2: Hydrothermal ore deposits related to post-orogenic extensional ...

80
are structurally related to evolved silicic dykes within
highly oxidized and water-rich shoshonitic volcanic
rocks. High-sulphidation Au–Cu–base-metal systems
in Greece are spatially associated with less oxidized
and less water-rich calc-alkaline and high-K calc-alkaline
magmas. An interesting type of sediment-hosted
low-sulphidation epithermal Au deposit (e.g., Ada
Tepe and Rosino) is related to detachment faults.
Close spatial and temporal relationships between
the ore deposits and local magmatism indicate that a
rapid succession of magmatic and hydrothermal processes
resulted from a thermal disturbance of the crust
and probably the underlying mantle by large-scale late
orogenic extension. Magmatic fluid input was likely
in the polymetallic and high-sulphidation Cu–Au
deposits, and possibly in the Madan-type Pb–Zn
deposits. The sediment-hosted deposits, including
Ada Tepe, were formed during late-stage brittle extension,
after cooling of the basement rocks in metamorphic
core complexes by fluids that may be of
metamorphic or deep magmatic origin.
Sr and Pb isotope compositions of sulphides and
gangue minerals of ore deposits show an increase of
206 204 207 204
Pb/ Pb and a decrease of Pb/ Pb and
87 86
Sr/ Sr ratios from west to east, correlating with a
similar pattern in magmatic rocks. These variations
reflect a decreasing input to the hydrothermal systems
of Palaeozoic or older crustal material from the much
thicker continental crust in the Central Rhodopes and
an increase of mantle contributions towards the Eastern
Rhodopes, which are underlain by thinned crust.
In contrast to deposits in the Eastern Rhodopes,
hydrothermal minerals in deposits of the Central Rho-
dopes have more radiogenic
87 Sr/ 86 Sr and
207 Pb/ 204 Pb isotope compositions than those of associated
silicic magmas. This reflects an additional
radiogenic basement input of Sr and Pb to the hydrothermal
fluids, consistent with a possible metamorphic
fluid contribution from the core complex, or largescale
circulation of mixed magmatic and meteoric
fluids through the extensionally fractured gneisses.
Acknowledgments
This study was carried out in the framework of the
European Science Foundation through GEODE and
was funded by several projects of the Swiss National
P. Marchev et al. / Ore Geology Reviews 27 (2005) 53–89
Science Foundation (No. 2000–59544.99 and
200020–100735/1) and the SCOPES programme
(7BUPJ062276). Critical reviews by Jeffrey Hedenquist
and Peter Larson greatly improved the paper. We
thank Derek Blundell for his efforts in organizing this
special issue.
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