关键词: 富铀地层, 沉积成岩作用, 氧化还原条件, 盆地开放程度, 下寒武统

Abstract: In this study, we made microscopic investigation on drilling bore hole black shale samples of the Lower Cambrian Series
which consists of the Wangyinpu Formation and overlying lower part of the Guanyintang Formation (uranium content ranging from
9.37×10-6~202×10-6) in Xiushui area of Jiangxi Province, and found that the bore hole samples have features that reflect sedimentation
and diagenesis without hydrothermal process or supergene leaching/illuviation process. We further analyzed the relationship between
uranium content of the strata and various aspects of environment factors such as redox condition of bottom water during deposition of
the black shale, primary productivity and degree of water communication between the sedimentary basin and the open ocean. In most of
the samples, uranium content is positively correlated with total organic carbon content (TOC). The uranium content (202×10-6) in one
sample that is located in the upper part of the Wangyinpu Formation is the highest, as well is the productivity reflected by organicmatter. In this sample, pitchblende has been found within the carbonized organic matter by using SEM and EPMA. The uranium may
have deposited with the organic matter into the sediments. Afterwards, the uranium formed the pitchblende, and the organic matter
become carbonized during diagenesis of the sediments. The Wangyinpu Formation has higher uranium content than the lower part of
the Guanyintang Formation. It is also revealed that the Wangyinpu Formation was deposited mainly under sulfidic bottom waters and
the lower part of the Guanyintang Formation was deposited mainly under anoxic bottom waters without sulfide. Under sulfidic
condition, sediments deposited in an environment with less restriction would have higher uranium content than sediments deposited in
an environment with more restriction. In summary, during the period of deposition of the upper part of the Wangyinpu Formation,
sedimentation and degradation of organic matter produced by high bioproductivity in the photic waters of the basin consumes much of
the oxygen in the bottom seawaters of the basin, and thus strongly reducing sulfidic environment would prevail in the bottom seawaters.
At the same time, appropriately well connection of the sedimentary basin to the open ocean would provide enough uranium into the
sulfidic environment to deposit, resulting in highly enrichment or even mineralization of uranium in the sediments.

Key words: uranium-enriched stratum, sedimentary and diagenic features, redox condition, restriction of sedimentary basin