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首页> 外文期刊>Contributions to Mineralogy and Petrology >Precious metal enrichment in the Platreef, Bushveld Complex, South Africa: evidence from homogenized magmatic sulfide melt inclusions
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Precious metal enrichment in the Platreef, Bushveld Complex, South Africa: evidence from homogenized magmatic sulfide melt inclusions

机译：南非布什维尔德综合体Platreef中的贵金属富集：均质岩浆硫化物熔体包裹体的证据

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Magmatic sulfide deposits are the most significant source of platinum-group elements (PGE) in the world. Key to understanding their genesis is determining the processes and timing of sulfide saturation, metal enrichment and crustal contamination. In this study, we have identified droplets of magmatic sulfide from the Platreef, South Africa, where droplets of sulfide have been trapped in the earliest crystallising phase, chromite. Due to their early entrapment at high temperatures, metal concentrations and ratios that they display are indicative of a very early-stage sulfide liquid in the system, as they will have cooled and fractionated within an essentially closed system, unlike interstitial blebs that crystallise in an open system as the magma cools. Analysis of these droplets in an opaque mineral like chromite by LA-ICP-MS is problematic as some of the fractionated inclusion is necessarily lost during cutting and polishing to initially identify the inclusion. This particularly affects the ability to representatively sample the most fractionated phases such as gold and platinum minerals. Here, using a novel technique whereby the inclusions are homogenized and quickly quenched, so that any cutting, polishing and subsequent LA-ICP-MS analysis samples a truly representative portion of the droplet. This has been used to show that early sulfide liquids in the Platreef were highly PGE-rich and had Pt/Pd ratios of close to unity that supports genetic models invoking sulfide saturation and metal enrichment prior to intrusion, with pre-enriched sulfides entrained within the Platreef magma.
机译：岩浆硫化物矿床是世界上铂族元素（PGE）的最重要来源。理解其成因的关键是确定硫化物饱和，金属富集和地壳污染的过程和时间。在这项研究中，我们从南非的普拉特里夫（Platreef）鉴定出岩浆硫化物的液滴，其中硫化物的液滴被捕获在最早的结晶阶段，即铬铁矿中。由于它们在高温下的早期捕获，所显示的金属浓度和比率表明该系统中的硫化物液体非常早期，因为它们将在基本封闭的系统中冷却并分馏，而与在玻璃中结晶的间隙气泡不同。岩浆冷却时开放系统。通过LA-ICP-MS分析不透明矿物（如亚铬酸盐）中的这些液滴是有问题的，因为在切割和抛光过程中某些分馏夹杂物必定会丢失以初步识别夹杂物。这尤其会影响代表性地采样最分离的相（如金和铂矿物质）的能力。在这里，使用一种新颖的技术，使夹杂物被均质化并快速淬火，因此任何切割，抛光和随后的LA-ICP-MS分析都将对液滴的真正代表部分进行采样。这已被用来表明，Platreef中的早期硫化物液体富含PGE，并且Pt / Pd之比接近于1，这支持遗传模型在入侵之前调用硫化物饱和和金属富集，而预富集的硫化物夹带在样品中。 Platreef岩浆。

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