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1.
内蒙古西乌旗白音查干矿床是大兴安岭南段锡矿带内最典型、规模最大的Sn-Ag-Zn-Pb矿床。电气石在成矿岩体花岗斑岩和围岩地层中均广泛发育，依据其产状可分为四类：Ⅰ团斑状电气石；Ⅱ热液角砾岩胶结物中电气石；Ⅲ热液脉状电气石；Ⅳ弥散状电气石。在详细的岩相学基础上，利用电子探针点分析和面扫描分析对不同产状和结构的电气石进行了详细的成分分析。结果显示，花岗斑岩体深部的团斑状电气石（Ⅰa类）以自形、环带发育为特征，至少可见三期生长环带：核部电气石（Ⅰa-1）极高的Fe/（Fe+Mg）和Al值暗示其岩浆成因；边部电气石（Ⅰa-3）较富Mg，且与热液矿物共生，是从早期热液流体中沉淀形成的；幔部电气石（Ⅰa-2）的结构和成分显示其形成可能与不混溶的富B-Fe-Na的熔体或流体有关。因此，电气石从核部到边部的生长记录了从晚期岩浆到早期热液阶段的演变过程。花岗斑岩体中上部的团斑状电气石（Ⅰb类）环带不发育，其与热液矿物共生的组合及成分暗示其形成更倾向于与热液过程相关，可能是岩浆顶部聚集的早期流体释放之后被固结岩浆"圈闭"的残余流体结晶的产物。随后，大规模释放的富B流体形成了大量以电气石为主要胶结物的热液角砾岩（Ⅱ类）、成矿前电气石-石英阶段脉系（Ⅲa类）及伴随围岩蚀变而形成的弥散状电气石（Ⅳ类）。对Ⅱ类和Ⅲa类电气石内存在的生长环带分析显示，成矿前可能存在多个脉冲期次且成分有差异的流体的叠加作用。同时，电气石从早期到晚期向富Mg方向的演化，及成分明显受围岩地层影响的现象，暗示岩浆热液流体与围岩地层发生的水岩反应可能在金属成矿过程中起了重要作用。此外，本研究显示，不同产状电气石的结构和成分信息能够有效记录矿床内岩浆-热液转变及热液演化过程的众多细节信息，为深入理解成矿过程提供了依据。 相似文献
2.
广西大厂地区笼箱盖黑云母花岗岩与区内晚白垩世锡多金属成矿作用在时空上密切相关。岩相学特征表明,笼箱盖黑云母花岗岩中的电气石可以分为三类:1)浸染状电气石; 2)石英-电气石囊; 3)电气石-石英脉。本文利用电子探针和激光剥蚀等离子体质谱系统测定三种不同产状电气石的化学组成。分析结果显示,三种产状的电气石均具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值,主体属于碱基亚类铁电气石。浸染状电气石为岩浆晚期结晶,其Fe/(Fe+Mg)比值变化于0. 85～0. 94,随着岩浆分异,电气石逐渐富集Li、F、Fe和Sn等元素。与浸染状电气石相比,石英-电气石囊中早阶段电气石具有低的Fe/(Fe+Mg)比值,高的V、Co和Sr含量,可能反映了岩浆演化晚期出现的不混溶富硼熔/流体对早期黑云母和长石的交代作用,从而使囊中早阶段电气石继承部分被交代矿物的化学组成特征;石英-电气石囊中晚阶段电气石的化学组成变化较大(如Li、F、Mg、Al、V、Fe和Zn),与热液成因电气石的推论一致。与浸染状和囊状电气石相比,石英脉中的电气石具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值;微量元素组成与囊状电气石相似。就成矿元素锡而言,三种产状的电气石均具有相对高的锡含量,与其他地区锡成矿花岗岩中电气石的成分特征相似。但是,从岩浆晚期到热液阶段,大厂地区电气石的锡含量并没有显著升高,可能反映了早期岩浆热液流体对熔体锡有限的萃取作用。 相似文献
3.
