埃及东部沙漠Mueilha花岗岩含氟长英质稀有金属体系流体介质叠印原生岩浆特征

IF 3.6 2区 地球科学 Q1 GEOLOGY
Julie A.-S. Michaud , François Holtz , Daniel J. Kontak , Simon Goldmann , Martin Oeser , Mohamed A. Abu El-Rus , Ali A. Khudeir
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引用次数: 0

摘要

流体是花岗岩系统中主要的分馏剂,因为它们在岩浆-热液转变过程中部分控制了包括稀有金属在内的元素的行为和分配,并在后期的次固体阶段重新分配。岩浆流体从挥发性饱和岩浆中析出及其随后的循环通常会导致重要的结构和地球化学变化,主要岩浆特征被完全重叠,早期矿物在化学上重新平衡。本文记录的变化可作为跟踪稀有金属花岗岩与相互作用流体平衡的基础。Mueilha F-Nb-Ta-REE-Y花岗岩体系(埃及东部沙漠)由“红色花岗岩”相和沿红色花岗岩西南边缘发育的“边界相”等不同相组成。对后一相的详细矿物学和结构研究表明,原始高度演化的花岗岩主要通过溶蚀-沉淀耦合作用进行了广泛而强烈的转化。在此基础上,结合互补的全岩、矿物量、微量元素化学,提出并讨论了岩浆-交代的复杂五阶段演化模式。作为这一演化的一部分,边界相代表了红色花岗岩结晶非常晚期提取的残余熔体。这一过程导致了边界相内Nb和Ta的选择性富集,以及Li、F、ree和Y的相应耗损,突出了萃取时间在形成残余熔体成分中的关键作用。认为该侵入体的弱过铝质特征,加上其低含量的F (<0.2 wt%),促进了侵入体内部稀有金属和REE-Y的自交代和相关重分布,形成了世界稀有金属花岗岩和伟晶岩中常见的岩浆和热液浸染型矿化。我们认为这项研究可以作为一个有用的参考点来调查其他地方的类似情况。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Overprinting of primary magmatic features by fluid-mediated processes in a F-bearing felsic rare-metal system: the Mueilha granite (Eastern Desert, Egypt)

Overprinting of primary magmatic features by fluid-mediated processes in a F-bearing felsic rare-metal system: the Mueilha granite (Eastern Desert, Egypt)
Fluids are major fractionation agents in granitic systems because they partly control the behaviour and partitioning of elements, including rare metals, during the magmatic-hydrothermal transition and their subsequent redistribution during the later subsolidus stage. The exsolution of magmatic fluids from a volatile-saturated magma and their subsequent circulation commonly result in important textural and geochemical changes with primary magmatic features being entirely overprinted and earlier minerals chemically re-equilibrated. The changes documented herein serve as a basis for tracking the equilibration of a rare-metal granite with interacting fluids. The Mueilha F-Nb-Ta-REE-Y granitic system (Eastern Desert of Egypt) is composed of different facies such as the “red granite”, representing the main volume of the intrusion, and the “border facies”, occurring along the red granite south-western margin. Detailed mineralogical and textural studies of the latter facies document the pervasive and intense transformation of the original highly-evolved granite primarily via coupled dissolution-precipitation. Based on these observations, and complementary whole rock, and mineral major and trace element chemistry, a complex five-stage model of evolution from magmatic to metasomatic is proposed and discussed. As part of this evolution, the border facies represents residual melts extracted at a very late stage of crystallization of the red granite. This process led to a selective enrichment in Nb and Ta, and a corresponding depletion in Li, F, REEs, and Y within the border facies, highlighting the critical role of the timing of extraction in shaping the composition of residual melts. It is suggested that the weak peraluminous character of the intrusion combined with its F content, albeit low (<0.2 wt%), facilitated the observed autometasomatism and associated redistribution of rare metals and REE-Y within the intrusion to form magmatic and hydrothermal disseminated style mineralization typically encountered in rare-metal granites and pegmatites worldwide. We suggest that this study may serve as a useful reference point for investigating comparable settings elsewhere.
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来源期刊
Ore Geology Reviews
Ore Geology Reviews 地学-地质学
CiteScore
6.50
自引率
27.30%
发文量
546
审稿时长
22.9 weeks
期刊介绍: Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers.
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