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通过在湘潭县毛塘海泡石黏土矿区留君庵矿段开展矿产勘查工作,基本查明了海泡石黏土矿床的地质特征。矿区海泡石黏土矿赋存于中二叠统小江边组“含泥质段”风化层中,矿体形态平面上呈长条带状,剖面上矿体形态呈透镜体状、似层状,矿床规模为小型。根据X衍射定量测试分析和化学分析,矿石主要矿物成分为海泡石、石英、方解石、滑石和蒙脱石等组成;矿石化学成分总体富硅、镁、低钾、钠。矿石中海泡石含量与MgO、SiO2含量呈正相关关系,与CaO含量总体呈负相关,结合矿石扫描电镜分析结果,区内海泡石形成于沉积过程的新生作用。综合矿区成矿地质特征和矿石物理化学特点,矿区位于古陆边缘局限性的富Mg2+、Si4+及高pH值的浅海环境中,海泡石经原生沉积于钙镁质页岩、泥灰岩,再经长期化学风化改造,在表生条件下不断富集形成海泡石黏土矿床,矿床成因类型为沉积风化残余型。 相似文献
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海泡石族矿物包括海泡石、凹凸棒石和坡缕缟石,是一组具链式层状结构的富镁硅酸盐粘土矿物。海泡石(Sepiolite)发现于1789年,原名是“Meerschaum”,指一种色白质轻的致密土状硅酸镁矿物,它可浮在水面,即德文“海的泡沫”意思,1847年正式叫海泡石。海泡石的典型化学式为Mg_8Si_(12)O_(30)(OH)_4(OH_2)_4·8H_2O其中化学组成变化较大,普遍存在Al对Si和A1、Fe、Ni对Mg的类质同象置换,结果形成不同类型的海泡石: 相似文献
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在浏阳永和浅海相沉积型海泡石矿床中,海泡石与滑石密切共生,二者或同层出现,或相间出现。即或在单独存在的海泡石矿体和滑石矿体,也属相同时代,相同层位,并伴生同种生物组合。通过X—射线衍射分析、红外光谱分析及电镜分析结果表明,海泡石矿物与滑石矿物之间存在着相互转换的关系,滑石是由海泡石在成岩过程中转化而来的。 相似文献
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X射线粉晶衍射仪定量测量海泡石矿样的实验条件 总被引：3，自引：3，他引：0
在完成海泡石矿石样品的矿物组成及相对含量测试、均匀性检验、稳定性和粒度分布特征检查的基础上,选择合适的X射线粉晶衍射定量测量海泡石的实验条件,利用海泡石、刚玉和萤石纯样配制一系列海泡石质量分数已知的标准样品,采用内标定量法、固体计数器和计数强度测试技术,对低、中、高3种不同含量的海泡石样品进行测量。结果表明:获得的海泡石样品定量测量数据符合现有的行业标准,采用的定量测试方法与测量条件满足黏土开采企业和实验研究单位测试要求,达到了X射线粉晶衍射法定量分析黏土矿物的目的。 相似文献
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《Journal of African Earth Sciences》2006,44(5):491-504
This paper presents mineralogical and geochemical data from several continental sequences located in Central (Ain Ghréwiss and Kébar) and Central-Southern Tunisia (Selja, Kef Schefeir, Shib, Oum El Kcheb and Haidoudi). These sequences vary in age from Late Palaeocene to Early Oligocene and contain considerable quantities of fibrous clays (up to 75% palygorskite and 90% sepiolite). These clays appear in assocation with carbonates (mainly dolomite), detrital aluminosilicates (illite, Al smectites, mixed-layers illite–smectite and kaolinite), quartz and lesser quantities of gypsum and halite. The textural characteristics observed by electron microscopy, the trace and rare earth elements contents and their distribution in the various mineral phases, together with the isotopic composition of dolomite and fibrous clays, provide good clues as to the genesis of the neoformed minerals. Thus, the sepiolite would have precipitated directly in lacustrine, playa-lake or sebka environments under alkaline conditions, high Si and Mg and low Al activity, and arid to semiarid climate. On the other hand, the palygorskite would have formed by transformation of already existing illite and/or smectite type aluminosilicates in solutions in equilibrium with isotopically heavier and, therefore, more evaporated solutions than the sepiolite. 相似文献
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台地泥质组分沉积记录了源—汇过程和环境演化等沉积学领域信息,可作为古气候和古环境重建的重要载体。然而,利用沉积物中的泥质组分进行古气候和古环境恢复时仍存在相当大的复杂性和局限性。鉴于此,笔者以上寺剖面中二叠统茅口组为例,通过研究该层位富泥质组分灰岩—泥灰岩韵律的宏微观形貌学和矿物学特征,发现其泥质组分主要由成岩黏土矿物海泡石构成,其次为少量滑石和蒙脱石。基于前人认识,进一步运用电子探针和激光原位元素地球化学分析手段,综合认为海泡石中镁元素来源于继承海水的孔隙水以及亚稳定矿物的转化释放,硅元素可能来源于上扬子台地的同沉积期断裂热液。此外,滑石主要形成于海泡石埋藏过程中的成岩转化,蒙脱石可能也具有类似成因,但不排除有少量蒙脱石来源于火山物质的海底改造。结合区域资料,华南中二叠统浅水碳酸盐台地上广泛发育自生成因（早期成岩作用和埋藏成岩作用）泥质组分。因此,在利用泥质组分来恢复古环境的时候,需要谨慎识别其成因,这将有利于提高沉积旋回识别和环境解释的准确性;另一方面,对自生成因泥质组分进行专门研究,在成岩过程以及成岩地球化学信号识别上也具有参考价值。 相似文献
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It has been assumed that soil pendants form in a similar manner as stalactites, in which innermost laminae are the oldest and outer laminae are the youngest. This study presents a new interpretation for soil pendant development. Pahranagat Valley, Nevada, pendants contain features indicating continued precipitation through time at the clast–pendant contact, implying that the oldest deposits are not always found at the pendant–clast contact, as other studies have assumed. These features include a void at the clast–pendant contact where minerals such as calcium carbonate, silica, and/or fibrous silicate clays precipitate. In addition, fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and/or dissolved and result in the formation of sepiolite. This study indicates that pendants are complex, open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses. 相似文献
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J. REINHARDT 《Journal of Metamorphic Geology》1987,5(4):451-472
