相山铀矿田铀多金属成矿时代与成矿热历史

Ore-forming age and thermal history of uranium-polymetallic mineralization in Xiangshan uranium orefield

相山铀矿田的铀多金属矿化主要可划分为碱性铀矿化、酸性铀矿化、铅锌银铜矿化和金矿化四种类型。通过沥青铀矿和矿化岩石U-Pb等时线、黄铁矿Rb-Sr等时线、绢云母40Ar-39Ar同位素年龄测定,结合铀多金属成矿特征研究,厘定了相山铀矿田铀多金属成矿时代,确定铀多金属矿化的成矿时序为:碱性铀矿化、铅锌银铜矿化、金矿化、酸性铀矿化。锆石裂变径迹研究表明,相山矿田铀多金属矿化样品的锆石裂变径迹峰值年龄与U-Pb、Rb-Sr和40Ar-39Ar同位素年龄一致性良好,裂变径迹年龄(峰值年龄)可以限定热液铀多金属成矿热事件时代。碱性铀成矿热事件的锆石裂变径迹峰值年龄为119. 8~125. 6Ma;金成矿热事件和铅锌银铜多金属成矿热事件的锆石裂变径迹峰值年龄为106. 1~113. 8Ma;酸性铀成矿热事件的锆石裂变径迹峰值年龄为86. 7~100. 0Ma;新发现一期锆石裂变径迹峰值年龄为66. 4~78. 6Ma的热事件,该期热事件可能为相山矿田最晚一期酸性铀成矿热事件。相山矿田66. 4~78. 6Ma的铀成矿热事件,与华南花岗岩型热液铀矿床的区域成矿热事件时代耦合,该发现对华南火山岩型铀矿成矿时代的重新认识,对火山岩型、花岗岩型铀矿床成矿统一性认识具有重要意义。

The uranium polymetallic mineralization in Xiangshan orefield could be divided into four types:alkaline uranium mineralization, acidic uranium mineralization, lead-zinc-silver-copper mineralization as well as gold mineralization. Throughout pitchblende and mineralized rock U-Pb, pyrite Rb-Sr and sericite 40Ar-39Ar isotopic age determination as well as mineralization characteristics, we determined the forming sequence of uranium-polymetallic process in Xiangshan orefield:alkaline uranium mineralizaiton, lead-zinc-silver-copper mineralizaiton, gold mineralization and acidic uranium mineralization, respectively. The fission track thermal study showed that the peak ages of zircon fission track using uranium-polymetallic mineralized samples in Xiangshan orefield are well consistent with U-Pb, Rb-Sr and 40Ar-39Ar isotopic ages, which indicate that fission track age (mainly referred to peak ages) can be used to limit the forming age of hydrothermal uranium-polymetallic events. The zircon fission track peak ages of alkaline uranium mineralization event range from 119.8Ma to 125.6Ma;the zircon fission track peak ages of thermal gold mineralization event and lead-zinc-silver-copper mineralization event range from 106.1Ma to 113.8Ma;the zircon fission track peak ages of acidic uranium mineralization event range from 86.7Ma to 100.0Ma. There is another group of peak ages concentrated at 66.4~78.6Ma which may reflect a new discovered acidic uranium mineralization event in Xiangshan orefield. The ore-forming thermal event formed at 66.4~78.6Ma in Xiangshan orefield is well consistent with the metallogenic event of the granite-type uranium deposit in South China. This study make us further understand the ore-forming ages of volcanic-type uranium deposits and the metallogenic uniformity of volcanic-type and granite-type uranium deposits in South China.