辽宁东部古元古界底部地层(南辽河群)中赋存着大型的硼酸盐矿床，含矿层位中广泛分布含电气石的变粒岩和电英岩。空间上这些含电气石的岩石与硼酸盐有着密切的联系，电气石可以作为区域硼矿找矿的标志。已有研究结果表明，该地区的硼酸盐矿床是变质蒸发岩成因。本研究对该区不同产状的电气石和硼酸盐的地质特征，全岩和矿物成分、硼同位素组成进行了分析。本区的电气石包括层状和脉状两大类，而电气石的富集与硼酸盐关系密切，电英岩往往分布在硼酸盐矿体的上盘。而矿体的下盘一般不产出富电气石的岩石。当长英质脉体穿过硼酸盐矿体时，脉体中往往会富集电气石。含电气石岩石的全岩地球化学分析表明，它们的REE及其他微量元素特征以及相关性关系与周围不含电气石的同类岩石十分相似，反映出一种成因上的联系。本区电气石主要属于镁电气石一铁电气石系列，靠近硼矿体的电气石比远离硼矿体的电气石更加富镁，有着更高的Mg／Fe比值。电气石和硼酸盐的硼同位素成分分析显示出二者在同位素组成上的相似性，前者比后者的δ^11B稍低，这可能是由于热液活动过程中同位素分馏的结果。电气石的硼同位素组成在空间上显示出变化规律：远离硼酸盐矿体的电气石的δ^11B值(-5．2‰- 3．6‰)比矿体附近的电气石低(平均 10．5‰)。以上空间和成分上的关系表明硼酸盐可能是形成电气石主要的硼来源，电气石是在热液过程中通过淋滤下伏含硼蒸发岩中的硼形成含硼热液，在与上覆沉积物交代过程中形成含电气石岩石。电气石的条带是热液顺层选择交代的结果。本区电气石与硼酸盐的关系表明，层状电气石可以通过含硼热液交代的方式形成。变质地体中的层状电气石岩石的出现可能与变质蒸发岩有关。这一认识对区域硼矿勘查工作和变质地体的沉积环境分析有借鉴意义。 相似文献
4.
变质地体中富电气石岩石的成因及其意义许虹（长春地质学院,长春,１３００２６）辽吉地区早元古宙硼酸盐矿床中的富电气石岩为研究变质地体中富电气石岩石的成因提供了一个极好的机会。在这些矿床中,富电气石岩石主要分布在硼酸盐矿体的顶板岩石中,在底板中电气石含量... 相似文献
5.
新疆白杨河U-Be矿床中电气石的矿物学特征及其成矿指示 总被引：3，自引：2，他引：1
新疆白杨河铀铍矿床是近年发现的亚洲最大的铍矿床,它位于新疆西准噶尔地区雪米斯坦(谢米斯台)火山岩带内。大地构造上处于哈萨克斯坦-准噶尔板块西北缘古生代陆缘活动带内晚古生代成熟岛弧之上。铀铍矿体主要赋存于杨庄花岗斑岩体与上泥盆统塔尔巴哈台组凝灰岩接触带以及花岗斑岩中。野外观察发现白杨河铀铍矿床中电气石以三种不同产状产出:(1)产于玄武岩中电气石;(2)产于凝灰岩中电气石;(3)产于花岗岩中电气石。电气石在玄武岩和凝灰岩中主要以球状集合体为主,部分沿裂隙充填;而在花岗岩中则主要呈针状以浸染状产出。本文在野外详细观察和岩相学基础上,利用电子探针点、面分析技术,对白杨河不同产状的电气石进行了详细的矿物化学研究工作。结果显示,白杨河铀铍矿床中的电气石均属于碱质黑电气石,但不同产状的电气石其化学成分存在明显差异。玄武岩中的富Ti、Mg和Ca,贫Al、Mn和F;凝灰岩中的富Fe和Na,贫Mg和Ca;花岗岩中的富Al、Mn、F,贫Ti、Fe和Na。不同类型的电气石中均具有较高的F(0. 343～1. 117apfu)和Al(5. 648～7. 351apfu)。白杨河U-Be矿床中电气石化学成分的变化是Al~(Y X)□(Y+Na)_(-1)、Al~(Y X)□(Y+OH)-1和FeMg_(-1)、Fe~(3+)Al_(-1)、AlO(MgOH)_(-1)和AlO(Fe3+OH)_(-1)等替代机制联合作用的结果。白杨河铀铍矿床中电气石化学成分表明形成电气石的流体是富Al、富F的流体; Be可能主要以氟化物或者氟络合物、U主要以氟化物或者氟碳酸盐的形式在热液流体中迁移;电气石或萤石的沉淀导致含U和含Be的氟化物或者氟络合物失稳,致使铍、铀富集成矿。 相似文献
6.
