摘要
深入理解构造变形与金富集的耦合关系,是阐明剪切带型金矿成因机制的关键前提。黄铁矿是剪切带型金矿中重要的载金矿物,其赋存的金不仅包括裂隙金、晶隙金和包裹体金等可见金,还包含以晶格金(Au+)或纳米金(Au 0)形式存在的不可见金。后者虽难以通过常规手段观测,但同样是重要的黄金资源。研究发现,黄铁矿晶体塑性变形位置常具有较高的不可见金含量,然而晶体塑性变形如何导致不可见金的迁移-富集目前尚不清楚,这也制约了对剪切带型金矿中Au元素富集机制的理解。本研究利用偏光显微镜、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对胶东三山岛金矿和乳山金矿中的黄铁矿进行了微观变形特征观察和原位微区微量元素空间分布规律分析,结果表明:(1)三山岛金矿黄铁矿中的不可见金主要以晶格金形式赋存,而乳山金矿黄铁矿中的不可见金既有晶格金,也有纳米金。(2)两个金矿的黄铁矿均发生了不同程度的晶体塑性变形,且Au元素在晶内低角度边界等塑性变形位置发生富集。同时显微观测未见所研究的低角度边界与晶体外部连通现象,因此认为这些不可见金的迁移-再分配主要由无外部流体参与的晶内扩散作用主导,即黄铁矿结晶过程中捕获的Au元素以缺陷(点缺陷或位错)方式占据晶格位置,成为黄铁矿晶体中的“杂质”,使晶体偏离完美晶格形态并处于高能状态。在构造剪切应力作用下,载金黄铁矿内部的点缺陷/位错密度进一步增大,同时降低了点缺陷/位错移动所需的活化能,进而启动位错滑移/蠕变机制。位错滑移/蠕变作用使黄铁矿发生晶体塑性变形以调节构造剪切应力引发的应变能,同时移动的位错又夹带大量“杂质金”(晶格金或纳米金)一起运动,最终促使Au元素迁移并聚集在低角度边界(位错壁)位置。这一过程促进了黄铁矿晶体内部原本分散的不可见金元素的聚集,这可能为后续形成可见金或高品位金矿体提供了重要的“预富集储库”。由构造剪切应力引发的晶格结构变化和/或化学键调整这一构造应力化学过程,是黄铁矿晶体塑性变形促进不可见金迁移-富集的关键。
Understanding of the relationship between deformation and gold enrichment is a key prerequisite for elucidating the genetic mechanism of shear zone type gold deposits.Pyrite is an important gold-bearing mineral in shear zone type gold deposits.The gold hosted in pyrite includes not only visible gold such as fissure gold,intercrystalline gold and inclusion gold,but also invisible gold in the form of lattice gold(Au+)or nano-gold(Au 0).Although the latter is difficult to observe by conventional means,it is also an important gold resource.It is found that the plastic deformation position of pyrite crystal often has a high content of invisible gold elements.However,at present,how the plastic deformation of crystal leads to the migration-enrichment of invisible gold is not clear,which restricts the understanding of the enrichment mechanism of Au elements in shear zone type gold deposits.In this study,polarized light microscopy,scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)were used to observe the microscopic deformation characteristics of pyrite in Sanshandao gold deposit and Rushan gold deposit in Jiaodong,and analyze their in situ trace elements spatial distribution.The results show that:(1)In Sanshandao gold deposit,the invisible gold in pyrite of mainly exists in the form of lattice gold,while in Rushan gold deposit the invisible gold in pyrite contains both lattice gold and nano-gold.(2)Different degrees of crystal-plastic deformation occurred in the pyrite of the two gold deposits,and the Au element was enriched in the plastic deformation positions such as the low-angle boundary of the crystal.At the same time,there is no low-angle boundary connected to the outside of the crystal by microscopic observation.Therefore,this study believes that these invisible gold migration-redistribution is mainly dominated by intracrystalline diffusion without intergranular fluid participation,i.e.,Au elements captured during pyrite crystallization occupy the lattice position in the form of defects(point defects or dislocations)and become‘impurities’in pyrite crystals,causing the crystal to deviate from the perfect lattice shape and be in a high-energy state.Under the action of tectonic shear stress,the point defect/dislocation density inside the gold-bearing pyrite further increases,and the activation energy required for point defect/dislocation movement is reduced,thereby initiating the dislocation slip/creep mechanism.The dislocation slip/creep effect causes the crystal-plastic deformation of pyrite to adjust the strain energy caused by the tectonic shear stress.At the same time,the moving dislocations entrain a large amount of‘impurity gold’(lattice gold or nano-gold)to move together,which ultimately promotes the migration of Au elements and accumulates at the low-angle boundary(dislocation wall).This process promotes the aggregation of originally dispersed invisible gold in pyrite crystals,which may provide an important“pre-enrichment reservoir”for the subsequent formation of visible gold or high-grade gold ore bodies.The tectono-chemical process of lattice structure change and/or chemical bond adjustment caused by tectono-shear stress are key to the migration and enrichment of invisible gold promoted by the plastic deformation of pyrite crystal.
作者
石梦岩
亢怡萱
侯泉林
程南南
马毓民
宋延斌
SHI MengYan;KANG YiXuan;HOU QuanLin;CHENG NanNan;MA YuMin;SONG YanBin(School of Resources and Environment,Henan Polytechnic University,Jiaozuo 454003,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;No.1 Institute of Geological and Mineral Resources Survey,Henan Geological and Mineral Exploration and Development Bureau,Luoyang 471023,China)
出处
《岩石学报》
北大核心
2025年第9期2912-2931,共20页
Acta Petrologica Sinica
基金
河南省科技攻关项目(242102320359)
河南省自然科学基金项目(232300420437、232300420439)
河南省高等学校重点科研项目(23A170009、23A170015)联合资助.
关键词
剪切带型金矿
黄铁矿
晶体塑性变形
位错移动
不可见金富集
Shear zone type gold deposit
Pyrite
Crystal-plastic deformation
Dislocation migration
Invisible gold enrichment
作者简介
第一作者:石梦岩,男,1991年生,博士,讲师,主要从事构造地质学研究,E-mail:shimengyan@hpu.edu.cn;通讯作者:程南南,女,1992年生,博士,讲师,主要从事构造地质与成矿研究,E-mail:chengnannan@hpu.edu.cn。
