The Radioactive Rare Metal Mineralization in the World-Class Sn-Nb-Ta-U-Th-REE-Deposit Madeira (Pitinga, Amazonas State, Brazil): With Special Reference to the Complex Alteration of Pyrochlore-Group Minerals

IF 2.2 4区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Minerals Pub Date : 2024-08-30 DOI:10.3390/min14090895
Ingrid W. Hadlich, Artur C. Bastos Neto, Vitor P. Pereira, Harald G. Dill, Nilson F. Botelho
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Abstract

This study focuses on the relationship between U and pyrochlore in the world-class Sn-Nb-Ta (U, Th, REE, Li) Madeira deposit within the Pitinga mining district of northern Brazil. The primary U mineralization is of intrusive-type and early magmatic origin, hosted in the peralkaline albite-enriched granite facies of the A-type Madeira granite (~1820 Ma). U-Pb-LREE-enriched pyrochlore is the only primary U ore and is widely and homogeneously dispersed in two albite-enriched granite subfacies: the albite-enriched granite core (AGC) and the albite-enriched granite border (AGB). In both zones, the pyrochlore crystals underwent strong hydrothermal alteration by F-rich, low-temperature aqueous fluids. During this hypogene alteration process, cations such as LREE, Nb, and F were selectively released, while others like Fe and Si were introduced. This led to the successive formation of various secondary pyrochlore varieties and a relative enrichment of U (up to 13.73 wt.% UO2). The alteration of pyrochlore eventually resulted in the breakdown of its structure, leading to the formation of U-bearing columbite pseudomorphs and the precipitation of U-rich silicates (up to 34.35 wt.% UO2), galena, and LREE-rich fluorides within pyrochlore vugs. In contrast to the homogeneous distribution of the primary ore mineralization, the secondary pyrochlore mineralization shows striking zonation, being most intense in the AGB and AGC proximal to a massive cryolite deposit. The U mineralization in the Madeira deposit exhibits grades of 328 ppm UO2, comparable to the main deposits of this type, with significant reserves of up to 52 kt U. However, it is different from those deposits in four key aspects: homogeneous dispersion of mineralization; pyrochlore as the exclusive primary ore mineral; U and Th mineralizations formed at different stages; and intense hydrothermal alteration. These characteristics are attributed to the special conditions imposed by the fluorine-rich nature of the peralkaline magma.
世界级 Sn-Nb-Ta-U-Th-REE 矿床马德拉(巴西亚马孙州皮廷加)的放射性稀有金属矿化:特别关注火成岩组矿物的复杂嬗变
本研究的重点是巴西北部 Pitinga 矿区世界级的马德拉锡铌钽(U、Th、REE、Li)矿床中铀和火成岩之间的关系。原生铀矿化属于侵入型早期岩浆成因,赋存于 A 型马德拉花岗岩的围岩白云石富集花岗岩层中(约 1820 Ma)。富含 U-Pb-LREE 的火成岩是唯一的原生铀矿石,广泛而均匀地分布在两个白云石富集花岗岩亚岩层中:白云石富集花岗岩岩芯(AGC)和白云石富集花岗岩边界(AGB)。在这两个区域,火成岩晶体在富含 F 的低温水性流体的作用下发生了强烈的热液蚀变。在这个低温蚀变过程中,LREE、Nb 和 F 等阳离子被选择性地释放出来,而 Fe 和 Si 等其他阳离子则被引入。这导致了各种次生火成岩的相继形成和铀的相对富集(最高达 13.73 wt.% UO2)。辉绿岩的蚀变最终导致了其结构的破坏,形成了含铀的铌铁矿假象,并在辉绿岩岩体中析出了富含铀的硅酸盐(最高达 34.35 wt.% UO2)、方铅矿和富含 LREE 的氟化物。与原生矿成矿作用的均匀分布不同,次生辉绿岩成矿作用呈现出明显的分带现象,在靠近块状冰晶石矿床的 AGB 和 AGC 地区最为强烈。马德拉矿床的铀矿化品位为百万分之 328,与该类型的主要矿床相当,储量高达 52 千吨铀。然而,该矿床与这些矿床的不同之处主要体现在四个方面:矿化均匀分布;辉绿岩是唯一的原生矿石矿物;铀和钍矿化形成于不同阶段;热液蚀变强烈。这些特点归因于碱性岩浆富含氟的特殊条件。
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来源期刊
Minerals
Minerals MINERALOGY-MINING & MINERAL PROCESSING
CiteScore
4.10
自引率
20.00%
发文量
1351
审稿时长
19.04 days
期刊介绍: Minerals (ISSN 2075-163X) is an international open access journal that covers the broad field of mineralogy, economic mineral resources, mineral exploration, innovative mining techniques and advances in mineral processing. It publishes reviews, regular research papers and short notes. Our aim is to encourage scientists to publish their experimental and theoretical results in as much detail as possible. There is no restriction on the length of the papers. The full experimental details must be provided so that the results can be reproduced.
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