尕林格矽卡岩型铁多金属矿床位于青海东昆仑祁漫塔格造山带与柴达木盆地结合带中部。电气石作为矿区内普遍出现的矿物,部分呈半自形-自形粒状出现在正接触带矽卡岩化蚀变火山岩中(Tour-Ⅰ),也有呈他形粒状形式出现在外接触带变质砂岩中(Tour-Ⅱ)。因其生长化学行为与寄主岩石和流体的化学属性强烈相关,所以电气石的主、微量元素成分为研究热液体系背景下的流体演化及成矿物质来源提供了渠道。尕林格电气石的化学成分包括富Na-Mg的镁电气石和富Ca-Mg的钙镁电气石。Tour-Ⅰ中的环带电气石存在早期核部(Gen-1)被晚期边部(Gen-2)交代的不连续反应边特征。Gen-1为钙镁电气石,而Gen-2为镁电气石。由于镁铁质火山岩的缓冲作用,Gen-1更多地显示出原地寄主岩石的化学成分。随着流体的持续补充,Gen-2则更多地与流体成分保持平衡,显示出较窄的变化范围,与成矿密切相关。Gen-1比Gen-2更加富Fe,意味着流体中Fe浓度降低;而Na含量逐渐上升则暗示流体p H值的升高。尕林格绝大部分矽卡岩电气石都是在早期成核阶段结晶生长的,因为电气石在酸性和中酸性溶液中更加稳定。除此之外,部分Tour-I中还存在沿早期电气石颗粒边缘生长的增生边结构(Gen-3)。Gen-3比Gen-1更加富Ca,推测Gen-3是在相对封闭环境下颗粒间隙溶液作用下的产物。Tour-Ⅱ则既包括钙镁电气石,又含有镁电气石。在Tour-Ⅰ中,Fe和Mg的含量变化范围较大,这与实际观测的Tour-Ⅰ围岩为镁铁质中-基性火山岩密不可分。Tour-Ⅱ比Tour-Ⅰ更加富集B、Ti、Sc、V、Cr、Ga、LREE等元素,这与B的溶解度随流体p H值的升高而升高有关。随着岩浆演化流体p H值的升高,B在相对碱性溶液中大量富集,而大部分微量元素和LREE易与挥发分结合成络合物的形式迁移,因此,B含量高的溶液中部分微量元素和稀土元素含量也会升高。 相似文献
7.
