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Anhydrite–pyrite–magnetite–pyroxene–type deposits occur in the Mesozoic volcanic areas of the Middle–Lower Yangtze Valley in China. These deposits are hosted in alkaline basaltic rocks, and are generally accompanied by melanocratic and leucocratic alteration zones, both of which are characterized by a distinct vertical zonation pattern. Investigation of these zones indicates that the chemical compositions of solid solutions and polymorphs of various minerals vary spatially in the alteration profile, upwards from the lowest level, and outwards from the center.Here we report a case study on the Luohe deposit. In the melanocratic-alteration zone, the composition of magnetite (including trace elements Ti, V, Mg, Mn), pyroxene (Mg, Fe2+, Fe3+, Al2O3), plagioclase (AnxAb1 − x), pyrite (Co, Ni) and apatite (F, CeO2 + Y2O3 + La2O3) changes with depth. The isotherms of hydrothermal fluids determined from fluid inclusion data, including homogenization temperature and salinity, also vary with depth.Activity diagrams were constructed from mineral and isotherm analysis to estimate the chemical constraints on the alteration-mineral assemblages and the coexisting hydrothermal solutions for the Na2O–K2O–CaO–MgO–FeO–Fe2O3–A12O3–SiO2–H2SO4–H2S–HCI–H2O system at 350 to 600 °C and 500 bars (50 MPa), assuming that the major alteration mineral assemblages along the profile reflect the nature of the coexisting hydrothermal solutions. The activity diagrams adopted the major minerals as buffers to fix the activities of the aqueous species in the system, simulating the physicochemical conditions of the magnetite–anhydrite–pyroxene equilibrium and of solid solutions of diopside–hedenbergite, grossular–andradite and anorthite–albite found in the profile.This study provides an approach to modeling the chemical constraints of coexisting fluids in ore-alteration zones based on field observations. 相似文献
173.
碳酸盐沉积物的成岩作用 总被引:4,自引:2,他引:2
化学沉淀碳酸盐矿物在沉积后很容易受到各种作用的影响,其中最重要的是其在成岩阶段所经历的成岩作用.碳酸盐沉积物在成岩过程中主要受大气降水、海水和埋藏过程中孔隙流体的控制,经历一系列压实、溶解、矿物的多相转变、重结晶、胶结等成岩作用,逐渐转变为固结的岩石.在成岩过程中,由于孔隙流体与沉积流体之间的异同以及温度的变化,碳酸盐沉积物的原始矿物成分、地球化学特征可能会很好的保存下来,但在许多情况下,也可能会改变,从而使我们无法准确反演碳酸盐沉积物在沉积时水体的特征.因此,我们在应用碳酸盐岩重建相关古环境和古气候变化的时候,必须要通过有效的方法来对碳酸盐岩是否受到成岩作用的影响进行鉴定. 相似文献
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Coal wastes produced during mining activities are commonly deposited in nearby dumps. These wastes mostly composed of minerals and variable amounts (usually 20-30%) of organic matter start to weather immediately after deposition. Oxidation of the organic matter can lead to self heating and self combustion as a result of organic and mineral matter transformations. The degree of alteration depends on the properties of the wastes, i.e., the maceral and microlithotype composition of the organic matter and its rank.Alteration of wastes also depends on the heating history, i.e., the rate of heating, final heating temperature, duration of heating, and the degree of air access. Although air is probably necessary to initiate and drive the heating processes, these usually take place under relatively oxygen depleted conditions. With slow heating, color of organic matter particles changes, irregular cracks and oxidation rims develop around edges and cracks, and bitumen is expelled. As a result, massive and detritic isotropic and strongly altered organic matter forms. On the other hand, higher heating rates cause the formation of devolatilization pores, oxidation rims around these pores and along cracks, vitrinite-bands-mantling particles, and bitumen expulsions.Organic compounds generated from the wastes include n-alkanes, iso-alkanes, alkylcyclohexanes, acyclic isoprenoids, mainly pristane, phytane and, in some cases, farnesane, sesquiterpanes, tri- and tetracyclic diterpanes, tri- and pentacyclic triterpanes, and steranes, polycyclic aromatic hydrocarbons (mostly with two- to five rings, rarely six rings), and phenols. The compounds formed change during the heating history. The fact that phenols are found in dumps where heating has not yet been completed, but are absent in those where heating ceased previously suggests the presence of water washing. The organic compounds formed may migrate within the dumps. However, when they migrate out of the dumps, they become a hazard to environment.This paper is a review on transformations of organic matter (both maceral composition and reflectance and chemical composition) in coal wastes deposited in coal waste dumps. Immediately after deposition the wastes are exposed to weathering conditions and sometimes undergo self heating processes. 相似文献
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在多种类覆盖区,由于植被、河道、阴影、第四系等干扰因素影响,难于客观有效提取与成矿有关的遥感蚀变信息。应用混合像元分解的方法技术可以区分出混合像元中各类干扰信息的反射率值及其所占丰度值,从混合像元光谱中减去各干扰因素的反射率值及其所占份额,可以获取土壤或岩石的反射率值及其所占丰度值,将土壤或岩石反射率值除以其所占的份额... 相似文献
179.
春都斑岩铜矿床地处著名的印支期中甸-义敦岛弧成矿带南端。矿区出露闪长玢岩-花岗闪长斑岩复式岩体,成矿岩体为印支晚期的花岗闪长斑岩。围绕成矿岩体,围岩蚀变强烈,蚀变分带明显,由中心向外,依次出现硅化钾化带→绢英岩化带→硅化带→硅化黑云母化带→青磐岩化带→绢云母化及泥化带。区内蚀变与矿化关系密切,蚀变类型决定矿化程度,蚀变... 相似文献
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