Chevkinite specimen from a rare-earth mineral deposit in Sichuan, southwest of China have been studied in detail by means of transmission electron microscope (TEM).The selected area electron diffraction (SAED)and conv...Chevkinite specimen from a rare-earth mineral deposit in Sichuan, southwest of China have been studied in detail by means of transmission electron microscope (TEM).The selected area electron diffraction (SAED)and convergent beam electron diffraction (CBED) patterns , obtained from different crystal zone axis direction , proved coincidently that the space group of chevkinite is C2/m . Fringe lattice image observation showed the mineral crystal is structurally uniform in microscale , and it is an ideal specimen for electron diffraction analysis . The mineral studied here is similar to the one from Bayan Obo , Inner Mongolia , China , in chemical composition and REE distribution . The chemical formula of the crystal is (Ce , La ,… , Ca) 4 Fe2+ (Fe, Ti, Nb) 2 O8 (Si2O7)2 From our study , we come to the conclusion that the space group of the natural chevkinite is C2/m , instead of P21/a as synthetic one . Up to now , chevkinite compositionally similar to the synthetic one , in which the complete replacements of Ce , La by Nd and Fe by Mg or Co occur , has not been discovered in nature . So we suggest that the name for synthesized chevkinite should be further discussed .展开更多
In the last five decades,Rare Earth Elements(REE)are mostly produced from carbonatite complexes and alkaline magmatic environments.In this respect,pyroclastic flows produced by the potassic-alkaline Gölcük v...In the last five decades,Rare Earth Elements(REE)are mostly produced from carbonatite complexes and alkaline magmatic environments.In this respect,pyroclastic flows produced by the potassic-alkaline Gölcük volcanism in the Isparta(SW,Turkey)angle stand out as an important target area where REE enrichments can be observed.This study focuses on the REE potential,geochemical and mineralogical characteristics of REE-bearing minerals as well as formation modeling of unconsolidated pyroclastic flows in Darıdere-Direkli-Yakaören(DDY)deposits in Turkey.REE-bearing minerals of DDY deposits which contain abundant trachytic-trachyandesitic rock fragments were determined as fluorapatite,britholite,and chevkinite by using XRD and SEM–EDX analyses.According to the geochemical analysis,the vast majority of RREE(up to 996 ppm)content is LREE such as La,Ce and Nd.Darıdere is the most REE enriched region followed by Yakaören and Direkli regions in terms of LREE(574.9 ppm),relative to MREE(38.5 ppm)and HREE(5.28 ppm)contents.These results are also on par with subduction-related Italian extrusive carbonatites such as Polino,Cupaello and San Venenzo.The DDY deposits can also be comparable with intraplate extrusive REE deposits in terms of LREE enrichments,however,HREE,Nb,Th and Zr values are generally lower.The RREE concentrations tend to rise with the increasing contents of alkaline elements(Na and K),HFSE(such as Nb and U),as well as LILE(Ba,Sr and Rb)and are negatively affected by sedimentary carbonate involvement.The economic value of the DDY deposits can gain importance due to the increasing global demand for LREE’s.展开更多
基金Financial support for this study was provided by the Scicnce Foundation of Doctorate Program 8849104-11 from the National Committce of Education
文摘Chevkinite specimen from a rare-earth mineral deposit in Sichuan, southwest of China have been studied in detail by means of transmission electron microscope (TEM).The selected area electron diffraction (SAED)and convergent beam electron diffraction (CBED) patterns , obtained from different crystal zone axis direction , proved coincidently that the space group of chevkinite is C2/m . Fringe lattice image observation showed the mineral crystal is structurally uniform in microscale , and it is an ideal specimen for electron diffraction analysis . The mineral studied here is similar to the one from Bayan Obo , Inner Mongolia , China , in chemical composition and REE distribution . The chemical formula of the crystal is (Ce , La ,… , Ca) 4 Fe2+ (Fe, Ti, Nb) 2 O8 (Si2O7)2 From our study , we come to the conclusion that the space group of the natural chevkinite is C2/m , instead of P21/a as synthetic one . Up to now , chevkinite compositionally similar to the synthetic one , in which the complete replacements of Ce , La by Nd and Fe by Mg or Co occur , has not been discovered in nature . So we suggest that the name for synthesized chevkinite should be further discussed .
基金supported by the CAYDAG(1001)from the Scientific and Technological Research Council of Turkey(TUBITAK)。
文摘In the last five decades,Rare Earth Elements(REE)are mostly produced from carbonatite complexes and alkaline magmatic environments.In this respect,pyroclastic flows produced by the potassic-alkaline Gölcük volcanism in the Isparta(SW,Turkey)angle stand out as an important target area where REE enrichments can be observed.This study focuses on the REE potential,geochemical and mineralogical characteristics of REE-bearing minerals as well as formation modeling of unconsolidated pyroclastic flows in Darıdere-Direkli-Yakaören(DDY)deposits in Turkey.REE-bearing minerals of DDY deposits which contain abundant trachytic-trachyandesitic rock fragments were determined as fluorapatite,britholite,and chevkinite by using XRD and SEM–EDX analyses.According to the geochemical analysis,the vast majority of RREE(up to 996 ppm)content is LREE such as La,Ce and Nd.Darıdere is the most REE enriched region followed by Yakaören and Direkli regions in terms of LREE(574.9 ppm),relative to MREE(38.5 ppm)and HREE(5.28 ppm)contents.These results are also on par with subduction-related Italian extrusive carbonatites such as Polino,Cupaello and San Venenzo.The DDY deposits can also be comparable with intraplate extrusive REE deposits in terms of LREE enrichments,however,HREE,Nb,Th and Zr values are generally lower.The RREE concentrations tend to rise with the increasing contents of alkaline elements(Na and K),HFSE(such as Nb and U),as well as LILE(Ba,Sr and Rb)and are negatively affected by sedimentary carbonate involvement.The economic value of the DDY deposits can gain importance due to the increasing global demand for LREE’s.