祖母绿是由微量Cr和/或V致色的绿色绿柱石。位于云南省麻栗坡县的大丫口祖母绿矿床是中国重要的祖母绿矿床,近年来取得了一系列的研究进展,但与祖母绿相关的电气石的研究工作还未展开。本文以大丫口矿床含祖母绿矿脉和非矿脉中的电气石为研究对象,在详细的野外调查和岩相学研究基础上,对电气石进行成分测试,旨在探讨电气石成因、查明物质来源和流体演化过程,进一步探究大丫口祖母绿矿床的成矿机制。结果显示:含矿脉电气石单位分子中Na含量为0.62~0.79 apfu,Al含量为5.36~6.17 apfu,Fe/(Fe+Mg)值为0.31~0.41;非矿脉电气石单位分子中Na含量为0.64~0.76 apfu,Al含量为5.66~6.38 apfu,Fe/(Fe+Mg)值为0.14~0.34。大丫口电气石具有富Mg、Y位(Y-site)上呈低Al或无Al的特征,属于碱族镁电气石,但是含矿脉电气石则显示更高的Fe/(Fe+Mg)值。电气石成分的差异可能主要与形成环境有关,电气石的成分差异具有指示祖母绿是否富集的潜力。大丫口电气石具有成分分带且V2O3含量为0.65%~4.76%,其形成与持续的热液流体交代围岩有关。大丫口矿床是一个岩浆起源的动态热液体系,流体通过碱交代作用参与水岩反应萃取围岩中的成矿物质。早期流体的物质组成以源于花岗质熔体的Si、Al、Be、F、P为主,而随着演化的进行,Ca、V等来自地层的成分逐渐增加。研究表明,铍的氟化物或氟铍络合物是大丫口成矿流体中Be的一种重要的迁移方式。萤石、氟磷灰石等含氟矿物的结晶促使铍的氟化物或氟铍络合物分解,流体中氟元素的减少可能是大丫口祖母绿成矿的重要机制之一。 相似文献
8.
新疆阿尔泰可可托海3号伟晶岩脉岩浆-热液过程:来自电气石化学组成演化的证据 总被引：2，自引：0，他引：2
新疆阿尔泰可可托海3号脉不同结构带及其蚀变围岩中电气石化学组成电子探针(EMPA)分析结果显示,蚀变围岩、外接触带和内接触带中电气石为是富钙-铁的镁电气石,电气石化伟晶岩中电气石为富镁-铁的锂电气石,伟晶岩早期结构带(Ⅰ-Ⅳ带)中电气石为黑电气石-锂电气石系列,而伟晶岩晚期结构带(Ⅴ-Ⅶ带)中电气石为锂电气石。蚀变围岩、外接触带和内接触带中电气石以Y位中低Al,高Mg、Ca以及显著低的Al/(Al+Fe)、Fe/(Fe+Mg)比值为特征,主要存在R3++O2-=R2++OH-的置换;伟晶岩内部结构带(Ⅰ-Ⅶ带)中电气石以Y位上极低Mg、Ca,高Fe、Al、Li以及显著高的Al/(Al+Fe)、Fe/(Fe+Mg)比值为特征,主要存在+Al3+=Na++Fe(Mg)2+和Li++Al3+=Fe(Mn)2++Mg2+的置换。蚀变围岩、外接触带和内接触带中电气石化学组成特征指示存在围岩-流体、围岩-熔体相之间的相互作用。伟晶岩早期结构带(Ⅰ-Ⅳ带)中电气石无明显组成分带,为岩浆成因;晚期结构带(Ⅴ-Ⅶ带)中电气石显示振荡环带,形成于岩浆-热液过渡阶段体系。随着伟晶岩由外向里固结,温度逐渐降低,伟晶岩内部结构带中电气石显示Y位上Al、Li、Mn及Fe/(Fe+Mg)比值逐渐增大的演化趋势;内部结构带中电气石几乎不含Mg,指示3号伟晶岩脉岩浆-热液演化是在相对封闭体系中进行的。 相似文献
9.
