The Petrova and Trgovska Gora Mts. (Gora=Mountain) are Variscan basement
units incorporated into the northwestern Dinarides during the Alpine
orogeny. They host numerous siderite-quartz-polysulphide,
siderite-chalcopyrite, siderite-galena and barite veins, as well as
stratabound hydrothermal-replacement ankerite bodies within carbonates
in non-metamorphosed, flysch-like Permo-Carboniferous sequences. The
deposits have been mined for Cu, Pb, Ag and Fe ores since Medieval
times. Fluid inclusion studies of quartz from
siderite-polysulphide-quartz and barite veins of both regions have shown
the presence of primary aqueous NaCl-CaCl(2)+/- MgCl(2)-H(2)O +/- CO(2)
inclusions. The quartz-sulphide stage of both regions show variable
salinities; 2.7-26.2 wt% NaCl eq. for the Trgovska Gora region and
3.4-23.4 wt% NaCl eq. for the Petrova gora region, and similar
homogenisation temperatures (100-230A degrees C). Finally, barite is
precipitated from low salinity-low temperature solutions (3.7-15.8 wt %
NaCl equ. and 115-145A degrees C). P-t conditions estimated via isochore
construction yield formation temperatures between 180-250A degrees C for
the quartz-sulphide stage and 160-180A degrees C for the barite stage,
using a maximum lithostatic pressure of 1 kbar (cc. 3 km of overburden).
The sulphur isotope composition of barite from both deposits indicates
the involvement of Permian seawater in ore fluids. This is supported by
the elevated bromium content of the fluid inclusion leachates (120-660
ppm in quartz, 420-960 ppm in barite) with respect to the seawater,
indicating evaporated seawater as the major portion of the ore-forming
fluids. Variable sulphur isotope compositions of galena, pyrite and
chalcopyrite, between -3.2 and +2.7aEuro degrees, are interpreted as a
product of incomplete thermal reduction of the Permian marine sulphate
mixed with organically- and pyrite-bound sulphur from the host
sedimentary rocks. Ore-forming fluids are interpreted as
deep-circulating fluids derived primarily from evaporated Permian
seawater and later modified by interaction with the Variscan basement
rocks. (40)Ar/(39)Ar data of the detrital mica from the host rocks
yielded the Variscan age overprinted by an Early Permian tectonothermal
event dated at 266-274 Ma. These ages are interpreted as those
reflecting hydrothermal activity correlated with an incipient
intracontinental rifting in the Tethyan domain. Nevertheless, 75 Ma
recorded at a fine-grained sericite sample from the alteration zone is
interpreted as a result of later resetting of white mica during
Campanian opening/closure of the Sava back arc in the neighbouring Sava
suture zone (Ustaszewski et al. 2008).