东胜地区直罗组含铀砂岩中方解石的碳氧同位素组成及铀成矿意义

方解石是东胜地区直罗组含铀砂岩中重要的胶结物类型,同时碳酸盐化与铀成矿作用关系密切。通过方解石胶结物岩石学、矿物学、碳氧同位素分析,研究了含铀砂岩中方解石碳氧同位素组成、沉淀机制及铀成矿意义。研究表明,东胜地区砂岩类型为长石岩屑砂岩、岩屑砂岩和石英砂岩,粘土矿物主要由蒙皂石、伊利石、高岭石和绿泥石组成,方解石类型以含铁矿方解石为主,其次为铁方解石。方解石δ~(13)C_(PDB)为-15.7‰~-1.6‰,平均-9.08‰,δ~(18)O_(PDB)为-15.6‰~-10‰,平均-12.4‰,显示其形成与有机酸脱羧作用有关,碳来源为有机碳。碳氧同位素分析数据计算表明,与方解石平衡的水相氧同位素组成变化范围较宽,为-7.66%-9.71‰,推测较轻的同位素组成具有封存大气降水的特征,而较重同位素组成则反映成岩成矿过程中深部富含油气低温热流体的加入。综合分析认为,东胜地区直罗组砂岩中方解石是地表水和深部油气共同作用的结果:早期有机酸促使长石类骨架颗粒溶蚀,形成石英颗粒次生加大边,并伴随着自生高岭石沉淀;后期随着大量烃类注入砂岩中,成岩成矿环境由酸性向碱性转变,还原性增强,介质水中的CO_2与Ca~(2+)圾Fe~(2+)结合形成含铁为特征的方解石,沉淀在原生粒间孔和各类次生溶蚀孔隙中。整个过程都伴随有铀元素运移和沉淀,暗示东胜铀矿床是地表水和深部油气混合作用形成的。     

MICP技术联合多孔硅吸附材料对锌铅复合污染土固化/稳定化修复的试验研究

近年来,工业和科技的快速发展使得重金属污染土固化/稳定化的修复研究成为热点。运用微生物诱导碳酸钙沉淀(MICP)技术联合吸附材料对锌铅复合重金属污染土进行固化/稳定化的修复,通过无侧限抗压强度试验、毒性浸出试验,评价处理前后污染土的固化效果与重金属的稳定化效果,结合扫描电镜(SEM)和X射线衍射(XRD)等检测手段,揭示MICP技术处理锌铅重金属污染土的修复机制。研究结果表明,采用MICP技术对锌铅重金属污染土进行固化/稳定化之后,可以有效降低污染土中有害重金属的浸出性。当矿化时间为10d时,试样无侧限抗压强度为942.5k Pa;铅的浸出浓度为4.20mg/L,比未处理时降低了44.81%;锌的浸出浓度为4.31mg/L,比未处理时降低了46.19%,效果显著。在此基础上,添加10%的多孔硅吸附材料后,试样无侧限抗压强度可达到1 021 kPa,强度提高了8.3%;铅的浸出浓度为2.45mg/L,与未经处理时相比,降幅达到了67.81%,与单纯MICP方法处理时相比,铅浸出浓度被二次降低了41.67%;锌的浸出浓度仅为2.93 mg/L,与未经处理时相比,降幅达到了63.4%,与单纯...     

埋藏条件下方解石热力学平衡及其在塔河油田埋藏岩溶预测中的应用

方解石在成岩环境中的溶解度与地下水化学特征、温度等有着极为密切的关系。通过CaCO3溶解沉淀反应平衡以及地下水中的Ca2+活度可以确定不同温压的地下水条件下方解石的溶解趋势。地下水溶液的pH值和温度是方解石溶解度最直接的控制因素。方解石溶解趋势可以通过CaCO3电离反应的吉布斯自由能(ΔG)来判断:ΔG<0时,反应向溶解方向进行;ΔG>0时,反应向沉淀方向进行。根据方解石的水岩反应理论,对塔河油田34口井的奥陶系地层水进行了ΔG的统计计算。结果显示:塔河油田现今地下水条件有利于方解石的溶解,西部地区较东部溶解趋势强,北部地区溶解趋势相对较弱。这为定量了解塔河地区埋藏岩溶趋势及该地区的储层评价预测提供了理论依据。     

