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通过对山西省马兰煤矿2号煤层采掘面在开采和封闭时期的矿井水和沉积物的研究,揭示采掘面封闭前后对矿井水水质和沉积物的影响机理。研究结果表明:马兰煤矿矿井水均为SO4-Ca型水质,矿井水均富含SO42-和Fe离子;随着上部煤层的不断开采,3处矿井水呈现相同的变化规律,矿井水的pH值升高,Eh值降低,SO42-、Fe、Mn和Zn离子浓度随之下降,其中北一暗斜井处的矿井水水质变化最显著;矿井水水质指标和流速变化能够控制其沉积物的矿物组成和结晶程度,北一暗斜井处的沉积物在两次采样中由斯沃特曼铁矿变为针铁矿,而其他两处的矿井水沉积物矿物组分没有发生变化,主要由针铁矿组成。研究结果能够提高对老空区积水水质的预测精度,并对煤矿突水水源判识具有重要意义。 相似文献
3.
L. Prez del Villar J. Bruno R. Campos P. Gmez J. S. Czar A. Garraln B. Buil D. Arcos G. Carretero J. Ruiz Snchez-Porro P. Hernn 《Chemical Geology》2002,190(1-4):395-415
In the frame of the ENRESA natural analogue programme, the uranium ore from the “Mina Fe” (Salamanca, Spain) has been studied as a natural analogue of radioactive spent fuel behaviour. This uranium mine is hosted in highly fractured schistose rocks, a geological setting that has not been envisaged in the Spanish options for radioactive waste burial. However, some analogies with the processes that might be involved in the evolution of these geological repositories suggested this investigation.
The pitchblende–pyrite–carbonate paragenesis has been studied “in situ” as natural analogue of the nuclear spent fuel behaviour under extremely oxidative dissolution conditions. Similarly, secondary Fe oxyhydroxides and clay minerals have also been considered as relevant analogue materials for the retention of uranium and other analogous trace metals. A multidisciplinary characterisation of the site has been performed in order to study these processes.
Though the intense mining activities in the site hindered precise determination of the original hydrogeological and hydrochemical features of the investigated zone (Boa fault zone), the mineralogy and geochemistry of fracture fillings, mineralisation and associated clayey materials have allowed the geochemical evolution of the system to be established. Three geochemical zones have been clearly differentiated: (i) the oxidised zone, from the surface to approximately 20 m depth, (ii) the redox transition zone, from 20 to 50 m depth, and (iii) the reduced zone, located below the transition zone.
The oxidised zone is characterised by the presence of the typical mineral association resulting from the strong acid conditions caused by the total oxidation of pyrite and other sulphides. The total oxidation, dissolution and leaching of U(IV), as uranyl–sulphate aqueous complexes, prevailed in this oxidised zone. The redox transition zone is characterised by the coexistence of the primary uranium paragenesis, oxidised minerals, as well as numerous secondary solid phases as a result of the physico-chemical changes in the environment. The optimal physico-chemical conditions for the coffinitisation of pitchblende and the co-precipitation of Fe(III)–U(VI) took place in this zone. In the reduced zone, where the primary uranium paragenesis is present, we currently find the necessary physico-chemical conditions to stabilise pitchblende, pyrite and carbonates.
The physico-chemical conditions of the oxidised zone are not relevant to disposal conditions. In the transition zone, two main geochemical processes take place: (i) the coffinitisation of pitchblende, which may be an important process for the stability of spent fuel in reducing conditions, and (ii) the co-precipitation of the Fe(III) and U(VI) as oxyhydroxides, another relevant mechanism for the retention of uranium. The physico-chemical conditions that prevail below 50 m depth should be sufficient to stabilise a spent nuclear fuel repository, in the same way as they have been able to preserve the 34-Ma-old uranium deposit of the Mina Fe. 相似文献
4.
