We studied compositional variations in columbite group minerals (CGM) from several granitic pegmatites of the beryl-columbite subtype in the Maršíkov district, Silesian Domain of the Bohemian Massif, Czech Republic. The CGM are characterized by distinct zoned patterns in BSE images. Primary magmatic homogeneous to oscillatory zoning is preserved in corroded crystal cores, whereas the majority of the crystal volume is replaced by secondary complexly zoned domains formed via post-magmatic processes. The primary domains show relatively uniform evolutionary trends from core to rim, generally with steeply increasing Ta/(Ta + Nb) and negligible to slightly increasing Mn/(Mn + Fe). In contrast, the compositions of secondary CGM domains indicate a reversed evolution, with: (1) steeply decreasing Ta/(Ta + Nb) and relatively constant Mn/(Mn + Fe) characteristics for CGM in the Bienergraben and Scheibengraben pegmatites, and (2) insignificantly decreasing Ta/(Ta + Nb) and strongly decreasing Mn/(Mn + Fe) characteristics for CGM in the Schinderhübel I and Lysá Hora pegmatites. Patchy zoning and secondary evolution in CGM result from metasomatic replacement processes related to fluids. These fluids are probably late-magmatic and exsolved from the residual melt and in later stages locally mixed with external Mg-enriched fluids derived from the host rocks. The presence of volatiles (mainly H2O, F) facilitated high mobility of the elements and replacement of the early CGM. Textural characteristics and compositional variations in CGM show the complex evolution of the pegmatite system from the magmatic stage to subsolidus-hydrothermal conditions.
{"title":"Compositional and textural variations of columbite-group minerals from beryl-columbite pegmatites in the Maršíkov District, Bohemian Massif, Czech Republic: Magmatic versus hydrothermal evolution","authors":"Š. Chládek, P. Uher, M. Novak","doi":"10.3749/canmin.1900093","DOIUrl":"https://doi.org/10.3749/canmin.1900093","url":null,"abstract":"\u0000 We studied compositional variations in columbite group minerals (CGM) from several granitic pegmatites of the beryl-columbite subtype in the Maršíkov district, Silesian Domain of the Bohemian Massif, Czech Republic. The CGM are characterized by distinct zoned patterns in BSE images. Primary magmatic homogeneous to oscillatory zoning is preserved in corroded crystal cores, whereas the majority of the crystal volume is replaced by secondary complexly zoned domains formed via post-magmatic processes. The primary domains show relatively uniform evolutionary trends from core to rim, generally with steeply increasing Ta/(Ta + Nb) and negligible to slightly increasing Mn/(Mn + Fe). In contrast, the compositions of secondary CGM domains indicate a reversed evolution, with: (1) steeply decreasing Ta/(Ta + Nb) and relatively constant Mn/(Mn + Fe) characteristics for CGM in the Bienergraben and Scheibengraben pegmatites, and (2) insignificantly decreasing Ta/(Ta + Nb) and strongly decreasing Mn/(Mn + Fe) characteristics for CGM in the Schinderhübel I and Lysá Hora pegmatites. Patchy zoning and secondary evolution in CGM result from metasomatic replacement processes related to fluids. These fluids are probably late-magmatic and exsolved from the residual melt and in later stages locally mixed with external Mg-enriched fluids derived from the host rocks. The presence of volatiles (mainly H2O, F) facilitated high mobility of the elements and replacement of the early CGM. Textural characteristics and compositional variations in CGM show the complex evolution of the pegmatite system from the magmatic stage to subsolidus-hydrothermal conditions.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2020-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3749/canmin.1900093","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42226042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Gadas, M. Novak, M. Galiova, A. Szuszkiewicz, A. Pieczka, J. Haifler, J. Cempírek
