含金毒砂中晶格金的确定及其形成机理研究

Determination of Structural Gold in Au-bearing Arsenopyrite and Its Formation Mechanism

利用电子探针(EPMA)和高分辨透射电子图像(HRTEM)分析技术,对湖南黄金洞金矿含金毒砂进行了背散射电子图像、X-射线面扫描、定量微区分析、线分析以及高分辨晶体结构观测等综合研究。结果表明,含金毒砂中没有发现纳米级乃至更小粒级的超显微包体金,毒砂晶格完整,无任何“异构体”,Au散布于整个毒砂颗粒中,以晶格金形式存在。此外,金含量在不同的生长环带中有显著变化,表明Au是在毒砂形成过程中进入其晶格的。金的加入导致毒砂晶体结构中(100)面网间距局部变宽,晶胞参数也发生了微弱变化,a轴变长。详细分析认为,Au主要是以Au^(3+)替代Fe^(3+)进入AsS^(3-)八面体空位中的,Eh值变化可能是控制毒砂中晶格金形成的主要因素。

Using EPMA and HRTEM, a systematic study is conducted on the gold-bearing arsenopyrites from Huangjindong gold deposit, Hunan province, by means of BSE observation, X-ray scanning, quantitative analyses and line analyses and HRTEM determination of crystal structure. It is revealed that no nanometer-grained or less grade inclusion gold grains are found, and that the structure of the arsenopyrites develops perfectly without any 'abnormally structural part' in them. This shows that Au elements are scattered in the whole ar-senopyrite crystal, i. e. , the gold exists in structural state or chemical state. It is also found that Au content varies substantially in different crystal striations, therefore it is proposed that Au came into the crystal structure of the arsenopyrites when they formed. The entrance of Au into the crystal structure results in widening of the distance of the crystal face (100) (d100) and lightly variation of the unit cell parameters, the crystallographic axis a becoming longer. Based on the detailed analysis, it is believed that Au mainly got into the the arsenopyrites in form of Au3+ to have replaced Fe3+ in the AsS3-octahedron spaces and that the variation of Eh values is possibly a most important factor to control the formation of the structural gold.