The ages for porphyry Mo deposits in south segment of Da Hinggan Mountains,Northeast China,are not well known.Five molybdenite samples from the Aolunhua(奥伦花) porphyry Mo deposit,five molybdenite samples from the Yangchang(羊场) porphyry-quartz vein Mo deposit and two molybdenite samples from the Banlashan(半拉山) porphyry Mo deposit were selected for Re-Os dating.Three deposits are spatial-temporally associated with the granite porphyry stock.Re-Os isochron age of 131.2±1.9 Ma was obtained for the Aolunhua porphyry Mo deposit.The Yangchang Mo deposit provides isochron age of 138.5±4.5 Ma for two groups of molybdenite(within porphyry ore and within quartz vein).The Banlashan porphyry Mo deposit provides model ages of 140.5±2.4 and 143±2.2 Ma.All of these Re-Os ages are consistent presumed Yanshanian ages for granite intrusions,formed in crust thinning setting in Cretaceous in North China.
The Bianbianshan deposit, the unique gold-polymetal (Au-Ag-Cu-Pb-Zn) veined deposit of the polymetal metallogenic belt of the southern segment of Da Hinggan Mountains mineral province, is located at the southern part of the Hercynian fold belt of the south segment of Da Hinggan Mountains mineral province, NE China. Ores at the Bianbianshan deposit occur within Cretaceous andesite and rhyolite in the form of gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite, chalcopyrite, galena and sphalerite. The deposit is hosted by structurally controlled faults associated with intense hydrothermal alteration. The typical alteration assemblage is sericite + chlorite + calcite + quartz, with an inner pyrite-sericite-quartz zone and an outer seicite - chlorite - calcite-epidote zone between orebodies and wall rocks. δ34 S values of 17 sulfides from ores changing from -1.67 to +0.49‰ with average of -0.49‰, are similar to δ34 S values of magmatic or igneous sulfide sulfur. 206Pb/204Pb, 207Pb/204Pb and 208Pb/ 204Pb data of sulfide from ores range within 17.66-17.75, 15.50-15.60, and 37.64-38.00, respectively. These sulfur and lead isotope compositions imply that ore-forming materials might mainly originate from deep sources. H and O isotope study of quartz from ore-bearing veins indicate a mixed source of deep-seated magmatic water and shallower meteoric water. The ore formations resulted from a combination of hydrothermal fluid mixing and a structural setting favoring gold-polymetal deposition. Fluid mixing was possibly the key factor resulting in Au-Ag-Cu-Pb-Zn deposition in the deposit. The metallogenesis of the Bianbianshan deposit may have a relationship with the Cretaceous volcanic-subvolcanic magmatic activity, and formed during the late stage of the crust thinning of North China.
