The epithermal Au-Ag Shkol'noe deposit is located in the Kandjol ore field, Kurama Mountains. This region is a part of the east-west trending Late Hercynian Bel'tau-Kurama volcanic belt of Andian type. The deposit comprises
a number of quartz-carbonate veins hosted by the syn-subductional Middle Carboniferous Karamazar granodiorites. The Au-Ag mineralization is considered to be the result of the earliest hydrothermal event in the region (Kozlova et al., 1967, Turlychkin, 1969; Koshlakov, 1969; Shevkalenko, 1972).
The Rb-Sr isochron age 296.3±1.3 Ma and initial 87Sr/86Sr0=0.7071±2 ratio were obtained for an adularia-albite-sericite-quartz-calcite sample from Au-Ag mineralization (Fig. 1). The 87Sr/86Sr ratio range from 0.70645±10 to 0.70741±10 was obtained for the calcites from the earlier and later mineral assemblages (Fig. 2).
The Rb-Sr age is interpreting as a real geological age of the Au-Ag mineralization. It corresponds to the initial stage of the Late Carboniferous - Early Permian collision followed the main syn-subduction stage of Bel'tau-Kurama volcanic belt evolution (Dalimov et al., 1990; Volkov et al., 1996).
The comparison of the Rb-Sr age with previously obtained 40Ar-39Ar and K-Ar data (Moralev et al., 1994) for adularia from Au-Ag mineralization implies that gangue minerals of the Shkol'noe deposit bear the fingerprint of at least three events in its history: the origin of Au-Ag mineralization at 296.3±1.3 Ma and two subsequent thermal pulses at 277±4 and 263-267±8 Ma. The minimal time scale for
the hydrothermal activity within the Shkol'noe deposit is thus about 30 million years. The general uniformity of the strontium source during the hydrothermal processes within the Au-Ag Shkol'noe deposit, as well as within Bel'tau-Kurama belt is suggested. The mobilization of low radiogenic strontium during the propylite alteration of the diabase dikes emplaced after the Au-Ag mineralization and before the Ag-Pb-Zn-Cu mineralization could be responsible for the comparatively low value of the 87Sr/86Sr ratio in the latest postmagmatic carbonates.
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