| The Nanling area is an important metallogenic belt of granite-type uranium deposits in southern China.The Xiazhuang ore field is located in the eastern part of the Guidong rock mass.It is the first area in China to find granite-type uranium deposits.The uranium resources in the ore fields are very rich.Over the years,researchers have noted that the uranium deposits in the Xiazhuang area are characterized by multiple stages of mineralization.In the early research,the U-Pb isochron method of whole rock or mixed single mineral was used,and the age obtained may be the mixed age of multiple stages and secondary ore formation.The granite-type uranium mine was once the most important type of uranium exploration in China.It explored and solved the problem of fine-grained years of granite-type uranium deposits,promoted the development of uranium chronology,and better guided the prospecting and exploration of this type of uranium.And the practice of enriching the mineral deposits to determine the direction of the year has important theoretical and practical significance.In this paper,the Xia Zhuang ore field Xiwang(330),Xianshi(339),and Zhaixia(335)granite-type uranium deposits are targeted at the domestic and international dating and granite-type uranium deposits based on comprehensive analysis and research,through electron probes.The ore mineral combination characteristics were analyzed;the combination of advanced secondary ion mass spectrometry(SIMS)and femtosecond laser ablation inductively coupled plasma mass spectrometry(fs-LA-ICP-MS)was used to directly target the main uranium minerals.The U-Pb isotope determination of the in-situ micro-area of the bituminous uranium deposit was successfully carried out,and the U-Pb dating of the in-situ micro-region of the granite-type uranium deposit was successfully completed,and the series of uranium mineralization spectra were obtained.The study of rare earth elements(REEs)in uranium minerals in micro-regions provides evidence for the exploration of sources of ore-forming materials.The chronological characteristics of uranium mineralization and its relationship with tectonic evolution,magmatism and hydrothermal action are discussed.Possible genetic types of granite-type uranium deposits.Initially established and explored aset of granite-type uranium ore fine determination method including sample preparation and multi-technical means.The main understanding are as follows:(1)The uranium ore-forming age of the Xianshi deposit is the late Upper Cretaceous(73.1±2.9 Ma,SIMS method),Eocene(46.1±1.9 Ma,SIMS method;54.9±3.1 Ma,fs-LA-ICP-MS method),Oligocene(29.33 ± 0.48 Ma;fs-LA-ICP-MS method).The uranium ore-forming age of the Zhaixia deposit is the late Upper Cretaceous(66±2.0 Ma,fs-LA-ICP-MS method;70.7±2Ma,SIMS method),Eocene(46.4±1.1 Ma,fs-LA-ICP-MS method).The uranium ore-forming age of the Xiwang deposit is Eocene(42.3±2.0 Ma;SIMS method),early Oligocene(31.0±2.0 Ma;SIMS method),Early Miocene(20.00±0.85 Ma,fs-LA-ICP-MS method).These data are significantly younger than the traditional full-rock U-Pb method performed by the predecessors;this time,the age older than the Cretaceous was not measured.The results are coupled with the geological,tectonic evolution and regional geological background characteristics of the Xiazhuang ore deposit;especially the Oligocene and Eocene metallogenic age data,provided strong evidence for the multi-stage extension activities of the Xiazhuang uranium field in South China to determine the metallogenic mechanism of uranium mineralization.(2)The characteristics of the coupling between the dating results and the regional tectonic dynamics are analyzed in detail,and the reliability of the test results is verified,and the evidence for the genetic types of the deposits is also provided.The results are in good correlation with the tectonic evolution,magmatic activity and hydrothermal activity of the Xiazhuang ore field.The large-scale magmatic activities in this area are mainly concentrated in the Indosinian-Early Yanshanian period,while the late faults and hydrothermal activities are mainly in the Late Yanshanian and Eocene-Miocene.The age results obtained in this time are inconsistent with the large-scale magmatic activity period and are coupled with the post-magmatic period structure and hydrothermal activity period,indicating that the uranium deposit type in this area is not a magmatic uranium deposit,but a hydrothermal uranium deposit after the magma period.The predecessors derived the mineral deposits as the medium and low temperature hydrothermal genesis from the basic characteristics of the deposit andthe role of fluids.And this is consistent with the Predecessor's understanding.However,the traditional Cretaceous U-Pb method in the measurement of the Lower Cretaceous or older age is inconsistent with the regional geological background and the characteristics of the deposit itself.It also shows that the age result of this in-situ micro-area test has great rationality,credibility and advancement. |
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