内蒙古额尔古纳地区比利亚谷大型铅锌银矿床稀土微量元素地球化学特征及成矿意义

比利亚谷铅锌银矿位于海拉尔-根河中生代火山盆地北西缘。该矿床赋存于上侏罗统满克头鄂博组酸性火山岩中,受NW向断裂构造控制,主矿体呈脉状产出。火山岩围岩及主要矿石矿物的微量稀土特征相似:具有富集Rb、Th等大离子亲石元素,而亏损Sr、Nb、Ta等高场强元素的特点,表明其均产于板内构造环境。不同之处为:1矿石矿物的稀土微量元素总量明显小于火山岩围岩;2火山岩围岩呈现出明显的负Eu异常,而矿石矿物则具有强弱不等的正Eu异常。综合分析认为比利亚谷铅锌银矿为火山-次火山热液型矿床,其主要成矿作用与晚侏罗世-早白垩世(140Ma左右)火山活动有着密切联系,区域地质背景上对应于构造体制大转折的晚期,但是成矿期后矿体受到了120Ma大规模岩浆活动的影响,本期岩浆活动是区域岩石圈快速减薄引起,产生了一期深变质作用以及壳幔相互作用有关的深部流体活动,受其强烈改造,引起了矿石矿物微量稀土元素含量的改变。

Geochemical Characteristics of REE and Trace Elements in the Biliyagu Large Pb Zn Ag Deposit of Eerguna Area, Inner Mongolia and Their Metallogenic Significance

Located in the northwest of Hailar-Genhe Mesozoic volcanic basin, the Biliyagu ultra-large Pb-ZN-Ag deposit occurs in the Upper Jurassic Manketouebo Formation acidic volcanic and is controlled by the NW-trending faults, with the ore bodies being mainly of veined type. Analysis about the REE and trace element between volcanic wall rock and main ore minerals show they have similar distribution trend: be enrichment of large ion lithophile elements such as Rb and Th, but depleted high field-strength element such as Sr, Nb and Ta, which show both of them developed in Plate tectonic environment. The differences lie in two points: 1. Total REE and trace element of the ore mineral are bviously less than those of volcanic wallrock; 2. The volcanic wallrock behave clear negative Eu anomalies, while the ore mineral show positive Eu anomalies with different grade. Comprehensive analysis show that the Biliyagu Pb-Zn-Ag deposit belong to Volcanic-hypovolcanic hydrothermal type, the main metallogenic epoch was eorrelated to the volcanic activities during Upper Jurassic- Lower Cretaceous (140Ma±), this period was correspond to the late stage of regional tectonic transition in the north areas of China. After this metallogenic period, the deposit was transformed by the large scale magmatic activities at 120Ma±, which was caused by the quickly regional lithospheric thinning. Magmatism in this stage caused deep metamorphism and deep fluid activities related to crust-mantle interantion which strong transformed the ores and lead to the change of the REE and trace element in the ore minerals.