Uranium Micromineralogy and Geochronology for Jiangtou Uranium Ore Field in the Qingzhangshan Granite pluton, North Guangdong: Constraints on the Genetic Relationship with Metallogenic Dynamic Background
Abstract:Qingzhangshan (Longyuanba) pluton who is located between Zhuguang and Guidong granitc complex which are two of the most important granite-type uranium concentration areas of South China, is the weak area in the study of granite-type uranium deposits. Jiangtou uranium mining area is located in the place where is the combination of northern part of Qingzhangshan pluton and Nanxiong fault basin. So far, no reports relevant to chronology of uranium have been reported. The micromineralogical characteristics of uranium in this area have been studied by means of electron microprobe. At the same time, the U-Th-Pb chemical ages of magmatic crystalline uraninite and hydrothermal pitchblende have been calculated and the dynamic background of uranium mineralization and geological bodies of ore-forming have been discussed. Results show that: the uranium minerals in the coarse-grained porphyritic biotite granite and medium-grained porphyritic biotite granite are mainly uraninite and coffinite, some uraninite have obvious characteristics of uranium release. The chemical ages of uraninite are 246.8±8.8 Ma and 161.5±8.0 Ma，which is consistent with the range of previous zircon U-Pb ages, representing the diagenetic ages of Indosinian and Yanshanian granites respectively. It shows that before the formation of Nanxiong fault basin, Qingzhangshan pluton and Zhuguang pluton were an organic whole with the same diagenetic and metallogenic environment. The uranium minerals in ore of Jiangtou mining area are mainly pitchblende which is disseminated and accompanied by a small amount of brannerite, coffinite, etc. The chemical ages of pitchblende are 121.3±9.8Ma, 98.8±8.0Ma and 73.2±8.8Ma, representing three stages of uranium metallogenesis age in the area. Combining with the six tectonic extensional movements since Mesozoic, it had been considered that uranium mineralization in this area is controlled by the dual-factor metallogenic dynamic background of deep fault depression activity in the margin of Mesozoic-Cenozoic basins and distribution of uranium-producing granite bodies. The Qingzhangshan pluton should have similar prospecting prospects with Zhuguang and Guidong pluton.