ABSTRACT The chemical compositions of titanite in igneous rocks, hydrothermal veins, skarns, and ... more ABSTRACT The chemical compositions of titanite in igneous rocks, hydrothermal veins, skarns, and hornfels from eight tungsten and molybdenum deposits in Yukon and British Columbia, Canada, were examined by electron probe and LA-ICP-MS. Four kinds of titanite were grouped in our study on the basis of genesis: magmatic titanite from the igneous rocks, hydrothermal titanite from the igneous rocks and hydrothermal veins, metasomatic titanite from the skarn samples, and metamorphic titanite from the hornfels samples. Magmatic titanite is hundreds of mu m long, euhedral or subhedral, and in planar contact with magmatic K-feldspar, plagioclase, and quartz. Compared to hydrothermal titanite, early magmatic titanite (cores) is enriched in Ti, HSFE, and REE, but depleted in Al and F. Magmatic titanite can be enriched in W or Mo, reflecting high concentrations of these elements in the source melt and suggesting that titanite has potential for identifying fertile W or Mo intrusions. The titanite from W skarn samples are enriched in W, Sn, and Nb, which also has a potential application as an indicator for W exploration.
ABSTRACT Niobium and tantalum do not occur naturally as free metals. The charge to ionic ratio of... more ABSTRACT Niobium and tantalum do not occur naturally as free metals. The charge to ionic ratio of tantalum and niobium results in strong bonds being formed with oxygen; in fact, most niobium–tantalum minerals are oxides, rather than silicates, sulfides or phosphates. Three types of niobium and tantalum deposits are: carbonatite-hosted deposits; alkaline to peralkaline granites and syenites; and peraluminous pegmatites and granites. Niobium is recycled when niobium-bearing steels and superalloys are recycled, but scrap recovery specifically for niobium is negligible. Niobium and tantalum ores do not pose any special environmental problems, and standard industry-wide safety and environmental precautions during mining and mineral concentration are satisfactory. Tantalum deposits are widely dispersed, and, like niobium, there are few mines in production. Neither niobium nor tantalum are exchange-traded commodities, with most transaction prices between buyers and sellers subject to long-term confidential contracts.
ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the... more ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of NbâOâ and SnOâ saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or â2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 C and 2 kbar under relatively reducing conditions. Three 'haplogranitic' compositions (a model granite in the system NaâO-KâO-AlOâ-SiOâ) were investigated: peralkaline (labeled 'ASI 0.6'), metaluminous ('ASI 1.0') and peraluminous ('ASI 1.2'). One series of haplogranitic glasses ('SQ') were synthesized at intermediate oxygen fugacity conditions (â10â»â¹ atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated.
ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the... more ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of Nb2O5 and SnO2 saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or ~2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 °C and 2 kbar under relatively reducing conditions. Three "haplogranitic" compositions (a model granite in the system Na2O-K2O-AlO3-SiO2) were investigated: peralkaline (labeled "ASI 0.6"), metaluminous ("ASI 1.0") and peraluminous ("ASI 1.2"). One series of haplogranitic glasses ("SQ") were synthesized at intermediate oxygen fugacity conditions (~10−9 atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated. The tin-bearing glasses show Sn K-edge XAFS spectra that resemble that displayed by eakerite, a Ca-Sn silicate in which Sn(IV)O6 octahedra share corners with SiO4 tetrahedra (Sn-O-Si: 150°). However, the most reduced glasses show significant contributions arising from weakly bound Sn(II)On complexes. The niobium-bearing glasses show Nb K-edge XAFS spectra that most closely resemble that displayed by vuonnemite, a Na-Ti-Nb silicophosphate. Niobium forms NbO6 clusters, also bonded to Si/Al second neighbors. The coordination geometry of niobium in the glasses is strongly influenced by both Nb content and alkalinity; H2O content does not strongly influence the speciation of niobium. Fluorine-bearing Nb-glasses show unusual XANES spectra, which might be related to a decrease in the coordination number of niobium from 6 to 4 (or 5). However, based on Nb K-edge XANES calculations (FEFF 8), fluorine does not appear to complex niobium.
Une série de minéraux et de verres naturels et synthétiques (0.1-5 wt.% Nb 2 O 5 , dopés en H 2 O... more Une série de minéraux et de verres naturels et synthétiques (0.1-5 wt.% Nb 2 O 5 , dopés en H 2 O, en fluor, ou les deux) ont été étudiés par spectroscopie XAFS au seuil K de Nb. Également, une nouvelle méthode ICP-AES est présentée qui permet d'analyser des ...
