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1.
Geochemical effects of oxidation products and framboidal pyrite oxidation in acid mine drainage prediction techniques 总被引：1，自引：0，他引：1
P. A. Weber W. A. Stewart W. M. Skinner C. G. Weisener J. E. Thomas R. St. C. Smart 《Applied Geochemistry》2004,19(12):1953-1974
Acid mine drainage predictive testwork associated with the Australian Mineral Industries Research Association (AMIRA) P387A Project: Prediction and Kinetic Control of Acid Mine Drainage (AMD) has critically examined static acid assessment and kinetic information from acid–base accounting techniques, including net acid production potential (NAPP), net acid generation (NAG) and column leach tests. This paper compares results on two waste rock samples that were obtained from the Kaltim Prima Coal mine (KPC) containing significant quantities of fine-grained framboidal pyrite. In agreement with other research, the authors' results indicated that framboidal pyrite is more reactive than euhedral forms due to the greater specific surface area of framboidal pyrite. This is evidenced by optical microscopy of reacted samples. Importantly, the results showed that NAPP testing is biased by the rapid acid generating oxidation of framboidal pyrite prior to, and during the acid neutralisation capacity (ANC) test. This can result in negative ANC values for samples containing significant framboidal pyrite (often “corrected” to zero kg H2SO4/t) when significant ANC is actually present in the sample. NAG testing using H2O2 indicated that samples containing a significant quantity of framboidal pyrite can result in the catalytic decomposition of the H2O2 prior to complete oxidation of the sulfide minerals present, requiring sequential addition of H2O2 for completion. A benefit of the NAG test, however, is that it assesses the net acid generation capacity of the sample without bias towards acid generation as is observed using NAPP methods. The kinetic NAG test also gives information on the reaction sequence of framboidal and euhedral pyrite. Periodic (kinetic) analysis of sub-samples from column leach tests indicated rapid oxidation of the framboidal pyrite compared to the euhedral pyrite, which was correlated with the greater framboidal pyrite surface area.Calculations to determine the sulfide/sulfate acidity derived from the oxidation of framboidal pyrite prior to; and during the ANC test have been developed to provide a better indication of the actual ANC (ANCActual) of the sample. Paste pH values of <pH 4–5 may be one suitable trigger mechanism for the implementation of this new method. This has led to an improved NAPP estimation of total acid production. Together with NAG and column leach testing this improved methodology has resulted in accurate AMD characterisation of samples containing acidic oxidation products and framboidal pyrite. 相似文献
2.
【研究目的】草莓状黄铁矿广泛存在于现代沉积物和沉积岩中,其成因机制总体上分为有机成因和无机成因两种,尽管两种机制均有理论与实验的支撑,但尚未建立一种具有普遍意义的形成机制。【研究方法】本文对目前草莓状黄铁矿的形成机理、氧化还原环境的应用及后期环境变化的影响进行了系统的综合研究。【研究结果】不同氧化-还原环境下形成的草莓状黄铁矿在粒径、形态以及硫同位素之间均存在较大的差异,可做为反演古氧化-还原环境的指标。草莓状黄铁矿的微晶尽管与粒径具有一定的正相关性,但是两者在形态演化序列、生长模式、聚集因素等方面与古氧化-还原环境的关系尚不清楚。仅凭草莓状黄铁矿粒径与铬还原法测定的硫同位素反演古氧化-还原环境存在一定的局限性,需要其他指标综合判定,尚需进一步开展草莓状黄铁矿原位硫同位素值与粒径对古氧化-还原环境反演的研究。后期氧化可使草莓状黄铁矿表面化学成分发生变化,但粒径分布依然具有古氧化-还原环境的指示意义。【结论】草莓状黄铁矿的实验模拟、理论体系和多学科交叉的研究中仍存在一些问题,尚需进一步研究。 相似文献
3.
