Hostname: page-component-78c5997874-ndw9j Total loading time: 0 Render date: 2024-11-19T13:26:14.706Z Has data issue: false hasContentIssue false
  • English
  • Français

Multiphase methane-rich fluid inclusions in gold-bearing quartz as illustrated at Pontal (Goias, Brazil)

Published online by Cambridge University Press:  05 July 2018

N. Guilhaumou ,
M. Santos ,
J. C. Touray ,
C. Beny  and
M. Dardenne
N. Guilhaumou
Affiliation:
Département de Géologie de l'Ecole Normale Supérieure, URA CNRS n° 1316, 24 rue Lhomond, 75005 Paris, France
M. Santos
Affiliation:
Instituto de Geociencias, Universidad de Brasilia, Brasilia, Brazil
J. C. Touray
Affiliation:
Laboratoire de Métallogénie et Géochimie minérale, Ecole Supérieure de l'Energie et des Matériaux, URA CNRS n, o 1366, Université d'Orléans, 45067, Orléans Cédex 02, France
C. Beny
Affiliation:
G.S. (BRGM-CNRS), 1A, rue de la Férollerie 45071, Orléans Cédex 02, France
M. Dardenne
Affiliation:
Instituto de Geociencias, Universidad de Brasilia, Brasilia, Brazil
Get access Rights & Permissions [Opens in a new window]

Abstract

In the Pontal auriferous lode, dominant saccharoidal quartz is associated with oligoclase, biotite, hornblende, tremolite-actinolite, sulphides (less than 2%), and disseminated native gold. Four main types of fluid inclusion have been distinguished based on their habit, distribution and spatial relation-ship with gold particles. Type S are primary multiphase large sized (100 to 200 µm) inclusions with homogenization temperatures (V + L → L) between 350 and 450°C. They contain siderite and/or calcite and graphite-like microcrystals as daughter phases. Commonly associated with these inclusions are tiny (50 to 100 µm) solid inclusions of biotite or actinolite. In most of these inclusions, only CH4 has been detected in the vapour phase. However some noticeable exceptions were observed (CO2/CH4 ratio near 0.85). Type C inclusions are later than gold and occur disseminated in quartz or along trails that crosscut quartz grain boundaries. They may contain nahcolite daughter crystals. CO2/CH4 ratios range from 0.0 to 0.5. Homogenization temperatures vary from 150 to 300°C. Type V are mainly gaseous CH4-H2O inclusions. They may occur as small-sized inclusions directly associated with gold particles. Type L are aqueous two-phase inclusions of late secondary origin.

The scattering of the CO2/CH4 ratios could be related to fluctuations of the oxygen fugacity that triggered gold precipitation at the time of trapping. These variations of fO2 with time could reflect unbuffered fluid-rock interaction with respect to redox conditions during quartz deposition.

Finally, gold deposition is interpreted to have occurred at elevated temperature (500°C) and pressure, compatible with boundary conditions between greenschist and amphibolites facies.

Keywords

gold depositquartz lodefluid inclusionsRaman microprobemicrothermometry
Type
Ore environments—gold mineralization
Information
Mineralogical Magazine , Volume 54 , Issue 375 , June 1990 , pp. 257 - 266
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

Bischoft, W. D., Sharma, S. K. and Mackenzie, F. T. (1985) Carbonate ion disorder in synthetic and biogenic magnesium calcites: a Raman spectral study. Am. Mineral. 70, 581-9.Google Scholar
Collins, P. J. L. (1979) Gas hydrates in CO2-bearing fluid inclusions and the use of freezing data for estimation of salinity. Econ. Geol. 74, 1435-44.CrossRefGoogle Scholar
Colvine, A. C., Fyon, J. A., Heather, K. B., Marmont, Soussan, Smith, P. M. and Troop, D. G. (1988) Archean lode gold deposits in Ontario. Ontario Geol. Surv. Misc. Pap. 139, 136pp.Google Scholar
Deer, W. A., Howie, R. A. and Zussman, J. (1963) Rock forming minerals, 3 (Sheet-silicates), 263pp. Longmans, London.Google Scholar
Dubessy, J. (1984) Simulation des équilibres chimiques dans le systéme C-OH. Conséquences méthodologiques pour les inclusions fluides. Bull. Minéral. 107, 155-68.CrossRefGoogle Scholar
Hollister, L. S. and Burruss, R. C. (1976) Phase equilibria in fluid inclusions from the Khtada Lake metamorphic complex. Geochim. Cosmochim. Acta, 40, 163-75.CrossRefGoogle Scholar
Kreulen, R. (1987) Thermodynamic calculations of the C-O-H system applied to fluid inclusion: are fluid inclusions unbiassed samples of ancient fluids. Chem. Geol. 61, 59-64.CrossRefGoogle Scholar
Moravek, P. and Pouba, Z. (1987) Precambrain and Phanerozoic History of Gold Mineralization in the Bohemian Massif. Econ. GeoL 82, 2098-114.CrossRefGoogle Scholar
Rouzaud, J. N. (1984) Thèse de doctorat d'Etat, Université d'Orléans, 139 pp.Google Scholar
Santos, M. (1989) Mestrado thesis, University of Brasilia, 134 pp.Google Scholar
Shenberger, D. M. and Barnes, H. L. (1989) Solubility of gold in aqueous sulfide solutions from 150°C to 350°. Geochim. Cosmochim. Acta, 53, 269-78.CrossRefGoogle Scholar
Touray, J. C. (1987) Transport et dépôt de l'or dans les fluides de la croûte continentale, l'apport des études d'inclusions fluides. Chron. Rech. Minière, 484, 43-53.Google Scholar
Touray, J. C., Beny, C., Bouhlel, S. (1988) Caractérisation, par analyse à la microsonde électronique et microspectro-métrie Raman, de barytocélestites de différentes compositions. C.R. Acad. So. Paris, 306, 1353-7.Google Scholar
Touray, J. C., Marcoux, E., Hubert, P. and Proust, D. (1989) Hydrothermal Processes and Ore Forming Fluids in the Le Bourneix Gold Deposit, Central France. Econ. Geol. 84, 326-37.CrossRefGoogle Scholar
Turner, F. J. and Verhoogen, J. (1958) Metamorphic reactions and metamorphic facies. New-York, Geol. Soc. Amer., 259 pp.Google Scholar
Winkler, H. G. F. (1974) Petrogenesis of metamorphic rocks. Berlin, Heidelberg, Springer Verlag, 220 pp.CrossRefGoogle Scholar