相山矿田邹家山铀矿床碱交代矿化蚀变岩地球化学

相山矿田邹家山铀矿床成矿作用与碱交代关系密切。钠、钾的带入和带出极大地影响铀成矿作用过程,钠交代和钾交代对铀成矿的影响差异明显。本文以邹家山铀矿床中典型的钠化和钾化矿体为研究对象,通过比较两矿体剖面的地球化学特征,研究其异同,探讨钠交代、钾交代与铀成矿作用关系,得出以下认识:(1)与矿体两侧的围岩相比,钠交代和钾交代矿石中都富U和Mo,而Ba含量明显降低;(2)钠交代对原岩化学成分的改变不强。除了钠含量明显增高、钾含量明显降低、钠钾摩尔比M(Na2O/K2O)明显增大外,矿石与原(或围)岩的化学成分相差不大,总碱摩尔数M(Na2O+K2O)几乎不变;(3)钾交代对原岩的矿物及化学成分改变很大。除钾高、钠低等含量变化外,强烈去Si和Na,M(Na2O+K2O)有20%~30%的减少,而且许多微量(成矿)元素含量明显增加,特别是稀土元素明显增高,且重稀土增加更快;(4)两类碱交代中行为反差最大的组分是Na2O、K2O、Si O2和REE。钠交代过程中,Na2O和Si O2增加,K2O和REE减少,M(Na2O/K2O)明显增大;而钾交代过程正相反;(5)在相山铀成矿过程中,仅有钠交代时铀的含量较低,强钾交代是形成富铀矿的必要条件。

Geochemistry of Alkali Metasomatized Rocks of Zoujiashan Uranium Ore-deposit in Xiangshan Ore-field

In the Zoujiashan ore deposit of the Xiangshan ore-field, uranium mineralization is closely related to alkali metasomatism. Sodium metasomatism and potassium metasomatism impact quite differently on uranium mineralization. Three ore-body profiles in the Zoujiashan ore-deposit are investigated to delineate the roles of sodium metasomatism and potassium metasomatism in uranium mineralization. The results showed that (1) Compared with the surrounding rock, ore bodies with sodium or potassium metasomatism are rich in U and Mo, but significantly poor in Ba; (2) Chemical changes of sodium metasomatism are less obvious, except the significant increase of Na/K ratios, whilst the alkali contents (Na2O+K2O) are somewhat constant; (3) Mineral and chemical changes of the potassium metasomatism are significant. Potassium metasomatism resulted in the intensive enrichment of K, and removal of Si and Na. Potassium metasomatism resulted in 20%?30% decrease of the total alkali, and significant increases of trace elements, and the heavy rare earth elements in particular; (4) In two alkali metasomatism types, the components with the biggest contrast in behavior are Na2O, SiO2, K2O and REE. In the sodium metasomatism, the contents of Na2O and SiO2 are increasing as well as decreasing in K2O and REE, so as to increase significantly in the mole ratio of Na2O/K2O. However, all are the contrary in the potassium metasomatism; (5) Strong potassium metasomatism is a prerequisite for the formation of high grade uranium ores in the Xiangshan ore-field, while the sodium metasomatism that predated the potassium metasomatism played a much less important role in the uranium mineralization.