黄铁矿是沉积物中较为常见的矿物之一,而草莓状黄铁矿是由等粒度的亚微米级黄铁矿晶体或微晶体紧密堆积而成。基于已有的草莓状黄铁矿相关研究成果,本文综述了草莓状黄铁矿的形成机制,阐述了其对古环境恢复的意义。目前普遍认为草莓状黄铁矿的成因主要有两种,即有机成因和无机成因,前者认为有机质或细菌参与草莓状黄铁矿形成;而后者主要认为过饱和的黄铁矿浓度是微球粒草莓状黄铁矿形成的必备条件。草莓状黄铁矿粒径的大小是其古沉积环境的直接反映,被作为比较可靠的古氧化还原条件判别指标,已被广泛应用于古代及现代海洋沉积物的古环境恢复。目前,虽然草莓状黄铁矿粒径判别古环境的大小及分布范围还不统一,但普遍认为封闭的水体环境（硫化环境）草莓状黄铁矿粒径较小且变化不大,且随着含氧程度增加,草莓状黄铁矿的粒径大小增大且分布范围趋于加宽。 相似文献
4.
Pyritization of tubes and burrows from Late Pleistocene continental shelf sediments off North Norway 总被引：1，自引：0，他引：1
Four different types of pyritized tubes and three types of pyritized burrow fillings are described from Pleistocene glaciomarine sediments in Andfjorden, northern Norway. The tubes and burrows probably originated from tubicolous and burrowing polychaetes respectively. The decomposition of the organic matter in the tubes and burrows created a reducing micro-environment favouring precipitation of pyrite. By comparison with Holocene tubes from marine sediments in Andfjorden and FugloSyfjorden, it is seen that pyritization commenced with isolated spherules. These spherules with incipient pyrite crystals and framboids were formed mainly on the inner wall of the tube. Presence of a monosulphide in the Holocene Fugløyfjorden material suggests that the pyritization process has reached a later phase; the final result would be a completely pyritized trace fossil. It is shown that single pyrite crystals (octahedra) generally attain greater size in the burrow fillings than in the tubes. The microstructure found in some of the pyritized tubes is interpreted as a reflection of the microstructure in the original wall. Finally, the implications for the depositional environment in Pleistocene in Andfjorden is investigated with reference to the benthic skeletal macrofaunal assemblage in the sequence. The pyritized trace fossils occur frequently in an opportunistic assemblage from a period (c. 14,000–13,000 yr BP) characterized by some oxygen deficiency. Later (13,000–10,000 yr BP) they play a minor role in an established assemblage under improved oxygen conditions. 相似文献
5.
ZHOU Yuefei WANG Rucheng LU Jianjun LI Yiliang 《《地质学报》英文版》2006,80(4):604-609
The Maochang bauxite in Guizhou Province is one of the important aluminum ore deposits in southwestern China. Ferruginous spherules, measuring about a few microns across, were found in the transitional layer of the deposit. The EDS and XRD results show that the microspherules are composed mostly of iron （hydr）oxide minerals （goethite） with only weak presence of aluminum and silicon. Occasionally, some pyrite micrograins with dissolved surface are found associated with goethite within the spherules. It is thus suggested that microspherules are linked to pyrite oxidization. It is also thought that microbial activities contribute not only to pyrite oxidization, but also to ball-like assemblage of the iron （hydr）oxides. The mechanism of the formation of ferruginous microspherules is also believed to be important in studying geomicrobiology of bauxite. 相似文献
6.
A. ELVERHØI 《Sedimentology》1977,24(4):591-595
Framboidal pyrite is identified in clayey Holocene sediments in the northwestern part of the Barents Sea, and also in clasts of black Jurassic (?) shale within these sediments. Two types of framboidal pyrite are distinguished. Framboids in the Holocene sediments lack a matrix between the microcrystals whereas the Jurassic specimens have a matrix. In contrast to the rest of the clastic sedimentary material in the area, the framboidal pyrite in the Holocene sediments is not reworked from the underlying Mesozoic rocks, but has formed recently. In some Holocene sediments the microcrystals are well organized and crystal-like faces are developed. The framboidal texture is probably a result of pyrite crystallization. The matrix is concluded to be due to diagenetic alteration and is not a primary feature of the framboidal pyrite. 相似文献
7.
