Contrasting fluid behavior during two styles of greisen alteration leading to distinct wolframite mineralizations: The Echassières district (Massif Central, France)

Abstract

 Fluid cooling, without evidence of sharp pressure variations, is the main cause for one wolframite mineralization episode.  Fluid flashing (vaporization), triggered by fracture-induced pressure drops, initiated crystallization of a second type of wolframite mineralization.  Greisenization of the Beauvoir granite is a continuous process (ca. 400°C down to 190°C), occurring at high temperature as pervasive alteration of the granite body, while at lower temperature it is localized to a vein system.  Globally, greisen-forming fluids have a strong potential for transporting and precipitating W. 2  In greisen systems worldwide, regional veins distal to the altered causative magmatic body can be mineralized by greisen-forming fluids.

Influence of Titaniferous Phases on Tungsten Mineralizing Processes at the Giant Sisson Brook W-Mo Deposit, New Brunswick, Canada: Mineral-Chemical and Geochronological Assessment

“…Multistage formation of W-mineralization (wolframite) from discrete hydrothermal episodes has been documented at the La Bosse stockwork in the Echassieres District of the Massif Central, France [49,50]. The Sisson Brook deposit may represent a similar case given the protracted magmatic and hydrothermal activity present in the area (ca.…”

Antimony in quartz as a vector to mineralization: A statistical approach from five Variscan Sb occurrences (France)

“…Collection samples from Bournac are part of a batch collected for the studies of Munoz and Moëlo (1982) and Munoz and Shepherd (1987). Finally, quartz veins from Nades and Pouzol-Servant districts were sampled on outcrop during the autumn 2016 and 2017, respectively (Monnier et al, 2018;Monnier et al, 2020). Samples from La Lucette, which were taken from different parts on the main mineralized vein, come from the rock collection of the French Geological Survey (BRGM).…”

“…We have seen above how the five districts studied display different quartz trace-element signatures, including the two neighbour districts in the Sioule Nappe, Pouzol-Servant and Nades. Monnier et al (2018Monnier et al ( , 2019Monnier et al ( , 2020 have shown that greisen alteration of the Beauvoir granite developed a regionalscale fluid circulation that gave rise to distal mineralizations, among which is the Nades district. A particular aspect of the latter is that it was the only site showing Sb mineralization, although quartz from all manifestation of the greisen event(s) at Beauvoir showed Sb enrichment in their traceelements signatures.…”

“…Moreover, the Sioule nappe is known to contain a large variety of mineralized quartz veins (Sb, Cu, W, Li, Sn, Nb-Ta), some of which have already been the subject of trace-elements studies in quartz (Monnier et al, 2018), thus allowing a comparison with systems mineralized to different degrees, or being all together barren. A model linking the greisenification of the nearby Beauvoir rare-metal granite, the formation of proximal veins (W, Sn) around it and of the more distal Sb mineralization was proposed to explain the genesis of the Nades district (Monnier et al, 2018;Monnier et al, 2020). This gave us the opportunity to compare quartz analyses from this district with the chemistry of quartz from the neighbouring Pouzol-Servant veins to evaluate whether or not the latter system was related to the same greisen hydrothermal event.…”

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

“…Addition of non-polar molecules such as N2, CO2, and CH4 yields a decrease of W concentration in solution (Dubessy et al, 1989;Gibert et al, 1992). Precipitation of wolframite at Puy-les-Vignes could have been triggered by several processes including cooling, depressurization, fluid mixing, and fluid-rock interaction (Heinrich et al, 1990;Wei et al, 2012;Dewaele et al, 2016;Chicharro et al, 2016;Lecumberri-Sanchez et al, 2017;Legros et al, 2019Legros et al, , 2020Monnier et al, 2020). In particular, fluid pressure drop induced by hydrofracturing of the host rocks results in significant decrease of CO2 solubility and pH increase, which can cause in turn wolframite precipitation (Liu et al, 2017).…”