Symplectic microstructures are abundant in copper–iron–sulfide minerals and are conventionally considered to form by solid-state diffusion processes. Here we experimentally demonstrate that coarsening of exsolution lamellae occurs ∼1000 times faster in the presence of a fluid compared to the equivalent dry system. Bornite–digenite solid solutions (Cu₅FeS₄–Cu_8.52Fe_0.11S_4.88) were synthesized hydrothermally via the replacement of chalcopyrite, and we compared the microtextures in the product subjected to different cooling histories: (i) dry annealing after synthesis; (ii) cooling to an annealing temperature immediately following hydrothermal synthesis; and (iii) annealing in a hydrothermal fluid following quenching to room temperature and then reheating. We interpret the rapid coarsening of the exsolution lamellae in the presence of a fluid phase to result from recrystallization associated with healing of the open porous microstructure in the parent phase. The porosity is a consequence of the synthesis of the parent bornite–digenite solid solutions via interface coupled dissolution reprecipitation. The texture coarsening is accompanied by the destruction of the transient open porous microstructure via coalescence of the pores and their migration to lamellae and grain boundaries. As a result, the final microstructure and the kinetics of textural coarsening depend upon the crystallization and cooling history of the parent mineral. Such fluid-driven textural evolution may be a major mode of reaction in ore systems, and is likely to affect oxide and silicate systems alike in the presence of aqueous fluids.

中文翻译：

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水热合成硼铁矿-褐铁矿固溶体中矿物微观结构的流体强化粗化

辛微结构在铜-铁-硫化物矿物中含量很高，通常被认为是通过固态扩散过程形成的。在这里，我们通过实验证明，与同等的干式系统相比，在存在流体的情况下，析出片的粗化速度快约1000倍。钙铁矿-褐铁矿固溶体（Cu ₅ FeS ₄ -Cu _8.52 Fe _0.11 S _4.88）是通过更换黄铜矿水热合成的，我们比较了经历不同冷却历史的产品中的微观组织：（i）合成后的干退火；（ii）在水热合成后立即冷却至退火温度；（iii）在淬火至室温然后再加热之后在水热流体中退火。我们解释了在存在液相的情况下，析出片的快速粗化是由于与母相中开放的多孔微观结构的愈合相关的重结晶所致。孔隙率是通过界面耦合溶解再沉淀合成母体贝氏体-亚地长石固溶体的结果。纹理粗化伴随着通过孔的聚结破坏了瞬时开放的多孔微结构，以及它们向薄层和晶界的迁移。结果，最终的微观结构和组织粗化的动力学取决于母体矿物的结晶和冷却历史。这种流体驱动的组织演化可能是矿石系统中主要的反应方式，并且可能在存在含水流体的情况下也影响氧化物和硅酸盐系统。