含Cu硫化物中S、Fe同位素分馏系数的第一性原理计算  

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

作　　者：刘善琪 梁家新 张秋院 李永兵 LIU Shan-qi;LIANG Jia-xin;ZHANG Qiu-yuan;LI Yong-bing(School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China;Southern Marine Science and Engineering Guangdong laboratory(Zhuhai),Zhuhai 519080,China;College of Earth and Planetarv Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Compulational Ceodynamics,Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中山大学地球科学与工程学院,广东广州510275 [2]南方海洋科学与工程广东省实验室(珠海),广东珠海519080 [3]中国科学院大学地球与行星科学学院,北京100049 [4]中国科学院计算地球动力学重点实验室,北京100049

出　　处：《岩石矿物学杂志》2021年第6期1171-1180,共10页Acta Petrologica et Mineralogica

基　　金：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)。

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(10^(3)lnβ_(34-32)),以及Cu-Fe硫化物的Fe同位素简约配分函数比(10^(3)lnβ_(57-54))。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>Cu_(8)Fe_(4)S_(8)(中温斑铜矿的可能变体)。含Cu硫化物的10^(3)lnβ_(34-32)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10^(3)lnβ_(57-54)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。In nature,copper mainly occurs in sulfide minerals.At present,only the sulfurβ-factors of several Cu-bearing sulfides and the ironβ-factor of chalcopyrite have been determined,and theβ-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(10^(3)lnβ_(34-32))for Cu-bearing sulfides as well as the reduced partition function ratio of Fe isotopes(10^(3)lnβ_(57-54))for Cu-Fe sulfides in the temperature range of 0~1000℃.10^(3)lnβ_(34-32)decreases in the order of covellite>cubanite>chalcopyrite≈villamaninite>bornite>chalcocite,and 10^(3)lnβ_(34-32)decreases in the order of cubanite≈chalcopyrite>low-bornite>high-bornite>intermediate-bornite>intermediate-Cu_(8)Fe_(4)S_(8).10^(3)lnβ_(34-32)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 10^(3)lnβ_(57-54)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.

关 键 词：S同位素分馏 Fe同位素分馏 第一性原理计算 斑岩铜矿 硫化物 

分 类 号：P597.2[天文地球—地球化学]