花岗岩型铀矿床中矿前期蚀变对铀活化溶解的实验研究及其找矿意义

产铀花岗岩岩体多为二云母花岗岩,其中黑云母遭受白云母化,进而改变晶体结构和铀的赋存状态,产生铀的活化溶解。大量实验结果表明,黑云母转变为白云母易发生于含钾、铝的氯化物酸性溶液中,形成温度多在350～500℃,压力(PH2O)20～100MPa。实验结果证实,酸性初始溶液对形成造岩矿物的白云母化和伊利石化更有利,并往往稳定于pH=3～4的范围,白云母化时转入溶液的铀含量最高可达30%。黑云母的绿泥石化易发生于400℃,50MPa含镁、钠,pH=6～8的弱碱溶液中。黑云母转变为绿泥石比其转变为白云母时释放出的铀要少得多,一般低于检测限。实验结果还表明,晶质铀矿在黑云母的白云母化条件下转入溶液的铀为104～130μg/L,比晶质铀矿在黑云母绿泥石化条件下转入溶液的铀(12.2μg/L)高近一个数量级。这种"矿前期蚀变"在"退色蚀变"过程中铀的丢失现象对于找矿具有普遍重要意义。

Alternation Effect on the Solution of Uranium in Granite Type Uranium Deposit and Its Significance for Ore Exploring

The muscovite alternation of biotite in Uranium-rich Two-Mica Granite reforms the crystal structure of biotite and the existing form of Uranium, and promotes the solution of Uranium. The results show that the transformation from biotite to muscovite activates easily in the acidic solution of potassium, aluminum chloride under 350~500 ℃ and 20~100 MPa (PH2O). It is confirmed by the experiment that the existence of initial acidic solution is more appropriate for the muscovite and illite alternation of Rock-forming minerals. The maximum Uranium solute content can reach 30% in pH=3~4 acidic solution. The chlorite alternation of biotite activates easily in pH=6~8 alkaline solution of magnesium and sodium. Less Uranium solutes during chlorite alternation compared with muscovite alternation. The results also suggest that the content of dissolved Uraninite during muscovite alternation is 104~130 μg/L, which is one order larger than 12.2 μg/L during chloride alternation. These results of U loss during alternation are significant for ore exploring.