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Late-kinematic gold mineralisation during regional uplift and the role of nitrogen: an example from the La Codosera area, W. Spain

Published online by Cambridge University Press:  05 July 2018

S. J. Dee  and
S. Roberts
S. J. Dee
Affiliation:
Department of Geology, The University, Highfield, Southampton SO9 5NH, U.K.
S. Roberts
Affiliation:
Department of Geology, The University, Highfield, Southampton SO9 5NH, U.K.
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Abstract

Vein formation occurred throughout a deformation sequence which involved early transpressive ductile deformation through to late-kinematic transpressive brittle structures which host a series of gold prospects. Fluid inclusion data from (S1) fabric parallel veins associated with early deformation suggest that a low-salinity aqueous fluid, with a mean salinity of 6.4 wt.%, was present during peak metamorphism, Pelite mineralogy and isochores constrain peak metamorphism to the lowermost part of the upper greenschist facies at 325 to 425°C and 1.4 to 3.4 kbar.

Fluid inclusion data from auriferous and barren late-kinematic quartz veins, both containing unmixing assemblages of aqueo-carbonic inclusions with low salinities of ≈2.7 wt.% NaCl equiv., indicate unmixing occurred at 300°C and 1.5 kbar.

Volatiles (CO2, N2, CH4) are observed in all the late-kinematic veins. The N2 contents of veins with elevated gold grades are typically higher than those with low gold grades. N2 reaches 8.7 mole% in a vein with 0.49−4.6 p.p.m. Au compared to <1 mole% in a vein with <0.05 p.p.m. Au. The CH4 content of late kinematic veins is generally less than 1 mole% and shows no relative enrichment in mineralised veins. The generation of N2 in the mineralising fluid most likely results from interaction of fluid with the ammonium ion, NH4+, in micas and feldspars. This interaction could take place either at source, due to metamorphic devolatisation reactions, or along those structures which acted as fluid conduits due to fluid-rock interaction.

Keywords

gold mineralisationnitrogenSpainfluid inclusions
Type
Research Article
Information
Mineralogical Magazine , Volume 57 , Issue 388 , September 1993 , pp. 437 - 450
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

