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Abiotic controls on copper isotope fractionation during the dissolution of copper sulfide minerals.

机译：硫化铜矿物溶解过程中铜同位素分级的非生物控制。

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摘要

Stable isotope measurements have long been used as a geochemical tool in the Earth sciences, and recent advances in analytical techniques have added intermediate mass stable isotopes (e.g. Cu, Zn, Fe, Ni) to this suite of interpretive methods. The Cu isotope system offers particularly high potential to solve geologic problems due to its large natural isotopic variation (∼12 ‰). However, the factors that control the fractionation of Cu isotopes, especially during the dissolution of Cu-sulfide minerals, remain incompletely resolved.;In this dissertation, I explore abiotic controls on Cu isotope fractionation during the dissolution of Cu-sulfide minerals by combining in situ time-resolved X-ray diffraction (TRXRD) coupled with stable isotope analysis. As a foundational part of this study, I modified a preexisting design for a TR-XRD flow-through cell in order to remove any metal content and to allow for automated sampling of the eluate fluid. The resulting device (described in Chapter 1) allowed us to correlate Cu isotope fractionation with changes in crystal structure during Cusulfide dissolution.;TR-XRD analyses of oxidative dissolution of chalcocite (Cu2S) and bornite (Cu5FeS4) enabled the development of rate equations that describe these reactions and the identification of the reaction sequences as Cu leached from the solid phase (Chapter 2). During chalcocite dissolution, XRD analysis revealed mineral transformations involving the following phases: djurleite (Cu1.94S), roxbyite (Cu1.75S), yarrowite (Cu1.13S), and covellite (CuS). Similarly, the dissolution of bornite by ferric sulfate solutions also produced changes to the mineral structure: a contraction of the bornite unit-cell volume as "non-stoichiometric bornite" formed. XRD results demonstrated that the structure of non-stoichiometric bornite is similar to mooihoekite (Cu2.25Fe2.25S 4). These results clarified the reaction sequences that occur when ferric sulfate solutions dissolve chalcocite and bornite.;By combining time-resolved diffraction data of these Cu sulfide dissolution reactions with real-time sampling and isotopic analysis of the eluates, we were able to discern structural controls on Cu isotope fractionation during dissolution. As described in Chapter 3, during the initial stages of bornite oxidative dissolution by ferric sulfate (<5 mol% of total Cu leached), dissolved Cu was enriched in isotopically heavy Cu (65Cu) relative to the solid, with an average apparent isotope fractionation (Delta aq-min = delta65Cuaq - delta65 Cumino, where delta65Cu aq is the isotope composition of the leached Cu and delta65 Cumino is the isotope composition of the beginning mineral powder) of 2.20 +/- 0.25. (Chapter 3). When >20 mol% Cu was leached from the solid, the difference between the Cu isotope composition of the aqueous and mineral phases approached zero, with Deltaaq-min o values ranging from -0.21 +/- 0.61‰ to 0.92 +/- 0.25‰. We propose that the decrease in the apparent isotope fractionation as the reaction progressed resulted from distillation of isotopically heavy Cu (65Cu) during dissolution or isotope effects associated with the formation of a leached layer on the surfaces of bornite particles.;Similarly, during the initial stages of chalcocite oxidative dissolution (Chapter 4), leached fluids were enriched in heavy Cu (65Cu) with delta65Cu values of ∼3‰. As the dissolution reaction progressed and chalcocite transformed to covellite, the leached Cu became isotopically lighter and delta65Cu values of the leachate decreased to as low as -3.01‰. Isotope box models are consistent with two isotope effects that influence the degree of fractionation observed during the reaction: one due to oxidation (alpha ∼ 1.003) and another due to changes in bonding during mineral transformations (alpha ∼ 1.001). These results may be useful in interpreting the extent of weathering in Cu ore bodies and the potential for Cu release from acid mine drainage environments.
机译：稳定的同位素测量长期以来一直被用作地球科学中的地球化学工具，分析技术的最新进展已将中等质量稳定同位素（例如Cu，Zn，Fe，Ni）添加到这套解释方法中。铜同位素系统由于其较大的自然同位素变化（〜12‰）而具有解决地质问题的特别高的潜力。然而，控制铜同位素分馏的因素，特别是在硫化铜矿物溶解过程中，仍未得到完全解决。原位时间分辨X射线衍射（TRXRD）与稳定同位素分析相结合。作为这项研究的基础部分，我修改了TR-XRD流通池的现有设计，以去除任何金属含量并允许对洗脱液进行自动采样。由此产生的装置（在第1章中进行了描述）使我们能够将Cu同位素分馏与Cus硫化物溶解过程中的晶体结构变化相关联; TR-XRD对球晶石（Cu2S）和斑铜矿（Cu5FeS4）的氧化溶解进行分析，从而开发了速率方程，描述了这些反应并鉴定了从固相中浸出的铜的反应顺序（第2章）。在球晶石溶解过程中，XRD分析显示出矿物转变涉及以下阶段：变长晶石（Cu1.94S），方铁矿（Cu1.75S），亚arrow石（Cu1.13S）和堇青石（CuS）。同样，硫酸铁溶液溶解的褐铁矿也使矿物结构发生变化：形成的“非化学计量的褐铁矿”使褐铁矿的晶胞体积收缩。 XRD结果表明，非化学计量的褐铁矿的结构类似于Mooihoekite（Cu2.25Fe2.25S 4）。这些结果阐明了硫酸铁溶液溶解菱铁矿和菱锰矿时发生的反应顺序。;通过将这些硫化铜溶解反应的时间分辨衍射数据与洗脱液的实时采样和同位素分析相结合，我们能够辨别结构控制溶解过程中铜同位素分馏如第3章所述，在硫酸铁还原氧化斑铜矿的初始阶段（浸出的总铜<5 mol％），相对于固体，溶解的铜富含同位素重的铜（65Cu），平均表观同位素分馏（δaq-min ＝ delta65Cuaq-delta65 Cumino，其中delta65Cu aq是浸出的Cu的同位素组成，而delta65 Cumino是起始矿物粉末的同位素组成）为2.20 +/- 0.25。 （第3章）。当从固体中滤出> 20 mol％的Cu时，水相和矿物相的Cu同位素组成之间的差接近零，Deltaaq-min o值在-0.21 +/- 0.61‰至0.92 +/- 0.25‰范围内。我们认为随着反应的进行，表观同位素分馏的降低是由于同位素溶解重铜（65Cu）期间的溶解或同位素效应的影响，而同位素效应与在斑岩质颗粒表面形成沥滤层有关。在球墨石的氧化溶解阶段（第4章），浸出的流体中富含重金属Cu（65Cu），δ65Cu值为〜3‰。随着溶解反应的进行和菱锰矿转变成贝壳沸石，浸出的Cu同位素变轻，渗滤液的delta65Cu值降低至-3.01‰。同位素盒模型与影响反应过程中观察到的分馏程度的两种同位素效应是一致的：一种是由于氧化（α〜1.003），另一种是由于矿物转化过程中键的变化（α〜1.001）。这些结果可能有助于解释铜矿体中的风化程度以及酸性矿山排水环境中铜释放的可能性。

著录项

  • 作者

    Wall, Andrew J.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Geochemistry.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 170 p.
  • 总页数 170
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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