Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland
Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland
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DOI：
10.1007/s00410-015-1203-y
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发表时间：
2015-11
影响因子：
3.5
通讯作者：
D. Holwell;R. Keays;I. McDonald;Megan R. Williams
中科院分区：
文献类型：
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作者：
D. Holwell;R. Keays;I. McDonald;Megan R. Williams
位于格陵兰岛东部斯卡尔加德侵入体中的普拉蒂诺瓦礁是岩浆分异后期形成的岩浆铜-铂族元素-金硫化物矿床的一个例子。正如此类矿床的特征一样，它含有少量的硫化物，显示出峰值金属偏移，并且富含铜但缺乏镍。然而，即使是这样的矿床，普拉蒂诺瓦礁的硫化物含量也极低，而钯和金的本质硫化物含量却是所有岩浆矿床中最高的。在这里，我们首次对来自 Platinova 礁的硫化物微滴进行了 LA-ICP-MS 分析，结果表明，它们具有所有已知岩浆硫化物矿床中最高的 Se 浓度（高达 1200 ppm）和最低的 S/Se 比（190-700），并且具有显着的 Te 富集。此外，当硫化物体积增加时，原位捕获的高钯质微滴会转变为更大的低质元硫化物。这两种硫化物状态之间的转变以 Au 中的尖峰为标志，然后是 Te 浓度，随后是 Se 中的较宽峰，随着高度的增加逐渐减小。矿物学证据表明，没有明显的岩浆后热液硫损失，并且金属剖面本质上是岩浆过程的函数。我们认为，为了产生这些极端的贵金属和半金属含量，硫化物必须是由异常富含金属的岩浆包形成的，可能是通过先前富含铂族元素的硫化物的溶解而形成的。其他过程（例如动力学扩散）也可能同时发生，以产生超高的男高音。观察到的特征金属偏移图案很大程度上受分配效应控制，产生的偏移峰顺序为 Pt+Pd>Au>Te>Se>Cu，与公布的 D 值完全一致。这项研究证实，硫化物液滴的极端富集可能发生在原位封闭系统层状侵入体中，但这将形成硫化物含量如此低的矿床，以至于它们不符合需要非常高的 R 因子和硫化物液体沉降的 Cu-Ni-PGE 硫化物的传统矿床模型。
The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu–PGE–Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190–700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu–Ni–PGE sulfides which require very high R factors, and settling of sulfide liquids.