. Gold occurs as free particles or locked with pyrite, arsenopyrite, chalcopyrite and tetrahedrite. Silver, copper, arsenic and antimony particularly appear to be good pathfinders and the best geochemical indicators of gold mineralization at Kyaukpahto. Electron microprobe analysis indicates that the fineness for the native gold ranges from 844 to 866. Present geological, mineralogical and geochemical investigations demonstrate that the Kyaukpahto gold deposit has been formed as a result of hydrothermal processes in a shallow level epithermal environment. 相似文献
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The effects of induced anisotropy on the undrained behaviour of very loose and saturated sands have been a subject of intensive investigation, both experimentally and theoretically, by several authors in the past few years. This paper proposes an original constitutive model well‐adapted to simulate the behaviour of sands subject to complex stress histories, in particular, the preloading cycle along the classical drained stress path in compression. The developed model belongs to the family of critical state models. Its construction is based on a few theoretical concepts taken from the theory of ‘Bounding Surface Plasticity’ developed among others by Y. Dafalias and Popov (1975), the ‘Clay And Sand Model’ (CASM) of H. Yu (2006), the CJS model (B. Cambou and K. Jafari (1988)) and the hyperelastic isotropic model of P. Lade (1987). To accurately simulate volume changes, which represent a key element in soil behaviour, a state‐dependent dilatancy rule is proposed, which can account for the influences of stress and void ratio. The current void ratio depends implicitly on the irreversible strains already accumulated hence the strain history. A kinematic hardening is combined with an isotropic hardening, involving rotation and distortion of the bounding surface, in order to capture correctly the experimental observations. Comparisons of experimental results to numerical simulations show that the model is able to simulate with a good precision the major trends of undrained responses of loose and presheared sands. It predicts correctly rapid static liquefaction at small or null drained preloading, as well as the progressive transition to a completely stable behaviour typical of dense sands, while the sample is loose in reality. At intermediate to large amplitudes of preloadings, the model also predicts correctly the temporary stage of instability when the deviatoric stress decreases slightly before rising up again. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Than Vinh-Du Aimedieu Patrick Pereira Jean-Michel Roux Jean-Noël Tang Anh Minh 《Acta Geotechnica》2020,15(5):1039-1055
The behavior of model granular materials (glass beads) wetted by a small quantity of liquid forming capillary bridges is studied by one-dimensional compression test combined with X-ray computed tomography (XRCT) observation. Special attention is paid to obtain very loose initial states (initial void ratio of about 2.30) stabilized by capillary cohesion. XRCT-based analyses involve spherical particle detection adapted to relatively low-resolution images, which enable heterogeneities to be visualized and microstructural information to be collected. This study on an ideal material provides an insight into the macroscopic compression behavior of wet granular materials based on the microstructural change, such as pore distance distribution, coordination number of contacts, coordination number of neighbors and number of contacts per grain.
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