棉花坑铀矿床红色硅化蚀变岩地球化学特征及对铀成矿的指示

Geochemical Characteristics of Red-silicification and Implications for Uranium Mineralization in Mianhuakeng Uranium Deposit

棉花坑铀矿床是我国重要的花岗岩型铀矿床,其铀成矿与硅化蚀变作用关系密切,但硅化蚀变与铀成矿之间的成因联系研究相对薄弱,尤其对早期红色硅化蚀变流体特征研究较少。文章选取棉花坑铀矿床早期红色硅化蚀变岩、微晶石英进行了主量、微量及稀土元素分析,结果表明:棉花坑铀矿床红色硅化蚀变岩亏损Zr、Nb、Ta等高场强元素,富集U等元素;w(∑REE)值较低,为(10.3~109.2)×10^(-6),且稀土元素配分模式与赋矿围岩基本类似,暗示红色硅化蚀变流体贫稀土元素,矿化物质主要来自赋矿围岩;同时其Sm/Nd、Pb/Ce和La/Ba值分别为0.27~0.39、0.97~8.11、1.76~16.81,指示了红色硅化蚀变流体为浅源和深源的混合。棉花坑铀矿床红色微晶石英中w(Al)值介于(45~157)×10^(-6)之间,含量相对较低且变化范围较小,暗示流体的pH值变化较小;结合红色微晶石英型铀矿化品位相对较低的特征,推测红色微晶石英中w(Al)值变化特征可作为红色微晶石英型铀矿化铀品位相对高低的重要判据。

Mianhuakeng uranium deposit is an important granite-type uranium deposit in South China.The uranium mineralization is closely related to silicification alteration,but research on the genetic link between silicification alteration and uranium mineralization is relatively weak,especially for the early red silicification alteration fluid characteristics.For this reason,this paper studied the petrographic and geochemical characteristics of red silicified altered rock and microcrystalline quartz in the uranium deposits,analyzed the major,trace and rare earth elements.The silicification altered red rocks of Mianhuakeng uranium deposit were found depleted in high-field-strength elements such as Zr,Nb,and Ta etc and enriched in U.The∑REE contents ranged from 10.3×10^(-6) to 109.2×10^(-6),meanwhile,the characteristics of the REE pattern were basically similar to the ore-hosting wall rock,suggesting that the silicified alteration fluid was depleted in rare earth elements,and the silicified mineralized material mainly came from the orehosting wall rock.At the same time,the ratios of Sm/Nd,Pb/Ce and La/Ba were 0.27~0.39,0.97~8.11,1.76~16.81,respectively,indicating that the altered mineralization fluid was a mixture of shallow and deep sources.The Al content in the microcrystalline quartz of the Mianhuakeng uranium deposit ranged from 45×10^(-6) to 157×10^(-6),the content was relatively low and the range of changes was small,suggesting that the pH change of the fluid was small.Combined with the relatively low grade of the red microcrystalline quartz,the contents change in the red microcrystalline quartz was surposed as an important criterion for the relatively grade of uranium in the red microcrystalline quartz.