Cordierite-group minerals (cordierite and sekaninaite) from granitic pegmatites are often strongly to completely altered to a fine- or coarse-grained mixture of muscovite, chlorite and/or, biotite, along with several less common secondary minerals, including mainly paragonite, tourmaline, and secondary beryl. The mixture is a common product of early subsolidus hydrothermal alteration at the examined pegmatites of the beryl-columbite subtype – Věžná I and Drahonín (Moldanubian Zone, Czech Republic) and Mount Begbie (Shuswap Complex, Canada); of the beryl-columbite-phosphate subtype – Szklary (Góry Sowie Block, Poland); and of miarolitic intragranitic pegmatites – Zimnik (Massif Strzegom-Sobótka, Poland). We studied in detail (EPMA, LA-ICP-MS) relics of primary cordierite/sekaninaite: Věžná I (Crd77–72Sek27–22MnCrd2–1, Be = 0.39–0.25 apfu, Li = 0.06–0.04 apfu), Drahonín (Crd13–9Sek74–71MnCrd17–16, Be = 0.24–0.18 apfu, Li = 0.07–0.05 apfu), Szklary (Crd50–49Sek30–26MnCrd25–21, Be = 0.45–0.41 apfu, Li ≤ 0.02 apfu), Mount Begbie (Crd34–33Sek53–43MnCrd24–14, Be = 0.33–0.29 apfu, Li = 0.26–0.23 apfu), and Zimnik (Crd2–1Sek75–71MnCrd28–23, Be = 0.25–0.15 apfu, Li = 0.18–0.12 apfu). Secondary beryl has a similar Mg/(Mg+Fe) ratio to its cordierite/sekaninaite precursor but is Mn depleted. The mineral assemblages and textures of the pseudomorphs were examined with a focus on secondary beryl, which forms anhedral grains to subhedral elongated crystals, up to 0.3 mm in size, or aggregates of these in textural equilibrium with associated phyllosilicates and tourmaline. Tourmaline is known from Věžná I, Drahonín, Mount Begbie, and Zimnik, the last also with topaz and “zinnwaldite” (a mineral with chemical composition between siderophyllite and polylithionite). Secondary beryl in pseudomorphs after cordierite/sekaninaite from granitic pegmatites and more evolved granites may have been often overlooked; hence, we present its textures and morphology so that it can be recognized during routine EPMA study and to study the source of elevated concentrations of Be in primary cordierite/sekaninaite. The empirical limit of detection of secondary beryl in pseudomorphs is ∼500–1000 ppm Be, which corresponds to ∼1–2 vol.% of secondary beryl. The chemical composition of the secondary beryl and other minerals indicate that the fluids responsible for the alteration were exsolved from the residual pegmatite melt and were not contaminated by fluids from the host rocks.
{"title":"Secondary beryl in cordierite/sekaninaite pseudomorphs from granitic pegmatites – A monitor of elevated content of beryllium in the precursor","authors":"P. Gadas, M. Novak, M. Galiova, A. Szuszkiewicz, A. Pieczka, J. Haifler, J. Cempírek","doi":"10.3749/canmin.2000014","DOIUrl":"https://doi.org/10.3749/canmin.2000014","url":null,"abstract":"\u0000 Cordierite-group minerals (cordierite and sekaninaite) from granitic pegmatites are often strongly to completely altered to a fine- or coarse-grained mixture of muscovite, chlorite and/or, biotite, along with several less common secondary minerals, including mainly paragonite, tourmaline, and secondary beryl. The mixture is a common product of early subsolidus hydrothermal alteration at the examined pegmatites of the beryl-columbite subtype – Věžná I and Drahonín (Moldanubian Zone, Czech Republic) and Mount Begbie (Shuswap Complex, Canada); of the beryl-columbite-phosphate subtype – Szklary (Góry Sowie Block, Poland); and of miarolitic intragranitic pegmatites – Zimnik (Massif Strzegom-Sobótka, Poland). We studied in detail (EPMA, LA-ICP-MS) relics of primary cordierite/sekaninaite: Věžná I (Crd77–72Sek27–22MnCrd2–1, Be = 0.39–0.25 apfu, Li = 0.06–0.04 apfu), Drahonín (Crd13–9Sek74–71MnCrd17–16, Be = 0.24–0.18 apfu, Li = 0.07–0.05 apfu), Szklary (Crd50–49Sek30–26MnCrd25–21, Be = 0.45–0.41 apfu, Li ≤ 0.02 apfu), Mount Begbie (Crd34–33Sek53–43MnCrd24–14, Be = 0.33–0.29 apfu, Li = 0.26–0.23 apfu), and Zimnik (Crd2–1Sek75–71MnCrd28–23, Be = 0.25–0.15 apfu, Li = 0.18–0.12 apfu). Secondary beryl has a similar Mg/(Mg+Fe) ratio to its cordierite/sekaninaite precursor