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1.
Pyrite is easily oxidized, and therefore unambiguous evidence of detrital pyrite grains in metasediments is a significant constraint on when an oxygenated atmosphere developed. Compact rounded pyrite in
2.
Petrographic and sulphur isotope studies support the long‐held contention that rounded grains of pyrite in siliciclastic sequences of the Late Archaean Witwatersrand Supergroup originated as placer grains. The grains are concentrated at sites where detrital heavy minerals are abundant within quartz‐pebble conglomerates and quartzose sandstones. Depositional sites with abundant pyrite are: (1) within the matrix of bar‐type, clast‐supported conglomerates; (2) on scoured or winnowed surfaces; and (3) on stratification planes. The grains are internally compact or porous, with truncation of internal structure at outer margins indicating fragmentation and rounding of pyritic source‐rocks during erosion and sediment transport. A large range in textures reflects source‐rock lithologies, with known varieties linked to sedimentary‐hosted diagenetic pyrite, volcanic‐hosted massive sulphide deposits and hydrothermal pyrite. Laser ablation sulphur isotope analysis of pyrite reveals a broader range in δ34S values (? 5·3 to + 6·7‰) than that of previously reported conventional bulk‐grain analyses (? 1 to + 4‰). Rounded pyrite from the Steyn Reef has significant variation in δ34S values (? 4·7 to + 6·7‰) that establishes heterogeneous sulphur compositions, with even adjacent grains having diverse isotopic signatures. The heterogeneity supports a placer origin for rounded pyrite. Euhedral pyrite and pyrite overgrowths which are undoubtedly authigenic have restricted δ34S values (? 0·5 to + 2·5‰), are chemically distinct from rounded pyrite and are probably the products of metamorphism or hydrothermal alteration. The placer origin of rounded pyrite indicates that pyrite was a stable heavy mineral during erosion and transport in the early atmosphere. Its distribution in three sequences (Witwatersrand Supergroup, Ventersdorp Contact Reef and Black Reef), and in other sequences not linked to Witwatersrand‐type Au‐U ore deposits, implies deposition of redox‐sensitive detrital heavy minerals during the Late Archaean. Consequently, rounded grains of detrital pyrite are strong indicators of an oxygen‐poor atmosphere. While not confirming a placer origin for gold in Witwatersrand Au‐U ore deposits, the palaeoenvironmental significance of rounded pyrite negates its link to hydrothermal mineralization. 相似文献
3.
Trace-element characteristics of different pyrite types in Mesoarchaean to Palaeoproterozoic placer deposits 总被引：7，自引：0，他引：7
Nikola Koglin Hartwig E. Frimmel W. E. Lawrie Minter Helene Brätz 《Mineralium Deposita》2010,45(3):259-280
A comparative in situ LA-ICP MS trace-element study on pyrite from three different, variably auriferous, Archaean to Palaeoproterozoic
palaeoplacer deposits in the Ouro Fino Syncline (Quadrilátero Ferrífero; Brazil), the Elliot Lake area north of Lake Huron
(SE Canada) and several deposits within the Witwatersrand Basin (South Africa) revealed systematic differences between morphologically
different pyrite types and between the various palaeoplacer deposits. Especially the Ni and Au concentrations as well as Co/Ni
and Mo/Ni ratios were found to be systematically different in detrital compact, detrital porous and post-sedimentary/hydrothermal
pyrite grains from different source areas. High Co/Ni ratios and low Au concentrations are typical of post-sedimentary pyrite,
which is hydrothermal in origin. In contrast, relatively low Co/Ni ratios and high Au contents characterise detrital porous
banded and concentric pyrite grains (Au > 1 ppm), which are syn-sedimentary in origin. In the Elliot Lake area and the Witwatersrand
Basin, detrital compact rounded pyrite is characterised by high Co/Ni ratios, which is in agreement with derivation from a
hydrothermal source. Low Au concentrations in this pyrite type support the contention of the gold and the pyrite in these
deposits coming from different source rocks. In contrast, derivation from an originally diagenetic pyrite is suggested for
the detrital compact pyrite in the Ouro Fino Syncline because of low to intermediate Co/Ni ratios. High Au contents may indicate