长江口氧化还原敏感元素的早期成岩过程 总被引：2，自引：0，他引：2
通过测试长江口沉积物及间隙水中Fe、Mn、U及Mo的含量,结合早期成岩模型及地球化学热力学分析,探讨了在河口环境中影响间隙水氧化还原敏感元素(Fe、Mn、U及Mo)分布的主要因素.根据Fick第一定律,估算了Fe、Mn、U及Mo在沉积物-水界面的扩散通量.结果表明,间隙水Fe、Mn、U及Mo的含量分别介于0.8~106μmol/L、14.8~258μmol/L、1.9~14.4nmol/L及60~546nmol/L之间.在垂直剖面上,间隙水Fe、Mn峰值分别出现在约5cm或10cm的深度.早期成岩过程是影响长江口沉积物间隙水Fe、Mn分布的主要因素.吸附系数对间隙水Fe、Mn的分布也有重要的影响.吸附系数越高,间隙水Fe、Mn浓度越低.影响间隙水U分布的主要因素为Fe,而Mo与Fe、Mn之间不存在相关性.通量计算结果显示Fe、Mn、U及Mo的扩散通量分别介于3.0~10.5μmol·(m2·d)-1、35.7~439.5μmol·(m2·d)-1、-2.3~0.2nmol·(m2·d)-1及-36.0~94.6nmol·(m2·d)-1之间.沉积物中自生铀组分约占总铀的6%~67%. 相似文献
5.
Magneticmineralsintheloess paleosolseriesaccountforabout 1 % -2 %ofthetotal (LiuTungshengandZhangZhonghu ,1 962 ) .Duetotheiraerolianorigin ,themagneticmineralsarecomplicatedincomposition ,largeingrainsizerange ,andsignificantlydifferentincrystallinity .Asaresult,researchonthesemagneticmineralswouldbesetwithalotofdifficulties.Previousre searchersemployedopticalmicroscopic ,X raydiffractionandM ssbauerspectrometrictechniquestostudythemagneticmineralsintheloess paleosolseries,andchieflyontheb… 相似文献
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The average contents of REE, Y, Fe, Mn, and clay minerals were determined in the subcolloid fraction of bottom sediments from the northern part of Amur Bay. The positive correlation of REE and Y contents with Fe and Mn is related to their flocculation and sorption on Fe, Mn oxyhydroxides and clay minerals (hydromica, smectites). The sediments are subdivided into three groups (sediments from the influence zone of the Razdol’naya River, sediments located along the eastern and western shores of the bay, and sediments weakly subjected to the river influence) with different average contents of REE, Y, Fe, and Mn. It is shown that REE and Y are mainly incorporated (98–100%) in clay minerals. 相似文献
7.
Scott G. Johnston Annabelle F. Keene Richard T. Bush Edward D. Burton Leigh A. Sullivan Lloyd Isaacson Angus E. McElnea Col R. Ahern C. Douglas Smith Bernard Powell 《Chemical Geology》2011,280(3-4):257-270
Tidal inundation is a new technique for remediating coastal acid sulfate soils (CASS). Here, we examine the effects of this technique on the geochemical zonation and cycling of Fe across a tidally inundated CASS toposequence, by investigating toposequence hydrology, in situ porewater geochemistry, solid-phase Fe fractions and Fe mineralogy. Interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation, redistribution and subsequent mineralogical transformations of Fe within the landscape. Reductive dissolution of Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6), resulted in elevated concentrations of porewater Fe2+ (> 30 mmol L?1) in former sulfuric horizons in the upper-intertidal zone. Tidal forcing generated oscillating hydraulic gradients, driving upward advection of this Fe2+-enriched porewater along the intertidal slope. Subsequent oxidation of Fe2+ led to substantial accumulation of reactive Fe(III) fractions (up to 8000 μmol g?1) in redox-interfacial, tidal zone sediments. These Fe(III)-precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation. Schwertmannite (Fe8O8(OH)6SO4) was the dominant Fe mineral phase in the upper-intertidal zone at mainly low pH (3–4). This was followed by increasing lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) at circumneutral pH within lower-intertidal and subtidal zones. Relationships were evident between Fe fractions and topography. There was increasing precipitation of Fe-sulfide minerals and non-sulfidic solid-phase Fe(II) in the lower intertidal and subtidal zones. Precipitation of Fe-sulfide minerals was spatially co-incident with decreases in porewater Fe2+. A conceptual model is presented to explain the observed landscape-scale patterns of Fe mineralisation and hydro-geochemical zonation. This study provides valuable insights into the hydro-geochemical processes caused by saline tidal inundation of low lying CASS landscapes, regardless of whether inundation is an intentional strategy or due to sea-level rise. 相似文献
8.
