Journal
ORE GEOLOGY REVIEWS
Volume 80, Issue -, Pages 116-140Publisher
ELSEVIER
DOI: 10.1016/j.oregeorev.2016.06.014
Keywords
Nb(Ta)-Zr(Hf)-REE-Ga mineralization; Emeishan; Alkaline volcanism; Hydrothermal fluids
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Funding
- National Key Basic Research Program of China [2014CB238902]
- National Natural Science Foundation of China [41420104001]
- Program for Changjiang Scholars and Innovative Research Team in University [IRT13099]
- China Scholarship Council [201406430026]
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A previous study briefly described the occurrence of a new type of Nb(Ta)-Zr(Hf)-REY-Ga (REY: rare earth elements and yttrium) polymetallic mineralization in eastern Yunnan, southwest China. In this paper, the mineralogical and geochemical features have been further advanced through a study of two regionally extensive and relatively flat-lying mineralized layers from No. XW drill core. The layers are clay-altered volcanic ash and tuffaceous clay, and are dominated by clay minerals (mixed layer illite/smectite, kaolinite, berthierine, and chamosite); with lesser amounts of quartz and variable amounts of anatase, siderite and calcite; along with trace pyrite, barite, zircon, ilmenite, galena, chalcopyrite, and REE-bearing minerals. The mineralized samples have higher Al2O3/TiO2 values (13.7-41.4) and abundant rare metal elements (Nb, Ta, Zr, Hf, REE, Ga, Th, and U) whereas less mineralized samples are rich in V, Cr, Co, and Ni and have lower Al2O3/TiO2 values (2.32-7.67). The mineralized samples also have strong negative delta Eu in chondrite-normalized REE patterns. Two processes are most likely responsible for the geochemical and mineralogical anomalies of the mineralized samples: airborne volcanic ash and multi-stage injection of low-temperature hydrothermal fluids. Based on paragenetic analysis, this polymetallic mineralization is derived from the interaction between alkaline volcanic ashes and subsequent percolation of low-temperature fluids. The intense and extensive alkaline volcanism of the early Late Permian inferred from this study possibly originated from the coeval Emeishan large igneous province (ELIP). This unique Nb(Ta)-Zr(Hf)-REE-Ga mineralization style has significant economic and geological potential for the study of mineralization of the lowest Xuanwei Formation. (C) 2016 Elsevier B.V. All rights reserved.
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