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

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dominated by quartz–adularia and carbonate, which is
consistent with the slightly lower temperature of
homogenization for fluid inclusions of the quartz–
sulphide assemblage (Petrov, in Breskovska and Gergelchev,
1988a). There are no direct age determinations,
but crosscutting relationships with precisely
dated fresh equivalents of high-silica rhyolite suggest
that mineralization is younger than 32.8 Ma (Marchev
et al., 2003).
4.2. Epithermal ore deposits in calc-alkaline to
shoshonitic complexes
In the Eastern Rhodopes, epithermal deposits are
mainly hosted by differentiated calc-alkaline, high-K
calc-alkaline and shoshonitic volcanoes, sometimes
associated with low-grade porphyry Cu–Mo occurrences
in monzonitic to granitic stocks intruded in the
volcanic rocks. They variably exhibit characteristics of
low-, intermediate-, and high-sulphidation deposits
P. Marchev et al. / Ore Geology Reviews 27 (2005) 53–89
(Hedenquist, 1987; Hedenquist et al., 2000; Sillitoe
and Hedenquist, 2003), previously known as adularia–sericite
and acid sulphate deposits (Heald et al.,
1987).
Intermediate-sulphidation epithermal Pb–Zn–
Cu FAg–Au deposits are located within major Palaeogene
shoshonitic to high-K calc-alkaline volcanointrusive
centres of the Bulgarian Eastern Rhodopes
(e.g., Spahievo in the Borovitsa complex; Zvezdel;
Madjarovo), or more rarely within acid volcanoes
(e.g., Losen; Fig. 3). Based on their well-expressed
vertical zonation and their sulphide mineralogy,
including Fe-poor sphalerite, high barite content and
elevated fluid salinity, they are clearly of intermediatesulphidation
character (Hedenquist et al., 2000; Sillitoe
and Hedenquist, 2003). Most of them are basemetal
rich, and for about 40 years until 1995 more than
16.5 Mt of Pb–Zn ore (Table 5) was extracted from
Spahievo, Zvezdel and Madjarovo (Milev et al., 1996).
At present, only the Pcheloyad mine from the Zvezdel
Fig. 6. Simplified geological map of the Madjarovo volcano, showing the distribution of intermediate-sulphidation veins and 40 Ar/ 39 Ar ages of
the host rocks and alteration; after Marchev and Singer (2002).