绿泥石化蚀变岩带位于虎皮峪杂岩体北部。六块地－哈达岭一带，东西长８．２ｋｍ，产在辽河群里尔峪组磁铁矿浅粒岩段与电气石变粒岩段之间，由外向内可划分为４个蚀变亚带，其中绿泥石化、黄铁矿化亚带赋含铀矿。依据矿物蚀变关系、脉体切割关系，蚀变带内矿物生成顺序可划分３期６个阶段，铀矿化产于热液蚀变期。铀矿化受ＥＷ向绿泥石化蚀变岩带控制，与铀矿化有关的蚀变有绿泥石化、硅化、赤铁矿化，主要的合矿围岩有大理岩、蚀变浅粒岩。铀与铁、锰、钙、磷、铜、铅、镧、铈、钴呈正相关，而与造岩元素硅，铝，钾，钠呈负相关。铀矿物主要为沥青铀矿，形成于早元古代。揭露工作证明是一有远景的矿点。 相似文献
9.
Acta Geochimica - Goethite (α-FeOOH) is one of the most abundant minerals on the Earth surface, occurring in temperate, tropical and equatorial climates. Fe in goethite can be substituted by... 相似文献
10.
Julien Mercadier Michel Cuney Michel Cathelineau Mathieu Lacorde 《Mineralium Deposita》2011,46(2):105-135
Proterozoic basement-hosted unconformity-related uranium deposits of the Athabasca Basin (Saskatchewan, Canada) were affected
by significant uranium redistribution along oxidation–reduction redox fronts related to cold and late meteoric fluid infiltration.
These redox fronts exhibit the same mineralogical and geochemical features as the well-studied uranium roll-front deposits
in siliclastic rocks. The primary hydrothermal uranium mineralisation (1.6–1.3 Ga) of basement-hosted deposits is strongly
reworked to new disseminated ores comprising three distinctly coloured zones: a white-green zone corresponding to the previous
clay-rich alteration halo contemporaneous with hydrothermal ores, a uranium front corresponding to the uranium deposition
zone of the redox front (brownish zone, rich in goethite) and a hematite-rich red zone marking the front progression. The
three zones directly reflect the mineralogical zonation related to uranium oxides (pitchblende), sulphides, iron minerals
(hematite and goethite) and alumino-phosphate-sulphate (APS) minerals. The zoning can be explained by processes of dissolution–precipitation
along a redox interface and was produced by the infiltration of cold (<50°C) meteoric fluids to the hydrothermally altered
areas. U, Fe, Ca, Pb, S, REE, V, Y, W, Mo and Se were the main mobile elements in this process, and their distribution within
the three zones was, for most of them, directly dependent on their redox potential. The elements concentrated in the redox
fronts were sourced by the alteration of previously crystallised hydrothermal minerals, such as uranium oxides and light rare
earth element (LREE)-rich APS. The uranium oxides from the redox front are characterised by LREE-enriched patterns, which
differ from those of unconformity-related ores and clearly demonstrate their distinct conditions of formation. Uranium redox
front formation is thought to be linked to fluid circulation episodes initiated during the 400–300 Ma period during uplift
and erosion of the Athabasca Basin when it was near the Equator and to have been still active during the last million years.
A major kaolinisation event was caused by changes in the fluid circulation regime, reworking the primary uranium redox fronts
and causing the redistribution of elements originally concentrated in the uranium-enriched meteoric-related redox fronts. 相似文献
11.
Scott G. Johnston Edward D. Burton Richard T. Bush Annabelle F. Keene Leigh A. Sullivan Douglas Smith Angus E. McElnea Col R. Ahern Bernard Powell 《Applied Geochemistry》2010
Tidal inundation was restored to a severely degraded tropical acid sulfate soil landscape and subsequent changes in the abundance and fractionation of Al, Fe and selected trace metals were investigated. After 5 a of regular tidal inundation there were large decreases in water-soluble and exchangeable Al fractions within former sulfuric horizons. This was strongly associated with decreased soil acidity and increases in pH, suggesting pH-dependent immobilisation of Al via precipitation as poorly soluble phases. The water-soluble fractions of Fe, Zn, Ni and Mn also decreased. However, there was substantial enrichment (2–5×) of the reactive Fe fraction (FeR; 1 M HCl extractable) near the soil surface, plus a closely corresponding enrichment of 1 M HCl extractable Cr, Zn, Ni and Mn. Surficial accumulations of Fe(III) minerals in the inter-tidal zone were poorly crystalline (up to 38% FeR) and comprised mainly of schwertmannite (Fe8O8(OH)6SO4) with minor quantities of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH). These Fe (III) mineral accumulations provide an effective substrate for the adsorption/co-precipitation and accumulation of trace metals. Arsenic displayed contrary behaviour to trace metals with peak concentrations (∼60 μg g−1) near the redox minima. Changes in the abundance and fractionation of the various metals can be primarily explained by the shift in the geochemical regime from oxic–acidic to reducing-circumneutral conditions, combined with the enrichment of reactive Fe near the soil surface. Whilst increasing sequestration of trace metals via sulfidisation is likely to occur over the long-term, the current abundance of reactive Fe near the sediment–water interface favours a dynamic environment with respect to metals in the tidally inundated areas. 相似文献
12.
