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WANG Zhong-qiang,LI Chao,ZHANG Ding-cai,JIANG Xiao-jun,ZHOU Li-min,YAN Qing-gao.Implication of in situ Sr Isotope of Scheelite for Tungsten Mineralization: A Case Study of the Nanyangtian Scheelite Deposit, Southeast Yunnan, China[J].Rock and Mineral Analysis,2020,39(2):285-299
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Implication of in situ Sr Isotope of Scheelite for Tungsten Mineralization: A Case Study of the Nanyangtian Scheelite Deposit, Southeast Yunnan, China
Received:August 12, 2019  Revised:September 17, 2019
DOI:10.15898/j.cnki.11-2131/td.201907310117
Key words: scheelite  in situ Sr isotope  mineralization epoch  source of ore-forming fluid  Nanyangtian
Author NameAffiliationE-mail
WANG Zhong-qiang Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China
National Research Center for Geoanalysis, Beijing 100037, China 
 
LI Chao National Research Center for Geoanalysis, Beijing 100037, China
Key Laboratory of Re-Os Isotope Geochemistry, Chinese Academy of Geological Sciences, Beijing 100037, China 
Re-Os@163.com 
ZHANG Ding-cai Wenshan Malipo Zijin Tungsten Group Co., LTD. Wenshan 663600, China  
JIANG Xiao-jun Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China  
ZHOU Li-min National Research Center for Geoanalysis, Beijing 100037, China
Key Laboratory of Re-Os Isotope Geochemistry, Chinese Academy of Geological Sciences, Beijing 100037, China 
 
YAN Qing-gao Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China  
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Abstract:
      BACKGROUND: The Nanyangtian scheelite deposit is an important skarn scheelite deposit in Yunnan Province, which is located in Laojunshan W-Sn deposit area, Southeast Yunnan. Due to its complex geological background and multi-stage metallogenic characteristics, its mineralization age and genesis remain controversial.
OBJECTIVES: To explore the metallogenic age, genesis and material origins of two types of scheelite deposits in order to explore formation patterns.
METHODS: Molybdenum Re-Os isotope dating was used to constrain the age, whereas in situ trace element and in situ Sr isotopes of scheelite were used to determine the composition of trace elements and Sr isotopes in scheelite.
RESULTS: The Re-Os isochron age of molybdenite associated with scheelite in the feldspar-quartz mineral vein of Nanyantian was 151.0±1.3Ma, younger than the age of skarn mineralization, indicating a later mineralization event. The skarn-type scheelite was enriched in light rare earth elements with negative Eu anomaly (δEu=0.46). The average content of ∑REE, Mo and Sr in skarn scheelite were 65.60, 240.16 and 883.43μg/g, respectively. Feldspar-quartz vein-type scheelite showed a flat rare earth pattern with positive Eu anomaly (δEu=2.8) and average content of ∑REE, Mo and Sr were 194.40, 16.01 and 129.26μg/g, respectively. respectively. The skarn scheelite had a relatively low and uniform 87Sr/86Sr value of 0.71319 to 0.71491, indicating that the ore-forming fluids were mainly magmatic-hydrothermal in origin, whereas feldspar-quartz vein type scheelite had a wide 87Sr/86Sr range of 0.71537 to 0.72803, with an average of 0.72079, characteristic of metamorphic fluids.
CONCLUSIONS: The differences in trace and rare earth element contents between two types of mineralization indicate that they have different fluid sources. The negative Eu anomaly of the skarn-type scheelite indicates a high oxygen fugacity environment, whereas the feldspar-quartz vein-type scheelite is formed in a reductive environment in terms of positive Eu anomaly. Sr isotopes of two different types of scheelite display a feature of binary mixing, indicating that feldspar-quartz vein-type scheelite has a superimposed transformation effect on skarn-type scheelite, and the strong metasomatism of ore-forming fluids and surrounding rocks is the key to the formation of scheelite.