The Study On Gemological And Mineralogical Characteristics Of Bastnasite From Pakistan

The bastnaesite crystals produced in Zagi Mountain in Pakistan are complete and large in size,which can reach gem level.Bastnaesite generally appears in deposits in the form of fine-grained aggregates.Bastnaesite crystals are relatively rare,so there are few studies on its gem mineralogical characteristics.In this paper,through conventional gemological observation test,infrared spectrometer,Raman spectrometer,cold and hot table,electron probe and main trace test of whole rock research on the gem mineralogical characteristics,spectral characteristics,fluid inclusions and surrounding rock of bastnaesite Systematic research on the petrological characteristics.The results of the study are as follows:1.The bastnaesite sample is hexagonal columnar,plate-shaped incomplete crystals or fragments,and the color presents different degrees of brown tones,including lighter orange brown,medium reddish brown,and darker dark brown.The refractive index is:No=1.719?1.735,Ne>1.78.The relative density is 4.61?5.14.Be inert under ultraviolet fluorescent lamp.2.The infrared spectrum test results show that the absorption peak of bastnasite at 870 cm^-1is related to the out of plane bending vibration of CO₃ ^2-,and the absorption peak at 1456 cm^-1,1473 cm^-1 and 1522 cm^-1is related to the asymmetric stretching vibration of CO₃ ^2-,and the similar parisite can be distinguished by the asymmetric stretching vibration.The Raman spectrum shows that the peak at 1096 cm^-1 is related to the symmetric stretching vibration of CO₃ ^2-,and the similar parisite can be distinguished by the symmetric stretching vibration.3.The fluid inclusions inside the bastnaesite crystals are negative crystal,elliptical and irregular,often distributed in isolated,scattered or banded shapes.The size is between 5 and 25?m,the gas filling degree is relatively consistent,and the gas phase percentage is generally between 5 and 15%.Through Raman analysis,it is found that all of them are pure H₂O inclusions,which are composed of liquid H₂O(L_H2O)+gas phase H₂O(V_H2O)at room temperature.The freezing point of inclusions varies from-7.8°C to-15.1°C;the uniform temperature varies from163°C to 302°C,mainly between 214°C to 297°C;fluid salinity ranges from 11.46 to 19.05%;the mineralization pressure is 46?85bar.4.The chemical formula of Pakistan bastnaesite crystal is(Ce0.560?0.610La0.160?0.208Nd0.109?0.167Gd0.031?0.041Sm0.001?0.025Pr0.018?0.024Eu0.006?0.009Y0.006?0.009)0.992(CO₃)F.The main cations are Ce³⁺,La³⁺,Nd³⁺,Pr³⁺,Gd³⁺,Sm³⁺,Eu³⁺,Y³⁺,all of which are rare earth elements.The main minerals of the rock samples are alexandrite,quartz,plagioclase,and albite,and the accessory minerals include zircon,sphene,stellite,manganese,ilmenite,etc.5.The rock sample is green-gray,with a medium-grained structure and a gneissic structure,with linear black materials distributed.The rock sample is quartz monzonite-syenite,which is characterized by potassium,alkalinity,and peraluminum saturation,and belongs to the A-type granite.The total amount of rare earths in rocks is high,the fractionation of light and heavy rare earths is relatively obvious,the light rare earths are relatively enriched,the heavy rare earths are relatively depleted,the?Eu negative anomaly,the rock large ion lithophile elements Rb,Th,U,K are relatively enriched,Nb,Ta,Zr,The content of high field strength elements such as Hf is relatively high.