科研之友
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摘要
The Dulong Sn-Zn polymetallic deposit is located in the western margin of Cathaysia and is one of the largest cassiterite-sulfide deposits in China. Ore bodies mainly occur as strata-bound in skarns within Neoproterozoic Xinzhaiyan Formation, overlying Late Cretaceous granite. The skarn alteration and mineralization can be divided into five stages: garnet-pyroxene stage, actinolite-chlorite stage, magnetite-cassiterite stage, cassiterite-pyrrhotite-sphalerite stage, sphalerite-chalcopyrite stage. The skarn in Dulong deposit was chosen as research object, and the major and trace elements of garnet and pyroxene were analyzed by EPMA and LATCP-MS based on the identification of mineral assemblage and structure. The results show that garnets can be divided into three types and show certain generation characteristics. In the early stage (Grt I ), garnet is andradite (And90-99Gr1-5), most of which is located in the nuclear part, and symbiosis with diopside; Grt II belongs to andradite-grossular solid solution series (And50-80Gr20-50), it is formed late around Grt I and symbiosis with hedenbergite; Grt III is fine-grained grossular (And30-40Gr60-70) formed in the latest stage, and most of which is irregular. The change of mineral assemblages of garnet and pyroxene indicates that the oxidization of fluid decreases gradually. Trace element characteristics show that Grt I displays LREE-enrichment and HREE-depletion, whereas Grt ]]_ displays HREE-enrichment and LREE-depletion. It is suggested that REE distribution may be influenced by the crystal chemical structure of garnet and the solid solution endmember components. Contents of In and Sn in different generations of garnet are also divergent significantly. Contents of In and Sn in andradite (Grt I ) are (63. 0-264. 0) × 10-6 with the average of 159.0 × 10-6, and (2 790-13 100) × 10-6with the average of 7 441 × 10-6, respectively. Contents of In and Sn in grossular (Grt II) are (1. 6-81.0)× 10-6 with the average of 20.0 × 10-6, and (436-4 740) × 10-6 with the average of 2 518 × 10-6, respectively. The positive correlation of contents of In and Sn in garnet implies the simultaneous and homologous relationship between them. There is a certain tendency of selective enrichment in the early stage of skarn formation. Thus, the systematic research of skarn mineralogy and mineral chemistry characteristics is of great significance to effectively constrain the evolution of ore-forming fluid in skarn alteration and mineralization process.
- 出版日期2020
- 单位中国科学院大学
