Mineralogical Behavior And Metallogenic Process Of Rare Metals In Granitic Rocks Of Heqiao Area,Northwest Zhejiang

Rare metals,as the"strategic key mineral resource",are always the focus and hotspot of earth science research.The granitic rocks from Heqiao area are located in Lin'an county,northwest Zhejiang Province,and eastern part of Qin-Hang metallogenic belt.A large amount of rare-metal minerals occur in these granitic rocks.In this study,Heqiao granite and Shishisi pegmatite dike have been systematically studied.Based on field and microscopic observations,in combination with petrology,geochemistry,mineralogy and Raman spectroscopy analyses,the aim of this study is to reveal the enrichment,migration,crystallization and mineralization processes of rare metal elements,and discuss the genetic relationships between Heqiao granite and Shishisi pegmatite.The results are as follows:(1)Heqiao granite is characterized by the high contents of SiO2,Al2O3 and F,but low contents of FeOT,MgO,MnO,CaO and P2O5,suggestive of a typical A-type granite.Shishisi pegmatite is typically enriched in Nb,Y and F elements,indicating an NYF-type pegmatite.The U-Pb dating of columbite-(Fe)LA-ICP-MS shows the Shishisi pegmatite formed at 130.5 ± 1.7 Ma,geology,chronology and mineralogy indicating its genetic relationship with Heqiao A-type granite.(2)From Heqiao granite to Shishisi pegmatite,mica evolved from lepidomelane,lepidomelane to zinnwaldite,feldspar gradually evolved into albite,and fluorite is enriched in Y.Besides,the contents of Li,Rb,Nb and Ta increase from the granite to pegmatite,a few amounts of tapiolite and microlite occur in the pegmatite.(3)A large amount of rare metal minerals in granitic rocks from Heqiao area are distinguished:Nb-Ta-W-bearing minerals(columbite-tantalite,tapiolite,Nb-W-bearing minerals,wolframite,microlite etc),Ce-bearing minearls(monazite,fluocerite,bastnaesite,synchysite and aeschynite-(Ce)),Y-bearing minearls(xenotime,fergusonite,polycrase and aeschynite-(Y)),Ti-bearing minearls(rutile and ilmenite),thorite and zircon.They are distributed in granite and pegmatite with different occurrence.The occurrence of the secondary Ce-bearing mineals and aeschynite indicate the hydrothermal activities of Ce,Nb,Ti and Y.(4)During the magmatic stage of Heqiao granitic rocks,zircon,thorite,monazite,xenotime,rutile and ilmenite crystallized;zinnwaldite,columbite-tantalite,fluocerite,polycrase and fergusonite formed in the magmatic-hydrothermal stage;while during hydrothermal stage,amounts of wolframite,wolframoixiolite and secondary Ce-bearing minerals formed.(5)The Nb-W-bearing minerals are characterized by the range from 8.30 to 70.51 wt.%WO3,in combination with the their laser Raman spectroscopy features,they may be one of the polysomic minerals between columbite and wolframite.