but is Mn depleted. The mineral assemblages and textures of the pseudomorphs were examined with a focus on secondary beryl, which forms anhedral grains to subhedral elongated crystals, up to 0.3 mm in size, or aggregates of these in textural equilibrium with associated phyllosilicates and tourmaline. Tourmaline is known from Věžná I, Drahonín, Mount Begbie, and Zimnik, the last also with topaz and “zinnwaldite” (a mineral with chemical composition between siderophyllite and polylithionite). Secondary beryl in pseudomorphs after cordierite/sekaninaite from granitic pegmatites and more evolved granites may have been often overlooked; hence, we present its textures and morphology so that it can be recognized during routine EPMA study and to study the source of elevated concentrations of Be in primary cordierite/sekaninaite. The empirical limit of detection of secondary beryl in pseudomorphs is ∼500–1000 ppm Be, which corresponds to ∼1–2 vol.% of secondary beryl. The chemical composition of the secondary beryl and other minerals indicate that the fluids responsible for the alteration were exsolved from the residual pegmatite melt and were not contaminated by fluids from the host rocks.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"785-802"},"PeriodicalIF":0.9,"publicationDate":"2020-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49185196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Santos, I. M. B. A. Souza, S. B. Barreto, José Ferreira de Araújo Neto, A. Müller
The recently discovered Serra Branca amazonite pegmatite in the state of Paraíba, Brazil, is an evolved niobium-yttrium-fluorine (NYF) granitic pegmatite, which belongs to the Vieirópolis pegmatite field, the first NYF pegmatite field described from the Borborema Province. The pegmatite is an unusually large resource (>300,000 tons) of intensely colored amazonite megacrysts up to 2 m in size, exploited in an open pit since ca. 2010 as an ornamental stone and gemological material. This study provides the first mineralogical and geochemical characterization of the Serra Branca amazonite pegmatite and its mineralogy, which are further compared with the mineralogy and composition of other NYF pegmatites. The Serra Branca pegmatite forms an approximately 800 m-long and up to 3 m-thick flat-dipping sheet that consists of two distinct structural-mineralogical zones with complex relationships: (1) the massive, megacrystic amazonite zone forming commonly in the upper part of the dike and (2) the fine-grained albite zone commonly occurring at the bottom of the dike. The amazonite zone, which comprises ca. 75 vol.% of the pegmatite body, is composed of amazonite and quartz, the major constituents, with accessory biotite, helvine, galena, ilmenite, hematite, columbite-(Mn), phenakite, titanite, magnetite, and rutile. The albite zone consists of saccharoidal albite and quartz and accessory spessartine, ilmenite, zircon, columbite-(Mn), pyrochlore, and fluorite. A younger minor intrusive pegmatitic unit composed of megacrystic euhedral amazonite and quartz and platy albite (cleavelandite) postdates the formation of the amazonite and albite zones. Geochemical analysis of the bulk pegmatite, amazonite zone, and albite zone shows that the bulk pegmatite and the amazonite zone have similar compositions, with high trace-element contents of Ba, Be, Rb, Sr, and Pb, whereas the albite zone is enriched in Zn, Nb, Zr, Ga, and Hf. The amazonite and albite zones display some similarities in terms of major elements, the presence of HFSE minerals, and the distribution of incompatible and REE, which indicates that the two zones originated from the same melt. The amazonite crystals are enriched in Rb, Pb, Sr, Cs, Ba, Tl, Fe, and Ga, characterizing the Serra Branca pegmatite as an evolved NYF pegmatite. This conclusion is confirmed by the low K/Rb ratio of biotite of ∼5.7. Higher Li and Ga and lower Sr and Ba in the amazonite of the minor unit suggests that this melt was even more highly fractionated than the melt of the first emplacement stage.