河北曲阳县中佐伟晶岩脉中电气石的类型和成岩成矿环境研究 总被引：1，自引：1，他引：0
电气石在成岩、成矿作用中具有重要的示踪意义,利用电气石化学组成特征可有效指示其形成的成岩、成矿环境,也是一种有用的找矿标志。我国华南、西部等地区伟晶岩型稀有金属矿床找矿已取得较大进展,但华北地台区伟晶岩型稀有金属矿床尚未取得找矿突破,亟待开展系统而深入的地质找矿工作。河北曲阳县中佐伟晶岩脉中分布有大量的灰黑色自形电气石,适合开展系统的矿物学研究。本文在详细野外地质调查的基础上,系统采集研究样品,结合镜下鉴定,采用粉晶X射线衍射和电子探针相结合的研究方法,对河北曲阳县中佐伟晶岩脉中电气石的化学成分进行测试,以查明电气石的类型及其成岩、成矿环境。粉晶X射线衍射和电子探针分析结果均显示中佐伟晶岩脉中电气石属镁电气石(但接近于铁电气石),而电气石化学成分Ca-Fe-Mg三角图解显示电气石成岩环境为贫Ca变质泥质岩、变质砂屑岩和石英-电气石岩。电气石化学成分常与围岩岩石类型存在明显关联,认为中佐伟晶岩脉中的镁电气石是在较高温度(700~600℃,早期结晶的伟晶岩)条件下,岩浆熔体与高温流体和围岩发生同化混染的过程中形成的,围岩中Mg、Fe等物质成分为电气石的形成提供了必要的物质来源。中佐伟晶岩脉中电气石化学成分的系统研究,为我国地台区伟晶岩矿床的找矿提供了基础地质资料和找矿方向。 相似文献
10.
通过系统的显微镜鉴定及扫描电镜观察,将黔西南普安泥堡金矿床中的黄铁矿按形貌特征划分为6种类型,即立方体状、草莓状、细粒状、粗粒状、环带状及长条状黄铁矿。黄铁矿电子探针分析结果表明,主要载金矿物为含砷黄铁矿(环带状黄铁矿、细粒状黄铁矿)和毒砂。环带状黄铁矿核部和环带形成于不同的成岩、成矿阶段,其核部贫Au、As,富Fe、S,属成岩期的产物;环带富Au、As,贫Fe、S,形成于主成矿期。黄铁矿环带中Au与As具有正对应关系,在一定的楔形空间呈正相关,高Au含量往往与中等As含量(2%~6%)相对应;而As与S呈明显负相关,说明富砷环带是As取代S而进入黄铁矿晶格所致。细粒状黄铁矿具有高Au、As,低Fe、S的特点,类似于环带状黄铁矿环带部位的特征,推测富As环带与细粒状黄铁矿同属主成矿阶段的产物。毒砂常穿插或沿含砷黄铁矿边缘分布,表明其形成晚于热液期含砷黄铁矿。因此,泥堡金矿床中载金矿物的结晶顺序大致为:贫砷沉积成因黄铁矿(核部)→富砷黄铁矿环带和细粒状黄铁矿→毒砂。电子探针点分析和面波普扫描显示,Au在载金矿物含砷黄铁矿和毒砂中具有不均匀分布的特征,根据Au的溶解度极限(Au/As 0.02)和lgw(As)—lgw(Au)图解,推测Au主要以"不可见"固溶体(Au~(+1))形式赋存于含砷黄铁矿和毒砂中,极少量可能为纳米级自然金(Au~0)。 相似文献
11.
