Study On The Genesis Of Tourmaline Quartzite In Nanyangtian Scheelite Deposit, Southeast Yunnan

Nanyangtian ore deposit is located in the north of “Yuebei block”, which is the biggest tungsten-based metallic mineral deposit of southeast Yunnan, China. Tourmaline-quartzite(vein) develops considerably with wide scheelite mineralization in the orefield, by which the main ore body is overprinted distinctly. This paper focusing on tourmaline, basing on stripped tourmaline-quartzite and tourmaline quartz vein in Nanyangtian scheelite deposit, through detailed field geological investigation, petrographic study, geochemistry, and B isotopic analysis, combined with fluid inclusion data of Tourmaline-quartzite(vein), makes an thorough study on fluid characteristics, fluid sources of Tourmaline-quartzite(vein) and the genesis of ore deposit. Main achievements are as follows:1. Unscramble and review research progress of tourmaline through three aspects including: genetic mineralogy, B isotopic analysis and application in mineral deposits.2. Find out material source、B source and genesis of tourmaline through major element、trace element and B isotopic geochemistry of tourmaline in “Nanyangtian” orefield. The tourmaline in Nanyangtian ore deposit is all dravite of alkaline tourmaline, without apparent optical zoning and composition zoning and is characteristic of Mgrich、Al-free or Al-poor in Y, higher Fe O/(Fe O+Mg O)(0.46-0.65, mean 0.53); REE distribution curve is similar to that of Laojunshan granite in Late Cretaceous; δ11B is close to δ11B of average crust(-10±3‰), concentrated on-14‰. This features are accordance to postmagmatic hydrothermal tourmaline, which is derived from Ca-poor metamorphic mudstone and sandstone.3. Determine the fluid character of ore-bearing tourmaline quartzite. Characteristics of fluid inclusions shows that homogenization temperature focuses on 250~340℃ and salinity is 3 ~10 wt%Na Cleq; indicate a medium-high tempetature、low salinity ore-forming fluid, which is supposed to be mixture of medium-low salinity magmatic water and low salinity meteoric water.4. Affirm that postmagmatic hydrothermal solution of Late Cretaceous overprinted and enriched the main ore body. The diagenesis and mineralization event caused by lithosphere extension of western Huanan in Late Cretaceous(80-96Ma) contributes to the formation of tungsten deposits.5. Propose that central distance to Late Cretaceous granitic pluton is favorable metallogenic zone, Tourmaline-quartzite(vein)is the significant symbol to find ore shoot. Indicate directions for prospecting in the peripheral area and depth of orefield...