微生物诱导碳酸盐在土体加固中的应用进展

微生物矿化是近年来在土体改良工程发展起来的一个新分支,主要研究微生物活性在改善土体颗粒特性方面的应用。微生物诱导碳酸盐沉积（MICP）是实现土体生物胶结最常用的方法之一,该技术借助脲酶菌的代谢行为诱导碳酸钙,将松散的砂颗粒胶结成整体,从而提高了土体的力学性能。文章系统性地介绍了MICP研究中的脲酶菌矿化机理、相关处理方法、影响因素、衍生新工艺脲酶诱导碳酸盐沉积EICP及MICP技术在岩土领域的相关现场试验,并对MICP的实用性进行了总结,最后简要讨论了现研究阶段MICP工程应用所面临的挑战和潜在解决方案。     

矿物对原油裂解影响的实验研究

在限定体系下（密封金管）,对原油、原油＋蒙脱石和原油＋方解石进行了裂解产气模拟实验。结果表明,原油＋蒙脱石裂解的甲烷和总气态烃（C1-C5）产率在大多数实验温度点与纯原油裂解基本相同,只有在高温度点才相对偏高,反映了蒙脱石对原油裂解的催化效应。原油＋方解石裂解的甲烷和总气态烃的产率则在大多数实验温度点比纯原油裂解相对偏低,并且在高温度点明显偏低,表明方解石对原油裂解具有抑制作用。纯原油和原油＋方解石裂解气态烃产物中异构烷烃和烯烃的相对含量基本相同,而原油＋蒙脱石裂解气态烃产物中异构烷烃和烯烃的含量则明显偏高。依据2℃／h和20℃／h两个升温速率甲烷和总气态烃产率,应用美国Lawrence Liverinore国家实验室开发的Kinetics软件模拟了纯原油、原油＋蒙脱石和原油＋方解石裂解生成甲烷和总气态烃的动力学参数,推算了在地质条件下原油裂解主要阶段的温度范围。     

Origin and development of tafoni in Tunnel Spring Tuff,Crystal Peak,Utah, USA

Bedding‐parallel tafoni are well developed over much of the surface of the Tunnel Spring Tuff (Oligocene) exposed in 300‐m‐high Crystal Peak, an inselberg. The Tunnel Spring Tuff is a crudely stratified, non‐welded rhyolite ash‐flow tuff with > 30 per cent porosity. Clasts of Palaeozoic dolomite, limestone and quartzite make up 10 per cent of the tuff. The tafoni are remarkable because of their size (up to 20 m wide but rarely wider than 4 m), shape of the openings (spherical, arch‐like or crescent‐shaped) and abundance (up to 50 per cent of an outcrop face). They are actively forming today. Calcite is abundant (10 to 40 per cent by weight) in tafoni as an efflorescence in spalling flakes of tuff on their roofs and walls. Halite and gypsum generally make up less than 0·01 per cent of the efflorescence. The absence of corroded quartz and feldspar grains in spall fragments indicates that chemical weathering is unimportant in development of the tafoni. Calcite, aragonite, halite and gypsum dust from modern salt pans less than 20 km from Crystal Peak are potential sources of salt in the tuff, but the prevailing winds are in the wrong direction for significant amounts of these evaporite minerals to reach the inselberg. Calcite is the only evaporite mineral present in the tafoni in more than trace amounts, and this mineral is readily available within the tuff itself as a result of rock weathering. We propose that meteoric water containing carbonic acid infiltrates the tuff, dissolves carbonate clasts, and migrates to the steep flanks (>20°) of the peak through abundant megapores and micropores. There it evaporates and precipitates calcite. Crystallization pressure spalls off grains and sheets as the physical manifestation of salt weathering. The quasi‐uniform spacing of tafoni suggests that a self‐organization process is active in the water flow. Copyright © 2000 John Wiley & Sons, Ltd.     

Spatial Variability of Living Coccolithophore Distribution in the Western Subarctic Pacific and Western Bering Sea