Friedemann Freund 《Physics and Chemistry of Minerals》1987,15(1):1-18
The dissolution of H2O and CO2 in structurally dense, nominally anhydrous and non-carbonate oxide matrices such as MgO and CaO is reviewed. H2O and CO2 are treated as gaseous oxide components which enter into solid solution with the refractory oxide hosts. They form anion complexes associated with cation vacancy sites. Evidence is presented that OH? pairs which derive from the dissolution of H2O are subject to a charge transfer (CT) conversion into peroxy moieties and molecular hydrogen, O 2 2? ... H2. Because the O 2 2? moiety is small (O?-O? distance ≈ 1.5 Å) high pressure probably favors the CT conversion. Mass spectroscopic studies show that molecular H2 may be lost from the solid which retains excess oxygen in the form of O 2 2? , leading to the release of atomic O. The dissociation of O 2 2? moieties into a vacancy-bound O? state and an unbound O? state can be followed by measuring the internal redox reactions involving transition metal impurities, the transient paramagnetism of the O? and their effect on the d.c. conductivity. Evidence is presented that CO2 molecules dissolve dissociatively in the structurally dense oxide matrix, as if they were first to dissociate into CO+O and then to form separate solute moieties CO 2 2? and O 2 2? , both associated with cation vacancy sites. In the CO 2 2? moiety (C-O? distance 1.2–1.3 Å, OCO angle ≈ 130°) the C atom probably sits off center. The transition of the C atom into interstitial sites is accompanied by dissociation of the CO 2 2? moiety into CO? and O?. This transition can be followed by infrared spectroscopy, using OH? as local probes. Further support derives from magnetic susceptibility, thermal expansion, low frequency dielectric loss and low temperature deformation measurements. The recently observed emission of O and Mg atoms besides a variety of molecules such as CO, CO2, CH4, HCN and other hydrocarbons during impact fracture of MgO single crystals is presented and discussed in the light of the other experimental data. 相似文献
12.
There are few inter-African country urban analyses because of the continent’s enormous size and socioeconomic diversity, language barriers, and wide variations in national and regional urban research capacity. Nevertheless, comparative urban studies are critical in understanding contemporary African urbanization. In this comparative spatial and temporal analysis of Ghana and Kenya’s urbanization, we find that both countries are urbanizing rapidly and are faced with many common urban problems. Moreover, Ghana is more urbanized than Kenya and has a larger indigenous urban imprint and a more widely dispersed urban pattern. Besides their physiographic and population conditions, we trace these countries’ convergent and divergent urban trends to their shared but unique experiences of colonialism, nationalism and globalization. 相似文献
13.
利用GC-MS（气相色谱—质谱仪）,对采自湖北清江流域和尚洞洞顶的土壤样品与洞内石笋样品进行分析,发现土壤中存在的七个系列单甲基支链烷烃在所有的石笋样品中均可以找到,呈现相似的分布模式,石笋中七个系列支链烷烃有可能来自洞穴滴水携带的土壤中的支链烷烃,但是也不能排除石笋原地生长的微生物的贡献。烷基环己烷的分布在土壤与石笋中呈现了相似的分布模式,但是主峰碳数有所变化,高碳数部分与低碳数部分的相对含量也发生了变化。主要原因可能是微生物选择性降解的结果,也有可能是土壤与石笋中微生物种类分布差异所造成的。本次研究初步显示了相对封闭稳定的洞穴沉积物与上覆土壤层中生物标志化合物的异同。 相似文献
14.
Using improved analytical techniques, which reduce the Re blanks by factors of 8 to 10, we report new Re-Os data on low Re and low PGE pallasites (PAL-anom) and IIIAB irons. The new pallasite samples nearly double the observed range in Re/Os for pallasites and allow the determination of an isochron of slope 0.0775 ± 0.0008 (T = 4.50 ± 0.04 Ga, using the adjusted λ187Re = 1.66 × 10−11 a−1) and initial (187Os/188Os)0 = 0.09599 ± 0.00046. If the data on different groups of pallasites (including the “anomalous” pallasites) are considered to define a whole-rock isochron, their formation would appear to be distinctly younger than for the iron meteorites by ∼60 Ma. Five IIIAB irons (Acuna, Bella Roca, Chupaderos, Grant, and Bear Creek), with Re contents ranging from 0.9 to 2.8 ppb, show limited Re/Os fractionation and plot within errors on the IIAB iron meteorite isochron of slope 0.07848 ± 0.00018 (T = 4.56 ± 0.01 Ga) and initial (187Os/188Os)0 = 0.09563 ± 0.00011. Many of the meteorites were analyzed also for Pd-Ag and show 107Ag enrichments correlated with Pd/Ag, requiring early formation and fractionation of the FeNi metal, in a narrow time interval, after injection of live 107Pd (t1/2 = 6.5 Ma) into the solar nebula. Based on Pd-Ag, the typical range in relative ages of these meteorites is ≤10 Ma. The Pd-Ag results suggest early formation and preservation of the 107Pd-107Ag systematics, both for IIIAB irons and for pallasites, while the younger Re-Os apparent age for pallasites suggests that the Re-Os system in pallasites was subject to re-equilibration. The low Re and low PGE pallasites show significant Re/Os fractionation (higher Re/Os) as the Re and PGE contents decrease. By contrast, the IIIAB irons show a restricted range in Re/Os, even for samples with extremely low Re and PGE contents. There is a good correlation of Re and Ir contents. The correlation of Re and Os contents for IIIAB irons shows a similar complex pattern as observed for IIAB irons (Morgan et al., 1995), and neither can be ascribed to a continuous fractional crystallization process with uniform solid-metal/liquid-metal distribution coefficients. 相似文献
15.
