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J. Ostwald 《Mineralium Deposita》1992,27(4):326-335
The Mary Valley manganese deposits exhibit mineralogy and textures characteristic of at least four parageneses. The deposits consist mainly of isolated occurrences of braunite, together with a number of lower and higher valency manganese oxides, and manganese silicates, in bedded radiolarian cherts and jaspers of Permian age. The parageneses are: (a) Braunite — quartz (primary), (b) Braunite — hausmannite — spessartine — tephroite — quartz (metamorphic). (c) Hydrated manganese silicates — barite — braunite — hausmannite (hydrothermal veins), (d) Tetravalent manganese oxides (pyrolusite, cryptomelane, manjiroite, nsutite) (supergene). The primary mineralisation is interpreted as the result of the geochemical separation of Mn from Fe in a submarine exhalative system, and the precipitation of Mn as oxide within bedded radiolarian oozes and submarine lavas. During diagenesis this hydrothermal manganese oxide reacted with silica to produce primary braunite. The later geological of evolution of this volcanogenicsedimentary deposit involved metamorphism, hydrothermal veining by remobilised manganese, and supergene enrichment. 相似文献
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Eskil Mattsson Madelene Ostwald S.P. Nissanka Björn Holmer Matilda Palm 《Ocean & Coastal Management》2009,52(1):1-9
By using an integrated approach, tsunami affected land, vegetation and inhabitants were assessed to evaluate the potential to restore and protect coastal land in the context of Kyoto Protocol's Clean Development Mechanism in Hambantota district in the south-eastern part of Sri Lanka. Firstly, assessments of the status of the tsunami affected area were carried out by collecting soil and well water samplings for carbon and salinity analysis. Secondly, identification of potential tree species for carbon sequestration and sustainable development was conducted to determine carbon stock and suitability to grow under the prevailing conditions. In addition, interviews to understand the local people's perception of forest plantations and land use were conducted. The results showed that the resilience process of salt intruded lands from the 2004 Asian tsunami has progressed rapidly with low salinity level in the soils 14 months after the event, while the well water showed evidence of salinity contamination. The carbon stock was highest in natural forests followed by coconut plantations. Land users could envision expanding their present plantations or establish new ones. The barriers were defined as lack of financial investment capital and limited land for extended plantations. If a Clean Development Mechanism project is to be established, the coconut tree was found to be the most appropriate tree species since it has high carbon content, had co-benefits and possesses a salt-tolerant characteristic. Finally, the tsunami event has triggered land users to perceive environmental benefits of protection from mangrove or other adequate vegetation such as coconut plantations as welcome and desired to decrease their vulnerability. The assessment of multi-functionality of forest plantations, such as small-scale community based Clean Development Mechanism, its generated income from carbon credits as well as the wish for environmental protection should be considered to increase the attractiveness of plantation projects in the coastal areas. 相似文献
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The Kajlidongri manganese deposit, Madhya Pradesh, India contains braunite belonging to at least two different parageneses, i.e. a fine-grained, metamorphic type and a younger, coarser-grained, hydrothermal type. Microanalyses of braunite from these paragenetic types indicate considerable variations in iron content from zero to 32.7% Fe3O3, which the writers consider is due to varying proportions of braunite I and bixbyite modules in polysomatic braunite. 相似文献
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J. Ostwald 《Mineralium Deposita》1993,28(3):198-209
Supergene manganese oxides, occurring in shales, breccias and dolomites of Proterozoic Age, in the Western Australian Pilbara Manganese Group, have Mn/Fe ranging from 1.9 to 254 and Mn4+ to Mn (Total) of 0.49–0.94. The manganese mineralogy is dominated by tetravalent manganese oxides, especially by cryptomelane, with lesser amounts of pyrolusite, nsutite, manjiroite, romanechite and other manganese oxide minerals. The manganese minerals are commonly associated with iron oxides, chiefly goethite, indicating incomplete separation of Mn from Fe during Tertiary Age arid climate weathering of older, manganiferous formations. These manganese oxides also contain variable amounts of braunite and very minor hausmannite and bixbyite. The braunite occurs in three generations: sedimentary-diagenetic, recrystallised sedimentary-diagenetic, and supergene. The mode of origin of the hausmannite and bixbyite is uncertain but it is possible that they resulted from diagenesis and/or low-grade regional metamorphism. The supergene manganese deposits appear to have been derived from manganiferous Lower Proterozoic banded iron formations and dolomites of the Hamersley Basin and overlying Middle Proterozoic Bangemali Basin braunite-containing sediments. 相似文献