ABSTRACT The chemical compositions of titanite in igneous rocks, hydrothermal veins, skarns, and ... more ABSTRACT The chemical compositions of titanite in igneous rocks, hydrothermal veins, skarns, and hornfels from eight tungsten and molybdenum deposits in Yukon and British Columbia, Canada, were examined by electron probe and LA-ICP-MS. Four kinds of titanite were grouped in our study on the basis of genesis: magmatic titanite from the igneous rocks, hydrothermal titanite from the igneous rocks and hydrothermal veins, metasomatic titanite from the skarn samples, and metamorphic titanite from the hornfels samples. Magmatic titanite is hundreds of mu m long, euhedral or subhedral, and in planar contact with magmatic K-feldspar, plagioclase, and quartz. Compared to hydrothermal titanite, early magmatic titanite (cores) is enriched in Ti, HSFE, and REE, but depleted in Al and F. Magmatic titanite can be enriched in W or Mo, reflecting high concentrations of these elements in the source melt and suggesting that titanite has potential for identifying fertile W or Mo intrusions. The titanite from W skarn samples are enriched in W, Sn, and Nb, which also has a potential application as an indicator for W exploration.
ABSTRACT Niobium and tantalum do not occur naturally as free metals. The charge to ionic ratio of... more ABSTRACT Niobium and tantalum do not occur naturally as free metals. The charge to ionic ratio of tantalum and niobium results in strong bonds being formed with oxygen; in fact, most niobium–tantalum minerals are oxides, rather than silicates, sulfides or phosphates. Three types of niobium and tantalum deposits are: carbonatite-hosted deposits; alkaline to peralkaline granites and syenites; and peraluminous pegmatites and granites. Niobium is recycled when niobium-bearing steels and superalloys are recycled, but scrap recovery specifically for niobium is negligible. Niobium and tantalum ores do not pose any special environmental problems, and standard industry-wide safety and environmental precautions during mining and mineral concentration are satisfactory. Tantalum deposits are widely dispersed, and, like niobium, there are few mines in production. Neither niobium nor tantalum are exchange-traded commodities, with most transaction prices between buyers and sellers subject to long-term confidential contracts.
ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the... more ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of NbâOâ and SnOâ saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or â2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 C and 2 kbar under relatively reducing conditions. Three 'haplogranitic' compositions (a model granite in the system NaâO-KâO-AlOâ-SiOâ) were investigated: peralkaline (labeled 'ASI 0.6'), metaluminous ('ASI 1.0') and peraluminous ('ASI 1.2'). One series of haplogranitic glasses ('SQ') were synthesized at intermediate oxygen fugacity conditions (â10â»â¹ atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated.
ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the... more ABSTRACT The speciation of niobium and tin in 29 silicate glasses was investigated by XAFS at the Nb and Sn K-edges using beamline 4-3 and 11-2 at SSRL (Stanford, USA). The metal content in the glasses varies between 100 ppm and 5 wt.% (to examine the effects of Nb2O5 and SnO2 saturation in the melt composition prior quenching). The glasses show variation in composition from peralkaline to peraluminous, with either zero or ~2 wt.% fluorine. In addition, hydrous glasses were quenched from water-saturated melts at 850 °C and 2 kbar under relatively reducing conditions. Three "haplogranitic" compositions (a model granite in the system Na2O-K2O-AlO3-SiO2) were investigated: peralkaline (labeled "ASI 0.6"), metaluminous ("ASI 1.0") and peraluminous ("ASI 1.2"). One series of haplogranitic glasses ("SQ") were synthesized at intermediate oxygen fugacity conditions (~10−9 atm.). In addition, 15 model oxide and silicate compounds of tin and niobium were investigated. The tin-bearing glasses show Sn K-edge XAFS spectra that resemble that displayed by eakerite, a Ca-Sn silicate in which Sn(IV)O6 octahedra share corners with SiO4 tetrahedra (Sn-O-Si: 150°). However, the most reduced glasses show significant contributions arising from weakly bound Sn(II)On complexes. The niobium-bearing glasses show Nb K-edge XAFS spectra that most closely resemble that displayed by vuonnemite, a Na-Ti-Nb silicophosphate. Niobium forms NbO6 clusters, also bonded to Si/Al second neighbors. The coordination geometry of niobium in the glasses is strongly influenced by both Nb content and alkalinity; H2O content does not strongly influence the speciation of niobium. Fluorine-bearing Nb-glasses show unusual XANES spectra, which might be related to a decrease in the coordination number of niobium from 6 to 4 (or 5). However, based on Nb K-edge XANES calculations (FEFF 8), fluorine does not appear to complex niobium.
Une série de minéraux et de verres naturels et synthétiques (0.1-5 wt.% Nb 2 O 5 , dopés en H 2 O... more Une série de minéraux et de verres naturels et synthétiques (0.1-5 wt.% Nb 2 O 5 , dopés en H 2 O, en fluor, ou les deux) ont été étudiés par spectroscopie XAFS au seuil K de Nb. Également, une nouvelle méthode ICP-AES est présentée qui permet d'analyser des ...
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