煤中气孔和镶嵌结构及其在煤变质研究中的意义 总被引：1，自引：0，他引：1
河南省禹县、新密和荥巩煤田山西组Ⅱ1煤的贫煤和无烟煤中,气孔发育。气孔形态有椭圆状（图版1）、圆状及不规则状（图版2）,有的几个气孔连在一起呈大的朵状气孔(图版3)。此外,在荥巩煤田西部无烟煤中还发育有镀嵌结构(图版4)。 相似文献
16.
At 31 sites in Finland the Zn content was determined of the epiphytic lichen Hypogymnia physodes (L.) Nyl. growing on pine and birch, the terricolous lichen Cladina spp. in pine bark, and the inner part of birch bark. The anomalous contents of Zn in H. physodes on pine and Cladina spp. in soil appeared to be strongly related to sulphide ore deposits. Anthropogenic Zn correlated closely with S and Fe in H. physodes on pine and with Fe in Cladina spp. The binding of geogenic Zn was related to iron hydroxides, and was attributed to the different uptake mechanism of S in these lichens. Elevated values of Zn in H. physodes on birch were due to both geogenic and anthropogenic sources. Zinc in pine bark increased with the Zn content in H. physodes and reached a limiting value. 相似文献
17.
Aqueous extraction contributes to the formation and weathering of planetary materials and renders electrolytes such as phosphate available for biology. In this context, the solubility of phosphate is measured in planetary materials, represented by the Mars meteorites Nakhla, Dar al Gani 476 (DaG 476), Elephant Morraine 79001 (EETA 79001), and terrestrial analogs, and in the Murchison CM2 and Allende CV3 carbonaceous chondrites. The Mars meteorites contain high levels of phosphate that is readily extracted by water, up to 15 mg kg−1 in Nakhla and DaG 476 and 38 mg kg−1 in EETA 79001, while the terrestrial analogs and the carbonaceous chondrites contain 0.5 to 6 mg kg−1. Correspondingly, high phosphate concentrations of 4 to >28 mg L−1 are obtained in extracts of the Mars meteorites at high solid/solution ratios, exceeding the concentrations of 0.4 to 2.0 mg L−1 in the extracts of the terrestrial analogs. A wide range of planetary conditions, including N2 and CO2 atmospheres, solid/solution ratios of 0.01 to 1.0 kg L−1, extraction times of 1 to 21 d, and temperatures of 20 to 121°C affect the amounts of extractable phosphate by factors of only 2 to 5 in most materials. Phosphate-fixing capacity and exchangeable phosphate are assessed by the isotopic exchange kinetics (IEK) method, which quantifies the amount of P isotopically exchangeable within 1 min (E1min) and between 1 min and 3 months (E1min-3m) and the amount of P that cannot be exchanged within 3 months (E>3m). The IEK results show that the DaG 476 Mars meteorite and terrestrial analogs have low P-fixing capacities, while the carbonaceous chondrites have high P-fixing capacities. Aqueous processing under early planetary CO2 atmospheres has large effects on the available phosphate. For example, the fraction of total P that is exchangeable in 3 months increases from 1.6 to 11%, 13 to 51.6%, and 43.9 to 90.4% in the DaG 476 Mars meteorite, Allende, and Murchison, respectively. The results show that solutions with high phosphate concentrations can form in the pores of planetary lava ash and basalts and in carbonaceous asteroids and meteorites. These solutions can help prebiotic synthesis and early microbial nutrition. The Martian and carbonaceous chondrite materials contain sufficient phosphate for space-based agriculture. 相似文献
18.
