广西油麻坡钨钼矿床成岩成矿年代学研究及其地质意义

广西博白_岑溪断裂带位于钦杭成矿带南段,既是一条长期活动的地体边界断裂带,也是一条岩浆活动频繁的W_Mo_Sn_Pb_Zn_Sb_Au_Ag多金属成矿带。文章以该带中的广西博白县油麻坡矽卡岩型钨钼矿床为研究对象,在详细的岩性鉴别和划分的基础上,对矿区内花岗岩类进行了单颗粒锆石LA_ICP_MS锆石U_Pb测年,获得深灰色花岗斑岩的等时线年龄为(479.7±3.9)Ma,灰色黑云母花岗闪长岩为(109.7±1.1)Ma,浅灰色细粒白云母花岗岩为(103.3±1.2)Ma。辉钼矿Re_Os测年获得加权平均年龄为(97.4±1.9)Ma。由此可见,油麻坡岩体为一个复式岩体,由早奥陶世(加里东期)的花岗斑岩和早白垩世(燕山晚期)的黑云母花岗闪长岩和细粒白云母花岗岩组成,其中,黑云母花岗闪长岩构成油麻坡岩体的主体。钨钼矿形成于早白垩世晚期(即燕山晚期),与黑云母花岗闪长岩和白云母花岗岩密切相关。这些高精度测年数据的获得,进一步表明博白断裂带是一条长期活动的断裂,其在加里东期已经活动,并伴有岩浆岩的侵位。燕山晚期,该断裂重新复活,并导致大量的岩浆活动和一定强度的W_Mo_Sn_Pb_Zn_Sb_Au_Ag成矿作用,形成由多个大_中型矿床组成的多金属成矿带。博白_岑溪成矿带属于华南100~80 Ma大规模成矿的一部分,成矿背景与华南地区白垩纪的地壳伸展、钦杭成矿带的再次裂陷有关。

Geochronology of YoumaPo W-Mo deposit in Guangxi and its geological significance

The Bobai-Cenxi fault belt in Guangxi is located in the southern section of the Qinzhou Bay-Hangzhou Bay (Qin-Hang) metallogenic belt. It is not only a long-term active boundary fault zone but also a W-Mo-Sn-Pb-Zn-Sb-Au-Ag polymetallic metallogenic belt with frequent magmatic activities. Choosing the Youmapo skarn type tungsten molybdenum deposit in Bobai County of Guangxi along the Qin-Hang metallogenic belt as the research object, the authors conducted zircon LA-ICP-MS U-Pb dating of these granitoids on the basis of the detailed division of magmatite lithology. The results show that the zircon U-Pb age of the dark gray granite porphyry, gray biotite granodiorite and grayish muscovite granite are (479.7±3.9) Ma, (109.7±1.1) Ma, and (103.3±1.2) Ma, respectively. The molybdenite Re-Os dating was also carried out for metallogenic epoch, and the result is (97.4±1.9) Ma. These high precision dating data suggest that the Youmapo stock is a multiple stock, which consists of granite porphyry of early Ordovician (Caledonian) as well as biotite granodiorite and muscovite granite of early Cretaceous. Biotite granodiorite makes up the bulk of Youmapo stock. The W-Mo deposit was formed in the late Early Cretaceous (i.e., late Yanshanian), and closely related to biotite granodiorite and muscovite granite. These high precision dating data also show that Bobai-Cenxi fault zone is a long-term active fault which was already active in Caledonian and accompanied by the emplacement of magmatic rocks. This fault reactived in the late Yanshanian, which led to magmatic activities and W-Mo-Sn-Pb-Zn-Sb-Au-Ag mineralization. Overall, the Bobai-Cenxi metallogenic belt belongs to large-scale mineralization during 100~80 Ma in South China. The mineralization background was related to the crustal extension of South China in Cretaceous and the second time rift-depression of the Qinzhou Bay-Hangzhou Bay metallogenic belt.