内蒙古红花尔基钨多金属矿床成岩成矿年代学研究

Metallogenic and diagenetic age of Honghuaerji tungsten polymetallic deposit in Inner Mongolia

红花尔基钨多金属矿床是近年在大兴安岭中北部新发现的一处储量达大型规模的钨多金属矿床,矿体受含矿花岗岩体控制,总体呈平缓似层状赋存于花岗岩体内的顶部接触带。含矿花岗岩为不等粒结构,岩体无显著变形变质特征,保存基本完好。岩体含矿部位均遭受强烈的绢云母化、云英岩化、硅化等蚀变,与成矿有关的蚀变主要为绢云母化。矿床主要有用金属矿物为白钨矿和辉钼矿,岩体内辉钼矿与白钨矿大体具上钼下钨的分带特点,其钨矿体呈细脉状或稀疏大脉状分布于灰白色蚀变花岗岩内,多伴随硅化石英脉。辉钼矿呈细脉状、薄膜状或团块状产于花岗岩内,地层中局部可见与黄铁矿、黄铜矿、白钨矿共生,显示该矿床为一高温热液脉型钨多金属矿床。笔者对矿区2件含矿花岗岩样品——黑云母花岗岩HHW-1、HHW-12进行了LA-ICP-MS锆石U-Pb测年,2件样品的年龄结果具有一致性,谐和年龄为(179.4±2.3)Ma^(179.2±1.8)Ma;同时,对矿区7件辉钼矿样品进行了铼-锇同位素分析,获得同位素等时线年龄为(176.8±2.2)Ma(MSWD=0.29),岩体的形成年龄稍早于成矿年龄,在测试误差范围内具有一致性。结合野外地质特征及岩相学研究,我们认为黑云母花岗岩体与成矿密切相关,矿床成岩及成矿时代均为早-中侏罗世,属燕山期构造-岩浆活动的产物。

Honghuaerji tungsten polymetallic deposit is a newly discovered large-size tungsten deposit, located in the middle and northern parts of the Da Hinggan Mountains in Inner Mongolia of northeastern China and lying on the southern margin of the Mesozoic Mongol-Okhotsk orogenic belt. The ore body is controlled by the ore-bearing biotite granite. The ores consist of scheelite and molybdenite, which occurred as veins or small veins at the top of the ore-hearing granite. The rock body has experienced strong alterations such as sericitization, greisenization and silicification, and the major ore-related alteration is serieitization. The deposit is a hydrothermal vein type tungsten polymetallic deposit. As a newly found deposit, it has no available research data. In this pa- per, systematic isotope dating was conducted to determine the ore-forming age of the deposit. LA-ICP-MS zir- con U-Pb dating indicates that the intrusion of the host granite emplaced at （179.2 ± 1.8） Ma-（179.4 ± 2.3） Ma. Meanwhile, seven Re-Os isotopic analyses of molybdenite separates from the main ore body yielded an isochron age of （176.8 ±2.2） Ma and model ages ranging from 174.9 Ma to 176.6 Ma with an average value of 176 Ma. These data show that the ore-forming process and the intrusion of the host rocks were finished in early Jurassic. These ages are in agreement with field geological evidence, and the molybdenite is coexistent with chalcopyrite, pyrite and scheelite, showing that the Re-Os isochron age represents the ore-forming time of the tungsten polymetallic mineralization in the Honghuaerji ore deposit. Combined with the approximate U-Pb age, the authors suggest that the ore-forming and rock-forming materials might have been the product of Mesozoie-Yanshanian tectonic and magmatic activities. The prospecting for this type of polymetallic deposits should therefore be focused on the magma or igneous activity belt of the period.