大兴安岭幔枝构造与银多金属成矿作用

Mantle Branch Structure and Silver-Polymetallic Mineralization in the Da Hinggan Mountains,Inner Mongolia

通过对大兴安岭地区构造演化、区域地质、地球物理、地球化学特征的研究,认为燕山期以来是该区地幔热柱强烈活动时期。最明显的表现是强烈的构造运动和大规模的岩浆活动,最显著的标志是兴蒙地区盆岭构造的形成和大规模的成矿作用。大兴安岭中南段是一较典型的幔枝构造,具有明显的核部岩浆-变质杂岩、外围拆离滑脱层及上叠断陷盆地,是该区重要的成矿控矿构造。大兴安岭地区6个多金属矿床103个硫同位素数据统计,值域主要集中在-4‰～3‰,均一化程度较高;4个大、中型多金属矿床24个铅同位素数据统计,206 Pb/204 Pb为18.441 4～17.666 7,207 Pb/204 Pb为15.665 1～15.488 3,208Pb/204Pb为38.642 6～37.710 9;12个矿床地幔氦比例为37.25%～76.96%,平均55.90%;成矿流体氦-氩同位素组成主要位于地幔流体区域。根据测试结果,矿质及成矿流体主要来源于地球深部,甚至源自于核-幔边界,通过地幔热柱-地幔亚热柱-幔枝构造-地壳构造扩容带迁移至有利的构造部位成矿。

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.