{"title":"The Serra Branca amazonite pegmatite of the Vieirópolis pegmatite field, Paraíba, Brazil: A new and unusual megacrystic amazonite deposit","authors":"G. Santos, I. M. B. A. Souza, S. B. Barreto, José Ferreira de Araújo Neto, A. Müller","doi":"10.3749/canmin.1900095","DOIUrl":"https://doi.org/10.3749/canmin.1900095","url":null,"abstract":"\u0000 The recently discovered Serra Branca amazonite pegmatite in the state of Paraíba, Brazil, is an evolved niobium-yttrium-fluorine (NYF) granitic pegmatite, which belongs to the Vieirópolis pegmatite field, the first NYF pegmatite field described from the Borborema Province. The pegmatite is an unusually large resource (>300,000 tons) of intensely colored amazonite megacrysts up to 2 m in size, exploited in an open pit since ca. 2010 as an ornamental stone and gemological material. This study provides the first mineralogical and geochemical characterization of the Serra Branca amazonite pegmatite and its mineralogy, which are further compared with the mineralogy and composition of other NYF pegmatites. The Serra Branca pegmatite forms an approximately 800 m-long and up to 3 m-thick flat-dipping sheet that consists of two distinct structural-mineralogical zones with complex relationships: (1) the massive, megacrystic amazonite zone forming commonly in the upper part of the dike and (2) the fine-grained albite zone commonly occurring at the bottom of the dike. The amazonite zone, which comprises ca. 75 vol.% of the pegmatite body, is composed of amazonite and quartz, the major constituents, with accessory biotite, helvine, galena, ilmenite, hematite, columbite-(Mn), phenakite, titanite, magnetite, and rutile. The albite zone consists of saccharoidal albite and quartz and accessory spessartine, ilmenite, zircon, columbite-(Mn), pyrochlore, and fluorite. A younger minor intrusive pegmatitic unit composed of megacrystic euhedral amazonite and quartz and platy albite (cleavelandite) postdates the formation of the amazonite and albite zones. Geochemical analysis of the bulk pegmatite, amazonite zone, and albite zone shows that the bulk pegmatite and the amazonite zone have similar compositions, with high trace-element contents of Ba, Be, Rb, Sr, and Pb, whereas the albite zone is enriched in Zn, Nb, Zr, Ga, and Hf. The amazonite and albite zones display some similarities in terms of major elements, the presence of HFSE minerals, and the distribution of incompatible and REE, which indicates that the two zones originated from the same melt. The amazonite crystals are enriched in Rb, Pb, Sr, Cs, Ba, Tl, Fe, and Ga, characterizing the Serra Branca pegmatite as an evolved NYF pegmatite. This conclusion is confirmed by the low K/Rb ratio of biotite of ∼5.7. Higher Li and Ga and lower Sr and Ba in the amazonite of the minor unit suggests that this melt was even more highly fractionated than the melt of the first emplacement stage.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"679-702"},"PeriodicalIF":0.9,"publicationDate":"2020-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42771897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Hatert, F. D. Bo, Yannick Bruni, N. Meisser, P. Vignola, A. Risplendente, François-Xavier Châtenet, Julien Lebocey
