Multiple Generations of Wolframite Mineralization in the Echassieres District (Massif Central, France)

Abstract

The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid responsible for greisen alteration that massively affected the Beauvoir granite. In the La Bosse stockwork, greisen alteration is characterized by hydrothermal topaz that is texturally and chemically distinct from that precipitated during topazification. Supergene alteration responsible for kaolinization of Beauvoir and Colettes granites caused remobilization of a non-negligible amount of tungsten (W) during replacement of wolframite by W-rich goethite in all units of the Echassières district. This model for multiple W mineralizing events is novel and can prove essential in distinguishing potential economic deposits worldwide.

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

“…A previous study ruled out a possible effect of contrasting composition of the greisen-forming fluid between granite and veins to explain this peculiar mode of occurrence (Monnier et al, 2018). The mineral paragenesis of these two wolframite generations suggest similar fluid properties (low-CO 2 , strong acidity and low salinity; Monnier et al, 2019), indicative of greisen affinity (Štemprok, 1987).…”

“…The Echassières district in central France is well suited to investigate the role that different parameters might play on the origin of W mineralization. In this area, most of the W is in the form of three wolframite generations related to three distinct hydrothermal events, separated in time (Monnier et al, 2019). The earliest W episode occurred in the form of wolframite a, outcropping in a stockwork vein system.…”

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.…”

“…Grains were selected to examine the relationship between ilmenite and titanite, and magmatic titanite was examined to determine zoning resulting from alteration during mineralization and variation imparted during growth. Elements measured with LA ICP-MS during mineral element mapping are 29 Si, 44 Ca, 45 Sc, 49 Ti, 51 Element maps were generated by rastering a laser beam across the sample, thereby ionizing a small portion of the grain [33]. Both LA ICP-MS mapping and U-Pb geochronology were conducted at the University of New Brunswick's LA ICP-MS facility using a Resonetics M-50-LR 193ns laser coupled to an Agilent 7700x ICP-MS equipped with dual external pumps.…”

“…376 Ma Re-Os molybdenite [7], and ca. 365 Ma late porphyry dykes [25]), but with the evolution of aFe/aCa resulting in episodes of wolframite followed by scheelite mineralization, rather than successive wolframite mineralizing events as is observed at the La Bosse stockwork [49]. Additional geochronological work on metasomatic phases is required to determine the timescales on which W mineralization was formed, and trace element geochemistry of mineralization could discriminate different mineralizing events [49].…”