| 其他摘要 | The Dulong tin-zinc ploymetallic deposit, which is one of the largest cassiterite-sulfide deposits in China, locates in the Maguan county, Yunnan Province, China. Due to the complexity of this deposit geological phenomenon, the magma, tectonic, formation and other factors have showed some certain ore-controlling significance, so that the genesis has been controversial greatly for a long time, and to some extent, seriously to restrict the deep and periphery prospecting. Based on the geological survey, by optical microscopy to carry out the detailed observation of the skarn minerals and metallic minerals, taking advantage of the electron microprobe and LA-ICP-MS in-situ technique to conduct systematically qualitative and quantitative analysis, this paper is in order to reveal the formation process of skarn, ore genesis and prospecting significance. Based on the conventional rock-forming and ore-forming chronology data, the U-Pb isotopic dating of cassiterite by the method of LA-MC-ICP-MS had been used to futher define mineralization age and to distinct genesis. The main conclusions are listed below. （1）The geological and geochemical characteristics of Dulong tin-zinc ploymetallic deposit indicated that this deposit was a magmatic hydrothermal genesis deposit controlled by magma-tectonic-formation composite factors. （2）The analytical data of garnet electron probe and in-situ micro-area LA-ICP-MS showed that the composition of garnet was closely associated with mineralization. The garnet was mainly grossular related with the W, Mo mineralization, which was mainly distributed in the range of 0-100m, 250-300 from the deep granite rock, respectively. Accordingly, garnet compositional changes in the vertical and related mineralization rules can be used to deep prospect. Sn element of garnet was in higher levels. Combined with the surface scan images, Sn were mainly distributed around the edge of garnet in the form of fine grain of cassiterite and some were isomorphously scattered in garnet lattice isomorphism. According of the relationship between garnet major- trace elements and Sn mineralization, it was suggested that Sn mineralization is mainly distributed in the range of 50-300m from the deep granite rock. At 80m, tin content was the highest, then gradually reduced with the increase of distance from deep granite, so we can looking for the rich Sn orebody near 80m. （3） The analytical data of pyroxene electron probe and in-situ micro-area LA-ICP-MS showed that the relationship between pyroxene composition and mineralization was complex. With the increase of distance from deep granite, the content of metal elements such Sn, Zn, Cu changed greatly and the pyroxene component associated with relevant mineralization had larger span, from diopside to hedenbergite. At the same time, manganese content of calcium pyroxene also changed greatly, regularity is not obvious. （4）Electron probe data of skarn minerals such as garnet, pyroxene, hornblende, epidote, chlorite and phlogopite indicated that the early skarn had been in an acidic environment of relative reduction, then gradually moved to the alkaline environment of relative oxidation. In the later alteration stage of degeneration, oxidation enhanced and oxygen fugacity had gradually increased. （5）The U-Pb dating results of cassiterite by the method of LA-MC-ICP-MS indicated that the large-scale tin mineralization of the Dulong orefield had mainly formed in 72.4～96.6Ma regarded as the late Cretaceous, which related closely to the later Yanshanian magmatic hydrothermal events. Compared to the data of the rock-forming and ore-forming chronology from the three super large tin polymetallic deposits of Gejiu, Bainiuchang, Dulong, it was further suggested that there were the Late Yanshanian large-scale granitic magmatism and relative tin polymetallic mineralization in the southeastern Yunnan. （6）Studies showed that magmatic hydrothermalism was the crucial factor for the formation of this deposit, so we should be around the granite, especially concealed granite and the contact zone, to expand the deep and periphery prospecting combined with a favorable structure and the stratigraphic lithology. Geological survey and laboratory study revealed that the early skarn minerals such as grossular, diopside-hedenbergite, vesuvianite still appeared away from areas of deep granite and was followed with certain metals. Hence, it was supposed that the mineralization of Dulong orefield was related to the multiphase magmatic hydrothermalism. So looking for the high-temperature mineralization such as W, Mo, we should not be limited to the area near the deep concealed granite and also should pay attention to the advantageous parts near the shallow granite porphyry vein. |
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