The Sr, Nd isotopic composition of lamprophyres in Laowangzhai gold orefield, Yunnan Province

Lamprophyres are widely spread over the Laowangzhai gold orefield in northern Mt. Ailao structure zone, Yunnan Province. Lampmphyres in the orefield are temporally and spatially related to gold mineralization. Lampmphyren in the orefield have anomalous Sr and Nd isotopic compositions, e.g. the⁸⁷Sr/⁸⁶Sr ratios (0.706 665–0.707 960, the⁸⁷Sr/⁸⁶Sr ratio of sample YLW-44 is 0.709 041) are higher than the modern value of the original mantle (0.704 5), the¹⁴³Nd/¹⁴⁴Nd ration (0.512 463–0.512 551) are lower than the modern value of the original mantle (0.512 638), and the calculated values ε_Sr > 0 (28.1–63.7) and ε_Nd< 0 (- 1.34- -3.07). The results of investigation inete that lampmphyres in the Laowangzhai gold orefield with anomalous Sr and Nd isotopic compositions would not be produced as a result of contamination of the primary magma with the isotopic features of MORB by the crust materials high⁸⁷Sr/⁸⁶Sr ratios and low¹⁴³Nd/¹⁴⁴Nd ratios in the ploeaws of rising or in the magma chamber, but the result of metasomatism of source mantle.