The Geochemical Characteristics And Tectonic Stress Field Of The 302 Uranium Deposit In Northern Guangdong Province

This paper takes the 302 uranium deposit as the major research object. Based on the results of previous studies and combined with field geological survey, this paper has carried out the research on the geochemical characteristics of trace elements, rare earth elements and stable isotopic of altered rocks, altered minerals and host rocks. Besides, tectonic stress field and chronology of altered minerals has also been studied. Furthermore, this paper discussed the relationship between the evolution of fault structure and mineralization, the sources of metallogenetic materials and ore-forming fluid, and the metallogenic geodynamic background. The conclutions are as follows:(1) By analyzed the element contents of some highly compatible elements of pitchblende, altered rocks, altered minerals and host rocks, it implicates that the sources of metallogenetic materials was mainly deprived from the granites rather than the diabase. The REE distribution patterns of pitchblende, altered rocks, altered minerals and granite all have the obvious negative Eu anomalies, while are obviously different with the diabase without obvious Eu depletion, it shows that the metallogenetic materials was mainly came from the granite.(2) The calculated δ18OH2O of the ore-forming fluid equilibrated with the pre-ore stage quartz, ore stage quartz and post-ore stage quartz, in general, had a trend of gradually decrease, which shows that there is a continuous influxing of meteoric water during uranium ore-forming process. Besides, from pre-ore stage to post-ore stage, in general, the values of δ13CPDB of calcite had a reducing trend, while the values of δ18OSMOW of calcite had an increasing trend, it may be caused by fluid degassing during ore-forming process. The characteristics of hydrogen and oxygen isotopic composition of altered minerals reveals that the mineralized hydrothermal water was not derived from metamorphic water, magmatic water or mantle fluid, but mainly was originated from the meteoric water, probably mixed with some tectonic pressolution fluid at the early metallogenic stage. In addition, the characteristics of carbon isotopic composition, sulfur isotopic composition and Sr-Nd isotopic composition demonstrates that the carbon and Sr, Nd mainly derived from the granite, and the sulfur was mainly derived from granite, probably with some strata sulfur.(3) Through observation and analysis of the faulted structural rocks, the analysis of stress fields of fault by conjugate joints and slickensides, and combined with the analysis of dike tectonic stress, we conclude that at least four period of tectonic stress in different direction can be identified in the Changjiang area.(4) According to the tectonic stress field evolution and the existing exploration data, the secondary nearly SN-trending structure is served as the ore-host structure which on the hanging wall and foot-wall of NE-trending ore-controlling structure and leading structure. The SN-trending ore-host structure has experienced at least two period of extensional tectonic activity. The multi-extensions of SN-trending faults is the dynamic background of U-mineralization. The first extensional tectonic activity is nearly SN-trending compression occurred in the second stage of Later Yenshanian period(later Early Cretaceous), and the second extensional tectonic activity is NW-SE-trending extension occurred in the third stage of Later Yenshanian period(Late Cretaceous). The uranium mineralization was mainly occurred in extensional background during the Late Cretaceous.(5) The whole rock-mineral Sm-Nd isochron ages of dark-purple fluorites which co-existing with pitchblende is(69±1) Ma, consistent with the age of pitchblende from other documents, it shows that this period of tectonic fluid were very closely related to uranium mineralization and further proved that the metallogenic epoch of the 302 uranium deposit.(6) Based on above arguments, concluded that the 302 uranium deposit is belongs to granite-type uranium deposit, which formed in tectonic extensional background of the late Cretaceous. That is the atmospheric precipitation cycles along the deep faults and heated, and that the process of circulation may probably mixed with some tectonic pressolution fluid, and then became hydrothermal fluid, the hydrothermal fluid thereafter leached uranium and other metallogenetic materials from U-rich geological body. As a result, uranium was eventually precipitated in the favorable places and formed the uranium deposit.