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51.
Peter Neumayr John Walshe Steffen Hagemann Klaus Petersen Anthony Roache Peter Frikken Leo Horn Scott Halley 《Mineralium Deposita》2008,43(3):363-371
Hydrothermal sulfide–oxide–gold mineral assemblages in gold deposits in the Archaean St. Ives gold camp in Western Australia
indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time. Reduced
alteration assemblages (pyrrhotite–pyrite) occur in deposits in the southwest of the camp (e.g., Argo, Junction deposits)
and moderately to strongly oxidized assemblages (magnetite–pyrite, hematite–pyrite) occur in deposits in the Central Corridor
in the northeast (e.g., North Orchin, Revenge deposits). Reduced mineral assemblages flank the Central Corridor of oxidized
deposits and, locally, cut across it along E–W trending faults. Oxidized mineral assemblages in the Central Corridor are focused
on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1,000 m below present surface.
Hydrothermal magnetite predates and is synchronous with early phases of gold-associated albite–carbonate–pyrite–biotite–chlorite
hydrothermal alteration. Later-stage, gold-associated pyrite is in equilibrium with hematite. The spatial distribution and
temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly
synchronous hydrothermal fluids with contrasting redox states. Sulfur isotope constraints support the argument that the different
mineral assemblages reflect differences in redox conditions. The δ
34S values for pyrite for the St. Ives gold camp range between −8.4‰ and +5.1‰ with the negative values occurring in oxidized
magnetite-rich domains and slightly negative or positive values occurring in reduced, pyrrhotitic domains. Preliminary spatial
and paragenetic analysis of the distribution of iron sulfides and oxides in the St. Ives camp suggests that gold grades are
highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite–pyrite
to relatively oxidized magnetite–pyrite and hematite–pyrite both in space and time. Gold deposition is inferred to have occurred
where fluids of contrasting redox state mixed. 相似文献
52.
2014年云南鲁甸地震触发地质灾害发育分布规律及与景谷、盈江地震对比研究 总被引:6,自引:0,他引:6
2014年8月3日16时30分,云南省鲁甸县龙头山镇Ms 6.5级地震造成617人死亡,触发1700多处崩塌滑坡等地质灾害点,同年,该省又发生了Ms 6.6级景谷地震和Ms 6.1级盈江地震。笔者在对鲁甸等3次地震区次生地质灾害现场调查和遥感解译的基础上,研究了鲁甸地震触发地质灾害的发育分布规律,首次提出了地震“干滑坡”的概念,并从震级、地形地貌、活动构造、人口密度等多个方面对比了鲁甸地震、景谷地震和盈江地震触发地质灾害的异同点。主要结论有:(1)鲁甸地震后新增地质灾害数量显著增加,其主要分布在水系的深切峡谷区,表现为“干滑坡”特征;(2)大型、特大型崩塌滑坡灾害点主要受活动断裂控制;(3)地震地质灾害的发育特征与地貌高程和微地貌具有很好的响应关系;(4)鲁甸震区的地形坡度明显大于景谷和盈江震区,地形坡度是鲁甸地震区地质灾害发育的主要控制因素;(5)我国西南高山峡谷区的断层、河流、阶地和城镇是相互依存,不可分割的地质环境载体,震后房屋选址、重建规划不仅要注意房屋抗震问题,还应充分考虑地质环境安全问题。 相似文献
53.
This article deals with the morpho- and lithodynamic role of ice in shaping the Arctic coasts. Taking the Pechora Sea as an example, the direct and indirect impact of ice on the sea floor and shores is described. Active gouging by ice floes, ice-rafting of sedimentary material, formation of strudel scour depressions and frozen rocks on shallows are all direct impacts. The indirect impact of ice that arrests the coastal zone for most of the year is a considerable reduction of the overall energy of waves and currents. Based on the performed analysis, we plot a schematic zonation of the Pechora Sea according to the probable impact of ice on the shores and seafloor. 相似文献
54.
DEM分辨率对小流域地形水文特征提取的影响 总被引:1,自引:0,他引:1
基于ArcGIS水文分析工具研究DEM分辨率对提取流域地形和水文参数的影响,选择黄土丘陵沟壑区典型小流域—韭园沟流域为实验区,该流域地形复杂,沟壑纵横,DEM分辨率变化对其地形表达有很大影响。研究表明,DEM分辨率对小流域面积、流域高程、坡向的表达或提取精度影响较小,而对坡度、河道长度、河网密度和河道分级等因子提取有较大影响。 相似文献
55.
