The Panasqueira Rare Metal Granite Suites and Their Involvement in the Genesis of the World-Class Panasqueira W–Sn–Cu Vein Deposit: A Petrographic, Mineralogical, and Geochemical Study

Filipe Pinto,Michel Cathelineau,Michel Cuney,Eleonora Carocci,Christian Marignac,Andreï Lecomte

doi:10.3390/min10060562

Filipe Pinto, Michel Cathelineau + Show 4 more

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https://doi.org/10.3390/min10060562

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Abstract

Elucidation of time-space relationships between a given wolframite deposit and the associated granites, the nature of the latter, and their alterations, is a prerequisite to establishing a genetic model. In the case of the world-class Panasqueira deposit, the problem is complicated because the associated granites are concealed and until now poorly known. The study of samples from a recent drill hole and a new gallery allowed a new approach of the Panasqueira granite system. Detailed petrographic, mineralogical, and geochemical studies were conducted, involving bulk major and trace analyses, BSE and CL imaging, EPMA, and SEM-EDS analyses of minerals. The apical part of the Pansqueira pluton consisted of a layered sequence of separate granite pulses, strongly affected by polyphase alteration. The use of pertinent geochemical diagrams (major and trace elements) facilitated the discrimination of magmatic and alteration trends. The studied samples were representative of a magmatic suite of the high-phosphorus peraluminous rare-metal granite type. The less fractionated members were porphyritic protolithionite granites (G1), the more evolved member was an albite-Li-muscovite rare metal granite (G4). Granites showed three types of alteration processes. Early muscovitisation (Ms0) affected the protolithionite in G1. Intense silicification affected the upper G4 cupola. Late muscovitisation (Fe–Li–Ms1) was pervasive in all facies, more intense in the G4 cupola, where quartz replacement yielded quartz-muscovite (pseudo-greisen) and muscovite only (episyenite) rocks. These alterations were prone to yield rare metals to the coeval quartz-wolframite veins.

Highlights

The genesis of hydrothermal W and Sn deposits is generally related to the emplacement of so-called specialized granites, enriched in a series of incompatible elements, such as Rb, Cs, Li, Sn, W, Ta, Nb (e.g., [1,2,3])
At the L2 level, the intrusive contacts of the greisenised granite (G4, defined in the geochemistry) with the surrounding metamorphic rocks showed a combination of steep (~N150◦ E) and flat interfaces, both oblique onto the near-vertical schistosity of the wall rock at ~N140◦ E (Figure 3B)
Large abundant crystals occurred in the G1 suite, where they were the only bearers of rare metals

Summary

Introduction

The genesis of hydrothermal W and Sn deposits is generally related to the emplacement of so-called specialized granites, enriched in a series of incompatible elements, such as Rb, Cs, Li, Sn, W, Ta, Nb (e.g., [1,2,3]). Most of the available works [11,12,13,14,15,16] have mostly addressed major element geochemistry, mainly based on drill-hole data, in general, with a limited number of samples, not located for most of them, commonly affected by deep hydrothermal alterations (greisenisation), and lacking a detailed petrographic-mineralogical description. For these reasons, it has been until now challenging to assign the Panasqueira granite to any reference granite trend. The overall consideration of Panasqueira granite suites, especially their magmatic evolution and related fluid-rock interactions, allowed us to examine the possible genetic links between magmatic and hydrothermal events at Panasqueira

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