Geology and Lead-Isotope Study of the Baiyinnuoer Zn-Pb-Ag Deposit, South Segment of the Da Hinggan Mountains, Northeastern China

摘要

The Baiyinnuoer deposit (32.74 Mt ore with grades of 5.44% Zn, 2.02% Pb and 31.36 g t~(-1) Ag), the largest Zn-Pb-Ag deposit in northern China, is hosted by crystalline limestone and slate of the Early Permian Huanggangliang Formation. Detailed cross-section mapping indicates stratigraphic and fold structural controls on the mineralization. The Zn-Pb-Ag mineralization is hosted predominantly by skarn, which occurs as bedding-parallel lens that pinch out at the margins of the main economic zone. Three skarn stages are identified at the deposit: (i) garnet-clinopyroxene; (ii) sulfides; and (iii) carbonate-epidote. Lead isotopic compositions were determined for galena and sphalerite of the ores, whole rock samples of the Yanshanian granite and granodiorite, Permian marble and tuff, and Jurassic volcanic and subvolcanic rocks in and around the Baiyinnuoer area in order to discuss the sources of ore-forming materials and the relationship between the ore formation and these whole rocks. Galena and sphalerite of the Baiyinnuoer ore have uniform isotopic ratios (~(206)Pb/~(204)Pb, 18.267-18.369; ~(207)Pb/~(204)Pb, 15.506-15.624; ~(208)Pb/~(204)Pb, 38.078-38.394) consistent with the granite and granodiorite (~(206)Pb/~(204)Pb,18.252-18.346; ~(207)Pb/~(204)Pb,15.504-15.560; ~(208)Pb/~(204)Pb, 38.141-38.320), whereas the ratios for Jurassic volcanic and subvolcanic rocks are variable and radiogenic (~(206)Pb/~(204)Pb, 18.468-18.614; ~(207)Pb/~(204)Pb, 15.521-15.557; ~(208)Pb/~(204)Pb, 38.304-38.375). These results indicate that the mineralization was not related to the Jurassic volcanism, but to the Yanshanian magmatism. The Permian strata may have a slight contribution to the mineralization. All features show that the Baiyinnuoer deposit is related to the Yanshanian granitic magmatism, and can be classified as a zinc-lead-silver skarn deposit.