Rare-Metal Granites

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (31 December 2024) | Viewed by 1343

Special Issue Editor


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Guest Editor
Centro Nacional Instituto Geológico y Minero de España (CN IGME-CSIC), 37001 Salamanca, Spain
Interests: protolith; parental magma; differentiation processes; magmatic-hydrothermal transition; rare-metal metallogeny; geochemistry; geochronology

Special Issue Information

Dear Colleagues,

Rare-metal granites, essentially A-type granites and peraluminous muscovite granites, host some of the most important deposits of rare metals, generally as high-tonnage, low-grade deposits. Much progress has been made in understanding this type of deposit, especially with the advent of analytical and geochronological techniques in the last 10 years, e.g., LA-ICP-MS, but there are still open questions that are poorly understood. For example, it is not clear how the particular geochemistry of rare-metal granites is achieved, what is their parent magma, or is a protolith of particular composition favors  development of rare-metal rich granites. The genesis of rare-metal enrichment is poorly understood and many processes have been proposed including: fractional crystallization, liquid immiscibility, chemical quenching, zone refining, magma mixing, gas-driven filter pressing, and fluid phase exsolution by undercooling or by first or second boiling, triggering the magmatic-hydrothermal transition. This Special Issue aims to bring together a series of papers that will help to address these and other open questions. Detailed mineralogical and textural studies of ore and gangue, and experimental and geochemical studies that provide the basis for understanding the crystallization and chemical fractionation of both gangue and ore minerals are welcomed. Isotopic, geochemical, and geochronological studies to establish the parental magma, protolith and geodynamic setting of these granites are also welcomed. This Special Issue aims to contribute to a better understanding of rare-metal enriched melts and ore formation processes.

Dr. Francisco Javier López-Moro
Guest Editor

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Keywords

  • protolith
  • parental magma
  • differentiation processes
  • magmatic–hydrothermal transition
  • rare-metal metallogeny
  • geochemistry
  • geochronology

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Published Papers (1 paper)

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Research

37 pages, 28889 KiB  
Article
Pyrochlore-Supergroup Minerals and Their Relation to Columbite-Group Minerals in Peralkaline to Subaluminous A-Type Rare-Metal Granites with Special Emphasis on the Madeira Pluton, Amazonas, Brazil
by Karel Breiter, Hilton Tulio Costi and Zuzana Korbelová
Minerals 2024, 14(12), 1302; https://doi.org/10.3390/min14121302 - 23 Dec 2024
Viewed by 834
Abstract
Niobium (Nb) and tantalum (Ta) are quoted as “strategic” or “critical” elements for contemporaneous society. The main sources of Nb and Ta are minerals of the pyrochlore supergroup (PSGM) and the columbite group (CGM) mined from different magmatic lithologies. Textures and chemical compositions [...] Read more.
Niobium (Nb) and tantalum (Ta) are quoted as “strategic” or “critical” elements for contemporaneous society. The main sources of Nb and Ta are minerals of the pyrochlore supergroup (PSGM) and the columbite group (CGM) mined from different magmatic lithologies. Textures and chemical compositions of PSGM and CGM often provide key information about the origin of NbTa mineralization. Therefore, we decided to carry out a detailed study of the relations between the PSGM and CGM and their post-magmatic transformations, and the Madeira peralkaline pluton (Brazil) is an ideal object for such a study. Textures of the PSGM and CGM were studied using BSE imaging and SEM mapping, and their chemical compositions were determined using 325 electron microprobe analyses. Pyrochlore from the Madeira granite can be chemically characterized as Na, Ca-poor, U- and Pb-dominant, and Sn- and Zn-enriched; REE are enriched only during alteration. Two stages of alteration are present: (i) introduction of Fe + Mn, with the majority of them consumed by columbitization; (ii) introduction of Si and Fe, and in lesser amounts also Pb and U: Si, Pb, and U incorporated into pyrochlore, iron forming Fe-oxide halos around pyrochlore. During both stages, F and Na decreased. In the case of a (nearly) complete pyrochlore columbitization, U and Th were exsolved to form inclusions of a thorite/coffinite-like phase. In contrast to altered pyrochlores from other localities, pyrochlore from Madeira shows a relatively high occupancy of the A-site. Although Madeira melt was Na-, F-rich, contemporaneous crystallization of cryolite consumed both elements and pyrochlore was, from the beginning, relatively Na-, F-poor. Full article
(This article belongs to the Special Issue Rare-Metal Granites)
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