Fluid inclusion evidence for the physicochemical conditions of sulfide deposition in the Olympias carbonate-hosted Pb-Zn(Au, Ag) sulfide ore deposit, E. Chalkidiki peninsula, N. Greece |
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Authors: | S P Kilias S I Kalogeropoulos J Konnerup-Madsen |
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Institution: | (1) Institute of Geology and Mineral Exploration (IGME), 1, Fragon Str., 546 26 Thessaloniki, Greece;(2) Rusvar Holdings BV, 4, Nikis Str., 105 62 Athens, Greece;(3) University of Copenhagen, Geological Institute, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark |
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Abstract: | The Olympias Pb-Zn(Au, Ag) sulfide ore deposit, E. Chalkidiki, N. Greece, is hosted by marbles of the polymetamorphic Kerdilia
Formation of Paleozoic or older age. The geologic environment of the ore also comprises biotite-hornblende gneisses and amphibolites
intruded by Tertiary pegmatite-aplite dikes, lamprophyre dikes, the 30-Ma Stratoni granodiorite, and porphyritic stocks. Only
limited parts of the deposit display shear folding and brecciation; most of it is undeformed. Microthermometry of fluid inclusions
in gangue syn-ore quartz indicates three types of primary and pseudosecondary inclusions: (1) H2O-rich, 1–18 wt.% NaCl equivalent, <3.6 mol% CO2; (2) H2O-CO2 inclusions, <4wt.% NaCl equivalent, with variable CO2 contents, coexisting in both undeformed and deformed ore; (3) aqueous, highsalinity (28–32 wt,% NaCl equivalent) inclusions
found only in undeformed ore. Type 2 inclusions are differentiated into two sub-types: (2a) relatively constant CO2 content in the narrow range of 8–15 mol% and homogenization to the liquid phase; (2b) variable CO2 content between 18 and 50 mol% and homogenization to the vapor phase. Type 1 and 2b inclusions are consistent with trapping
of two fluids by unmixing of a high-temperature, saline, aqueous, CO2-bearing fluid of possible magmatic origin, probably trapped in type 2a inclusions. Fluid unmixing and concomitant ore mineralization
took place at temperatures of 350 ± 30 °C and fluctuating pressures of less than 500 bar, for both undeformed and deformed
ores. The wide salinity range of type 1 inclusions probably represents a complex effect of salinity increase, due to fluid
unmixing and volatile loss, and dilution, due to mixing with low-salinity meteoric waters. High solute enrichment of the residual
liquid, due to extreme volatile loss during unmixing, may account for high salinity type 3 inclusions. The Olympias fluid
inclusion salinity-temperature gradients bear similarities to analogous gradients related to Pb-Zn ores formed in “granite”-hosted,
low-T distalskarn, skarn-free carbonate-replacement and epithermal environments. |
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