Mineralogical Characteristics and TIMS U-Pb Dating of Tantalite-(Mn) from the Bieyesamas Rare Metal Deposit, Xinjiang

Abstract

BACKGROUND Tantalum is a scarce resource in China. A new breakthrough in ore prospecting was obtained on the tantalum ore in the Bieyesamasi area, Xinjiang, including new occurrences as well as the exploration of pegmatite-type rare metal resources. OBJECTIVES To explore the mineralization age of ore-bearing veins and the mineralogical characteristics of typical columbite-tantalite minerals, tantalite-(Mn) from L18 pegmatite veins, and to evaluate one of the most distinctive minerals in this area. METHODS Electron microprobe was used to characterize mineralogy of tantalite-(Mn), and TIMS U-Pb geochronology of this mineral was used to constrain the age. RESULTS The content of Ta2O5 in tantalite-(Mn) from L18 pegmatite veins ranged from 51.58% to 74.80%, with an average of 68.49%, while Nb2O5 contents varied from 6.15% to 27.63%. Some of the major elements were unevenly distributed and did not show regular banding, with the CaO content in the center of a mineral particle lower than at the edge, and the SiO2 content relatively stable in the cross section. TiO2 and WO3 showed irregular fluctuations. This feature indicated that the tantalite-(Mn) was not formed solely by crystal differentiation, but may be affected by later metasomatism. CONCLUSIONS TIMS U-Pb dating of tantalite-(Mn) yields an age of 160Ma, indicating that the mineralization of L18 pegmatite was formed in the early period of Late Jurassic, different from the surrounding Hercynian granite. It is inferred that Hercynian granite is not the source of L18 pegmatite vein.

Keywords

• tantalite-(mn)
• bieyesamasi deposit
• rare metals
• pegmatite vein
• tims u-pb dating
• columbite-tantalite ore