矿化信息提取的混合蚀变遥感模型——以鹰嘴山金矿区为例   总被引：12，自引：0，他引：12  

杨波  吴德文  陈云浩  李京  朱谷昌 《国土资源遥感》2005,16(1):20-25

在围岩蚀变类型丰富、成矿作用复杂的甘肃省鹰嘴山金矿区,依据矿化蚀变岩与其围岩的波谱特征差异,通过对地面实测光 谱数据及其岩矿石多元数据的统计分析,建立混合蚀变遥感模型。选择最佳变量图像或变量图像组合,最终提取出该地区的混合蚀变 遥感异常信息。实践证明,该方法在矿化信息的提取上效果显著。  相似文献   

Simulated thermal alteration of sterols and keto—Alcohols in marine sediments of the Okinawa Trough     

Jiang Shanchun  John K. Volkman  Teresa O'Leary  Zhang Huizhi  Luan Zuofeng 《中国海洋湖沼学报》1993,11(4):343-350

Compositional data on the sterol and alcohol fractions isolated from deep-sea marine sediments from the Okinawa Trough were obtained to determine the relative contribution from marine and terrestrial inputs. Following extraction, the sterol plus alcohol fraction was isolated by layer chromatography, derivatized with BSTFA and then analysed by capillary GC and GC—MS. A suite of C₂₆−C₂₉ stenols and stanols and C₃₀−C₃₂ keto—alcohols were identified in the sediments. The thermal stability of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 hours at temperatures from 50°C to 200°C. The C₂₇ stanol/stenol ratio increased when temperatures went up to 175°C, but the distribution of C₃₀−C₃₂ Keto—alcohols remained unaffected. At 200°C most of the sterols and Keto—alcohols were destroyed. Supported by the National Natural Foundation of China.  相似文献   

鲁西峄山花岗岩中粗大钾长石斑晶成因探讨     

仲卫国  王聿军  臧学农  董作森 《山东国土资源》2005,(Z1)

在鲁西地区新太古代晚期(五台期)峄山花岗岩的黑石查和望子山花岗质岩体的岩石中,钾长石粗大斑晶内有自形程度较高的斜长石等矿物包裹体沿其环带定向排列。根据野外观察及岩石、矿物学特征测试分析,钾长石斑晶属于岩浆结晶形成的原生斑晶,受化学成分及侵位结晶过程中的物理化学条件影响,钾长石的生长速度大于其成核密度,因而形成粗大斑晶。估算岩浆温度>950℃,钾长石斑晶快速生长时岩浆温度为750℃,过冷度ΔT≈150℃,基质结晶时岩浆温度为600℃,ΔT≈300℃。  相似文献   

Structural controls on hydrothermal alteration and gold–antimony mineralisation in the Hillgrove area,NSW, Australia     

P.?M.?AshleyEmail author  D.?Craw 《Mineralium Deposita》2004,39(2):223-239

The Hillgrove gold–antimony deposit is hosted in late Palaeozoic, biotite-grade metasedimentary rocks and Permo-Carboniferous granitoid intrusions of the New England Orogen. Mineralisation occurred at a range of structural levels during rapid uplift in the orogen at 255–245 Ma. Hydrothermal fluids were controlled by extensional faults in a regional-scale sinistral strike-slip fault system. Principal faults in this system were developed in, and possibly evolved from, mylonite zones which were active during Late Permian tectonics. Earliest mineralisation formed scheelite-bearing quartz veins, and these were followed by auriferous arsenopyrite–pyrite–quartz–carbonate veins with minor base metal sulphides. This latter type was accompanied by sericitisation and carbonation of the host rock, with addition of sulphur, arsenic and gold, in zones up to 20 m from veins. Quartz–stibnite veins with electrum, gold, aurostibite, and arsenopyrite form a prominent and economically important hydrothermal type, with little wall-rock alteration but extensive hydrothermal breccia formation and local open-space filling textures. Below a mining depth of 300–500 m, this type passes over a short distance downwards into stibnite-poor gold-bearing veins. Late-stage carbonate–stibnite veins with gold and silver sulphosalts cut all earlier veins, and have open-space filling textures. Aspects of the Hillgrove deposit have similarities to many other orogenic gold deposits in the SW Pacific which have been formed at different structural levels. Hillgrove is distinctive in having evidence for mineralisation at this wide range of structural levels in the one deposit, formed progressively during syn-orogenic uplift. Editorial handling: N. White  相似文献   

Stratovolcano stability assessment methods and results from Citlaltépetl,Mexico     

D.?R.?ZimbelmanEmail author  R.?J.?Watters  I.?R.?Firth  G.?N.?Breit  G.?Carrasco-Nunez 《Bulletin of Volcanology》2004,66(1):66-79

