关键词: 贵东复式岩体, 花岗质小岩体, SHRIMP锆石U-Pb年龄, 铀成矿

Abstract: The Guidong complex massif composed of multistage and multi-type intrusive mass is the host rock for one of the most important granite-related uranium ore fields. However, up to now, the discovered uranium deposits are only distributed in the eastern part of this complex massif. In order to understand the relations of magmatism to uranium metallogenesis, it is crucial to understand the differences of petrological characteristics and to define the petrogenic ages of intrusive masses both in the eastern part and in middle-west part of Guidong complex massif. Taking the Guiweishan fault as the boundary roughly, the previous studies indicated that Guidong complex massif is dominated by early Yanshanian granitic batholith in the middle-western part and by early Indosinian granitic batholith with late stage mafic dykes in the eastern part. It is generally agreed that the late-stage mafic dykes of Yanshanian ages closely link to uranium mineralization. However, the ages of widely distributed late-stage small granitic bodies in the middle-eastern part of Guidong complex massif are still under debate, and further study is necessary to reveal the spatial-temporal relationship and the possible genetic links of late-stage small granitic bodies to uranium mineralization. Zircon SHRIMP U-Pb dating of the late-stage small granitic bodies in the middle-eastern part of Guidong complex massif was conducted in this paper. The results show that highuranium zircons are common in the late-stage small granitic bodies, which can explain the difference of zircon U-Pb ages from a granite body by different scholars. Eliminating the 206Pb/238U ages with high-uranium zircons in the weighted average age data processing, samples collected from the Aizi, Siqian and Chendong granitic bodies in the western part of the Guiweishan fault yielded the early Yanshanian magmatism with the ²⁰⁶Pb/²³⁸U zircon weighted average ages of 163.0±1.6

Ma, 163.1±1.6 Ma and 160.7±1.9 Ma, respectively. While samples collected from the Maofeng, Fenshuiao and Guiweishan granitic bodies in the eastern part of the Guiweishan fault yielded the Indosinian magmatism with the ²⁰⁶Pb/²³⁸U zircon weighted average ages of 230.0±2.7 Ma, 225.9±2.9 Ma and 232.6±3.1 Ma, respectively. Therefore, the ages of the late-stage small granitic bodies in the middle-eastern part of Guidong complex massif are diverse in different locations. As the host rock of uranium deposits, the Indosinian small granites in the eastern part of the Guiweishan fault have the close links to high temperature sericitization type uranium mineralization. And the small granitic bodies may also provide the uranium sources based on the results of previous element geochemical st udies. 

Key words: Guidong complex massif, small granitic body, zircon SHRIMP U-Pb age, uranium mineralization