诸广中段鹿井地区辉绿岩40Ar-39Ar年代学特征

Ar-Ar Geochronological Characteristics of Diabase in Lujing Area of Middle Zhuguangshan

诸广—贵东地区作为华南热液型铀矿最为重要的花岗岩型铀矿大型矿集区,区内发育了大量与铀矿化作用密切相关的基性岩脉。为了厘定区内基性岩年代学数据,更好地约束铀成矿时限,以诸广中段鹿井地区辉绿岩脉为研究对象,开展了40Ar-39Ar年代学研究。结果表明:辉绿岩全岩40Ar-39Ar同位素年龄为(171.7±1.6)、(169.1±3.8)Ma,反映鹿井地区在中侏罗世(约170 Ma)发生了一次岩石圈伸展裂解作用。诸广—贵东地区至少存在200、170、140、105和90 Ma 5期基性岩浆活动,195、165、125、90、75和55 Ma 6期铀成矿事件,成矿热液往往紧随每次区域性玄武岩事件之后(5~20 Ma),铀成矿与以辉绿岩墙为代表的区域玄武岩事件有紧密的时间、空间和成因联系。辉绿岩脉与成矿构造上的关联性以及来源于地幔的深部岩浆浅部表现形式的成因特点,决定了其可以为铀成矿提供一定的挥发分(矿化剂)和后期铀沉淀富集场所,提高成矿热液对铀的携带能力,进而促进铀的成矿作用。

The Zhuguang-Guidong area is the most important granite-related hydrothermal uranium ore deposit cluster in South China. The Mesozoic mafic dykes are widely distributed in this area, and they are closely associated with the uranium mineralization. In order to confirm the geochronological data of the mafic dykes and the uranium metallogenic time, a whole-rock 40Ar-39Ar analysis was carried out. The 40Ar-39Ar isotopic ages of the whole diabase are(171.7±1.6) Ma and(169.1±3.8) Ma, indicating that the Lujing area underwent a lithosphere extension in the Middle Jurassic(170 Ma). The results show that at least five major episodes of mafic dykes occurred at 200, 170, 140, 105, and 90 Ma, and at least six major events of uranium mineralization occurred at 195, 165, 125, 90, 75, and 55 Ma, which is consistent with the previously published geochronological data. The ore-forming hydrothermal fluid followed right after each regional basalt event(5-20 Ma),so the uranium mineralization was closely related to the regional basalt events represented by the diabase wall in time, space, and genesis. The correlation between the diabase veins and metallogenic structures and the genesis characteristics of the shallow forms of the mantle hypomagma indicate that it may provide a certain amount of volatile matter(mineralizer) for uranium mineralization and the enrichment place for ore deposits;The ore-forming hydrothermal fluid may improve the carrying capacity of uranium and promote uranium mineralization.