YAN Guo-qiang1,2，DING Jun2，HUANG Yong2，LI Guang-ming2，DAI Jie2，WANG Xin-xin1,3，BAI Jing-guo4
(1. Department of Earth Science, Chengdu University of Technology, Chengdu 610059, China;
2. Chengdu Institute of Geology and Mineral Resource, Chengdu Center, China Geological Survey, Chengdu 610081, China;
3. 217 Geological Team, Shanxi Bureau of Geology and Exploration, Datong 037008, China;
4. Sichuan Institute of Metallurgical Geology and Exploration, Chengdu 610066, China)
Abstract: Scheelite is the main ore mineral in the Nuri Cu-Mo-W deposit, Tibet. Geochemical characteristics of rare earth elements (REE) and trace elements compositions in scheelite were studied. Results show that the scheelite is depleted in V, Cs, Hf and Ta, with extremely low ratios of Rb/Sr, Zr/Hf and Nb/Ta. Ratios of Hf/Sm, Nb/La and Th/La are far less than 1, indicating the feature of original W-rich ore-forming fluid source is from deep crustal magmatic crystallization and differentiation, which is Cl-rich and hydrothermal. Scheelite collected from different locations is characterized by enrichment in light REE and obvious positive Ce anomalies (δCe 1.066－1.107) and weak negative Eu anomalies (δEu 0.768－0.910), showing that REE between scheelite and fluid do not have obvious differentiation. Moreover, both scheelite and the biotite granite connected with skarn have similar distribution of ΣREE, δCe and δEu (basically the same in both) implying that the rock contributes to form scheelite. The original ore-forming fluid is at mid-high temperature with mid-low salinity migrating along structural fractures. It contacted and experienced a metasomatic reaction with the Bima formation layer. With increasing CO2 and Ca contents, the initial balance system was disrupted, and eventually led to the formation of massive scheelite on the basis of Ca2+ and WO42- in combination.
Keywords: scheelite; rare-earth elements; trace elements; ore-forming fluid; Cu-Mo-W deposit; Nuri, Tibet
E-mail: Geoygqiang@163.com
ACTA MINERALOGICA SINICA Vol. 35, No. 1, 2015, Page 87-94