Limousinite, ideally BaCa[Be4P4O16]·6H2O, is a new beryllophosphate mineral discovered in the Vilatte-Haute pegmatite, Chanteloube near Razès, Limousin, Haute-Vienne, France. The new mineral is intimately associated with microcrystalline pale brown greifensteinite, black amorphous vitreous Mn-oxyhydroxide, triplite, and quartz. It forms isolated, partly corroded, colorless to snow-white crystals up to 0.9 mm long, showing rhombic cross sections. Limousinite is transparent with a vitreous luster, non-fluorescent, without cleavage planes; its calculated density is 2.58 g/cm3. Optically, the mineral is biaxial negative, α = 1.532(2), β = 1.553(3), γ = 1.558(2) (measured under 589 nm wavelength light), 2Vcalc. = 18°, non-dispersive, with Z parallel to the elongation of the prismatic crystals. Electron-microprobe analyses indicate an empirical formula of (Ba0.91K0.07)Σ0.98(Ca0.87Na0.05)Σ0.92[(Be3.87Al0.13)Σ4P4O16]·5.56H2O, calculated on the basis of 4 P atoms per formula unit, assuming 4 (Be + Al) pfu and a water content calculated from refined site-occupancy factors. A single-crystal structure refinement was performed to R1 = 4.90%, in the P21/c space group, with a = 9.4958(4), b = 13.6758(4), c = 13.4696(4) Å, β = 90.398(3)°, V = 1749.15(10) Å3, Z = 4. The crystal structure is characterized by a beryllophosphate framework similar to that of phillipsite-group zeolites, based on corner-sharing BeO4 and PO4 tetrahedra forming interconnected four- and eight-membered rings. Large cages within this zeolite framework contain Ba, Ca, and water molecules. Limousinite is the third known natural zeolite-type beryllophosphate, together with pahasapaite and wilancookite; it is also the first phosphate with a framework identical to that of a natural zeolite silicate.
{"title":"Limousinite, BaCa[Be4P4O16]·6H2O, a new beryllophosphate mineral with a phillipsite-type framework","authors":"F. Hatert, F. D. Bo, Yannick Bruni, N. Meisser, P. Vignola, A. Risplendente, François-Xavier Châtenet, Julien Lebocey","doi":"10.3749/canmin.2000007","DOIUrl":"https://doi.org/10.3749/canmin.2000007","url":null,"abstract":"\u0000 Limousinite, ideally BaCa[Be4P4O16]·6H2O, is a new beryllophosphate mineral discovered in the Vilatte-Haute pegmatite, Chanteloube near Razès, Limousin, Haute-Vienne, France. The new mineral is intimately associated with microcrystalline pale brown greifensteinite, black amorphous vitreous Mn-oxyhydroxide, triplite, and quartz. It forms isolated, partly corroded, colorless to snow-white crystals up to 0.9 mm long, showing rhombic cross sections. Limousinite is transparent with a vitreous luster, non-fluorescent, without cleavage planes; its calculated density is 2.58 g/cm3. Optically, the mineral is biaxial negative, α = 1.532(2), β = 1.553(3), γ = 1.558(2) (measured under 589 nm wavelength light), 2Vcalc. = 18°, non-dispersive, with Z parallel to the elongation of the prismatic crystals. Electron-microprobe analyses indicate an empirical formula of (Ba0.91K0.07)Σ0.98(Ca0.87Na0.05)Σ0.92[(Be3.87Al0.13)Σ4P4O16]·5.56H2O, calculated on the basis of 4 P atoms per formula unit, assuming 4 (Be + Al) pfu and a water content calculated from refined site-occupancy factors. A single-crystal structure refinement was performed to R1 = 4.90%, in the P21/c space group, with a = 9.4958(4), b = 13.6758(4), c = 13.4696(4) Å, β = 90.398(3)°, V = 1749.15(10) Å3, Z = 4. The crystal structure is characterized by a beryllophosphate framework similar to that of phillipsite-group zeolites, based on corner-sharing BeO4 and PO4 tetrahedra forming interconnected four- and eight-membered rings. Large cages within this zeolite framework contain Ba, Ca, and water molecules. Limousinite is the third known natural zeolite-type beryllophosphate, together with pahasapaite and wilancookite; it is also the first phosphate with a framework identical to that of a natural zeolite silicate.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"815-827"},"PeriodicalIF":0.9,"publicationDate":"2020-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46291367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. A. Galliski, E. Roda-Robles, F. Hatert, M. F. Márquez-Zavalía, Viviana A Martínez
