Minerals and/or their compositions (substituted minor elements) can become metastable in changing conditions or if formed outside of equilibrium. Unstable minerals undergo chemical and/or structural modifications at rates determined by re-equilibration processes, such as diffusion, coupled dissolution-reprecipitation and recrystallization. However, re-equilibrated domains with sharp contacts that lack porosity or deformation microstructures are difficult to reconcile with previously documented processes. In this study, we investigate the mechanism by which Au-rich pyrite re-equilibrates to Au-poor pyrite. Gold and As-rich {100} oscillatory bands are truncated by Au-As-poor pyrite along {100} re-equilibration interfaces. At the nanoscale, dislocations oriented consistently along <100>, are enriched in Ni, As, Cu, Sb, Pb, and Au. Dislocations are located at the re-equilibration interfaces between the Au-As-rich and Au-As-poor pyrite. Quantitative crystallographic orientation maps do not show the presence of deformation-related boundaries along the re-equilibration interfaces, indicating that the dislocations are not deformation-related but are misfit dislocations to accommodate for lattice stain between As-rich and As-poor pyrite. The co-location of steps along the re-equilibration interfaces and dislocations suggests that pyrite can re-equilibrate by the migration of dislocations. The process is likely driven by lattice strain minimisation induced by As impurities. Element transport is achieved by a two step process with (1) capture of impurities by dislocation-impurity pair diffusion during the migration of dislocations and (2) pipe diffusion along the dislocation network towards the exterior of the crystal. We propose that re-equilibration of Au-rich arsenian pyrite, and the resulting remobilisation of Au, can operate through a dislocation-mediated interfacial re-equilibration (DMIR) process. This new mechanism may be active in a range of mineral reactions, particularly in metamorphic settings where limited fluid availability precludes interface-coupled dissolution-reprecipitation processes.

中文翻译：

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位错介导的黄铁矿界面再平衡：界面耦合溶解-再沉淀和金再活化的替代模型


矿物质和/或其成分（取代的微量元素）在变化的条件下或在平衡之外形成时可以变得亚稳定。不稳定的矿物以由再平衡过程（例如扩散、耦合溶解-再沉淀和再结晶）决定的速率进行化学和/或结构改变。然而，具有缺乏孔隙率或变形微观结构的尖锐接触的重新平衡域很难与先前记录的过程相一致。在本研究中，我们研究了富金黄铁矿与贫金黄铁矿重新平衡的机制。金和富砷的 {100} 振荡带沿着 {100} 再平衡界面被贫金砷黄铁矿截断。在纳米尺度上，位错始终沿 <100> 方向取向，富含 Ni、As、Cu、Sb、Pb 和 Au。位错位于富金砷黄铁矿和贫金砷黄铁矿之间的再平衡界面处。定量晶体取向图没有显示沿再平衡界面存在与变形相关的边界，这表明位错与变形无关，而是错配位错，以适应富砷黄铁矿和贫砷黄铁矿之间的晶格染色。沿着重新平衡界面和位错的台阶的共置表明黄铁矿可以通过位错的迁移来重新平衡。该过程可能是由砷杂质引起的晶格应变最小化驱动的。元素传输是通过两步过程实现的，其中（1）在位错迁移过程中通过位错-杂质对扩散捕获杂质，以及（2）沿着位错网络向晶体外部进行管道扩散。 我们提出，富金砷黄铁矿的重新平衡以及由此产生的金的再活化可以通过位错介导的界面重新平衡（DMIR）过程进行。这种新机制可能在一系列矿物反应中很活跃，特别是在变质环境中，其中有限的流体可用性阻碍了界面耦合的溶解-再沉淀过程。