Hexavalent uranium [U(VI)] dissolved in a modified lactate-C medium was treated under anoxic conditions with a mixture of an Fe(III)-(hydr)oxide mineral (hematite, goethite, or ferrihydrite) and quartz. The mass of Fe(III)-(hydr)oxide mineral was varied to give equivalent Fe(III)-mineral surface areas. After equilibration, the U(VI)-mineral suspensions were inoculated with sulfate-reducing bacteria, Desulfovibrio desulfuricans G20. Inoculation of the suspensions containing sulfate-limited medium yielded significant G20 growth, along with concomitant reduction of sulfate and U(VI) from solution. With lactate-limited medium, however, some of the uranium that had been removed from solution was resolubilized in the hematite treatments and, to a lesser extent, in the goethite treatments, once the lactate was depleted. No resolubilization was observed in the lactate-limited ferrihydrite treatment even after a prolonged incubation of 4 months. Uranium resolubilization was attributed to reoxidation of the uraninite by Fe(III) present in the (hydr)oxide phases. Analysis by U L3-edge XANES spectroscopy of mineral specimens sampled at the end of the experiments yielded spectra similar to that of uraninite, but having distinct features, notably a much more intense and slightly broader white line consistent with precipitation of nanometer-sized particles. The XANES spectra thus provided strong evidence for SRB-promoted removal of U(VI) from solution by reductive precipitation of uraninite. Consequently, our results suggest that SRB mediate reduction of soluble U(VI) to an insoluble U(IV) oxide, so long as a suitable electron donor is available. Depletion of the electron donor may result in partial reoxidation of the U(IV) to soluble U(VI) species when the surfaces of crystalline Fe(III)-(hydr)oxides are incompletely reduced. 相似文献
13.
《矿物学报》2013,(Z1)
Weathering of manganese-bearing carbonate could form chalcophanite. In this paper, the occurrence of Fe (hydro) oxides and Mn-bearing minerals in Qixiashan were identified by XRD and SEM, mainly consisted of goethite, hematite, pyrolusite and chalcophanite. From the microscope investigation, stromatolite-like structure phenomenon is widespread existed, which may be caused by microbial activities. To identify the mineral structure in the Fe-Mn crust, Raman and XPS were used to identify the mineral structure and valence of Fe, Mn and Zn. This work could help us to know the relationship of Fe and Mn during the weathering of manganese-bearing carbonate. And the enrichment of Mn and Zn from the supergene environment could provide a path for the contamination of heavy metals. 相似文献
14.
Yiyang Zhao 《中国地球化学学报》1982,1(3):338-342
The following conclusions can be drawn from the work reported in this paper:
- Sixteen samples were determined for uranium by spectrophotometric method. The uranium content in the sea floor sediments of the Bohai Gulf ranges from 1.6 to 6.3 ppm, with an average of 4.3 ppm.
- Statistical data show close relationship between U concentration and grain size. Relatively larger amount of uranium was found accumulated in mud than in sand. The bulk of uranium is assumed to be derived from terrestrial detrital minerals.
- A positive correlation between U and Fe is recognized. Similar relation also can be seen between U and Al. The plot of U concentration vs. Fe is linear, and can be expressed by the linear regression equation:Y=?0.37+1.35X. The plot of U against Al gives an equation ofY=?2.48+1.01X.
- The average U/Corg. ratio for these sediments is 7×10?4, and the average ratios of U/P, U/Mn, and U/CaCO3 are 100×10?4, 50×10?4 and 2×10?4, respectively.
- Compared with the abundances of other shelf sediments, the average concentration of U in the area under consideration is close to that of sediments on the selves of Japan and the Gulf of Mexico, and the Black Sea. Uranium concentration in the Bohai Gulf sediments is comparable to that of the continental crust, but differs from that of deep-sea clay.
15.
