花岗岩铀地球化学特征新认识——以赣南富城产铀花岗岩体为例

对富城花岗岩U、T h含量分析结果进行的频数统计分析表明富城花岗岩U的均值为8.92×1-0 6、众数为8.0×10-6、中位数为7.03×1-0 6,其概率密度曲线偏向高端呈右偏非对称分布(偏度系数CSK=1.10)。T h的均值、众数和中位数三者一致,分别为25.7×10-6,25.75×10-6,25.8×1-0 6,其概率密度曲线呈对称正态分布(偏度系数CSK=0.11)。核诱发裂变径迹研究查明富城花岗岩中铀有4种存在形式:(1)显微粒状铀矿物(晶质铀矿);(2)以类质同像形式存在于锆石、磷灰石等副矿物之中;(3)均匀分散赋存在造岩矿物晶格之中的结构铀;(4)沿造岩矿物(长石、石英)微裂隙及粒间分布的非结构铀。对富城花岗岩铀配分研究发现,赋存在造岩矿物中均匀分散状的结构铀含量与全岩铀不呈消长关系,而是存在一定的极限值:长石、石英<3×1-0 6,白云母<5×10-6,黑云母<9×10-6。溶浸实验结果表明,富城花岗岩活动性铀浸出率很高(平均值52%),为富城花岗岩具有较大铀成矿潜力提供了佐证。

New cognition for uranium geochemical characteristics of granite:Taking the Fucheng uranium-bearing granite pluton in southern Jiangxi as an example

The frequency analysis of U and Th for Fucheng granite pluton shows： the PDF （probability density function） curve for U displays an asymmetric normal distribution to the right （skewness CsK= 1.10） with mean--8.92 X 10^-6, mode--8.0X 10^-6 and median-- 7.03 X 10^-6; the PDF curve for Th displays a symmetrical normal distribution （skewness CsK =0. 11） with mean--25.7 X 10^-6, mode--25.75 X 10^-6 and median--25.8 X 10^-6, which are consistant on the whole. Using nucle-induced fission-track method, it has been estab- lished that the uranium in Fucheng granite can be present in the following forms of occurrence： （1） micro-grained uranium mineral （uraninite） ; （2） isomorphic uranium in accessory minerals （such as zircon, apatite,etc）; （3） lattice-seated uranium homogeneously scattered in rock-forming minerals; （4） non-lattice-seated uranium distributed in micro-fissures or along the interstices of rock-forming minerals （such as feldspar, quartz, ete）. On the basis of the research on uranium distribution in Fucheng granite, the lattice-seated uranium contents in rock-forming minerals are not tend to increase as the whole-rock ura- nium content rise, but are limited to a certain value： quartz and feldspar contain uranium less than 3 ）〈 10^-6, muscovite less than 5 X 10-6 , biotite less than 9 X 10^-6. The leaching rate of mobile uranium of Fucheng granite is higher （52%^ in average） and suggests evidence for relatively great uranium metallogenetic potential of Fucheng granite.