a genetic relationship between pyrite and gold there. Systematic differences exist between the three areas with respect to
Au, Ni, Co, Mo and Cu distributions in detrital pyrite, which reflects differences in the provenance. A predominantly mafic/ultramafic
source is indicated for the Ouro Fino, a felsic source for the Elliot Lake, and a mixed felsic–mafic provenance for the Witwatersrand
pyrite populations. Independently of pyrite type, the higher Au endowment of the studied Witwatersrand and Ouro Fino conglomerates
are also reflected by an overall higher Au concentration in the respective pyrite grains compared to the relatively Au-poor
samples from Elliot Lake. In general, a strong positive correlation between Au and Pb levels in the various pyrite grains
is noted. Analogous to Pb, which is well known for not being easily accommodated in the pyrite crystal lattice but occurring
as discrete PbS phases, Au is considered to be present mainly in the form of discrete Au phases in minute pores and interstices
of the pyrite grains rather than within the pyrite lattice. 相似文献
4.
《International Geology Review》2012,54(1):65-72
Chert-plus-pyrite pebbles have been known for some time in a number of Witwatersrand conglomerates, but their distribution is highly variable. A wide variety of textures in chert-plus pyrite pebbles are documented here, and these textures place constraints on the origin of such pebbles. Replacement of chert pebbles by pyrite is indicated (pyrite grains and aggregates continue across many pebble boundaries), and both distributional and textural evidence favors a post-burial timing for this process. Significant mobility of sulfur after burial is indicated. Whether this replacement was diagenetic or metamorphic is not certain. 相似文献
5.
Microstructural analysis of pyrite from a single sample of Witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation. Internal deformation associated with dislocation creep is heterogeneously developed within grains, shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the Central Rand conglomerates. In contrast, brittle deformation, manifest by grain fragmentation that transects dislocation-related microstructures, is spatially related to grain contacts and is interpreted to represent post-depositional deformation of the Central Rand conglomerates. Analysis of the low-angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of <010>{100} slip systems. However, some orientation boundaries have geometrical characteristics that are not consistent with simple <010>{100} deformation. These boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized <001>{120} slip system. These boundaries are associated with order of magnitude enrichments in As, Ni and Co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast-diffusion pathways. The results confirm the importance of grain-scale elemental remobilization within pyrite prior to their incorporation into the Witwatersrand gold-bearing conglomerates. Since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite, the results have implications for the application of minor element geochemistry to ore deposit formation, suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing. 相似文献
6.
J. E. J. Martini 《Mineralium Deposita》1986,21(4):306-312
An early Proterozoic palaeosol, developed on basalt and the basal part of an overlying transgressive marine sedimentary sequence, contains pyrite which is auriferous in places. The mineralization is stratiform and continuous over a distance of several hundred kilometres. Although this mineralization can be explained by a number of genetical models the author concluded that the mineralization took place during pedogenesis and/or diagenesis. Gold is considered to have been leached from the basalt and from the B horizon of the palaeosol by sulphide-rich groundwater and was then precipitated by the effect of the lowering of the HS– activity. The latter is thought to have been caused by atmospheric oxidation and by reaction with Fe-rich leachate from the A horizon, and pyritization of pre-existing iron oxide minerals may also have contributed. It is concluded that a pedogenic gold protore may explain the origin of at least some of the gold of the Witwatersrand type of deposit. 相似文献
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9.
