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

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.

Post-measurement compressed calibration for ICP-MS-based metal quantification in mine residues bioleaching

“…Panasqueira is a wolframite deposit and contains associated granites with alterations that are prone to yield rare metals to the coeval quartz-wolframite veins 44 so the leached elements and the increase in critical metals Ga and Y were expected. The element Al was the IC leached in the highest concentrations.…”

“…Under the same conditions, the elements Cu and Zn were found also in high concentrations in the pore water reaching 300 and 500 ppm, respectively. Al is a major element and is expected to come from the feldspar microliths in the quartz and granite or the micas of the ore deposit 44 , 45 . As opposed to the other elements, the Fe concentration increased steadily over time.…”

High pressure and temperatures during the early stages of tungsten deposition at Panasqueira revealed by fluid inclusions in topaz

“…Quartz-wolframite veins then intersected the later rare metal granite sequence found in the "Greisen cupola" (Marignac et al, 2020), indicating that granites could not be considered as a heat source either. However, the presence in the SW of the deposit of both the topaz rich (± cassiterite) zone and the geophysical anomalies at close distance (Fig.…”

“…Feeding through vertical dykes is the commonly accepted way for such an emplacement (Petford et al, 2000) and indeed, geophysical modelling (Ribeiro, 2017) shows the existence of NE-SW root that may be related to such a dyke. Third, the recurrence of rare metal granite emplacement (Marignac et al, 2020) argues for the persistence of a weakness zone under the deposit, the more if effectively tin and fluor of stage III must be related to a new input of rare metal magma. Ascent of magmas are favored by a transpression zone of transcurrent shear, in particular in extensional segments of the associated strike-slip system (Brown, 1994, Brown, 2013.…”

Editorial for the Special Issue “Development of W-Sn and Rare-Metal Metallogenic Systems in an Orogenic Belt”

“…The paper by Marignac et al [4] opens the issue by establishing the time-space relationships between the world-class Panasqueira W(Sn) deposit and the associated concealed granite system, thanks to the recent availability of drill core samples. Remarkably detailed petrographic, mineralogical, and geochemical studies allow for establishing that the apical part of the Panasqueira pluton represents a layered sequence of a succession of four granite injections of the high-phosphorus peraluminous rare-metal granite type, which underwent intense polyphase alteration.…”