Hostname: page-component-848d4c4894-jbqgn Total loading time: 0 Render date: 2024-07-03T10:56:44.148Z Has data issue: false hasContentIssue false
  • English
  • Français

Fluids in Hercynian Au veins from the French Variscan belt

Published online by Cambridge University Press:  05 July 2018

M. C. Boiron ,
M. Cathelineau ,
J. Dubessy  and
A. M. Bastoul
M. C. Boiron
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54501 Vandoeuvre les Nancy Cedex, France
M. Cathelineau
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54501 Vandoeuvre les Nancy Cedex, France
J. Dubessy
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54501 Vandoeuvre les Nancy Cedex, France
A. M. Bastoul
Affiliation:
CREGU and GS CNRS-CREGU, BP 23, 54501 Vandoeuvre les Nancy Cedex, France
Get access Rights & Permissions [Opens in a new window]

Abstract

Fluids, together with alteration and ore mineral assemblages, were studied in representative hydrothermal gold-bearing quartz veins from the western part of the Variscan belt in France (La Bellière, Montagne Noire district, Villeranges-Le Châtelet district, and Limousin province). Petrographic studies of the relationships between ores, fluid inclusions, microfracturing and quartz textures show that chronological and genetic relationships between gold deposition and fluid trapping may be very complex and difficult to establish for veins which show multi-stage fracturing and shearing. Systematic studies of secondary fluid inclusions in microcracks and recrystallized zones of the early quartz veins indicate two contrasting physical-chemical conditions: 1 relatively high temperature (250–400°C) and pressure (>1 kbar) event with CO2-CH4-H2S-N2 (±H2O-NaCl)-rich fluids related to the early sulphide deposition; 2 lower temperature (150–250°C) and pressure with aqueous fluids related to the late native-gold-sulphide (or sulphosalt) assemblage, which constitutes the economic ores in some deposits.

In deposits where gold occurs predominantly in a combined state within arsenopyrite and pyrite (Châtelet and Villeranges), primary fluid inclusions in authigenic quartz combs cogenetic with arsenopyrite are almost purely aqueous (H2O-NaCl) and have a low salinity (1–4 wt. % NaCl). P-T conditions (150–250°C), nearly hydrostatic pressures) are similar to those of the second stage in the multi-stage quartz veins.

Consideration of chemical equilibria in the C-O-H-N-S system using microthermometric and Raman spectrometric analysis for the fluids, together with data obtained from mineralogical studies, show that during gold deposition, fO2 was below hematite-magnetite buffer at Villeranges and around the Ni-NiO buffer at La Bellière and Montagne Noire. fS2 calculations based on H2S analyses are in good agreement with mineral assemblage estimates and close to that fixed by the pyrite-pyrrhotite boundary at high temperature. Ore fluid pH was significantly lower than in the host rocks as shown by the complete alteration of the host rocks into a quartz-K-mica assemblage. The data illustrate that during the late Hercynian, fluid circulation evolved from high P-T conditions, in some cases linked to late magma intrusions, towards conditions typical of later hydrothermal systems of the geothermal type.

