THE AGE AND GENESIS OF THE W-SN MINERALIZATION AT THE VERKHNEURMIISKII ORE FIELD, AMUR AREA - SM-ND AND RB-SR ISOTOPIC DATA

The Verkhneurmiiskii ore held in the Amur area is restricted to the ea stern outer contact zone of the Verkhneurmiiskii granite massif, which intrudes Late Cretaceous liparite ignimbrite. The Rb-Sr age of all ty pes of granites in the massif is 98 +/- 4 Ma. The Sn-W mineralization of the Pravourmiiskoe deposit is localized in the ignimbrites along a granite porphyry dike and, as separate ore occurrences, in the inner a nd outer contact zones of the Verkhneurmiiskii Massif. The age of the early Sn-W mineralization was estimated, using the Sm-Nd isotopic syst ematics of the fluorite, siderophyllite, and wolframite, at 95 +/- 6 M a and agrees, within the analytical error, with the age of the Verkhne urmiiskii granite. According to our Sm-Nd data on the fluorite and wol framite, the ore mineralization developed 20 m.y. after the granite cr ystallization. The granitoids and fluids that formed the rare-metal mi neralization came from a single long-living deep-seated source, whose isotopic characteristics were as follows: epsilon(Nd) ranged from -1 t o -2, I-Sr = 0.7080-0.7085. The granite melted out in the crust, and t he mineralizing fluids formed most probably under the effect of a flow of mantle-derived fluids. The role of these intratelluric solutions d ecreased during the development of the later sulfide mineralization, a nd the influence of crustal sources increased.