Amphibole and chlorite in mafic and ultramafic rocks in the lower crust and upper mantle 总被引：4，自引：0，他引：4
Stabilities of amphibole and chlorite in mafic and ultramafic compositions have been considered in the model system CaO+MgO+Al2O3+SiO2+H2O. From topological arguments two petrogenetic grids have been constructed. Although available experimental data in CMASH are compatible with the grid in which amphibole reacts out before chlorite in model ultramafic compositions for the pressure range 6 to 15 kbar, naturally observed mineral assemblages and some experimental data in more complex systems favour the other grid in which chlorite reacts out before amphibole at all pressures. This discrepancy between natural and model systems is due to differential movement of the dehydration equilibria of the two hydrates reflecting the variation of activity of H2O or of components other than CMASH. 相似文献
19.
Discovery of Cinnabar in Soils in Hg Anomalous Zones in City and Town Areas and Their Surroundings and Its Significance 总被引：1，自引：1，他引：0
ZHU Lixin MA Shengming WANG Zhifeng China University of Geosciences Beijing Institute of Geophysical Geochemical Exploration Chinese Academy of Geological Sciences Langfang Hebei 《《地质学报》英文版》2005,79(2):286-290
As a result of systematic study on heavy minerals in soils at city and town areas and their surroundings,cinnabar was discovered for the first time in areas of Hg anomalies in China, and it was found that the distribution of cinnabar was basically coincident in scope with that of Hg anomalies, showing that Hg anomalies were‘closely related to cinnabar. This finding provides a theoretical basis for a verification of Hg anomalies in soils in city and town areas and their surroundings, as well as evaluation of its ecological effects, and is significant to revealing the occurrence modes and origin of Hg in soils. 相似文献
20.
Temporal and spatial variations in water discharge and sediment load in the Alaknanda and Bhagirathi Rivers in Himalaya, India 总被引：2，自引：0，他引：2
The Alaknanda and Bhagirathi Rivers originate in the mountainous regions of the Himalayas (Garhwal) and result in high sediment yields causing flood hazards downstream of the Ganga River and high sediment flux to the Bay of Bengal. The rivers are perennial, since runoff in these rivers is controlled by both precipitation and glacial melt. In the present study, three locations in the upper reaches of the Ganga River were monitored for 1 yr (daily observations of, more than >1000 samples) for suspended sediment concentrations. In addition, more than one hundred samples were collected from various locations of the Alaknanda and Bhagirathi Rivers at different periods to observe spatial and temporal variations in river suspensions. Further, multi-annual data (up to 40 yrs) of water flow and sediment concentrations were used for inferring the variations in water flow and sediment loads on longer time scales. In most previous studies of Himalayan Rivers, there has been a general lack of long term water flow and sediment load data. In the present study, we carried out high frequency sampling, considered long term discharge data and based on these information, discussed the temporal and spatial variations in water discharge and sediment loads in the rivers in the Himalayan region. The results show that, >75% of annual sediment loads are transported during the monsoon season (June through September). The annual physical weathering rates in the Alaknanda and Bhagirathi River basins at Devprayag are estimated to be 863 tons km−2 yr−1 (3.25 mm yr−1) and 907 tons km−2 yr−1 (3.42 mm yr−1) respectively, which are far in excess of the global average of 156 tons km−2 yr−1 (0.58 mm yr−1). 相似文献