Abstract Cordierite-anthophyllite rocks and related cordierite-rich, talc-rich and chlorite-rich rocks occur in the Rosebud Syncline, north-west Queensland, Australia, as part of a Proterozoic metasedimentary sequence. Field relations and rock compositions attest the sedimentary origin of these rather unusual metamorphic rocks. Their chemical composition is comparable to that of unmetamorphosed, alkali- and Ca-poor pelites, which are associated with some evaporite deposits. Other occurrences of cordierite-anthophyllite rocks have commonly been interpreted as metamorphosed chloritic alteration products derived from mafic or felsic volcanics. A comparative chemical study, using analyses of cordierite-anthophyllite rocks from such alteration zones and analyses of unmetamorphosed magnesian pelites, demonstrates the general chemical similarity between these two rock groups of entirely different origin. However, distinct differences in major element relations help to distinguish these two genetic groups. Particularly useful are Al2O3–FeO–MgO plots, in which evaporitic pelites occupy the Fe-poor side. The highly magnesian metamorphic rocks from the Rosebud Syncline fall entirely into the compositional field of evaporitic clays and shales. Furthermore, analyses of relatively immobile trace elements give supporting evidence for the sedimentary origin of these cordierite-anthophyllite rocks. The correlation with trace element ranges of clays and shales is very good. However, the correlation with trace element ranges of mafic and felsic volcanics is poor, and major discrepancies occur with Cr, Ni, Co, Nb, Sc, Th and Ti. Thus, the magnesian metamorphics of the Rosebud Syncline appear to be derived from evaporitic clays rich in magnesian clay minerals, such as palygorskite, sepiolite, chlorite or corrensite. The complete metamorphic rock assemblage of interlayered calcareous, aluminous and magnesian rocks is interpreted as a metamorphosed carbonate-evaporite-pelite sequence. 相似文献
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Pellets, ooids, sepiolite and silica in three calcretes of the southwestern United States 总被引：1，自引：0，他引：1
Pellets and ooids are widespread and locally abundant in mature calcrete profiles in the Argus Range, California; near Wickieup, Arizona; and in Kyle Canyon, Nevada. Most concentrations of pellets and ooids either overlie laminar calcrete at various levels in the calcrete profile or fill subhorizontal fractures in the petrocalcic horizon. In all three profiles the petrocalcic horizon has been thickened by the pelletal, chemically deposited fracture fillings. Pellets range from 0.02 to 8.0 mm in diameter and consist principally of micritic calcite and sepiolite. Ooid coatings are chiefly calcite and opal or calcite and sepiolite. The pellets represent small concretions, some of which grew by accretion, either in void space or by displacing adjacent sediment, and the others of which were formed by cementation of pellet-shaped bodies of porous micrite. Ooid coatings with opal or sepiolite may have been deposited as a gel with sufficient strength for surface tension to thin the coatings over angular corners of nuclei so as to increase the roundness and sphericity of the particles. Major problems in calcrete genesis are (1) the cause of subhorizontal fractures and the mechanism for widening a fracture as sediment accumulates in it and (2) what determines the deposition of calcite, sepiolite, and opal as pellets and ooid coatings or as laminar layers. 相似文献
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A massive white sepiolite deposit at Amboseli precipitated from magnesium and silica released during the ground water dolomitization of an earlier lacustrine sepiolite. Kerolite has since formed in proximity to the massive sepiolite as an alteration product of sepiolite and as a ground water precipitate when the pH is below 8. Authigenic sepiolite also occurs in the overlying younger sediments. Kerolite is likely to occur but has not yet been positively identified.Presently, ground waters within the Amboseli Basin are supersaturated with respect to sepiolite and kerolite. This supersaturation results from the weathering of alkaline olivine basalts on the edge of the basin. The precipitation of sepiolite and/or kerolite does not control ground water compositions in the basin. These reactions are slow compared to other aqueous-mineral reactions such as those maintaining carbonate mineral equilibria. Equilibrium between disordered-dolomite and calcite buffers the log a
