SM-ND AND RB-SR SYSTEMS OF THE RUDNOE WOLFRAMITE-SCHEELITE DEPOSIT, PRIMORIE

This paper describes the results of using Sm-Nd and Rb-Sr systems for elucidating the genesis and age of vein-hosted wolframite-scheelite mi neralization. The vein-hosting rocks are biotite metasomatites, develo ped after Valanginian (K-1) and Late Triassic sandstones and siltstone s. Two stages of mineral deposition were distinguished: a high-tempera ture feldspar-wolframite-scheelite stage and a low-temperature sulfide -carbonate stage. The Rb-Sr isochron for the high-temperature phase mi nerals shows an ore-deposition age of 80 +/- 1 Ma. The time of the met asomatism, 87 +/- 10 Ma, dated using whole-rock samples, is compatible within analytical precision with the age of the veins. The model Sm-N d ages of the sedimentary rocks are 1.1 Ga for the siltstones and 1.8 - 2.6 Ga for the sandstones. Isochron relations could not be obtained for the vein minerals because of a substantial epsilon(Nd) variation: it decreases from +2.7 - -5.9 in the orthoclases to -3.3 - -11.9 in th e other minerals. The epsilon(Nd) and I-Sr values for the vein mineral s and metasomatites fall within a respective range for the sediments, with the exception of a few samples that yielded a positive epsilon(Nd ) value (+3) and low I-Sr values (0.702 - 0.708). This definitely indi cates a depleted mantle source of the fluids (I-Sr = 0.702, epsilon(Nd ) = +10) The partial assimilation of sedimentary rocks by the mantle f luid resulted in the following depositional sequence: the early high-t emperature phase mineral assemblage of orthoclase, wolframite, scheeli te, and biotite [I-Sr (average) = 0.7136], and the later low-temperatu re phase mineral assemblage [I-Sr (average) = 0.7162], which exhibits an obvious predominance of the crustal over the mantle component.