Mineral replacement reactions are one of the most important phenomena controlling the geochemical cycle of elements on Earth. In the early years, solid-state diffusion was proposed as the main mechanism for mineral replacement reactions, but over the past 20 years the importance of the coupled dissolution-reprecipitation (CDR) mechanism has been recognized. In the presence of a fluid phase and at low temperatures (e.g., <300 °C), CDR is the predominant mineral replacement process compared to relatively slow solid-state diffusion. However, in the present case study, we show that the rate of solid-state diffusion is comparable to the rate of CDR processes during the replacement of bornite (Cu₅FeS₄) by copper sulfides at 160-200 °C. The experiments initially produced chalcopyrite lamellae homogeneously distributed in the entire bornite grain, and each lamella was enveloped by digenite. The lamellae were formed by removing Fe³⁺ from bornite via solid-state diffusion, since there was no evidence for fluid entering bornite during lamellae formation. An interesting discovery is that the solid-state exsolution of chalcopyrite lamellae was induced by the bulk hydrothermal fluids surrounding the mineral grains, because in the absence of fluids under otherwise identical conditions, no exsolution occurred, and because the exsolution rate and lamellae size were sensitive to the composition of hydrothermal fluids. We hypothesize that this fluid-induced solid-state diffusion (FI-SSD) mechanism is made possible by the similar topology of the crystal structure of these phases. The solid-state diffusion of Fe³⁺ within bornite and across the resultant chalcopyrite and digenite phase boundaries is facilitated by the near-identical S framework. Parallel to and after lamellae exsolution, CDR reactions proceeded from the surface to the interior of the grains or along fractures, replacing chalcopyrite by digenite, and digenite by covellite and/or chalcocite, depending on experimental conditions. The synergy between FI-SSD and CDR resulted in complex reaction pathways for reactions in five acidic hydrothermal fluids with or without added Cu²⁺, Cu⁺, Cl^-, SO₄^2-, and SO₃^2-. The outcomes of these experiments imply that (1) under conditions where cation diffusion rates are of the same order of magnitude as dissolution and precipitation rates, hydrothermal fluids can induce and control solid-state diffusion processes, e.g., exsolution; (2) mineral replacement can be a result of the synergy between FI-SSD and CDR mechanisms; this happens at low temperatures (≤200 °C) in chalcogenide systems, but could affect silicate and oxide systems at amphibolite to granulite to eclogitic metamorphic grade; and (3) the synergy between FI-SSD and CDR mechanisms can lead to complex reaction pathways that cannot be easily predicted empirically.

矿物替代反应是控制地球上元素的地球化学循环的最重要现象之一。早些年，固态扩散被提出为矿物替代反应的主要机制，但是在过去的20年中，溶解-再沉淀耦合（CDR）机制的重要性得到了认识。在液相存在且处于低温（例如，<300  °C）的情况下，与相对缓慢的固态扩散相比，CDR是主要的矿物替代过程。但是，在本案例研究中，我们显示出固态扩散速率与160-200硫化铜替换斑铜矿（Cu ₅ FeS ₄）期间的CDR过程速率相当。 ℃。实验最初产生的黄铜矿薄片均匀地分布在整个褐铁矿晶粒中，并且每个薄片都被地长石包裹着。通过去除Fe ³⁺形成薄片由于没有证据表明在片层形成过程中流体会进入褐铁矿，因此它通过固态扩散从褐铁矿中脱出。一个有趣的发现是，黄铜矿片晶的固态脱附是由矿物颗粒周围的大量热液引起的，因为在其他条件相同的情况下，在没有流体的情况下，不会发生脱附，并且因为脱附速率和片晶尺寸都很敏感。热液的成分。我们假设，通过这些相的晶体结构的相似拓扑结构，可以使这种流体诱导的固态扩散（FI-SSD）机制成为可能。Fe ³⁺的固态扩散几乎相同的S框架促进了在褐铁矿内部以及跨合成的黄铜矿和地闪石的相界。平行于片晶的剥落和之后，CDR反应从晶粒的表面到内部或沿着裂缝进行，视实验条件而定，用地gen石代替黄铜矿，并用角铁石和/或黄铜矿代替di石。FI-SSD和CDR之间的协同作用导致了复杂的反应途径的反应在有或没有添加Cu的5个酸性热液²⁺，铜⁺，氯^-，SO ₄ ^2-和SO ₃ ^2-。这些实验的结果表明（1） 在阳离子扩散速率与溶解和沉淀速率处于相同数量级的条件下，热液可以诱导和控制固态扩散过程，例如析出；（2） 矿物替代可能是FI-SSD和CDR机制之间协同作用的结果；这发生在 硫属元素化物系统的低温（≤200 °C）下，但可能会影响角闪石到粒料到渐渐变质等级的硅酸盐和氧化物系统。（3） FI-SSD和CDR机制之间的协同作用会导致复杂的反应途径，而这些反应途径很难凭经验进行预测。