Multistage development of a hydrothermal W deposit during the Variscan late-orogenic evolution: the Puy-les-Vignes breccia pipe (Massif Central, France)

Abstract

The Puy-les-Vignes W deposit, located in the northwestern French Massif Central (FMC), is a rare occurrence worldwide of a wolframite-mineralized hydrothermal breccia pipe hosted in high-grade metamorphic gneisses. We present here an integrated study of this deposit aiming to characterize the ore-forming hydrothermal system in link with the Variscan late-orogenic evolution of the FMC. Based on a set of representative samples from the host rocks and mineralization, we describe a detailed paragenetic sequence and we provide the major and trace element geochemistry of the host rocks and W-Nb-Ta-Sn-Ti oxide minerals, in situ U-Pb and 40Ar/39Ar geochronology, and a fluid inclusion study in quartz and wolframite. We demonstrate that the formation of this W-mineralized breccia pipe results from a multistage development between ca. 325 and 300 Ma related to four major episodes during the late Carboniferous. The first episode corresponds to the emplacement of an unexposed peraluminous granite at ca. 325 Ma, which generated microgranite dykes exposed at the present-day surface. The second episode is the formation of the quartz-supported breccia pipe and wolframite mineralization at ca. 318 Ma at a paleodepth of 7 km. The mineralizing fluids have a H2O-NaCl-CO2-CH4-N2 composition, a moderate-salinity (<9 wt.% NaCl eq) and were trapped at high-temperatures (400-450°C) during lithostatic to hydrostatic pressure variations caused by intense hydraulic fracturing of the host rocks. Wolframite deposition is interpreted to result from the mixing between a W-rich intermediate-density magmatic fluid exsolved from an evolved leucogranite and low-salinity volatile-rich metamorphic fluids of distal origin. The third episode corresponds to a magmatic-hydrothermal Nb-Ta mineralization overprinting the W-mineralized system and related to the intrusion at ca. 314 Ma of a rare-metal granite, which is part of a regional peraluminous rare-metal magmatism during the 315-310 Ma period. Finally, the last episode corresponds to the formation of a disseminated Bi±Au-Ag mineralization at ca. 300 Ma, which shares similar textural and mineral features with orogenic gold deposits in the FMC. The Puy-les-Vignes W deposit records, therefore, a multistage and long-lived development that extends over a timespan of 25 million years in a regional setting dominated by protracted peraluminous magmatism and HT-LP metamorphism. Although the local environment of ore deposition is atypical, our results show that the mineral assemblages, alteration styles, and fluid characteristics of the Puy-les-Vignes breccia pipe are similar to those of other peri-granitic W deposits in the FMC.

Le gisement à étain–cuivre–indium de Charrier (Allier) : un skarnoïde viséen (340 Ma) traceur de la métallogenèse varisque du nord Massif central

“…12) et appuyant une cristallisation à la fin de l'étape magmatique-hydrothermale. Les cassitérites des gisements tardi-hercyniens proches (Montebras, Échassières-Beauvoir, Puy-les-Vignes) possèdent des compositions plus variables, plus riches en Nb et Ta, mais ces gisements montrent plusieurs générations de cassitérite (Monnier et al, 2019 ;Harlaux et al, 2021 ;. Enfin, la gangue à biotite-chlorite et fluorapatite, mais sans topaze ni tourmaline, dénote un magma probablement assez pauvre en fluor et sans bore.…”

U/Pb geochronology of wolframite by LA-ICP-MS; mineralogical constraints, analytical procedures, data interpretation, and comparison with ID-TIMS

“…Element distribution maps (e.g., SEM-EDS or µXRF) can be also used to target internal zones, or to exclude samples for ID-TIMS analyses. Near-infrared microscopy (e.g., Ortelli et al 2018;Harlaux et al 2021) and X-ray computed tomography (CT; Harlaux et al 2018a) are also promising tools to investigate the textures of wolframite and to provide 3D information about the relative proportions and the spatial distribution of micro-inclusions and/or alteration zones.…”

Depositing >1.5 Mt of Tin Within <1 m.y. of Initial Granitic Intrusion in the San Rafael Tin (-Copper) Deposit, Southeastern Peru

“…New insight has been provided for the timing and duration of Sn±W ore deposit formation via U-Pb dating of ore minerals such as cassiterite and wolframite (e.g., Zhang et al, 2017;Harlaux et al, 2018a;Moscati and Neymark, 2020;Tang et al, 2020;Denholm et al, 2021;Gemmrich et al, 2021;Carr et al, 2021). Importantly, most of the latter studies focused on several mineralized districts whereas there are only a few reported detailed geochronological results that have bracketed the duration of magmatic-hydrothermal events in a single Sn±W deposit (Hu et al, 2012;Chen et al, 2019;Carr et al, 2020;Mohammadi et al, 2020;Tapster and Bright, 2020;Legros et al, 2020;Harlaux et al, 2021a). This paper presents a detailed geochronological study of the San Rafael Sn (-Cu) deposit, one of the world's largest granite-related cassiterite-bearing lode systems, that is located in the Central Andean tin belt of southeast Peru.…”