The Grammatiko Iron oxide deposit (NE Attica region, Greece) is one of the economically most significant iron deposits in the Attic-Cycladic metallogenic province which was extensively mined until 1912. Mineralization is hosted in marbles and developed in the form of replacement bodies. These bodies are structurally controlled and follow large subvertical fracture zones with a NNE-trending strike that are associated with the Late Miocene extensional tectonic regime in the region. The mineral paragenesis consists mainly of Fe-Mn-Ba minerals including hematite, Mn-goethite, pyrolusite, hollandite, barite as well as traces of sulfides (e.g. galena). Gangue minerals are mostly calcite, ankerite and minor quartz and muscovite. Supergene minerals include limonite and Fe-Mn and Zn- oxy-hydroxides. Bulk ore analyses show concentrations of Mn up to 3 wt% and high contents of Pb and Cu. Microscopic observations, textural relationships and detailed SEM/EDS analyses showed minor contents of sulfur (<1 wt %) in some coarse grains with tetrahedral morphologies possibly indicating hematite formation after primary pyrite. Carbon and oxygen isotope analyses of carbonates collected along a traverse extending from the ore-bearing zone to the unaltered/non-mineralized marble show δ13C values between −10.5 and −4.5‰ and δ18O values from 20.9 to 24‰. For the non-mineralized marble host rock, δ13C values range from 2.2 to 2.8‰ with δ18O values between 26 and 30.3‰, respectively. The isotopic composition records the variable degree of hydrothermal alteration of the marble host rock as well as the characteristics of the ore-forming fluid. Unmineralized marbles exhibit a marine signature whereas vein calcite in the mineralized parts reflects a contribution of isotopically light carbon, likely from oxidized organic matter. In summary, δ13C and δ18O values from the Grammatiko mineralized carbonates record a complex interaction between marine carbonate and surface (meteoric) fluid.
Mineralogy, geochemistry and C-O isotope study of the iron oxide deposit at Grammatiko, NE Attica, Greece: ore genesis in an extensional setting
Konstantinos Mavrogonatos
2019-01-01
Abstract
The Grammatiko Iron oxide deposit (NE Attica region, Greece) is one of the economically most significant iron deposits in the Attic-Cycladic metallogenic province which was extensively mined until 1912. Mineralization is hosted in marbles and developed in the form of replacement bodies. These bodies are structurally controlled and follow large subvertical fracture zones with a NNE-trending strike that are associated with the Late Miocene extensional tectonic regime in the region. The mineral paragenesis consists mainly of Fe-Mn-Ba minerals including hematite, Mn-goethite, pyrolusite, hollandite, barite as well as traces of sulfides (e.g. galena). Gangue minerals are mostly calcite, ankerite and minor quartz and muscovite. Supergene minerals include limonite and Fe-Mn and Zn- oxy-hydroxides. Bulk ore analyses show concentrations of Mn up to 3 wt% and high contents of Pb and Cu. Microscopic observations, textural relationships and detailed SEM/EDS analyses showed minor contents of sulfur (<1 wt %) in some coarse grains with tetrahedral morphologies possibly indicating hematite formation after primary pyrite. Carbon and oxygen isotope analyses of carbonates collected along a traverse extending from the ore-bearing zone to the unaltered/non-mineralized marble show δ13C values between −10.5 and −4.5‰ and δ18O values from 20.9 to 24‰. For the non-mineralized marble host rock, δ13C values range from 2.2 to 2.8‰ with δ18O values between 26 and 30.3‰, respectively. The isotopic composition records the variable degree of hydrothermal alteration of the marble host rock as well as the characteristics of the ore-forming fluid. Unmineralized marbles exhibit a marine signature whereas vein calcite in the mineralized parts reflects a contribution of isotopically light carbon, likely from oxidized organic matter. In summary, δ13C and δ18O values from the Grammatiko mineralized carbonates record a complex interaction between marine carbonate and surface (meteoric) fluid.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
