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我们曾经对采自科罗拉多洲包尔特(Boulder)附近的包尔特花岗闪长岩岩体的前宾夕耳法尼亚纪之风化剖面的十一个样品进行了γ-射线光谱分析及化学分析,测定了其中 U、Th 含量。为了确定这些样品中 U、Th 的可能赋存形态,还以浓度为2 N 的热盐酸作样品的淋滤试验。新鲜的花岗闪长岩可合有9.3 p.p.m.Th 和2.5 p.p.m.U。在第一期的风化阶段里,所释出的Th.U 含量分别为新鲜花岗闪长岩 Th 含量的25%,U 含量的60%。由新鲜花岗闪长岩的淋滤试验可知,酸性的淋滤溶液足以带出原岩中90%的 Th 以及60%的 U。据此可知,新鲜岩石中的 Th、U,绝大部份存在于可溶于酸的那些矿物中,或者是存在于一些矿物颗粒之间的物质之内。U、Th 含量在风化壳最下部岩石中降低,然后即逐渐升高,在风化壳的最顶部亦即风化最强烈的岩石中,U、Th 含量至少增加四倍。风化岩石的淋滤试验表明,铀大部份赋存在原始的难以风化的矿物中,如锆石、磷钇矿和磷灰石之内。而 Th 则赋存在粘土矿物之中,或是赋存在那些在风化环境下所形成的次生稳定矿物之中。
We conducted a gamma-ray analysis of eleven samples from a former Pennsylvania-Southern Peninsula weathering section of the boulder granodiorite from the Boulder, Colo. Chemical analysis, determination of which U, Th content. In order to determine the possible occurrence of U and Th in these samples, a hot-acid solution with a concentration of 2 N was used as the leaching test. Fresh granodiorite can hold 9.3 p.p.m.Th and 2.5 p.p.m.U. During the first stage of weathering, the released Th.U contents are 25% of the Th content of fresh granodiorite and 60% of the U content, respectively. From the leaching test of fresh granodiorite, it is known that an acidic leaching solution is sufficient to bring out 90% of Th and 60% of U in the original rock. From this we can see that most of Th, U in fresh rocks are present in those minerals that are soluble in acid, or in substances that exist between some mineral grains. The contents of U and Th decrease in the lowermost crust of the weathered crust, and then increase gradually. At the top of the weathered crust, the most weathered rocks, the U and Th contents increase at least fourfold. Leaching experiments on weathered rocks show that most of the uranium is present in the original hard to weathering minerals such as zircon, xenotime and apatite. Th, on the other hand, is found in clay minerals or in secondary stable minerals formed under weathering conditions.