Evidence for a magmatic origin for Carlin-type gold deposits: isotopic composition of sulfur in the Betze-Post-Screamer Deposit, Nevada, USA 总被引：6，自引：0，他引：6
We report here new sulfur isotope analyses from the Betze-Post-Screamer deposit, the largest Carlin-type gold deposit in the
world. Carlin-type deposits contain high concentrations of arsenic, antimony, mercury, tellurium and other elements of environmental
interest, and are surrounded by large volumes of crust in which these elements are also enriched. Uncertainty about the source
of sulfur and metals in and around Carlin-type deposits has hampered formulation of models for their origin, which are needed
for improved mineral exploration and environmental assessment. Previous studies have concluded that most Carlin-type deposits
formed from sulfide sulfur that is largely of sedimentary origin. Most of these studies are based on analyses of mineral separates
consisting of pre-ore diagenetic pyrite with thin overgrowths of ore-related arsenian pyrite rather than pure, ore-related
pyrite. Our SIMS spot analyses of ore-related pyrite overgrowths in the Screamer zone of the Betze-Post-Screamer deposit yield
δ34S values of about −1 to 4‰ with one value of about 7‰. Conventional analyses of realgar and orpiment separates from throughout
the deposit yield δ34S values of about 5–7‰ with one value of 10‰ in the Screamer zone. These results, along with results from an earlier SIMS
study in the Post zone of the deposit and phase equilibrium constraints, indicate that early arsenian pyrite were formed from
fluids of magmatic origin with variable contamination from sulfur in Paleozoic sedimentary rocks. Later arsenic sulfides were
formed from solutions to which sulfur of sedimentary origin had been added. The presence of Paleozoic sedimentary sulfur in
Carlin-type deposits does not require direct involvement of hydrothermal solutions of sedimentary origin. Instead, it could
have been added by magmatic assimilation of Paleozoic sedimentary rocks or by hydrothermal leaching of sulfur from wall rocks
to the deposit. Thus, the dominant process delivering sulfur, arsenic, gold and mineralizing fluids to Carlin-type systems
and their surrounding country rocks was probably separation of fluids from a magmatic source.
Editorial handling: G. Beaudoin 相似文献
10.
Dipl.-Geol. Thomas Utter 《International Journal of Earth Sciences》1978,67(2):774-804
The morphology of pyrites from the Proterozoic, auriferous and uraniferous conglomerates of the Upper Witwatersrand System of the Klerksdorp Goldfield (South Africa) was studied by means of scanning electron microscopy (SEM). The pyrite particles were recovered by hydrofluoric acid leaching, thus making a three-dimensional SEM examination possible. According to morphological criteria the pyrites were classified into three types. Trace-element analysis by atomic absorption spetrophotometry (Au, Co, Ni, Cu, Zn, Pb, Mn, As) and the statistical evaluation of the results confirmed the morphological classification: Type 1: Authigenic, idiomorphic to hypidiomorphic pyrites or pyrite accumulations, which were formed in the conglomerates during diagenesis or metamorphism. Type 2: Allogenic, rounded, compact pyrites. This type was eroded from primary deposits in the hinterland of the Witwatersrand basin and deposited with the Witwatersrand sediments. It shows the closest trace-element affinity to pyrites from the Barberton Mountain Land, the source area model for the Witwatersrand sediments. The recognition of this pyrite type from the Klerksdorp Goldfield is in agreement with observations on detrital compact pyrites described from other goldfields of the Witwatersrand. Type 3: Allogenic, rounded, porous pyrites. These were formed from pyritic muds and iron sulfide gels existing on the surface of the alluvial fan, and later were reworked as mud balls or fragments and deposited with the conglomerates. Indentations with radial fracture patterns point to transport partly in a plastic state. The occurrence of colloform pyrites among this type supports the postulation of pyritic muds or iron sulfide gels. Only in this type of pyrite various inclusions such as gold, quartz, silicates, brannerite, copper- and titanium-bearing minerals were found. It is suggested that these inclusions were trapped as dust-like particles in the pyritic muds or iron sulfide gels on the surface of the alluvial fan. Only the presence of the allogenic, porous pyrites could be correlated with high gold values in the conglomerates. The three-dimensional SEM examination of the pyrites has shown that the pyrite types described by previous authors from the Witwatersrand System can be classified into the three types of pyrite given here. 相似文献
11.
