含Cu硫化物中S、Fe同位素分馏系数的第一性原理计算
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P597+.2

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广东省基础与应用基础研究基金(2020A1515011441);广州市科技计划项目(202102020943)


First-principles calculations of S and Fe isotope fractionation in Cu-bearing sulfides
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    摘要:

    Cu在自然界主要以硫化物的形式存在,目前只确定了几种含Cu硫化物的S同位素分馏系数以及黄铜矿的Fe同位素分馏系数,而且不同研究者确定的系数有很大的差别,使得S、Fe同位素在研究铜矿床的形成、演化等方面不能很好地发挥示踪作用。因此,本文基于第一性原理计算确定了0~1 000℃温度范围内主要含Cu硫化物的S同位素简约配分函数比(103lnβ34-32),以及Cu-Fe硫化物的Fe同位素简约配分函数比(103lnβ57-54)。重S同位素在这些含Cu硫化物中的富集顺序为铜蓝>方黄铜矿>黄铜矿≈黑硫铜镍矿>斑铜矿>辉铜矿,重Fe同位素在Cu-Fe硫化物中的富集顺序为方黄铜矿≈黄铜矿>低温斑铜矿>高温斑铜矿>中温斑铜矿>Cu8Fe4S8(中温斑铜矿的可能变体)。含Cu硫化物的103lnβ34-32与S原子的配位数、金属-S平均键长、S原子形成的所有化学键的平均键长没有明显的相关性,而Cu-Fe硫化物的103lnβ57-54与Fe—S平均键长基本成线性负相关关系。辉铜矿相变引起的S同位素分馏特别大,而斑铜矿相变时产生的S同位素分馏却可以忽略不计。本文的计算结果将会为探讨斑岩铜矿及其它类型的硫化物矿床的成因提供支持。

    Abstract:

    In nature, copper mainly occurs in sulfide minerals. At present, only the sulfur β-factors of several Cu-bearing sulfides and the iron β-factor of chalcopyrite have been determined, and the β-factors determined by different researchers are different, impeding the application of S and Fe isotopes as powerful tracers in tracing the formation and evolution of porphyry copper deposits. In this study, the first-principles methods are used to compute the reduced partition function ratio of S isotopes (103lnβ34-32) for Cu-bearing sulfides as well as the reduced partition function ratio of Fe isotopes (103lnβ57-54) for Cu-Fe sulfides in the temperature range of 0~1 000℃. 103lnβ34-32 decreases in the order of covellite>cubanite>chalcopyrite ≈ villamaninite>bornite>chalcocite, and 103lnβ57-54 decreases in the order of cubanite ≈ chalcopyrite>low-bornite>high-bornite>intermediate-bornite>intermediate-Cu8Fe4S8. 103lnβ34-32 of Cu-bearing sulfides displays weak correlations with S coordination number, the average metal-sulfur bond length, and the average bond lengths of all the bonds formed by S, while 103lnβ57-54 of Cu-Fe sulfides displays an approximately negative correlation with the average Fe-S bond length. S isotope fractionation caused by the phase transition of chalcocite is very large, while S isotope fractionation caused by the phase transition of bornite is negligible. The results of this study can provide theoretical evidence for tracing porphyry copper deposits and other types of sulfide deposits.

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刘善琪,梁家新,张秋院,李永兵,2021,含Cu硫化物中S、Fe同位素分馏系数的第一性原理计算[J].岩石矿物学杂志,40(6):1171~1180.

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  • 收稿日期:2021-02-09
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  • 在线发布日期: 2021-11-15
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