Stable isotope geochemistry of the carboniferous Zn-Pb-Cu sediment-hosted sulfide deposits, northeastern Spain
Por:
Canet C., Alfonso P., Melgarejo J.C., Fallick A.E.
Publicada:
1 ene 2005
Resumen:
Carboniferous sedimentary rocks in the southwestern Catalonian Coastal Ranges contain stratiform (Zn, Pb, Cu) sulfide deposits. Stable isotope compositions of sulfur, oxygen, and hydrogen were studied in five localities in order to establish the source of hydrothermal fluids and the influence of metamorphism on these deposits. Sulfur isotopes were analyzed in pyrrhotite, pyrite, sphalerite, chalcopyrite, and galena. The d34S(CDT) values lie mostly between -1.0 and +7.0‰ (average +4.4‰). Except for pyrrhotite-pyrite pairs, all the sulfide minerals show isotopic disequilibrium. d 34S values suggest that sulfur was derived by thermochemical reduction of seawater sulfate in a deep-circulating convective system. Fluid inclusions were studied in qu artz crystals from the sediment-hosted stratiform occurrences. They are two-phase (L-V), with salinity between 1.1 and 18.0 wt% NaCl eq., and homogenization temperatures mainly in the range of 220-260°C. Oxygen and hydrogen iso topes were analyzed in chlorite crystals from four ore-bearing beds. dD(V-SMOW) values in chlorite range from -63 to -33‰, whereas d18O values lie between +2.7 and +6.8‰. d17O(V-SMOW) values in quartz range between +8.4 and +10.7‰. Most of the calculated oxygen and hydrogen isotope compositions of ore-forming fluids plot close to the isotopic composition of seawater. Therefore, the ore-forming fluid must have been mainly seawater that interacted with sedimentary rocks during convective circulation within a basin. This process took place in a subsiding Carboniferous basin divided into sedimentary highs and depressions by synsedimentary normal faults, which acted as permeable areas that favored fluid circulation. Copyright © 2005 by V.H. Winston & Son, Inc. All rights reserved.
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