在华南374和331花岗岩型铀矿床矿石内及人工合成沥青铀矿的模拟实验中均发现有针状沥青铀矿与沥青铀矿球粒紧密共生的现象。结合对沥青铀矿球粒的形态、结构、粒度及共生矿物等特征的研究,作者确认沥青铀矿球粒是球状结晶的表现,而针状及长柱状沥青铀矿则是铀氧化物相变中间产物(α-U_2O_8或β-U_3O_8)的假象。沥青铀矿的高温高压人工模拟实验表明,一些沥青铀矿在快速结晶生长过程中,由于结晶生长的限制而具有非生物成因的显微草莓状和花瓣状结构特征。 相似文献
8.
In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate–methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate. 相似文献
9.
龙马溪组页岩黄铁矿微观赋孔特征及地质意义 总被引：4，自引：3，他引：1
随着页岩气地质理论的不断完善,页岩气储层研究也更加精细、量化,黄铁矿作为页岩气储层普遍发育的物质成分,其矿物学特征、赋孔特征与地质意义引起了关注。为细化、量化对页岩储层黄铁矿的地质认识,通过氩离子抛光-场发射扫描电镜（FE-SEM）、能谱（EDS）、X射线衍射（XRD）等实验手段结合图像处理技术（Image Processing）,以渝东南地区龙马溪组中下部优质页岩储层样品为例,探究页岩储层黄铁矿的发育类型和特征,量化表征评价页岩基质莓状黄铁矿在纳米尺度下的孔隙发育特征,并在此基础上讨论黄铁矿的页岩气地质意义,尤其是其储层意义。实验结果表明,莓状黄铁矿是龙马溪组页岩基质中最主要的黄铁矿类型,集合体直径介于3~10 μm之间;莓状黄铁矿集合体内部晶体间有机质纳米孔发育,孔隙直径主要分布在100 nm以下,在页岩储层孔隙分类中莓状黄铁矿孔隙应归入有机成因孔隙类型;莓状黄铁矿集合体及其控制的有机质可以为页岩储层贡献0.7%~7%的孔隙比例,是对储集空间具有正贡献的、不应忽视的孔隙类型;基于图像处理技术（Image Processing）的孔隙分类表征与评价技术可以为储层孔隙研究提供新思路,是实现不同类型孔隙量化研究的可行方法。龙马溪组基质黄铁矿既可以贡献一定储集空间,也与有机质具有成因联系,可以为优质储层发育机理研究与优质储层勘探预测提供依据,在页岩气储层研究与勘探开发中具有重要地质意义。 相似文献
10.
11.
George W. Luther Anne Giblin Robert W. Howarth Robert A. Ryans 《Geochimica et cosmochimica acta》1982,46(12):2665-2669
We used scanning electron microscopy and energy dispersive X-ray analysis to examine sediments from vegetated portions of three salt marshes, the Great Sippewissett Marsh (Cape Cod, MA), Sapelo Island (Georgia), and the Hackensack Meadowlands (N.J.), and from the sediments of an estuary, Newark Bay (N.J.). Pyrite particles were abundant in sediments from all sites. Both fine grained pyrite crystals and framboids were found. Single, fine grained crystals (diameter = 0.2 to 2.0 micrometers) predominated in all samples, strong evidence for rapid formation of pyrite.We also found both microcrystalline and framboidal iron-oxyhydroxide phases in many of the sediment samples. This is evidence of pyrite oxidation within the sediments and suggests that iron is conserved in salt marshes even as pyrite is oxidized. The thermodynamic stability of iron phases in marsh sediments, and recent pyrite oxidation studies in coal, suggest goethite as the crystalline iron-oxyhydroxide phase present. In addition, we sometimes found a red amorphous coating on grass roots from the Great Sippewissett and Sapelo Island marshes. This coating is likely a form of hydrated iron (III) oxide. 相似文献
12.
