Weathering of Bi-bearing tennantite
Weathering of Bi-bearing tennantite
复制标题
含铋铁矿的风化
DOI：
10.1016/j.chemgeo.2018.07.032
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Markl G.
中科院分区：
文献类型：
--
作者：
Keim M. F;Staude S;Marquardt K;Bachmann K;Opitz J;Markl G.
钙钛矿-四方铅矿固溶体系列[又称辉绿岩；(Cu，Ag)6Cu4(Fe，Zn，Cu，Hg，Cd)2(Sb，As，Bi，Te)4(S，Se)13]广泛存在于多种地质环境中。由于它含有重金属和有毒元素，更好地了解它的风化行为和风化过程的细节，对于评估环境风险(主要来自As-Sb-Bi的动员)以及溪水和海洋中的当地和全球金属通量非常重要。本研究利用显微镜、电子显微镜、扫描电子显微镜、透射电子显微镜、LA-ICPMS、拉曼光谱、μX射线衍射仪和MLA对该矿物群富铋矿物的风化进行了研究。观测结果表明，该矿物群的风化经历了四个不同的阶段：在第一阶段，砂岩中的不规则管状矿物表现为一组纳米到μm大小的软锰矿组矿物、闪锌矿、晶态铜氧化物和铜硫化物。阶段1结构和次生硫化物指示低氧化还原电位和低流体/岩石比，这是胶结带的典型特征。物质平衡计算表明，在这一阶段，所有的锌和大部分的砷、S都被释放到风化流体中。在这一阶段，铋是不活动的，如果铋从土壤中充分可用，Sb和Fe也是不活动的，但如果土壤中没有足够的铋，两者都被部分释放。在第二阶段，无定形和纳米晶态的砷酸盐取代藻土作为风化锋面。这种组合表明，氧化还原电位高于阶段1，这是氧化带的典型特征。质量平衡计算表明，锌、锑、S和部分铜都是亏损的。砷和铋是不可移动的。阶段3只发生在局部，溶解以前的风化阶段和/或在微区中沉淀无定形的砷酸铜/硅酸盐反射过程，这不是一般风化过程的特征。第四阶段的特征是形成晶态的含铋、铜、钡、钙或铝的砷酸盐和铜碳酸盐，它们在空间上独立于前驱动物群。铜和砷来自较老的风化组合，而许多其他元素来自外部(Ca、Ba、Al)。这一阶段反映了当地寄主岩石和脉石矿物学的日益重要，因为它在氧化带或矿山排土场的近地表环境中是典型的，那里的元素具有高活动性和高流体/岩石比(铁帽矿化)。风化结构的时间演化反映了新鲜矿石向胶结带、氧化带和铁帽组合的转变。因此，一个辉石颗粒可以记录风化矿床随时间的抬升和侵蚀以及流体/岩石相互作用的增强。在其他风化环境和各种元素、氧化物、砷化物和硫化物相中，也有类似阶段1中观察到的管状结构的报道。它们也是在钛铁矿的实验工作中产生的。这是一个明确的证据，表明与蚀变流体首次接触时的扩散过程是一个基本的物理过程，它不仅对绿壤有效。本工作表明，铋对稳定含Sb表生相(从而固定有毒Sb)的重要性，可能会促进进一步研究风化过程中伴生金属对有毒元素的环境固定作用。
The tennantite-tetrahedrite solid-solution series [called fahlore; (Cu,Ag)6Cu4(Fe,Zn,Cu,Hg,Cd)2(Sb,As,Bi,Te)4(S,Se)13] is widespread in many geological environments. Since it incorporates heavy metals and toxic elements, a better understanding of its weathering behaviour and details of its weathering process is important to evaluate environmental risks (emerging mainly from the mobilization of As-Sb-Bi) and local and global metal fluxes in stream waters and oceans. In this study, weathering of Bi-rich members of this mineral group was investigated using microscopy, EMPA, SEM, TEM, LA-ICP-MS, Raman, μXRD, and MLA.Observations reveal a succession of four distinct stages of weathering: During stage 1, irregular tubes within fahlore show an assemblage of nm- to μm-sized roméite group minerals, tripuhyite, crystalline Cu-oxides and Cu-sulfides. Stage 1 textures and secondary sulfides indicate a low redox-potential and a low fluid/rock ratio, typical of cementation zones. Mass balance calculations show that during this stage all Zn and the majority of As and S are released to the weathering fluids. Bismuth is immobile in this stage and Sb and Fe are immobile, if Bi is sufficiently available from fahlore, but both are partly released, if the fahlore did not contain sufficient Bi. During stage 2, amorphous and nano-crystalline arsenates replace fahlore as weathering fronts. Such assemblages indicate a higher redox-potential than in stage 1, typical for oxidation zones. Mass balance calculations reveal that Zn, Sb, S and partially Cu are lost. Arsenic and Bi are immobile. Stage 3 occurs only locally, dissolving former weathering stages and/or precipitating amorphous Cu-arsenates/silicates reflecting processes in micro-compartments, not characteristic for the general weathering process. Stage 4 is characterized by the formation of crystalline Bi-, Cu-, Ba-, Ca- or Al-bearing arsenates and Cu-carbonates, spatially independent of the precursor fahlore. Copper and As originate from older weathering assemblages, whereas many other elements are derived externally (Ca, Ba, Al). This stage reflects the increasing importance of the local host rock and gangue mineralogy, as it is typical in near-surface environments of oxidation zones or on mine dumps, where elements are highly mobile and a high fluid/rock ratio prevails (gossan mineralization).The temporal evolution of fahlore weathering textures reflects the transition from fresh ore to cementation zone, oxidation zone and gossan assemblages in one hand specimen. Thus, one fahlore grain can record the uplift and erosion and the increasing fluid/rock interaction of a weathered ore deposit with time. Tube-like textures similar to the ones observed in stage 1 have been reported from other weathering environments and from a variety of element, oxide, arsenide, and sulfide phases. They also were produced during experimental work in ilmenite. This is clear evidence, that the diffusive process during the first contact with alteration fluids is a basic physical process and that it is not only valid for fahlore.The importance of Bi to stabilize Sb-bearing supergene phases (and thereby for the immobilization of toxic Sb) shown in the present work, may stimulate further investigations on the environmental immobilization of toxic elements by “companion metals” during weathering processes.
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影响因子：
5
作者：
F. Burmann;Maximilian F. Keim;Y. Oelmann;Holger Teiber;M. Marks;G. Markl
通讯作者：
F. Burmann;Maximilian F. Keim;Y. Oelmann;Holger Teiber;M. Marks;G. Markl
亚利桑那州 Rich Hill 浅近系和表近系过程中铅同位素对天然金形成的见解
DOI：
--
发表时间：
2013
期刊：
影响因子：
--
作者：
G. Kamenov;E. Melchiorre;Faye Ricker;E. Dewitt
通讯作者：
E. Dewitt
影响因子：
2.7
作者：
Janssen, A.;Putnis, A.;Putnis, C. V.
通讯作者：
Putnis, C. V.
影响因子：
3.9
作者：
Eva Kocourková;O. Sracek;S. Houzar;J. Cempírek;Z. Losos;J. Filip;Pavla Hršelová
通讯作者：
Eva Kocourková;O. Sracek;S. Houzar;J. Cempírek;Z. Losos;J. Filip;Pavla Hršelová
铋：无机化学
DOI：
--
发表时间：
2006
期刊：
影响因子：
--
作者：
K. Whitmire
通讯作者：
K. Whitmire