Citlaltépetl volcano is the easternmost stratovolcano in the Trans-Mexican Volcanic Belt. Situated within 110 km of Veracruz, it has experienced two major collapse events and, subsequent to its last collapse, rebuilt a massive, symmetrical summit cone. To enhance hazard mitigation efforts we assess the stability of Citlaltépetl's summit cone, the area thought most likely to fail during a potential massive collapse event. Through geologic mapping, alteration mineralogy, geotechnical studies, and stability modeling we provide important constraints on the likelihood, location, and size of a potential collapse event. The volcano's summit cone is young, highly fractured, and hydrothermally altered. Fractures are most abundant within 5–20-m wide zones defined by multiple parallel to subparallel fractures. Alteration is most pervasive within the fracture systems and includes acid sulfate, advanced argillic, argillic, and silicification ranks. Fractured and altered rocks both have significantly reduced rock strengths, representing likely bounding surfaces for future collapse events. The fracture systems and altered rock masses occur non-uniformly, as an orthogonal set with N–S and E–W trends. Because these surfaces occur non-uniformly, hazards associated with collapse are unevenly distributed about the volcano. Depending on uncertainties in bounding surfaces, but constrained by detailed field studies, potential failure volumes are estimated to range between 0.04–0.5 km³. Stability modeling was used to assess potential edifice failure events. Modeled failure of the outer portion of the cone initially occurs as an "intact block" bounded by steeply dipping joints and outwardly dipping flow contacts. As collapse progresses, more of the inner cone fails and the outer "intact" block transforms into a collection of smaller blocks. Eventually, a steep face develops in the uppermost and central portion of the cone. This modeled failure morphology mimics collapse amphitheaters present at many of the world's stratovolcanoes that have experienced massive failure events.Editorial responsibility: H. Shinohara  相似文献   

Flank spreading and collapse of weak-cored volcanoes   总被引：1，自引：1，他引：0  

Emmanuelle?CecchiEmail author  Benjamin?van?Wyk de Vries  Jean-Marc?Lavest 《Bulletin of Volcanology》2004,67(1):72-91

Volcanoes subjected to hydrothermal activity develop weak cores as a result of alteration and due to elevated pore pressures. Edifices constructed at the angle of repose of volcanoclastics, or at even more gentle slopes, respond to internal weakening by initially deforming slowly, but may then collapse catastrophically. Such a process has so far been described for only a few volcanoes, such as Casita, Nicaragua; however, the conditions for flank spreading are widespread and many, if not most volcanoes should suffer some alteration-related flank spreading. We provide analogue models that characterise the structure — surface deformation fields and internal structures — of a spreading flank. Deformation creates a characteristic concave-convex-concave flank profile producing structures such as basal thrusts, summit normal faults, grabens and strike-slip relay faults. Three deformation regimes are found: a pit collapse regime is associated with very small volumes of ductile material located far from the edifice surface. This would not appear in nature, as time for deformation is greater than the lifetime of a volcano, unless very low rock viscosities are present. The other two regimes are flank spreading regimes, one symmetric and one asymmetric. The latter is the most common, as most volcanic structures are asymmetrical in form and in distribution of physical properties. The deformation is controlled by altered region dimensions, volume and position relative to the edifice, and to a lesser extent by its shape. As the flanks spread, landslides are created, initially on the steepened portion, but also from fault scarps. Major flank collapse may occur leading to explosive hydrothermal decompression and to a debris avalanche rich in hydrothermally altered material. We provide several new examples of volcanoes that have structures and morphologies compatible with flank spreading. We suggest that it is a common feature, important in the tectonics and hazards of many volcanoes.Editorial Responsibility: J. Gilbert  相似文献   

Melting of subducted continent: Element and isotopic evidence for a genetic relationship between Neoproterozoic and Mesozoic granitoids in the Sulu orogen   总被引：6，自引：0，他引：6  

Jie Huang  Yong-Fei Zheng  Zi-Fu Zhao  Jian-Bo Zhou 《Chemical Geology》2006,229(4):227-256

Zircon U-Pb and hornblende Ar-Ar ages, major and trace elements, and Sr, Nd and O isotope compositions of Neoproterozoic and Mesozoic granitoids from the Wulian region in the Sulu orogen of China demonstrate that post-collisional granitoids were generated by Early Cretaceous melting of subduction-thickened continental crust that has geochemical affinities to Neoproterozoic protolith of ultrahigh-pressure metaigneous rocks that were derived from the Yangtze Block. The Mesozoic granitoids share the following features with the Neoproterozoic granites: (1) occurrence of Neoproterozoic U-Pb ages in zircon; (2) strong LREE enrichment but HFSE (Nb, P and Ti) depletion; (3) variable δ¹⁸O values for constituent minerals; (4) significantly negative ε_Nd(t) values with Paleoproterozoic Nd model ages. Thus the two ages of granitoids have a genetic relationship in source nature. However, they differ significantly in both the O isotope composition of zircon and the concentration ratios of fluid-mobile to fluid-immobile elements. These differences are interpreted to reflect differences in the depth of magma sources, and in the nature of subsequent water-rock alteration. The Neoproterozoic granites were derived from hydration melting of Paleoproterozoic crust during breakup of the supercontinent Rodinia at ca. 780 to 740 Ma along the northern margin of the Yangtze Block, with subsequent overprinting of high-T meteoric-hydrothermal alteration and rifting-induced low-¹⁸O magmatism. In contrast, the Mesozoic granitoids were derived from dehydration melting of subduction-thickened crust that was unaffected by meteoric-hydrothermal alteration. The source of the Mesozoic granitoids may be coeval middle-lower crustal counterparts of the Neoproterozoic granites.  相似文献   

