大兴安岭南段双尖子山银矿床成因研究

The Shuangjianzishan deposit, located in the south Great Xing’an Range, is a new found large silver-polymetallic deposit. Orebodies are mainly hosted by the Permian strata and by its associated tectonic altered rocks of which occurring as veins and veinlets, with some as breccias in the Middle Jurassic strata and as veins in the Triassic granodiorite porphyry. Owing to lack of precise isotopic ages and elements geochemistry, two distinctive views which are vein-type deposit relating to the Early Cretaceous magmatism, and superimposed and tectonically reworked deposit, have been proposed regarding the genesis of the Shuangjianzishan deposit. Base on sufficient field and experiment works, methods of 40Ar/39Ar dating of potassium-bearing mineral, Re-Os dating of pyrite and Rb/Sr dating of sphalerite, and of LA-ICP-MS analyzing the concentration and occurrence of trace elements in galena and sphalerite are used, in an attempt to evaluate the genesis of the Shuangjianzishan deposit. Our works are meaningful for the understanding of ore-forming regularities of silver mineralization in the south Great Xing’an Range and helpful for the guidance of mineral prospecting in Shuangjianzishan deposit.

双尖子山矿床是大兴安岭南段最新发现的大型银铅锌矿床，矿体主要赋存于二叠系及其构造蚀变岩中，以脉状或细脉状产出，也可见中侏罗统中的角砾状矿化及三叠纪花岗闪长斑岩中的脉状矿化。由于缺乏可靠的同位素年龄和元素地球化学等判别标志，导致对该矿床存在两种不同的成因认识：即与早白垩世岩浆活动有关的热液脉型矿床和多期成矿作用下的叠加改造型矿床。鉴于此，本申请拟在充分的野外和室内工作基础上，采用热液蚀变含钾矿物的40Ar/39Ar、黄铁矿的Re/Os和闪锌矿的Rb/Sr相结合的定年方法，同时拟采用激光剥蚀电感耦合等离子体质谱（LA-ICP-MS）技术来获得不同矿化类型中方铅矿和闪锌矿的微量元素信息，结合矿床的成矿物质来源研究，揭示矿床的成因，以期丰富和完善对大兴安岭南段银铅锌矿床成矿规律的认识，并为矿区深部及外围的找矿预测工作提供一定线索。

双尖子山矿床是大兴安岭南段最新发现的大型银铅锌矿床，由于缺乏可靠的同位素年龄和元素地球化学等判别标志，导致对该矿床的成因存在不同的认识。本项目围绕双尖子山矿床开展矿床成因研究，聚焦成矿物质来源和成矿时代等关键科学问题，对矿床开展了矿物学、岩石学、成矿时代、与成矿有关岩体地球化学特征等方面的研究。过野外地质、矿物学和岩石学等证据，确定矿床的形成于碱性长石花岗岩有关；通过锆石U-Pb年代学和锆石Hf同位素分析，确定了碱性长石花岗岩形成于早白垩世，成岩物质来源于古老下地壳物质的重熔；通过对与成矿有关的白云母40Ar/39Ar定年，确定了矿床形成于早白垩世（139.5±1.5Ma）。项目查明了矿床的成因类型为与碱性长石花岗岩有关的中-低硫型浅成银多金属矿床，成矿物质来源于古老下地壳物质的重熔。大兴安岭南段银多金属的超常富集与古老下地壳物质的重熔有关。