Harish Veeramani Daniel S. Alessi Juan S. Lezama-Pacheco Jonathan O. Sharp Urs Dippon John R. Bargar 《Geochimica et cosmochimica acta》2011,75(9):2512-6510
Reductive immobilization of uranium by the stimulation of dissimilatory metal-reducing bacteria (DMRB) has been investigated as a remediation strategy for subsurface U(VI) contamination. In those environments, DMRB may utilize a variety of electron acceptors, such as ferric iron which can lead to the formation of reactive biogenic Fe(II) phases. These biogenic phases could potentially mediate abiotic U(VI) reduction. In this work, the DMRB Shewanella putrefaciens strain CN32 was used to synthesize two biogenic Fe(II)-bearing minerals: magnetite (a mixed Fe(II)-Fe(III) oxide) and vivianite (an Fe(II)-phosphate). Analysis of abiotic redox interactions between these biogenic minerals and U(VI) showed that both biogenic minerals reduced U(VI) completely. XAS analysis indicates significant differences in speciation of the reduced uranium after reaction with the two biogenic Fe(II)-bearing minerals. While biogenic magnetite favored the formation of structurally ordered, crystalline UO2, biogenic vivianite led to the formation of a monomeric U(IV) species lacking U-U associations in the corresponding EXAFS spectrum. To investigate the role of phosphate in the formation of monomeric U(IV) such as sorbed U(IV) species complexed by mineral surfaces, versus a U(IV) mineral, uranium was reduced by biogenic magnetite that was pre-sorbed with phosphate. XAS analysis of this sample also revealed the formation of monomeric U(IV) species suggesting that the presence of phosphate hinders formation of UO2. This work shows that U(VI) reduction products formed during in situ biostimulation can be influenced by the mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute-solid chemistry of the solid-phase reductant. 相似文献
16.
《Geochimica et cosmochimica acta》1999,63(19-20):2971-2987
Many sediment and soil systems have become significantly contaminated with cadmium, and earth scientists are now required to make increasingly accurate predictions of the risks that this contamination poses. This necessitates an improved understanding of the processes that control the mobility and bioavailability of cadmium in the environment. With this in mind, we have studied the composition and structure of aqueous cadmium sorption complexes on the iron oxyhydroxide minerals goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH), and schwertmannite (Fe8O8(OH)6SO4) using extended X-ray adsorption fine structure spectroscopy. The results show that adsorption to all of the studied minerals occurs via inner sphere adsorption over a wide range of pH and cadmium concentrations. The bonding mechanism varies between minerals and appears to be governed by the availability of different types of adsorption site at the mineral surface. The geometry and relative stability of cadmium adsorption complexes on the goethite surface was predicted with ab initio quantum mechanical modelling. The modelling results, used in combination with the extended X-ray adsorption fine structure data, allow an unambiguous determination of the mechanism by which cadmium bonds to goethite.Cadmium adsorbs to goethite by the formation of bidentate surface complexes at corner sharing sites on the predominant (110) crystallographic surface. There is no evidence for significant cadmium adsorption to goethite at the supposedly more reactive edge sharing sites. This is probably because the edge sharing sites are only available on the (021) crystallographic surface, which comprises just ∼2% of the total mineral surface area. Conversely, cadmium adsorption on lepidocrocite occurs predominately by the formation of surface complexes at bi- and/or tridentate edge sharing sites. We explain the difference in extended X-ray adsorption fine structure results for cadmium adsorption on goethite and lepidocrocite by the greater availability of reactive edge sharing sites on lepidocrocite than on goethite. The structures of cadmium adsorption complexes on goethite and lepidocrocite appear to be unaffected by changes in pH and surface loading. There is no support for cadmium sorption to any of the studied minerals via the formation of an ordered precipitate, even at high pH and high cadmium concentration. Cadmium adsorption on akaganeite and schwertmannite also occurs via inner sphere bonding, but the mechanism(s) by which this occurs remains ambiguous. 相似文献
17.
One deposit and four occurrences of uranium minerals in the Permo-Triassic sedimentary rocks of the Stara Planina in eastern Serbia were ascertained using data from years of multidisciplinary geological research. The minerals are the fissure-filling type, and were assigned to the exogenic mineralization group, being mostly epigene in nature. Relevant geological information was used to derive a genetic model of uranium mineralization in the Permo-Triassic sedimentary rocks of the Stara Planina. The model explains the formation of Permo-Triassic rocks and three stages of the complex process of U mineralization. The genetic model treats: (1) the primary sources of the uranium; (2) the mobility of uranium; and (3) accessory metals from the parent rocks to their deposition in host rocks and the postmineral change in ore bodies. A geochemical barrier zone was identified in the sedimentary rocks that contained uranium mineral ore. This geochemical barrier area included crescent-shaped, flat-lens, or vein-like ore bodies. The U-containing mineral described is comparable with those from the relatively common fissure-filling uranium minerals found around the world. 相似文献
18.