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
12.
拉拉铜矿黄铁矿微量元素地球化学特征及其成因意义 总被引：6，自引：0，他引：6
四川会理拉拉铜矿床是我国著名大型富铜矿床,针对该矿床中黄铁矿的微量元素、稀土元素地球化学分析表明:拉拉铜矿经历了早期火山喷发成岩成矿和晚期变质成岩成矿作用.条带状矿石中的黄铁矿Co/Ni比值集中于4.92～79.2之间,落入火山成因黄铁矿区,稀土元素分布具有Eu正异常和轻稀土富集的特征,反映矿床具有伴随河口群火山喷流沉积成岩过程的同生沉积成矿作用.脉状矿石中的黄铁矿Co/Ni比值集中于1.10～3.45,落在热液成因黄铁矿区,稀土元素较河口群岩石及其他典型块状硫化物矿床矿石稀土元素更加富集轻稀土元素,稀土含量变化范围更大,显著的负Eu异常,则又说明,矿床形成的主要成矿作用是伴随新元古代晋宁运动而发生的大规模的变质作用. 相似文献
13.
滇东南马关都龙是一个以锡锌为主,共-伴生铟、铜、铅、钨、铁、银等多种元素的锡锌多金属超大型矿床。虽然前人从矿物学、矿床地球化学、年代学等不同角度开展了较多的研究,该矿床锡锌多金属矿化为燕山晚期岩浆热液活动的产物已是不争的事实,但关于该矿床是否存在热水沉积作用及其与锡锌多金属成矿作用的关系依然存在较大争议。本文选取都龙矿区广泛存在的黄铁矿作为主要研究对象,在矿相学基础上利用LA-ICPMS对不同阶段黄铁矿的微量元素组成开展了系统的研究。野外及显微鉴定结果表明,矿区存在四种类型(期次)的黄铁矿,即:鲕状黄铁矿Py1;穿切或交代Py1的细脉状黄铁矿Py2;与闪锌矿等硫化物共生的自形黄铁矿Py3;包裹早期黄铁矿或闪锌矿等硫化物的他形黄铁矿Py4。LA-ICPMS分析结果表明,该矿床黄铁矿中富集多种微量元素,其中Co、Ni、As、Ge等元素以类质同象的形式存在黄铁矿晶格中,而其余元素多以显微矿物包体形式赋存于黄铁矿中。上述四期黄铁矿微量元素组成存在较大差别,Py1相对富集Zn和As,而其余微量元素含量较低,Co与Ni含量较低,Co/Ni比值远低于1.00,其微量元素组成与典型沉积作用形成黄铁矿基本一致; Py2与Py1具有相似的微量元素组成特征,其Co/Ni比值接近Py1变化范围; Py3和Py4除富集Zn、As外,Mn、Co、Ni、Cu、Sb、Pb、Bi元素含量也相对较高,其Co/Ni比值相对较高,多大于1,与典型岩浆热液型黄铁矿微量元素组成相似,而与沉积型黄铁矿差异明显。结合各阶段黄铁矿产出地质特征,对比不同类型黄铁矿微量元素组成,本研究认为:Py1鲕状黄铁矿为热水沉积作用形成; Py2为Py1变质改造形成的细脉状黄铁矿,其微量元素继承了Py1; Py3为岩浆热液活动形成的自形黄铁矿; Py4为岩浆热液活动晚期形成的他形黄铁矿,Ag和Bi组成作为区分不同成因类型黄铁矿的化学指标的潜力。矿区早期沉积作用形成鲕状黄铁矿过程可能为后期成矿作用提供了部分硫源及少量Zn等成矿物质,海西-印支期区域变质改造作用对矿区成矿作用影响不大,而燕山晚期岩浆热液活动才是矿区锡多金属大规模成矿作用的主导因素。 相似文献
14.
