Mineralogy And Metallogenic Characteristics Of Beryl In Pingjiang,Hunan Province

Mountain in Pingjiang,located in the northeast of Hunan Province,is an important rare metal mineral producing area in South China.It is rich in beryllium,lithium,niobium,tantalum,copper,lead,zinc and other rare metal deposits and occurences.Beryl is the most important beryllium-containing mineral in this area,which has strong development potential and scientific research value.However,there are currently few studies on the mineralogy and spectroscopy of beryl in this area,and the mineralization characteristics of beryl in this area are lacking.The purpose of this study is to reveal the mineralogical and geochemical characteristics of beryl in Pingjiang by means of conventional gemmological testing,infrared spectroscopy,Raman spectroscopy,electron probe,laser ablation plasma mass spectrometry,etc.,and further analyze the metallogenic characteristics of beryl in Pingjiang by combining with the geochemical characteristics and regional geological situation of granite and pegmatite in each beryl ore spot in this area.Beryl in the area is mostly hexagonal columnar,yellow green,blue green,green blue,with dichroism,low transparency,and relative density of 2.61?2.68.Fractures are developed in the crystal,quartz,mica and other light colored mineral inclusions are common,and fluid inclusions are abundant.The test results of electron probe and laser plasma mass spectrometer show that the mass fraction of R₂O of Pingjiang beryl is almost all greater than 0.5%,which belongs to alkali-containing beryl;Fe(4379?4825 ppm)and Mg(301?700 ppm)are high in content and can be Replaces Al in the beryl lattice;Li is the main element to replace Be,and the unit atom number in the crystal chemical formula is about 0.028?0.060 apfu;Fe is the most important color element,and its content is much higher than that of Cr and V The regular changes of Fe,Mg,Ga,Rb,Cs,Li and other chemical elements in the beryl reflect the chemical composition changes in the magma crystal evolution process.In addition,by comparing the Cs,Na/Cs value,Fe/Mg and Mg content in beryl,and the relationship of Cs-K/Rb value in syngenetic mica inclusions,it reflects the difference of beryl ore-bearing pegmatites at different mining sites.The degree of differentiation evolution is Xiabai Village?Xiangao Village?Tianbao Mountain.The IR and Raman spectra indicate the type I and II water in the beryl.In the Raman spectra of beryl from Pingjiang,the Raman peak at 3595 cm^-1 is wider than that at 3605 cm^-1,which means that the content of type I water is significantly higher than that of type II water.The granite and pegmatite from three beryl sites in Tianbaoshan,Xiabaicun,and Xiangao Village were collected for whole-rock geochemical analysis.The results show that all samples have high Si O₂(73.73?76.23 wt.%)content and aluminum supersaturation index ASI>1,belongs to peraluminous granite.Among them,the geochemical characteristics of the granite xg-1 and pegmatite xg-3 are similar,and the geochemical characteristics of pegmatite xg-3 are close to the basic conditions of rare metal bearing pegmatite.Based on the regional geological and geochemical characteristics,it is found that the fault in Mufushan area of Pingjiang is the structural basis of mineralization;Felsic rocks of I-type or S-type origin are the main material basis of pegmatite magma in this area.Mica rich protoliths provide abundant be sources;Frequent and long-term magmatic activities and continuous crystallization differentiation make be and other rare metal elements gradually enrich in the magma.After intruding into the structural fault zone,they crystallize to form pegmatite without ore first.In the middle and late stage,be mineralization occurs to form beryl,and then Nb,Ta,Li and other rare metal elements will be enriched in this area.