La Viquita is a rare-element pegmatite of LCT signature, REL-Li subclass, spodumene subtype, that shows Fe > Mn mineral paragenesis instead of Mn > Fe, which is more common in the rare-element pegmatite population of the San Luis ranges. The phosphate mineral association of this pegmatite can be subdivided into (1) primary, with dendritic triphylite [(Fe/(Fe + Mn) = 0.72] and montebrasite–amblygonite as main phases; (2) metasomatic, with subsolidus replacement of triphylite by ferrisicklerite and heterosite; and (3) hydrothermal, with secondary growth of alluaudite at the expense of heterosite and wardite from montebrasite caused by Na-metasomatism. A Ca-rich influx under oxidizing conditions produced childrenite–eosphorite–ernstite, jahnsite-(CaMnFe), and kingsmountite. Apatite-group minerals are present throughout the processes. Very late-stage solutions formed millimetric crystals of hydroxylherderite associated with hydroxylapatite in cavities in K-feldspar.
{"title":"The Phosphate mineral assemblages from La Viquita Pegmatite, San Luis, Argentina","authors":"M. A. Galliski, E. Roda-Robles, F. Hatert, M. F. Márquez-Zavalía, Viviana A Martínez","doi":"10.3749/CANMIN.1900106","DOIUrl":"https://doi.org/10.3749/CANMIN.1900106","url":null,"abstract":"\u0000 La Viquita is a rare-element pegmatite of LCT signature, REL-Li subclass, spodumene subtype, that shows Fe > Mn mineral paragenesis instead of Mn > Fe, which is more common in the rare-element pegmatite population of the San Luis ranges. The phosphate mineral association of this pegmatite can be subdivided into (1) primary, with dendritic triphylite [(Fe/(Fe + Mn) = 0.72] and montebrasite–amblygonite as main phases; (2) metasomatic, with subsolidus replacement of triphylite by ferrisicklerite and heterosite; and (3) hydrothermal, with secondary growth of alluaudite at the expense of heterosite and wardite from montebrasite caused by Na-metasomatism. A Ca-rich influx under oxidizing conditions produced childrenite–eosphorite–ernstite, jahnsite-(CaMnFe), and kingsmountite. Apatite-group minerals are present throughout the processes. Very late-stage solutions formed millimetric crystals of hydroxylherderite associated with hydroxylapatite in cavities in K-feldspar.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"733-746"},"PeriodicalIF":0.9,"publicationDate":"2020-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43948577","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fábio André Craveiro Martins, M. Azevedo, B. V. Aguado, E. P. Gomes, C. Tassinari, J. Neto
The Variscan Bemposta Migmatite Complex (BMC) in northern Portugal (Central Iberian Zone) is a NE–SW-trending high-grade metamorphic core complex comprising upper-amphibolite- to lower-granulite-facies metapelites and metagreywackes of Ediacaran-Cambrian age and subordinate Ordovician orthogneisses showing evidence of intense migmatization. The available petrological data indicate that these rocks attained peak metamorphic conditions at the end of the first Variscan contractional deformation event (D1), followed an isothermal decompression path during D2 crustal extension, and underwent subsequent retrogression during D3 shearing. The whole BMC complex hosts numerous concordant intrusive bodies (sheets several meters thick) of syn-D2 two-mica granites, genetically linked to the leucosomes, suggesting that the emplacement of these magmas was synchronous with core complex extension. U-Pb SHRIMP ages obtained from zircons from one of these syn-D2 tabular plutons (the Faia d'Água Alta granite) yielded a crystallization age of 324 ± 3 Ma, providing a good estimate for the age of the D2 anatectic event in the region.