通过在滇池开展原位实验,研究探讨了湖泊沉积物中磷灰石制约水铁矿分解和转化的机制,以及二者共存时的环境效应。结果表明:将水铁矿放置到沉积物中1个月,矿物保持稳定;放置时间达到3个月时,添加磷灰石实验中水铁矿发生了显著物相转变。冬天(12—2月)实验中,转化产物随深度的变化趋势为针铁矿+磁(赤)铁矿→针铁矿+纤铁矿→针铁矿;夏天(6—9月)实验中,转化产物随深度的变化趋势为针铁矿+纤铁矿+磁(赤)铁矿→针铁矿+纤铁矿→未转化。透射电镜分析结果显示冬天实验中生成的磁性铁氧化物为纳米磁铁矿和磁赤铁矿,夏天实验中产生的则主要为纳米磁铁矿。X射线光电子能谱分析结果显示冬天表层实验样品具有较高P含量。分析表明的湖泊沉积物中磷灰石促进水铁矿转化的过程为:(1)微生物促进磷灰石溶解;(2)磷灰石溶解释放的P促进铁还原菌生长;(3)铁还原菌促进水铁矿还原;(4)水铁矿还原产生的溶解态Fe2+催化水铁矿向针铁矿、纤铁矿和磁铁矿转化。冬天及沉积氧化-还原界面最适宜磷灰石分解菌和铁还原菌生长,水铁矿的转化和P释放能力也更强,相应地内源磷释放的风险也更大。 相似文献
19.
铁锰氧化物矿物胶膜是我国黄棕壤中重要的铁锰元素富集载体,选取我国华中地区典型的铁锰氧化物矿物胶膜样品,采用电感耦合等离子体原子发射光谱(ICP-AES)、偏光显微镜(POM)、环境扫描电子显微镜(ESEM)、能谱仪(EDX)、高分辨透射电子显微镜(HRTEM)、高能量X射线粉末衍射(XRD)等研究方法,对原位和分离处理后的黄棕壤铁锰胶膜进行了详细的矿物学表征.结果表明,黄棕壤铁锰氧化物矿物胶膜由表及里,由外到内依次呈现富锰条带、富铁锰条带、富铁条带、富锰铁条带、富铁条带,并且锰铁元素含量之比不规则降低,其所含铁锰氧化物矿物主要为锰钡矿、针铁矿、水钠锰矿、六方水锰矿、水羟锰矿,粒度为纳米级,形貌多样. 相似文献
20.
M. J. Duane 《Mineralium Deposita》1988,23(1):50-57
The Gortdrum Cu-Ag-As-Sb-Hg-U orebody occurs in Lower Carboniferous strata on the downthrown side of an ENE transcurrent fault system in Southern County Tipperary, Republic of Ireland. The deposit comprises a linear discordant zone of brecciated carbonates and country rocks that are altered and mineralised. Research has indicated anomalous radioelement concentrations associated with the main copper orebody and in particular with the altered breccias within this zone. The metal association (Cu-Ag-As-Sb-Hg-U) is considered unique for Irish Carboniferous carbonate-hosted copper deposits. However, the low temperature mineral assemblage of early uranium-bearing minerals with later sulphide stages is reminiscent of many vein-type hydrothermal ore deposits. The geochemistry of uranium-enriched rocks indicates that the alteration of the basic dykes was a most significant event in the trapping of uranium within the limestones. Propylitization of the early basic dykes by CO2-bearing fluids produced the alteration which led to the development of hematite, leucoxene and clay minerals. The reducing environments attendant with such mineralogy created a favourable environment for uranium precipitation. The reduction of U+6 to U+4 by oxidation of reduced Fe in dolomitized brecciated limestone occurred prior to the main sulphide mineral sequences. The genesis of uranium in the deposit is linked to radioelement remobilization from uranium-bearing heavy minerals in sediments of upper Devonian-Lower Carboniferous age. The uranium became available to low temperature hydrothermal fluids which carried then deposited the uranium along a transcurrent fault system. The source of the heavy minerals is considered to be the Leinster Granite to the east, by which time in the Carboniferous, unroofing of the main pluton had commenced.Previous address: Department of Geology, Trinity College, Dublin 2, Ireland 相似文献