海南岛罗葵洞钼矿床成岩成矿时代及矿床成因探讨

摘要

the molybdenite. This indicates that mineralization is the product of ore-bearing hydrothermal activity occurring during a relatively short period after volcanism and pluton emplacement. Ti-in-zircons thermometry of porphyritic granite gives an average temperature of 690 ℃, approximately representing the near liquidus temperature of granite and the minimum temperature of magmatic origin, which implies that it is derived from rocks that experienced partial melting under near-water-saturated conditions. The Re content of molybdenite (26.04~50.39 μg/g) indicates the source of metallogenic material is possibly the mixture of mantle and crust, with crust as the dominant material. The zircons Hf isotope of porphyritic granite and its border facies masanophyre display similar signatures, with εHf(t) values ranging from -5.38 to -2.2 and -4.55 to 2.37, respectively. The two-stage crust model ages (tDM2) of the terrace vary from 1016 to 1508 Ma, indicating that the porphyritic granite and masanophyre were formed by remelting of the Mesoproterozoic lower crust with the addition of a certain amout of mantle-derived materials. The analysis of the ages of host-rocks and Mo mineralization in Hainan Island and inland China shows that the youngest ore-forming age of Mo metallogenic provinces in South China occurs in Hainan Island, and focus in Cretaceous (ca. 72~112 Ma) period, and possibly corresponds to the large-scale stretching and thinning tectonic setting occuring in Eastern China.%罗葵洞钼矿床是海南岛目前发现的大型低品位、受火山机构控制的斑岩型钼矿床, 其赋矿围岩主要为斑状花岗岩, 其次为火山碎屑岩、石英二长斑岩等.本文分别对赋矿火山碎屑岩(流纹质晶屑凝灰熔岩)、斑状花岗岩及其边缘相石英二长斑岩进行了 LA-ICP-MS 锆石 U-Pb 定年, 获得加权平均年龄分别为(104.1±0.7) Ma、(102.4±0.5) Ma和(102.3±0.7) Ma; 对7件辉钼矿进行Re-Os同位素定年, 获得等时线年龄为(100.1±1.8) Ma,均为早白垩世晚期-晚白垩世早期的产物, 成岩时代略早于成矿时代, 表明钼矿化是继火山作用——岩体侵位后在较短时间内含矿岩浆热液活动的产物.由斑状花岗岩锆石 Ti 温度计获得的平均温度为690 ℃, 近似代表花岗岩近液相线的温度, 也近似代表岩浆起源时温度的最小值, 表明其岩浆可能来源于在水近饱和条件下发生的部分熔融.罗葵洞矿床7件辉钼矿的Re含量为26.04~50.39 μg/g, 表明成矿物质来源可能属于壳幔混合产物且以壳源为主.斑状花岗岩及其边缘相石英二长斑岩中的锆石Hf同位素组成较相似, εHf(t) 值分别为-5.38 ~ -2.2和-4.55 ~ 2.37, 两者二阶段地壳模式年龄tDM2范围为1016~1508 Ma, 表明岩浆可能来源于中元古代古老下地壳的重熔, 伴有部分幔源物质的加入.综合海南岛和国内其他钼矿床的成矿年龄和成矿岩体的年龄数据, 发现华南钼成矿省中最年轻钼成矿事件发生在海南岛、且集中在白垩纪(约72~112 Ma), 该时期对应于中国东部岩石圈大规模拉伸减薄的构造环境.