Mg2+/(a
H+)2 as a function of log f
CO
2 in ground waters in the proximity of the massive sepiolite. This reaction can help explain the presence of sepiolite associated with dolomites in other near-surface deposits besides Amboseli. 相似文献
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Olive green clays likely to be bentonitic in composition have been mineralogically and chemically studied. They occur in association with other lacustrine sediments at Lake Manyara. Radiocarbon dates from four diatom horizons indicate ages ranging from 12 Ka to 135 Ka suggesting a Mid-Holocene age. Middle Pleistocene age have been assigned to the ridged oncolites of Lake Manyara. The olive green coloured clays in the Manyara basin are known to occur in association with other lake beds including phosphorite deposits, stromatolites, bioturbated silty clays, partly silicified marls, conglomerates and olive green coloured opal beds. The results presented herein are from the olive green coloured clays. The olive green clays (bentonite?) are a result of devitrification or alteration of volcanic ashes and/or pyroclasts. The green clays occur in different forms as they are separated from each other by other lacustrine sediments. The alteration might have taken place in slightly different environments in terms of salinity and alkalinity. One of the top layer is friable and shows conchoidal fractures when dry. The other beds below in the lacustrine sequence are cemented with calcite and some dolomite as well as zeolites. The lowermost layer in the sequence is friable and shows cracks filled with coarse crystalline calcite. Mineralogically the bentonite is composed of the clay minerals illite, illite-smectite mixed layer clays, and chlorite. Other authigenic minerals include various zeolites (analcime, clinoptilolite, erionite and some traces of mordenite), opal, and fluorapatite. The clays have magnesium contents varying from 3.01% to 7.43%. The calcium contents vary widely due to presence or absence of one of the two minerals calcite or apatite. Trace elements like Ba, Ce, Sr, Zr are equally attributed to the presence of calcite and apatite. The formation of the illite-smectite mixed layer clays in an alternating manner with other lake sediments depicts different episodes of volcanic eruptions in the area. The mineralogical composition of smectites, zeolites, and opal in the green clays suggests a deposition of pyroclasts and volcanic ashes in a closed lake system with fluctuating levels. Due to evaporation alkalinity and salinity levels were fluctuating. The clays might have been bentonite which have undergone illitisation, a phenomena noted in other neighbouring rift basins. 相似文献
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Sepiolite phase-transformation has been successfully imitated in laboratory for many years, but no natural example has been reported yet. In this paper the authors intend to provide a good natural example in southern China, especially in the Pingle depression, where the Permian sepiolite has been generally converted to talc and minor stevensite (magnesium montmorillonite) due to anadiagenesis during post-sedimentation. In our opinion, the degree of transformation can be indicated by the degree of metamorphism of coal (rank of coal). In order to study the relationship between clay transformation and coal rank, the authors have proposed some parameters of coalification correlated with sepiolite conversion. It happens that volatile matter in the Permian coal comprises 30–52% and a vitrinite reflectance of approximately 0.4–0.8% (R°) is reliable to indicate the existence of sepiolite. The consideration that sepiolite phase-transformation has a linear relationship with the rank of coal can be justified on the trend surface analysis diagrams which show that the areas of lower coal rank are obviously consistent with the sepiolite-distributed areas. Therefore, there is such a possibility as to predict new occurrences of sepiolite on the basis of the distribution of the lower coal ranks. 相似文献