矿床地球化学国家重点实验室知识库

The Dulong Sn-Zn polymetallic deposit, Yunnan Province, is one of the largest cassiterite-sulfide deposits in China. Being lack of the accurate and reliable geochronological data, the genesis of this deposit is controversial greatly, so that it is very serious to restrict the further development of the geological prospecting. This paper has reported the U-Pb isotope dating of cassiterite by the method of in-situ LA-MC-ICP-MS from the Manjiazhai section of the Dulong ore-field. The result showed that the Pb-206/(207) Pb-U-238/Pb-207 isochron ages of cassiterite samples DL12-716, DL12-722 and DL12-740 were 89. 2 +/- 4. 1Ma ( N = 22, MSWD = 4. 5 ), 88.0 +/- 1. 6Ma ( N = 24, MSWD = 2. 3) and 87.2 +/- 3. 9Ma ( N = 31, MSWD = 14 ) respectively, and the (207)pb/(206) pb-U-238/(206) pb concordia ages of the corresponding cassiterite samples were 96. 6 +/- 3. 5Ma ( MSWD = 8. 1 ), 93. 6 +/- 1. 6Ma ( MSWD =5. 8 ) and 82. 0 +/- 2. 5Ma ( MSWD = 11 ) separately. Combining with geology and previous petrogenetic-minerlization geochronology, indicated that the tin minealization of this deposit might mainly be in the Late Cretaceous, which related closely to the later Yanshanian magmatic hydrothermal events. Meanwhile, the basis of the geological facts revealed that the later Yanshanian magmatic hydrothermal events were the key factor of the W-Sn polymetallic deposit mineralization in the Laojunshan area. Moreover, regional geology and geochronology further suggested that there were Late Cretaceous larger-scale granitic magmatism and relative tin mineralization events in the southeastern Yunnan.