Distinguishing between natural and aquaculture-derived sediment concentrations of heavy metals in the Broughton Archipelago, British Columbia 总被引:5,自引:0,他引:5
Marine sediment samples were collected in the Broughton Archipelago, British Columbia, to assess the use of a geochemical normalization technique in the identification of a chemical tracer of aquaculture waste material. Zinc and copper were suggested as tracers of feed pellets, while copper was considered an indicator of anti-foulant agents used on netpen systems. The sediment samples were analyzed for carbon, nitrogen, organic matter, water, trace-element, and free sulfide concentrations, and sediment grain-size distribution. Sediment texture analysis revealed a wide range of substrate types from sand to silty loam categories. Strong relationships between sediment texture, sediment porosity, and organic content were observed across both near-field and far-field stations. Excess zinc and copper sediment concentrations, identified using a lithium-normalization technique, were restricted to near-field sampling stations (0 and 30m from netpen systems). The relationships between these metal tracers and organic content and sulfur concentrations were explored to account for variations in sediment concentrations of zinc and copper. 相似文献
56.
Marie Maar Karsten Bolding Jens Kjerulf Petersen Jrgen L.S. Hansen Karen Timmermann 《Journal of Sea Research》2009,62(2-3):159
The development of off-shore wind farms along the coastline of north-west Europe is rapidly increasing; it is therefore important to study how this will affect the marine environment. The present study modelled the growth and feed-backs of blue mussels in natural beds and on turbine foundations in an off-shore wind farm (OWF) located in a shallow coastal ecosystem by coupling a dynamic energy budget (DEB) model to a small-scale 3D hydrodynamic–biogeochemical model. The model results showed that blue mussels located higher up in the water column on turbine pillars achieved a 7–18 times higher biomass than those located on the scour protection because the former experience an enhanced advective food supply. Secondly, the high biomasses of blue mussels on foundations created local ‘hot spots’ of biological activity and changed ecosystem dynamics due to their feed-backs e.g. ingestion of microplankton and copepods, excretion of ammonium and egestion of faecal pellets. The model results were supported by field measurements around foundations of Chl a concentrations and biomasses of the fauna community. Our study emphasised that OWFs seem to be particularly favourable for blue mussels in the western Baltic Sea and that the functioning of the OWFs as artificial reef ecosystems depends upon how the blue mussels interact with their local pelagic and benthic environment. 相似文献
57.
丹宁棉分离富集—发射光谱法同时测定地质样品中微量铌钽锆铪 总被引:1,自引:1,他引:1
采用丹宁棉对地质样品溶液中的铌、钽、锆、铪进行分离富集,将写信后的丹宁棉在600℃灼烧30min,灰分用发射光谱法同时测定四元素。检出限与通常的发射光谱法相比降低约2个数量级,经国家级标准物质检验,结果与标准值相符,精密度试验,各元素的RSD(n=20)为2.6%-7.9%。 相似文献
58.
59.
Jon Steen Petersen 《Contributions to Mineralogy and Petrology》1980,73(2):161-172
Quantitative analysis of REE distribution in differentiated, clearly intrusive charnockites from southwest Norway, reveal extreme variation in both absolute abundances and fractionation patterns. The pyroxene-bearing, charnockitic facies show uniform REE patterns with slight enrichment of the light-REE (about 150x chondrites) and positive, neutral or negative Eu-anomalies. Subsequent amphibole-bearing, adamellitic facies show progressive, preferential enrichment of light-REE, reaching La-values higher than 500x chondrites, and increasingly negative Euanomalies. Finally, highly differentiated biotite-granites show a marked depletion of ight-REE, ending with chondrite-normalized La/Lu ratios about 1 and Eu/ Eu* ratios less than 0.2.Using geochemical model calculation, relating major element variations between three main stages of differentiation in terms of refractory mineral assemblages, stepwise quantitative modelling of the REE distributions reproduces the observed changes, and support an origin of the charnockite series as progressively fractionated residual liquids.Close similarity with the REE patterns of charnockite-rapakivi suites elsewhere implies that these may constitute a series of co-magmatic rocks, derived from related more basic source magmas. The fact that the least differentiated members of the series, the charnockites, generally display remarkably uniform REE-patterns, suggests that they equilibrated with a refractory crystal fraction that produces a uniform, bulk partition coefficient. The present analysis suggests that this would be plagioclase and orthopyroxene in a ratio of about 41 and including minor apatite, which in turn points towards affinity with potentially plagioclase-rich cumulates. 相似文献
60.
Al- and Mg-doped titanomagnetites were synthesized at 1300°C using the gas-mixing technique. A composition, representative of average natural titanomagnetites in ocean floor basalts, was sought.
The samples were ball-milled in acetone to average grain sizes of 0.5 μm and 5 μm and the material was then oxidised, in air, at temperatures below 300°C. This procedure formed titanomaghemite, a cation-deficient titanomagnetite.
Low-temperature oxidation is described as the diffusion of Fe-ions out of the spinel lattice and the process is observed to be distinctly dependent upon grain size. 相似文献