Vertical distributions of coccolithophores were observed in the depth range 0–50 m in the western subarctic Pacific and western Bering Sea in summer, 1997. Thirty-five species of coccolithophores were collected. Overall, Emiliania huxleyi var. huxleyi was the most abundant taxon, accounting for 82.8% of all coccolithophores, although it was less abundant in the western Bering Sea. Maximum abundance of this species was found in an area south of 41°N and east of 175°E (Transition Zone) reaching >10,000 cells L⁻¹ in the water column. In addition to this species, Coccolithus pelagicus f. pelagicus, which accounted for 4.2% of the assemblage, was representative of the coccolithophore standing crop in the western part of the subarctic Pacific. Coccolithus pelagicus f. hyalinus was relatively abundant in the Bering Sea, accounting for 2.6% of the assemblage. Coccolithophore standing crops in the top 50 m were high south of 41°N (>241 × 10⁶ cells m⁻²) and east of 170°E (542 × 10⁶ cells m⁻²) where temperatures were higher than 12°C and salinities were greater than 34.2. The lowest standing crop was observed in the Bering Sea and Oyashio areas where temperatures were lower than 6–10°C and salinities were less than 33.0. From the coccolithophore volumes, the calcite stocks in the Transition, Subarctic, and the Bering Sea regions were estimated to be 73.0, 9.7, and 6.9 mg m⁻², respectively, corresponding to calcite fluxes of 3.6, 0.5, and 0.3 mg m⁻²d⁻¹ using Stoke's Law. This revised version was published online in July 2006 with corrections to the Cover Date.     

内蒙古东胜地区砂岩型铀矿赋矿地层方解石胶结物C、O同位素特征和成因模型

砂岩型铀矿赋矿地层方解石胶结物C、O同位素组成对研究成矿机制具有重要的理论和实践意义。前人在成矿流体来源定性判断方面做了大量的研究工作,但缺乏对成矿混合流体的组分特征及相关参数的定量认识。根据内蒙古东胜地区东南部皂火壕和西北部纳岭沟铀矿床赋矿地层直罗组方解石胶结物C、O同位素组成特征,建立了渗出热卤水和渗入地层水两种不同流体混合生成方解石胶结物C、O同位素组成定量成因模型,并研究了两种流体来源、溶解碳的浓度比、流体比例以及热液温度等综合因素。除少数样品方解石胶结物为地层沉积时形成外,大部分方解石胶结物是热卤水与地层水两种流体混合作用的结果,古生界有机酸脱羧作用导致热卤水中富含CO_2。东胜地区砂岩型铀矿成矿流体地层水与热卤水比例为0.5～0.9,地层水所占的比例较大;热卤水与地层水溶解碳浓度比主要范围为1.5～5.0,部分大于10.0,热卤水中溶解碳浓度较高,是富含CO_2的流体。混合流体温度分为两个主要范围55～80℃、90～140℃,结合古盐度和盐度指数反演,表明成矿流体为有机与无机混合成因的低温热液流体。用砂岩型铀矿赋矿地层方解石胶结物C、O同位素组成,可定量模拟两种流体溶解碳浓度比、流体比例和方解石形成时温度等流体成矿条件,解释碳酸盐胶结物成因,以便从成矿流体角度更好地理解成矿作用过程。     

微生物矿化作用改善岩土材料性能的影响因素

基于微生物诱导碳酸钙沉淀作用（MICP）的土体改性技术近年来在岩土工程领域引起了人们的广泛关注。该技术在改善岩土材料的强度、刚度、抗液化、抗侵蚀及抗渗透性等性能的同时,还能维持土体良好的透气性和透水性,改善植物的生长环境。由于微生物矿化作用涉及一系列生物化学和离子化学反应,固化过程中的反应步骤较多,因此,MICP固化效果受许多因素的制约与影响。基于大量文献资料,系统总结了细菌种类、菌液浓度、温度、pH值、胶结液配比及土的性质等关键因素对微生物改善岩土材料性能的影响,讨论了这些影响因素的优化方式和未来的研究方向,主要得到了以下几点结论：菌种类型、菌液浓度、温度、pH、胶结液性质会从微观上影响碳酸钙的晶体类型、形貌和尺寸,进而在宏观层面影响岩土体的胶结效果;菌液浓度尽可能高、温度在20～40℃间、pH值在7.0～9.5左右、胶结液浓度在1 mol/L以内的因素条件对微生物加固岩土体具有较好的效果。上述范围内的低温、较高的pH值、低浓度胶结液有助于提高土体的抗渗性,而高温、较低的pH值以及中高浓度胶结液有助于提高土体的强度;MICP加固土体的有效粒径范围为10～1 000 ?m,相对密度越大、级配越好则加固效果越好。分步灌浆法、多浓度相灌注法及电渗灌浆法有助于提高土体固化均匀性,0.042 (mol/L)/h以下的注浆速度有利于提高胶结液利用率,砂土试样的灌浆压力一般在10～30 kPa之间,粉黏土试样的灌浆压力不宜超过110 kPa,过高的灌浆压力会破坏土体结构,降低固化效果。