Record details

Title
    Mixing of metamorphic and surficial fluids during the uplift of the Hercynian upper crust: consequences for gold deposition
Statement of responsibility
    Marie-Christine Boiron, Michel Cathelineau, David A. Banks, Serge Fourcade, Jean Vallance
Author
    Banks, David A.
    Boiron, Marie-Christine
    Cathelineau, Michel
    Fourcade, Serge
    Vallance, Jean
Language
    anglicky
Source title - serial
    Chemical geology (including isotope geoscience)
Vol./nr.
    Vol. 194, no. 1-3
Pages
    p. 119-141
Year
    2003
Notes
    9 obr.
    Bibliografie na s. 139-141
    il.
    Zkr. název ser.: Chem. Geol. (Isotope Geosci.)
Classfication no.
    55(1)
    551.2
    553.3/.4
Conspectus category
    55
    553
Subject group
    geneze ložiska
    halogeny
    inkluze fluidní
    izotopy stabilní
    jílovské pásmo
    krystalinikum
    křemen
    kůra svrchní
    metamorfóza
    mikropuklina
    oxid uhličitý
    podmínky P-T
    prvky ryzí
    rudy Au
    salinita
    sulfidy
    sulfosoli
    tektonika extenzní
    uplift
Geographical name
    ČR-Čechy
    Francie
    Mokrsko (Příbram, Dobříš)
    Španělsko-Galicie
Keyword
    Consequences
    Crust
    Deposition
    During
    Fluids
    Gold
    Hercynian
    Metamorphic
    Mixing
    Surficial
    Uplift
    Upper
Abstract (in english)
   A detailed geochemical study of fluids from representative quartz-sealed faults hosting late Hercynian gold concentrations shows that fluids percolating the mineralised faults had two main distinct reservoirs: one was a quite shallow and the other rather deep-seated. Both fluids have lost a great part of their original geochemical signature through interactions with host metamorphic formations. Early fluids, present during the primary sealing of the faults by quartz, are considered to have effectively equilibrated with the metamorphic pile and then predominantly flowed upwards along the faults. They are characterised by CH4/CO2/H2O ratios rather typical of fluids equilibrated with graphite, and moderate to medium chlorinities with a high Br/Cl ratio. The striking feature of the gold-bearing quartz is that gold is not synchronous within any quartz deposition, and appears located in late microfractures and associated with Pb-Bi-Sb sulphosalts and sulphides.
   These late stages are characterised by fluids whose salinities decrease to very low values indicating their progressive dilution by waters of more surficial origin in the fault system. The long-lived activity of the fault favoured the connection between two distinct fluid reservoirs at a critical time during the basement uplift. The fluids evolved through two main driving mechanisms which were responsible for the Au deposition: (i) decrease in temperature accompanying decompression from supra-lithostatic to hydrostatic conditions which yielded, in some instances, volatile unmixing in the faulted systems, (ii) mixing of the resulting fluids with waters entering the hydrological systems from shallower reservoirs. In addition to dilution and fluid mixing which are favourable factors for decreasing the gold solubility, the presence of microfractured sulphides could have enhanced gold precipitation through electrochemical processes
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    6. 12. 2006
Import date
    8. 8. 2012