Various Fe–S minerals of the mackinawite–greigite–pyrite association, ubiquitous in biogenic remains from Jurassic mudstones, have been described in detail in an SEM–EDS study. Two diagenetic stages of Fe sulphide formation and preservation in the Jurassic organic skeletons are identified. In the first stage, pyrite formed as euhedra and framboids shortly after deposition, mainly in the interiors of the skeletons which still contained labile organic matter. The second stage of iron sulphide formation was related to the later stages of diagenesis, when the influence of the surrounding sediment was more dominant, although some organic matter was still present in the biogenic skeletons. A Fe-rich carbonate–aluminosilicate cement was then introduced between the earliest iron sulphides and later subsequently sulphidized, to form a metastable iron monosulphide of mackinawite composition and then greigite. 相似文献
13.
Z. Sawlowicz 《International Journal of Earth Sciences》1993,82(1):148-156
It has been suggested that the two morphologies of sedimentary pyrite, framboids and euhedra, may reflect two distinct pathways of pyrite formation. Framboids form indirectly via iron monosulphides, whereas euhedra form from direct precipitation from solution. A third pathway which is bridging these two forms is proposed here, namely the continuous growth from a monosulphide globule through framboids to a euhedral single crystal. It is also suggested that framboids probably occur over a range of three orders of magnitude, from the least complex microframboids through framboids to polyframboids.Dedicated to Professors G. C. Amstutz and L. G. Love for their unrivalled contribution to the knowledge of pyrite framboids 相似文献
14.
N. D. MacRae M. E. Fleet A. J. Andrews 《Contributions to Mineralogy and Petrology》1977,63(3):309-317
Two types of secondary sulfides occur on the walls of a vesicle in slightly altered basalt recovered from site 332A of DSDP
Leg 37. The first consists of euhedral crystals of pure pyrite, with occasional small partial overgrowths of fibrous chalcopyrite,
embedded within smectite (altered glass) which lines the vesicle. The second type occurs as small composite sulfide spherules
lightly attached to the surface of the smectite. The spherules are composed of pyrite crystallites arranged in approximate
pyritohedral symmetry, with marcasite crystallites decorating the pyritohedron edges. Precession camera photographs and optical
studies suggest the marcasite and pyrite grew simultaneously from a pyrite nucleus, with marcasite adopting the pyrite growth
habit. These spherules differ sharply from the magmatic sulfide spherules previously described. 相似文献
15.
Evidence for,and implications of,a primary FeS phase in the lead-zinc bearing sediments at Mount Isa
Quantitative mineral data from the lead-zinc bearing sediments at Mount Isa were studied using linear correlation analysis and R-mode cluster analysis. Pyrrhotite was found to be preferentially associated with galena and sphalerite. It is postulated that during sedimentation, formation of lead and zinc sulphides depleted an already limited sulphur supply to the point where the field of FeS stability was entered. The primary iron monosulphide formed was, or has since become, pyrrhotite. This hypothesis is in contrast to the widely held opinion that pyrrhotite in stratiform ores formed by metamorphic decomposition of pyrite. Empirical support for the sedimentary formation of pyrrhotite is provided by textural and qualitative mineralogical data from Mount Isa and other stratiform lead-zinc deposits. 相似文献
16.
S. C. Tripathi 《Journal of Earth System Science》1985,94(3):315-321
The present paper records the occurrence of framboidal pyrite and algal pyrite in the Mussoorie phosphorite deposit. The significance
of organic matter and sediment composition have also been discussed. The petrographic and analytical data indicate the dominant
role of organic matter in the formation of pyrite. It is concluded from the textural study of pyrite that framboids have formed
earlier in the sediment and subsequently the euhedral pyrite nucleated on them, gradually increasing in its abundance. 相似文献
17.