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J. Ostwald 《Mineralium Deposita》1975,10(1):1-12
The manganese ores on Groote Eylandt occur in a flat-lying horizon in a series of Lower Cretaceous sands and clays which overly unconformably the Middle Proterozoic sandstone basement. The ore horizon exhibits a variety of textural and compositional ore types. Textural types include pisolites and concretions, either free or cemented into massive, bouldery or pebbly horizons. Compositional variations result from varying degrees of admixture of the manganese materials with the sands and clays of the formation. — The ore minerals are pyrolusite and cryptomelane, with minor amounts of lithiophorite, psilomelane, nsutite and todorokite. Gangue minerals include kaolinite, quartz and goethite. — Mineralogical studies indicate that three microtypes of cryptomelane occur. Low levels of cobalt, nickel and zinc in certain of the ore types are associated with the mineral lithiophorite. 相似文献
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Pyrite masses composed of compacted pyrite framboids in chalcedony in weathered andesites at Allandale, New South Wales, Australia, show evidence of colloidal origin and contemporaneous deposition of pyrite and silica. Free framboids and framboidal clusters in the chalcedony show indications of crystallization into pyrite polyhedra and pyrite octahedra. 相似文献
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Climate Variability and Land-use Change in Danangou Watershed, China—Examples of Small-Scale Farmers' Adaptation 总被引：2，自引：0，他引：2
Johanna Hageback Jenny Sundberg Madelene Ostwald Deliang Chen Xie Yun Per Knutsson 《Climatic change》2005,72(1-2):189-212
With global concern on climate change impacts, developing countries are given special attention due their susceptibility.
In this paper, change and variability in climate, land use and farmers' perception, adaptation and response to change are
examined in Danangou watershed in the Chinese Loess Plateau. The first focus is to look at how climate data recorded at meteorological
stations recently have evolved, and how farmers perceived these changes. Further, we want to see how the farmers respond and
adapt to climate variability and what the resulting impact on land use is. Finally, other factors causing change in land use
are considered. Local precipitation and temperature instrumental data and interview data from farmers were used. The instrumental
data shows that the climate is getting warmer and drier, the latter despite large interannual variability. The trend is seen
on the local and regional level. Farmers' perception of climatic variability corresponds well with the data record. During
the last 20 years, the farmers have become less dependent on agriculture by adopting a more diversified livelihood. This adaptation
makes them less vulnerable to climate variability. It was found that government policies and reforms had a stronger influence
on land use than climate variability. Small-scale farmers should therefore be considered as adaptive to changing situations,
planned and non-consciously planned. 相似文献
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Deep sea manganese nodules from the Southern Ocean have been studied using chemical analysis, X-ray diffraction, optical mineragraphic and electron probe microanalysis techniques. The nodules were lower in manganese, iron and associated elements than the average grade of manganese nodules from other localities. A number of chemical relationships have been observed. Nickel, copper, cobalt, barium, zinc, molybdenum, strontium, sulphur and phosphorus are associated with the manganese rich phases and titanium with the iron rich phases. X-ray diffraction analysis and electron probe microanalysis results indicate that the manganese phases are similar to the disordered -MnO2 and manganite phases reported by other workers.
Zusammenfassung Tiefsee-Manganknollen aus dem südlichen Ozean wurden mit Hilfe von chemischen Analysen, Röntgenbeugung, mikroskopischer Untersuchung und Anwendung von Mikroelektronensonden untersucht. Die Knollen enthielten weniger Mangan, Eisen und Begleitelemente als das Durchschnittsquantum in Manganknollen aus anderen Gebieten. Eine Anzahl chemischer Ähnlichkeiten wurde beobachtet. Nickel, Kupfer, Kobalt, Barium, Zink, Molybdän, Strontium, Schwefel und Phosphor treten gemeinsam mit den manganreichen Erscheinungsformen, und Titan zusammen mit den eisenreichen auf. Ergebnisse der Röntgenbeugungsanalyse und Mikroelektronensondenuntersuchung ergaben, daß die Manganphasen Ähnlichkeit haben mit ungeordneten -MnO2 und manganitischen Erscheinungsformen, über die andere Wissenschaftler berichtet haben.相似文献
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