Alteration Information Extraction by Applying Synthesis Processing Techniques to Landsat ETM＋ Data： Case Study of Zhaoyuan Gold Mines, Shandong Province, China   总被引：2，自引：0，他引：2  

刘福江吴信才  孙华山郭艳 《中国地质大学学报(英文版)》2007,18(1):72-76

Satellite remote sensing data are usually used to analyze the spatial distribution pattern of geological structures and generally serve as a significant means for the identification of alteration zones. Based on the Landsat Enhanced Thematic Mapper （ETM＋） data, which have better spectral resolution （8 bands） and spatial resolution （15 m in PAN band）, the synthesis processing techniques were presented to fulfill alteration information extraction： data preparation, vegetation indices and band ratios, and expert classifier-based classification. These techniques have been implemented in the MapGIS-RSP software （version 1.0）, developed by the Wuhan Zondy Cyber Technology Co., Ltd, China. In the study area application of extracting alteration information in the Zhaoyuan （招远） gold mines, Shandong （山东） Province, China, several hydorthermally altered zones （included two new sites） were found after satellite imagery interpretation coupled with field surveys. It is concluded that these synthesis processing techniques are useful approaches and are applicable to a wide range of gold-mineralized alteration information extraction.  相似文献   

基于典型相关分析的遥感影像变化检测   总被引：3，自引：0，他引：3  

陈垒  马润赓申维 《地质通报》2007,26(7):16-920

多通道遥感影像由于通道之间相关性的影响,相对于单通道影像的变化检测更为困难,因此需要有效的集中分布在各个通道上的变化信息,构造出不同时相之间的差异影像,以便于变化信息的分析解译。针对多通道变化信息集中的难点和通道之间相关性的影响难以消除的问题,引入多元统计分析中的典型相关分析方法,将2个时相的多通道遥感影像示作2组多元随机变量,采用多元变化检测变换,对多个波谱通道上的所有差异信息或变化信息进行重组,分配到一组互不相关的结果变量中,最大限度地消除通道间的相关性对变化检测的不利影响,初步解决了差异影像构造的问题。  相似文献   

Geotechnical characterisation of stratocone crater wall sequences, White Island Volcano, New Zealand     

Vicki Moon  Jennifer Bradshaw  Richard Smith  Willem de Lange 《Engineering Geology》2005,81(2):146-178

Geotechnical characterisation is undertaken for 3 broad units comprising the bulk of the stratigraphy identified on White Island Volcano, Bay of Plenty, New Zealand, an active island stratovolcano. Field and laboratory measurements were used to describe rock mass characteristics for jointed lava flow units, and ring shear tests were undertaken to derive residual strength parameters for joint infilling materials within the lavas. Rock Mass Rating (RMR) and Geological Strength Index (GSI) values were calculated and converted to Mohr-Coulomb strength parameters using the Hoek-Brown criterion. Backanalysis of known landslide scarps was used to derive strength parameters for brecciated rock masses and hydrothermally altered rock masses. Andesite lava flows have high intact strength (σ_ci = 184 ± 50 MN m^− 2; γ = 24.7 ± 0.3 kN m^− 3) and typically 3 wide, infilled joint sets, one parallel to flow direction and two steeply inclined, with spacings of 0.3-1.7 m. Joints are rough, with estimated friction angles for clean joints of ?_j = 42-47°. Joint infill materials are clayey silts derived from weathering of wall rocks and primary volcanic sources; they have low plastic (54%) and liquid (84%) limits and residual strength values of c_r = 0 kN m^− 2 and ?_r = 23.9 ± 3.1°. RMR values range from 70 to 73, giving calculated strength parameters of c′ = 1161-3391 kN m^− 2 and ?′ = 50.5-62.3°. Backanalysis suggests brecciated rock masses have c′ = 0 kN m^− 2 and ?′ = 35.4°, whereas GSI observations in the field suggest higher cohesion (c′ = 306-719 kN m^− 2) and a range of friction angles bracketing the backanalysed result (?′ = 30.6-41.7°). Hydrothermally altered rock masses have c′ = 369 kN m^− 2 and ?′ = 14.9°, indicating considerable loss of strength, especially frictional resistance, compared with the fresh lava units. Values measured at outcrop scale in this study are in keeping with other published values for similar volcanic edifices; backanalysed data suggest weaker rock mass properties than those determined at outcrop. This is interpreted as a scale issue, whereby rock mass characteristics of a large rock mass (crater wall scale) are weaker than those of small outcrops, due in part to the overestimation of friction angle from measurements on small exposures.  相似文献