Iron monosulphide globules and tubes grown in the laboratory have similar morphologies to the fossil pyrite botryoids and chimneys found in the Silvermines exhalative sedimentary ore-body of Carboniferous age in Ireland. We envisage analogous fine structures growing at hot springs (100–200°C) in the earliest oceans as having provided the culture chambers and flow reactors for life to originate by phosphorylation and growth of organic molecules on the iron sulphide surfaces. Such sulphide structures grown in the laboratory could be used in origin-of-life experiments. 相似文献
18.
Occurrence and morphology of pyrite in Bulgarian coals 总被引：2，自引：0，他引：2
Coals with different degrees of coalification (ranging from lignite to anthracite) from seven Bulgarian coal basins have been investigated. The forms of pyrite and their distribution have been established. The types found are: massive pyrite, represented by the homogeneous, cluster-like and microconcretionary varieties; framboidal pyrite, appearing in inorganic and bacterial forms; euhedral pyrite, which is either isolated or clustered; anhedral pyrite, in its infilling and replacement varieties; and infiltrational pyrite, as a replacement or infilling mineral.Most of the forms of the euhedral, framboidal and massive pyrite developed during peat deposition. The anhedral replacement pyrite formed in the peat bed during early diagenesis. Infiltrational pyrite filled fractures and cleats formed during the diagenesis, catagenesis and metagenesis.Both similarities and differences with respect to the distribution of the pyrite types have been determined between coals of different ranks from Bulgarian coal basins. These differences are due to: the presence of Fe and S in the rocks adjacent to ancient peat bogs; the activities of ground and surface waters which brought Fe and S into the peat bogs; the geochemical character (pH and Eh) of the peat bogs and the sulphur bacteria development; and the tectonic situation during diagenesis, catagenesis and metagenesis. 相似文献
19.
北京十三陵中元古代常州沟组底部的粗砂岩（1.8 Ga）和大红峪组硅化碳酸盐岩（1.6 Ga）中都发现了众多铁质宇宙球粒。大多数未喷膜的二次电子像宇宙球粒是圆形的,少数呈长条状,由于在大气层中熔融作用,多数球粒表面具有金相饰纹和“排气”孔洞。使用电子探针分析对30个颗粒中44个测点的检测结果（%）:FeO 80～95,Cr2 O30.78～6.56,NiO 0.06～0.41,CoO 0.02～0.46。相对比较Cr2O3 在常州沟组中较多一些,而FeO在大红峪组中稍多一些。宇宙球粒的氦同位素分析值却截然不同;3He/4He×10-8分别为:57.50±2.16（常州沟组）和1.23±0.43（大红峪组）;4He×10-8 cm3STP/g分别为:55.54（常州沟组）和809.6（大红峪组）;然而宇宙球粒的氦同位测定值都比各自的母岩高出许多;氦同位素的异常为所发现的宇宙球粒的地外来源更加确定。 相似文献
20.
位于湖南中部的城步铺头黄铁矿床,是产于泥盆系基维特阶的层状矿床,1984年作者在本刊报导过这个矿床的沉积环境。根据新的资料,再次对它的成因进行研究。该矿床位于华南古大陆边缘裂谷系的北东向深水盆地中,含矿岩系由暗色的硅质岩-泥灰岩组成,矿体呈层状整合产出,以黄铁矿为主,硫同位素以富含32S为特点（δ34S＝-17．4‰～-30.10‰）。含矿岩系及矿石中,有机质含量较高（3％～5％）,有机质类型为腐殖-腐泥混合类型,成熟度较高。矿石具致密块状及条带状构造,由大量草莓状黄铁矿组成,它们主要出现在致密块状矿石中。矿石及含矿围岩的稀土元素、微量元素组成,与现代大洋裂谷或隆起区中的热液沉积物的特征相似,表明它们具有相同的来源和成因,应属海底热液喷流沉积矿床,大量存在的有机质,对于矿床的形成也起了重要的作用。 相似文献