关键词: 成矿作用, 幔枝构造, 控矿构造, 大兴安岭

Abstract:

Based on a study of the regional tectonic evolution, regional geology, geophysics and geochemistry of the Da Hinggan Mountains, the authors hold that this region has gone through intense mantle plume evolution since the Yanshanian movement, as obviously evidenced by intense structural movement and large-scale magmatism. The most prominent representation is the formation of the mountain-basin structural pattern and the extensive metallogenesis. The middle to southern region of the Da Hinggan Mountains is a typical mantle branch. It consists of magmatic-metamorphic core complex, surrounding detachment zones and overlapped fault basin, constituting an important ore-forming and ore-controlling tectonic unit. In Da Hinggan Mountain region, sulfur isotope values of 103 samples from six polymetallic deposits range from -4‰ to 3‰, suggesting high uniformity. Lead isotope values of 24 samples from four polymetallic deposits indicate that ²⁰⁶Pb/²⁰⁴Pb ratios range from 18.441 4 to 17.666 7,²⁰⁷Pb/²⁰⁴Pb range from 15.665 1 to 15.488 3, and  ²⁰⁸Pb/²⁰⁴Pb range from 38.642 6 to 37.710 9. The mantle helium ratios of 12 deposits range from 37.25% to 76.96%, with the average being 55.90%. The helium-argon isotopes of hydrothermal fluids are mainly concentrated in the mantle fluid domain. All geochemical analyses indicate that metallogenic materials and hydrothermal fluids mainly came from the depth of the earth, even from the core-mantle boundary. They passed through mantle plume, sub-mantle plume, mantle branch and crustal expanding structure zones and eventually moved to favorable structural positions and precipitated to form ore deposits.

Key words: mineralization, mantle branch structure, ore-controlling structures, Da Hinggan Mountain