柴达木盆地北缘中新生代热演化及其对铀成矿的意义

Mesozoic-Cenozoic Thermal Evolution and Its Significance to Sandstonetype Uranium Mineralization in the Northern Margin of Qaidam Basin

文章在阐述柴达木盆地北缘砂岩型铀矿成矿地质特征的基础上,以磷灰石裂变径迹特征分析为依据,系统研究了该地区中新生代热演化及其与砂岩型铀矿成矿作用的关系。资料显示,区内中侏罗统具备较好的铀成矿条件,成矿类型以层间氧化带型和潜水氧化带型为主。磷灰石裂变径迹分析结果表明,样品的平均径迹长度为(11.71±0.17)μm±1σ^(12.58±0.18)μm±1σ,说明均经历过退火作用;样品的表观年龄为64.4~85Ma,说明区内构造活动具有多期、多阶段特点;基于裂变径迹的t-T曲线模拟结果表明,自120Ma以来,该地区的构造演化可以分为挤压隆升、断陷沉降、快速抬升3个阶段。因此,认为区内砂岩型铀矿主体应是早白垩世早期-古新世早期挤压隆升阶段形成的古矿体。现今的找矿方向,应是在活动强度相对较弱的构造活化区中寻找残留铀矿体,同时注重深部找矿。

Geological features of sandstone type uranium mineralization and the dating feature of apatite fission track was systematically combined to study the relationship between the Meso-Cenozoic thermal history and uranium mineralization in the north margin of Qaidam basin. Analysis on uranium metallo- genic conditions and characteristics in the northern area of Qaidam shew that the middle Jurassic was fa- vorable to uranium mineralization, the main mineralization types are interlayer and phreatic oxidation zone type. Statistics of fission track dating shew that the mean track length ranging from （11.71±0.17）μm±1σ-（12.58±0.18）μm±1σ, which suggest that the track underwent thermal annealing process after their formation, and the apparent ages was between 86Ma and 64.4Ma which mean the multiphase and multi-stage tectonic evolution. The simulation result of apatite fission track t-T curve shew that the tectonic evolution from 120Ma can be divided into compressional uplift-rift, subsidence and rapid uplift three stages. And therefore the sandstoneqype uranium body in research area was mainly formed in the Early Cretaceous and Early Paleocene by regional compressional uplift stage, the prospecting direction should be residual uranium ore body in relative weak structural action area under the strong tectonic background and the deep prospecting space.