摘要:
概述了外生铀矿床的基本特点,即近源、浅成、层控、有机萃取、多阶段成矿、多种成因类型。根据成矿作用和矿床成因,把外生成矿的铀质来源分为:1.同生铀源;2.再造铀源;3.后生铀源等三类。着重讨论了外生铀矿资源评价的若干问题,即铀源岩石的原始铀丰度及活化丢失情况;花岗岩类铀源岩的岩石化学标志;各种铀源地质体形成的大地构造背景;外生铀矿成矿省、成矿带的评价准则。
Abstract:
Some problems on the uranium source and the resource evaluation for exogenic uranium deposits are discussed in this paper. 1. According to the exogenic mineralization and geneses of ore deposits, uranium sources can be classified into three types: (a)syngenetic, (b)reformed and (c)epigenetic. It is very important to konw the temporal and spatial distribution of various geologic bodies of uranium sources for recognizing metallogenetic provinces and belts. 2. The prerequisite for evaluation of uranium resourses is utilizing the continuous growth model of U-Pb isotopic evolution and studying the initial uranium abundance of uranium source rocks and the effects of all kinds of geological processes on uranium mobillization after diagenesis (Table 1,2). 3. According to research on petrochemical characteristics of uranium source rocks, some chemical parameters of uranium preconcentration and petrogenesis can be used as the criteria of recognization for geological bodies of uranium source (Table 3). 4. The distribution of uranium metallogenic provinces is determined by regional tectonic settings which control the maturity of the earth's crust and control the uranium prsconcentration related to the maturity. For example, the Archean granite-greenstone zones, back-arc magmatic and thrust bolts, collision foreland thrust-magmatic belts are favourable for the formation of uranium-rich granitoid, and continental rift basins and marginal sea and embayment-lagoon basins are favourable for forming uranium source beds. 5. The following evaluation criteria can be used for the determination of the metallogenetic provinces and belts of exogenic uranium deposits. a. Distribution of the geological bodies of various uranium source, initial uranium abundance and uranium mobillization in the source rocks. b. Tectonic settings and tectonic units favourable for forming various geological bodies of uranium source. c. The characteristics of sedimentary formations, facies, and paleoclimatic conditions of various uraniferous rock series. d. Epigenetic reformation of various uraniferous rock series such as structure-lithofacies-paleohydrogeologic conditions for uranium mobillization and reconcentr-ation.
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