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References

Arthaud, F. and Matte, P. (1975) Les drcrochements tardi-Hercyniens du sud-ouest de l'Europe. Gromrtry et essai de reconstitution des conditions de la deformation. Tectonophysics, 25, 139–71.Google Scholar
Barker, C. E. and Pawlewicz, M. J. (1986) The correlation of vitrinite reflectance with maximum temperature in humic organic matter. In Lecture Notes in Earth Sciences 5: Palaeogeothermics (Bunte-barth, G. and Stegena, L., eds.). Springer Verlag, Berlin, 79–93.Google Scholar
Bottrell, S. H., Shepherd, T. J., Yardley, B. W. D., and Dubessey, J. (1988a) A fluid inclusion model for the genesis of the Dolgellau gold belt, North Wales. J. Geol. Soc., 145, 139–45.Google Scholar
Bottrell, S. H., Car, L. P., and Dubessy, J. (1988b) A nitrogen rich metamorphic fluid and coexisting minerals in slates from North Wales. Mineral. Mag., 52, 451–7.Google Scholar
Bowers, T. S. and Helgeson, H. C. (1983a) Calculation of the thermodynamic and geochemical consequences of non-ideal mixing in the system H2O-CO2-NaCl on phase relations in geological systems: Equation of state for H2O-CO2-NaCl fluids at high temperatures and pressures. Geochim. Cosmochirn. Acta, 47, 1247–75.Google Scholar
Brown, P. E. (1989) FLINCOR: A fluid inclusion data reduction and exploration program. In PACROFIII. Programme with Abstracts, 14.Google Scholar
Brown, P. E. and Lamb, W. M. (1989) P-V-T properties of fluids in the system H2O-CO2-NaCL: New graphical presentations and implications for fluid inclusion studies. Geochim. Cosmochim. Acta, 53, 1209–21.Google Scholar
Burg, J. P., Inglesias, M., Laurent, P. H., Matte, P. H., and Ribeiro, A. (1981) Variscan intercontinental deformation: the Coimbra Cordoba Shear Zone (SW Iberian Peninsula). Tectonophysics, 78, 161–77.Google Scholar
Dubessy, J., Audeoud, D., Wilkins, R., and Koszto-lanyi, C. (1982) The use of the Raman microprobe MOLE in the determination of the electrolytes dissolved in the aqueous phase of fluid inclusions. Chem. Geol., 37, 137–50.Google Scholar
Dee, S. J. (1992) Tectonic controls and fluid evolution of auriferous quartz veins in the La Codosera area SW Spain. Unpublished PhD. thesis, University of Southampton, U.K., 353 pp.Google Scholar
Duit, W., Jansen, J. B. H., Van Breemen, A., and Bos, A. (1986) Ammonium micas in metamorphic rocks as exemplified by Dome de L'Agout (France). Am. J. Sci., 286, 702–32.Google Scholar
Groves, D. I. and Foster, R. P. (1991) Archean Lode Gold Deposits. In Gold metaUogeny and Exploration. (R. P. Foster, ed.), Blackie, London, 63–103.Google Scholar
Haendel, D., Mtihle, K., Striihl, G., and Wand, U. (1979) Variationen der slickstoffisotopen in regional-metamophen gesteinen: Zentralinstuit fiir Isotopen: Stralenforsch. Mitt., 26, 64–6.Google Scholar
Hallam, M. and Eugster, H. P. (1976) Ammonium silicate stability relations. Contrib. Mineral. Petrol., 57, 227–44.Google Scholar
Hoffman, J. and Hower, J. (1979) Clay mineral assemblages as low grade metamorphic geother-mometers: application to the thrust faulted disturbed belt of Montana, U.S.A. In Aspects of Diagenesis (Scholle, P. A and Schluger, P. R., eds.). Spec. Publ. Soc. Econ. Pal. Min., 26, 55-79.Google Scholar
Lefort, J. P. and Ribeiro, A. (1980) La faille Porto-Badajoz-Cordonne a-t-elle controll6 l'Révolution de l'ocean Palrozoique Sud Armorican. Bull. Soc. Geol. Fr. 7. XXII., 3, 455–62.Google Scholar
Naden, J. and Shepherd, T. J. (199l) Fluid inclusion volatiles and gold mineralisation in central Iberian granite and schist terranes. Plinius, 5, 157.Google Scholar
Nesbitt, B. E. (1991) Phanerozoic Gold Deposits. In Gold MetaUogeny and Exploration (R. P. Foster, ed.). Blackie, London, 104-32.Google Scholar
Nitsch, K. H. (1970) Experimentelle bestimmung der oderen stabilitatsgrange von stilpnomelam. (Abstract) Fortsch. Mineral., 47, 48–9.Google Scholar
Potter, R. W., Clynne, M. A., and Brown, D. L. (1978) Freezing point depression of aqueous sodium chloride solutions. Econ. Geol., 73, 284–5.Google Scholar
Powell, R., Will, T. M., and Phillips, G. N. (1991) Metamorphism in Archaean greenstone belts: calculated fluid compositions and implications for gold mineralisation. J. Met. Geol., 9, 141–50.Google Scholar
Price, L. C. (1983) Geologic time as a parameter in organic metamorphism and vitrinite reflectance as an absolute palaeogeothermometer. J. Petrol Geol., 6, 5–38.Google Scholar
Ramboz, C., Schnapper, D., and Dubessy, J. (1985) The P-V-T-X-fo2 evolution of a H2O-CO2-CH4 bearing fluid in a wolframite vein: Reconstruction from fluid inclusion studies. Geochim. Cosmochim, Acta, 49, 205–19.Google Scholar
Roberts, S., Sanderson, D. J., Dee, S. J., and Gumiel, P. (1991) Controls on gold mineralisation in the La Codosera area, SW Spain. Econ. Geol., 86, 1012-22.Google Scholar
Sanderson, D. J., Roberts, S., McGowan, J. A., and Gumiel, P. (1991) Hercynian transpressional tec-tonics at the southern margin of the Central Iberian Zone, west Spain. J. Geol. Soc. Lond., 148, 893–8.Google Scholar
Seward, T. M. (1989) The hydrothermal chemistry of gold and its implications for ore formation: boiling and conductive cooling as examples. Econ. Geol. Monograph, 6, 398–404.Google Scholar
Shepherd, T. J. (1981) Temperature programmable, heating-freezing stage for microthermometric analysis of fluid inclusions. Ibid., 76, 1244-7.Google Scholar
Shepherd, T. J. Rankin, A. H., and Alderton, D. H. M. (1985) A practical guide to fluid inclusion studies. Blackie, London, 239 pp.Google Scholar
Wilkinson, J. J. (1991) Volatile production during contact metamorphism: the role of organic matter in pelites. J. Geol. Soc., 148, 731–6.Google Scholar
Zhang, Y. and Frantz, J. D. (1987) Determination of the homogenisation temperatures and densities of supercritical fluids in the system NaCl-KCl-CaClE-H2O using synthetic fluid inclusions. Chem. Geol., 64, 335–50.Google Scholar