A Preliminary Model for the Migration of Sulfide Droplets in a Magmatic Conduit and the Significance of Volatiles
A Preliminary Model for the Migration of Sulfide Droplets in a Magmatic Conduit and the Significance of Volatiles
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DOI：
10.1093/petrology/egaa005
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发表时间：
2019-12
影响因子：
3.9
通讯作者：
Z. Yao;J. Mungall;K. Qin
中科院分区：
文献类型：
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作者：
Z. Yao;J. Mungall;K. Qin
Ni-Cu-(PGE)硫化物矿床和岩浆管道系统之间的密切关系已被广泛接受，但我们目前的理解仍然依赖于经验归纳，即硫化物液体在岩浆上升过程中被夹带并聚集在水动力陷阱处，例如通往更大岩浆体的管道的开口。在本文中，开发了垂直岩浆管道中毫米级硫化物液滴动力学的初步定量模型，研究了尺寸、传输速度和岩浆对硫化物液滴的最大承载能力等限制参数。大量致密硫化物液滴的添加显着降低了岩浆浮力并迅速增加了体积粘度，并且在传播导管岩脉中产生的压力梯度限制了上升岩浆可以携带的液滴的最大体积分数。对于单独的硫化物液滴，最大承载能力较低，但通过添加挥发物可显着提高最大承载能力，从而降低硅酸盐熔体的密度和粘度。减压过程中潜在的挥发脱气通过降低岩浆体积密度进一步促进硫化物夹带，并且形成浮力复合蒸气-硫化物液泡滴也大大增强了承载能力。在低压下，可能会发生通过部分蒸气泡或硫化物液滴分离而导致化合物液滴破裂，这会从上升的化合物液滴中释放出硫化物液体，可能会收集在管道系统中的捕集器中。当含硫化物的岩浆流经加宽的管道时，扩展部分下游的再循环流可以捕获许多液滴，随后硫化物液体积聚，并通过与再循环岩浆的扩散交换增强化学相互作用，从而可能形成经济的高吨位矿体。我们将我们的模型应用于诺里尔斯克富含硫化物的岩浆悬浮液的侵位，结果表明，当岩浆携带从管道系统中预先存在的硫化物堆积物夹带的重新悬浮的硫化物液体达到其由浮力决定的极限硫化物承载能力并偏转到洪水主要管道两侧的盲基时，可能会形成侵入岩中的浸染式矿化。 玄武岩火山作用。
A close relationship between Ni–Cu–(PGE) sulfide deposits and magmatic conduit systems has been widely accepted, but our present understanding still rests on empirical inductions that sulfide liquids are entrained during magma ascent and aggregated at hydrodynamic traps such as the opening of a conduit into a larger magma body. In this contribution, a preliminary quantitative model for the dynamics of mm-scale sulfide droplets in a vertical magmatic conduit is developed, examining such limiting parameters as the size, transport velocity and the magmas’ maximum carrying capacity for sulfide droplets. Addition of numerous dense sulfide droplets significantly reduces magma buoyancy and rapidly increases the bulk viscosity, and the resulting pressure gradient in the propagating conduit dyke restricts the maximum volume fraction of droplets that can be carried by ascending magma. For sulfide droplets alone, the maximum carrying capacity is low, but it will be improved dramatically by the addition of volatiles which reduces the density and viscosity of silicate melt. Potential volatile degassing during decompression further facilitates sulfide entrainment by reducing bulk magma density, and the formation of buoyant compound vapour-sulfide liquid bubble drops also greatly enhances the carrying capacity. The breakdown of compound drops by detachment of parts of the vapour bubble or sulfide droplet may occur at low pressure, which liberates sulfide liquids from rising compound drops, potentially to collect in traps in the conduit system. When sulfide-laden magma flows through a widening conduit, many droplets can be captured by the re-circulation flow just downstream of the expanding section, followed by sulfide liquid accumulation and enhanced chemical interaction via diffusive exchange with the recirculating magma, potentially resulting in an economic, high-tonnage ore body. We apply our models to the emplacement of sulfide-rich magmatic suspensions at Noril’sk and show that the disseminated mineralization in intrusions could have formed when magmas carrying re-suspended sulfide liquid entrained from pre-existing sulfide accumulations in the conduit system reached their limiting sulfide carrying capacity as dictated by buoyancy and were deflected into blind sills flanking the principal conduit for flood basalt volcanism.