山东烟台南张家金矿黄铁矿的标型特征 总被引：8，自引：1，他引：8
通过对烟台南张家金矿黄铁矿的形态、成分和热电性标型的分析和测试 ,对金矿的深部成矿远景进行了评价。南张家金矿黄铁矿的形态以 { 1 0 0 } +{ 2 1 0 }为主 ,反映了成矿溶液中硫浓度较高 ,金具有明显的亲硫性。黄铁矿成分贫 Co、Ni,富 As、Hg。热电导型主要为 P型 ,表明所采矿体为浅部矿 ,深部仍有远景。同时 ,黄铁矿 P型导型出现率由上到下变化很小 ,成矿环境稳定 ,显示矿体向下继续延伸。另外 ,矿石中的黄铁矿与磁山二长花岗岩中的副矿物黄铁矿在形态、成分和热电性上具相似性 ,表明二者具有继承关系 ,佐证了金矿的形成与岩体的演化有关。 相似文献
15.
邦布金矿床是目前在雅江缝合带研究程度最高且唯一正在开采的大型造山型金矿床.为理解邦布金矿床中金的来源及迁移沉淀机制,运用原位微区分析技术对邦布矿床中不同世代含金黄铁矿的微量元素组成进行测定.结果显示,亲铁元素Co、Ni主要以类质同象的形式进入到黄铁矿的晶格中替代Fe,As和Se呈类质同象形式替换S,Au是以纳米颗粒的形式均匀或不均匀的分布于不同产状的黄铁矿之中.邦布金矿床中的含金石英脉中三个不同世代的黄铁矿的Co/Ni比值均小于1,保存了围岩中黄铁矿的信息,显示出一种沉积或沉积改造成因.Au与As和Se具有明显的正相关关系,As和Se对Au的迁移及富集具有重要的作用. 相似文献
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新康猫金矿床热液矿物微量元素地球化学特征及成因探讨 总被引：2，自引：0，他引：2
通过对与新康猫金矿金成矿有关的石英、方解石和黄铁矿的微量元素、稀土元素等地球化学特征的测试分析发现:这些数据较好地反映了该矿床的成矿流体来源和成因信息证实其为受层位和构造复合控制的微细浸染型金矿床,矿体赋存于北北东向与北北西向构造复合部位,在垂向上构造对成矿具有分带控制的特征。石英形成于氧化环境下石英中Au与亲岩浆元素Cr,Co,Rb,Zr,Hf,Th,V,W,O正相关,说明有较多深部流体或岩浆流体参与。黄铁矿中Au,As含量很高,其稀土元素配分模式与岩石有一定的相似性,而石英与方解石的则与岩石的有较大的差异,显示形成的流体是有深部流体的参与。 相似文献
18.
Denis Fougerouse Steven M. Reddy Christopher L. Kirkland David W. Saxey William D. Rickard Robert M. Hough 《地学前缘(英文版)》2019,10(1):55-63
The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite(FeS_2), we have combined electron backscatter diffraction(EBSD) and atom probe microscopy(APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth(~3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a highangle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization.Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ~2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation. 相似文献
19.
江南造山带上产出有大量金矿,但其成因存在争议,为厘清其成因,对该造山带上的正冲金矿床中的黄铁矿进行了LA-ICP-MS微量元素分析和流体包裹体研究.结果显示,正冲金矿的流体包裹体有含CO2包裹体、富CO2包裹体和水溶液包裹体,其中富CO2包裹体与水溶液包裹体共存,具有相似的均一温度,但盐度不同,说明流体不混溶可能导致了... 相似文献
20.
以大平山铜矿、天台山黄铁矿矿为例，阐述了该区的矿区、矿床地质及火山机构特征，并从成矿时间、空间及成因三个方面论述了矿床成矿与古火山机构的关系。 相似文献