Percolation de fluides tardi-hercyniens dans le granité de Saint-Sylvestre (Nord-Ouest du Massif central français) : données des inclusions fluides sur un profil Razès-Saint-Pardoux

André, Anne-Sylvie; Lespinasse, Marc; Cathelineaua, Michel; Cuneya, Michel; Leroy, Jacques

doi:10.1016/s1251-8050(99)80223-7

Cited by 2 publications

(1 citation statement)

References 16 publications

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“…An example of the formation of large alteration halos induced by granitic intrusions is the pervasive chloritization of granites around percolation zones, the so‐called ‘episyenite’ alteration, which is due to hot fluid circulation at rather low pressures (e.g. André et al . 1999; Lespinasse & Cathelineau 1990; ≥350°C, ≥0.5 kbar).…”

Section: Discussionmentioning

confidence: 99%

Retrograde P–T evolution and high temperature–low pressure fluid circulation in relation to late Hercynian intrusions: a mineralogical and fluid inclusion study of the Charroux‐Civray plutonic complex (north‐western Massif Central, France)

Freiberger¹,

Boiron²,

Cathelineau³

et al. 2001

Geofluids

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The calc‐alkaline plutonic complex from Charroux‐Civray (north‐western part of the French Massif Central) displays multiphase hydrothermal alteration. Plutonic rocks, as well as early retrograde Ca–Al silicate assemblages, which have crystallized during cooling and uplifting of the plutonic series, are affected by multiphase chlorite–phengite–illite–carbonate alteration linked to intense pervasive fluid circulation through microfractures. The petrographic study of alteration sequences and their associated fluid inclusions in microfissures of the plutonic rocks, as well as in mineral fillings of the veins, yields a reconstruction of the P–T–X evolution of the Hercynian basement after the crystallization of the main calc‐alkaline plutonic bodies. This reconstruction covers the uplift of the basement to its exposure and the subsequent burial by Mesozoic sediments. Cooling of the calc‐alkaline plutonic series started at solidus temperatures (∼650°C), at a pressure of about 4 kbar (1 bar = 105 N m−2), as indicated by magmatic epidote stability, hornblende barometry and fluid inclusion data. Cooling continued under slightly decreasing pressure during uplift down to 2–3 kbar at 200–280°C (prehnite–pumpellyite paragenesis). Then, a hot geothermal circulation of CO2‐bearing fluids was induced within the calc‐alkaline rocks leading to the formation of greisen‐like mineralizations. During this stage, temperatures around 400–450°C were still high for the inferred depths (∼2 kbar). They imply abnormal heat flows and thermal gradients of 60–80°C km−1. The hypothesis of the existence of one large or a succession of smaller peraluminous plutons at depth, supported by geophysical data, suggests that localized heat flows were linked to concealed leucogranite intrusions. As uplift continued, greisen mineralization was subsequently affected by the chlorite–phengite–dolomite assemblage, correlated with aqueous and nitrogen‐bearing fluid circulations in the temperature range of 400–450°C. In a later stage, a continuous temperature decrease at constant pressure (∼0.5 kbar) led to the alteration of the dolomite–illite–chlorite type in the 130–250°C temperature range.

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Section: Discussionmentioning

confidence: 99%

Retrograde P–T evolution and high temperature–low pressure fluid circulation in relation to late Hercynian intrusions: a mineralogical and fluid inclusion study of the Charroux‐Civray plutonic complex (north‐western Massif Central, France)

Freiberger¹,

Boiron²,

Cathelineau³

et al. 2001

Geofluids

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

Vallance¹,

Boiron

Cathelineau³

et al. 2004

Mineralium Deposita

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The Moulin de Che´ni 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 quartzsulfide (Fe-AsS) 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.

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Percolation de fluides tardi-hercyniens dans le granité de Saint-Sylvestre (Nord-Ouest du Massif central français) : données des inclusions fluides sur un profil Razès-Saint-Pardoux

Cited by 2 publications

References 16 publications

Retrograde P–T evolution and high temperature–low pressure fluid circulation in relation to late Hercynian intrusions: a mineralogical and fluid inclusion study of the Charroux‐Civray plutonic complex (north‐western Massif Central, France)

Retrograde P–T evolution and high temperature–low pressure fluid circulation in relation to late Hercynian intrusions: a mineralogical and fluid inclusion study of the Charroux‐Civray plutonic complex (north‐western Massif Central, France)

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

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