| 其他摘要 | The Dulong tin-zinc polymetallic deposit, or one of the largest cassiterite-sulfide deposits in China, is located in the Maguan County, Yunnan Province, China. Based on the studies of the field geology and ore microscope analysis, the microbeam analyses on chlorite, oolitic pyrite, intergrowths of hexageonal and monoclinic pyrrhotites, and “chalcopyrite disease” texture etc.have been studied systematically through the Electron Microprobe, Raman Spectroscopy and X-ray Diffraction. Combining with the geochronological studies through the 40Ar/39Ar dating of biotite and the TIMS U-Pb dating of cassiterite, the characteristics of each ore-forming period of the deposit and a relative metallogenetic model have been suggested.
The main conclusions are listed below:
（1）The chlorite and cassiterite were formed in the Yanshanian magmatic hydrothermal mineralization event. The studies of chlorite indicated that this event was happened under the reductive condition with low-moderate temperature.
（2）The oolitic pyrites were formed in the SEDEX mineralization event, being an important potential source of Fe, Zn, S, etc. which were enriched in the later mineralization events.
（3）The pyrrhotites were mainly transformed from the (oolitic) pyrite by losing sulfur in the metamorphic mineralization event. The monoclinic pyrrhotites occurred in the Lazizhai ore section indicated that the Yanshanian magmatic hydrothermal mineralization event was happened under the low-moderate temperature condition.
（4）The “chalcopyrite-disease” was mainly resulted from the reaction between the copper-rich magmatic hydrothermal fluid and the iron-rich sphalerites.
（5）The assemblage of native bisumth, native silver, cassiterite, chalcopyrite and galena indicated the reductive condition of the low sulfur concentration and the low-moderate temperature in the magmatic hydrothermal mineralization event.
（6）The biotite Ar-Ar dating yielded plateau ages of the low and high temperature section, 179.0± 5 .0Ma and195.7± 6.6Ma, respectively, through the IR-Laser step heating method. Based on the study of the biotite fabrics, 179.0± 5 .0Ma might represent the age of the metamorphic mineralization event.
（7）The Dulong tin-zinc ploymetallic deposit is a multi-genetic deposit, and three main periods of its forming process were identified the SEDEX, the metamorphic and magmatic-hydrothermal metallogenetic periods, respectively. Zn-rich oolitic pyrite was formed in the SEDEX metallogenetic period. The metamorphic metallogenesis should be related to the late Indosinian regional deformation-metamorphism, and these minerals such as iron-rich sphalerites and pyrrhotites were mainly formed in this period. The magmatic hydrothermal metallogenesis should be related to the long-lasting activity of the later Yanshanian Laojunshan granite, and the large-scale mineralization of tin, copper, silver, lead and bismuth occurred in this period.
In addition, native bismuth and native silver have been firstly found in the studying area in this research. The ore-forming significance of these minerals should be an interesting problem for the further studies. |
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