Abstract The motion of dense Fe-rich immiscible sulphide liquids is generally supposed to be dominated by gravitational settling in crustal magma chambers, however they may become buoyant by attachment to low-density vapour bubbles to form compound drops, possibly contributing to the upward transfer of sulphur and transition metals in degassing magma bodies. Here, using numerical models, we consider constraints on the flotation of compound drops, and find a wide range of morphologies that would be expected to be capable of migrating through magmatic systems, including both melt- and mush-dominated domains, but also some situations where the compound drops will spontaneously separate to allow the vapour to rise while the sulphide phase is sequestered in the mush. The stability of compound drops is empirically related to a function f ( B o ) = | σ M V − σ M S | σ M S ⋅ 1 / B o S + | σ V S − σ M S | σ M S ⋅ 1 / B o V , where M, V, and S denote silicate melt, vapour, and sulphide liquid, σ is surface tension (N⋅m−1), and Bo is the Bond number. Over a range of plausible conditions in magmas, f(Bo) must exceed values of 3 to 4 for capillary forces to overcome buoyancy forces tending to pull them apart. Using published thermodynamic models for vapour and sulphide solubility in silicate melts, we show that in many magmas the second boiling of vapour occurs synchronously with the saturation of sulphide liquid, increasing the potential for coupling of vapour and sulphide droplets. Diffusive coarsening produces mm-sized bubbles within 100-500 years, generating enough buoyancy to trigger the migration of compound drops. During compaction-driven expulsion of interstitial melt, compound drops can pass through constrictions between crystals in mush. The flotation of sulphide-vapour aggregates is likely to occur in crustal magma reservoirs and provides a feasible mechanism for the removal of sulphide liquid from crystal mushes, promoting its ability to participate in the generation of magmatic sulphide and porphyry copper deposits, emissions of the metals during volcanic eruptions, and even the remobilization of chalcophile metals sequestered in deep arc cumulates to generate porphyry Cu-(Au) deposits.

中文翻译：

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部分熔融岩浆系统中硫化物熔体在蒸汽泡上的浮选机理

摘要 稠密的富铁不混溶硫化物液体的运动一般以地壳岩浆房中的重力沉降为主，但它们可能通过附着在低密度蒸汽泡上形成复合液滴而变得有浮力，这可能有助于向上转移脱气岩浆体中的硫和过渡金属。在这里，使用数值模型，我们考虑了对化合物液滴浮选的约束，并找到了预计能够在岩浆系统中迁移的广泛形态，包括熔体和糊状域，但也包括某些情况当硫化物​​相被隔离在糊状物中时，化合物滴将自发分离以允许蒸汽上升。复合液滴的稳定性根据经验与函数 f ( B o ) = | 相关。σ MV − σ MS | σ MS ⋅ 1 / B o S + | σ VS − σ MS | σ MS ⋅ 1 / B o V ，其中 M、V 和 S 表示硅酸盐熔体、蒸汽和硫化物液体，σ 是表面张力 (N⋅m−1)，Bo 是键数。在岩浆中的一系列合理条件下，f(Bo) 必须超过 3 到 4 的值才能使毛细管力克服倾向于将它们分开的浮力。使用已发表的蒸汽和硫化物在硅酸盐熔体中溶解度的热力学模型，我们表明，在许多岩浆中，蒸汽的第二次沸腾与硫化物液体的饱和同步发生，增加了蒸汽和硫化物液滴耦合的可能性。扩散粗化会在 100-500 年内产生毫米大小的气泡，产生足够的浮力来触发化合物液滴的迁移。在间隙熔体的压实驱动排出过程中，化合物液滴可以通过晶体之间的收缩。硫化物-蒸气聚集体的浮选很可能发生在地壳岩浆储层中，为从结晶糊中去除硫化物液体提供了可行的机制，促进其参与岩浆硫化物和斑岩铜矿床的生成，金属的排放在火山喷发期间，甚至被隔离在深弧中的亲硫金属的再迁移也会累积产生斑岩铜 (Au) 矿床。