关键词: NYF型伟晶岩, 稀有稀土矿物, 铌铁矿-黑钨矿多体系列, 铌铁矿U-Pb定年

Abstract: Shishisi pegmatite, a typical Nb-Y-F (NYF) type pegmatite with different kinds of rare and rare earth minerals, occurs in the northwest of Heqiao granite pluton, Lin’an county, Zhejiang Province. Based on field and microscopic observations, in combination with back-scattered electron (BSE) imaging and quantitative electron-microprobe technology (EMPA), the rare and rare earth minerals from Shishisi NYF-type pegmatite are systematically analyzed for the enrichment, migration, crystallization, and mineralization processes of rare and rare earth metal elements in this paper. The results show that (1) many rare and rare earth metal minerals in the Shishisi pegmatite are recognized including Nb-Ta oxide minerals (columbite, tapiolite, microlite etc.), Y-bearing minerals (fergusonite
and polycrase), W-bearing minerals (wolframite, scheelite and Nb-W-bearing minerals), Ce-bearing minerals (monazite, fluocerite and bastnaesite) and Th-bearing minerals. (2) The WO3 content ranges from 8.30 to 70.51 wt.% in Nb-W-bearing minerals, suggesting a series of polysomic minerals between columbite and wolframite. (3) LA-ICP-MS U-Pb dating of columbite-(Fe) from the Shishisi pegmatite yields an age of 133±2 Ma, indicating its genetic relationship with Heqiao granitic pluton. (4) The rare and rare earth elements mineralization processes in Shishisi NYF-type pegmatite were closely related to the crystallization and evolution of magma. During the magmatic stage, zircon, thorite and monazite were crystallized; polycrase, columbite, fergusonite and fluocerite were formed
in the magmatic-hydrothermal stage; wolframite and wolframoixiolite were crystallized in the hydrothermal stage. In the meantime, the early monazite and fluocerite were altered to secondary Ce-bearing minerals by late hydrothermal fluids.

Key words: NYF-type pegmatite, rare and rare earth minerals, polysomic minerals between columbite and wolframite, columbite U-Pb dating