Keywords

fluidsHercyniangold veinsVariscan beltFrance
Type
Ore environments—gold mineralization
Information
Mineralogical Magazine , Volume 54 , Issue 375 , June 1990 , pp. 231 - 243
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ahmadzadeh, H. (1984) Unpubl. 3° Cycle Doct. Thesis, Clermont Ferrand, 98 pp.Google Scholar
Bache, J. J. (1980) Mem. B.R.G.M. 118, 102pp.Google Scholar
Boiron, M. C. (1987) Geol. Geochim. Uranium, Mem. Nancy, 15, 310 pp.Google Scholar
Boiron, M. C. and Cathelineau, M. (1989a) AIPEA meeting, Strasbourg, August 1989.Google Scholar
Boiron, M. C. and Cathelineau, M. (1989b) Water-Rock Interaction 6 (Miles, ed.) 103-6.Google Scholar
Boiron, M. C. and Cathelineau, M., Dubessy, J. and Bastoul, A. M. (1988) Proceedings of the SIMP meeting, Verbania, Ital, ‘Granites and their surroundings’, 1987. Rendiconti Soc. Ital. Min. Petrol. 43, 485-98.Google Scholar
Boiron, M. C. and Cathelineau, M., Dubessy, J. and Bastoul, A. M., Kibonzi, B., Tollon, F. and Normand, M. (1989a) Gold 89 in Europe. Terra Abstract, 1, S3-2P, p. 28.Google Scholar
Boiron, M. C. and Trescases, J. J. (19896) Econ. Geol. Special monograph on the Hercynian deposits in France, 84-5, 1340-62.CrossRefGoogle Scholar
Bonnemaison, M. and Marcoux, E. (1987) Chron. Rech. Min. 478, 29-42.Google Scholar
Bonnemaison, M., Crouzet, J., Thiercelin, F. and Tollon, F. (1986) Proceedings of Gold ’86 symposium, Toronto, 457-69.Google Scholar
Bouchot, V. (1989) Unpublished Thesis, Orléans Univ.Google Scholar
Bril, H. and Nenert, S. (1987) IX Symposium on Euro¬pean Current Research on fluid inclusions, Porto, p. 135.Google Scholar
Calli, M. (1988) Unpubl. Thesis, Toulouse Univ. 246 pp.Google Scholar
Cathelineau, M. and Nieva, D. (1985) Contrib. Mineral. Petrol. 91, 235-44.CrossRefGoogle Scholar
Cathelineau, M. and Nieva, D. and Izquierdo, G. (1988) Ibid. 100, 418-28.Google Scholar
Cathelineau, M., Boiron, M. C., Holliger, P. and Marion, P. (1988) Extended abstract, Bicentennial Gold 88, Melbourne, May 1988, 235-40.Google Scholar
Cathelineau, M., Boiron, M. C., Holliger, P., Marion, P. and Denis, M. (1989) Econ. Geol. Monograph 6, 320-33.Google Scholar
Crouzet, J., Recoing, M. and Tollon, F. (1979) Chron. Rech. Min. 452, 5-38.Google Scholar
Dubessy, J. (1984) Bull. Mineral. 107, 157-68.Google Scholar
Dubessy, J., Ramboz, C., Nguyen Trung, C., Cathelineau, M., Charoy, B., Cuney, M., Leroy, J., Poty, B. and Weisbrod, A. (1987) Bull. Mineral. 110, 261-81.Google Scholar
Dubessy, J., Poty, B. and Ramboz, C, (1989) Eur. J. Mineral. 1, 517-34.CrossRefGoogle Scholar
Essarraj, S. (1989) D.E. A., Nancy I Univ., 71 pp.Google Scholar
Hubert, P. (1986) Documentdu B.R.G.M. 114, 350pp.Google Scholar
Jacobs, G. K. and Kerrick, D. M. (1981) Geochim. Cosmochim. Acta, 45, 607-14.CrossRefGoogle Scholar
Kerrick, D. M. and Jacobs, G. K. (1981) Am. J. Sci. 281, 735-67.CrossRefGoogle Scholar
Lépine, J. (1989) Unpublish. Thesis, Toulouse Univ.Google Scholar
Marion, P. (1988) Unpublish. Doct. thesis, INPL, Nancy.Google Scholar
Marion, P., Regnard, J. R. and Wagner, F. E. (1986) C.R. Acad. Sci. Paris, 302, ser. II, 8, 571-4.Google Scholar
Picot, P. and Marcoux, E. (1987) Ibid. 304, ser. II, 6, 221-6.Google Scholar
Poty, B., Leroy, J. and Jachimowicz, L. (1976) Bull. Soc. Fr. Mineral. Cristallogr. 99, 182-6.Google Scholar
Ramboz, C., Schnapper, D. and Dubessy, J. (1985) Geochim. Cosmochim. Acta, 49, 205-19.CrossRefGoogle Scholar
Roedder, E. (1972) U.S. Geol. Surv., Prof Pap 440-JJ, 164 pp.Google Scholar
Romberger, S. (1986) Gold in Western Shield (Clark, , ed.) Spec. vol. Canadian Institute of Mining and metallurgy, 168-86.Google Scholar
Sandras, A. (1988) Unpubl. Thesis, Nancy I Univ. 216pp.Google Scholar
Seward, T. M. (1973) Geochim. Cosmochim. Acta, 37, 379-99.CrossRefGoogle Scholar
Seward, T. M. (1984) Gold ’82 proceedings, 165-81.Google Scholar
Shemberger, D. M. and Barnes, H. L. (1989) Geochim. Cosmochim. Acta, 53, 269-78.CrossRefGoogle Scholar
Smith, T. J., Cloke, P. L. and Kessler, S. E. (1984) Econ. Geol. 79, 1265-85.CrossRefGoogle Scholar
Touray, J. C. (1987) Chron. Rech. Min. 488, 43-54.Google Scholar
Velde, B. (1965) Am. J. Sci. 263, 886-913.CrossRefGoogle Scholar
Wood, P.C., Burrow, D. R., Thomas, A. V. and Spooner, E. T. C. (1986) Proceedings of Gold ’86. symposium, Toronto, 56-80.Google Scholar
Wu, X., Beny, C., Zimmermann, J. L. and Touray, J. C. (1989) Abstract Geo-Raman Toulouse.Google Scholar
Zappettini, E. O. (1983) Unpubl. 3° cycle Thesis, Limoges, 151 pp.Google Scholar
Zhang, Y. G. and Frantz, J. D. (1987) Chem. Geol. 64, 335-50.CrossRefGoogle Scholar