The granite hosted gold deposit of Moulin de Chéni (Saint-Yrieix district, Massif Central, France): Petrographic, structural, fluid inclusion and oxygen isotope constraints

Jean Vallance, Marie Christine Boiron, Michel Cathelineau, Serge Fourcade, Michel Varlet, Christian Marignac

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

The Moulin de Chéni orogenic gold deposit is the only granite-hosted deposit of the Saint-Yrieix district, French Massif Central. It occurs in 338 ± 1.5 Maold peraluminous leucogranites and is characterized by intense microfracturing and bleaching of the granite in relation to pervasive sulfide crystallization. Formation of quartz veins and gold deposition occurred in two successive stages: an early "mesozonal" stage of quartz-sulfide (Fe-As-S) deposition, usually devoid of gold and a late "epizonal" stage of base metal and gold deposition. Both stages postdate peak metamorphism and granite intrusion. The genesis of the deposit is the result of four successive fluid events: (1) Percolation of aqueous-carbonic metamorphic fluids under an assumed lithostatic regime of 400-450 °C, at a maximum depth of 13 km; (2) Formation of the main quartz lodes with coeval K-alteration and introduction of As and S from aqueous-carbonic fluids percolating along regional faults. Arsenopyrite and pyrite deposition was linked to the alteration of Fe-silicates into K-feldspar and phengite at near-constant iron content in the bulk granite. Temperature was similar to that of the preceding stage, but pressure decreased to 100-50 MPa, suggesting rapid uplift of the basement up to 7.5 km depth; (3) The resulting extensional tectonic leads to the deposition of gold, boulangerite, galena and sphalerite in brecciated arsenopyrite and pyrite from aqueous fluids during a mixing process. Temperature and salinity decrease from 280 to 140 °C and 8.1 wt% eq. NaCl to 1.6 wt% eq. NaCl, respectively; (4) Sealing of the late fault system by barren comb quartz which precipitated from dilute meteoric aqueous fluids (1.6 wt% eq. NaCl to 0.9 wt% eq. NaCl) under hydrostatic conditions at 200-150 °C.

Original languageEnglish
Pages (from-to)265-281
Number of pages17
JournalMineralium Deposita
Volume39
Issue number3
DOIs
StatePublished - May 2004
Externally publishedYes

Keywords

  • Fluid mixing
  • Orogenic gold
  • Oxygen isotopes
  • P-T conditions
  • Variscan belt

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