{"title":"SHRIMP U-Pb ages and REE patterns for zircon from an anatectic Variscan two-mica granite from the Bemposta Migmatite Complex (Central Iberian Zone)","authors":"Fábio André Craveiro Martins, M. Azevedo, B. V. Aguado, E. P. Gomes, C. Tassinari, J. Neto","doi":"10.3749/CANMIN.2000015","DOIUrl":"https://doi.org/10.3749/CANMIN.2000015","url":null,"abstract":"\u0000 The Variscan Bemposta Migmatite Complex (BMC) in northern Portugal (Central Iberian Zone) is a NE–SW-trending high-grade metamorphic core complex comprising upper-amphibolite- to lower-granulite-facies metapelites and metagreywackes of Ediacaran-Cambrian age and subordinate Ordovician orthogneisses showing evidence of intense migmatization.\u0000 The available petrological data indicate that these rocks attained peak metamorphic conditions at the end of the first Variscan contractional deformation event (D1), followed an isothermal decompression path during D2 crustal extension, and underwent subsequent retrogression during D3 shearing.\u0000 The whole BMC complex hosts numerous concordant intrusive bodies (sheets several meters thick) of syn-D2 two-mica granites, genetically linked to the leucosomes, suggesting that the emplacement of these magmas was synchronous with core complex extension.\u0000 U-Pb SHRIMP ages obtained from zircons from one of these syn-D2 tabular plutons (the Faia d'Água Alta granite) yielded a crystallization age of 324 ± 3 Ma, providing a good estimate for the age of the D2 anatectic event in the region.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"847-861"},"PeriodicalIF":0.9,"publicationDate":"2020-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44040358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Kampf, M. Cooper, B. Nash, J. Marty, P. Adams, J. Plášil, J. Sejkora
Fulbrightite (IMA2019–032), Ca(VO)2(AsO4)2·4H2O, is a new mineral from the Packrat mine, near Gateway, Mesa County, Colorado, USA, and from the Rovnost mine, Jáchymov, Czech Republic. It is a low-temperature secondary phase. The mineral most typically occurs in shades of light green and forms rosettes of roughly square (pseudotetragonal) plates. The streak is colorless to pale green and the luster is vitreous to pearly. The Mohs hardness is about 2½. Crystals are brittle, but slightly flexible in thin plates. Cleavages are (001) perfect, (100) and (010) excellent, (110) and fair. Fracture is stepped, irregular, and curved. The measured density is 3.12(2) g/cm3. The mineral is optically biaxial (–), α = 1.675(3), β = 1.718(3), and γ = 1.718(3) (white light); 2V ≈ 5°; orientation: X ≈ c; pleochroism: X colorless, Y and Z pale green (X < Y = Z). Electron-microprobe analyses gave the empirical formulae Ca0.99(V4+1.00O)2[(As5+0.98V5+0.02)O4]2·4(H2.005O) (Packrat mine) and (Ca1.02Fe0.01Ba0.01)Σ1.04(V4+O)1.96[(As5+0.99P0.01)O4]2·4.04H2O (Rovnost mine). X-ray powder diffraction (coupled with the chemical analyses) showed fulbrightite to be the arsenate analog of sincosite. The mineral is triclinic, space group P1, with cell parameters a = 6.434(8), b = 6.480(8), c = 6.718(8) Å, α = 107.90(6), β = 94.06(4), γ = 90.06(3)°, V = 265.8(6) Å3, and Z = 1. The Raman and infrared spectra of fulbrightite and sincosite are consistent with them being arsenate and phosphate analogs, respectively.
{"title":"Fulbrightite, the Arsenate Analog of Sincosite","authors":"A. Kampf, M. Cooper, B. Nash, J. Marty, P. Adams, J. Plášil, J. Sejkora","doi":"10.3749/canmin.2000034","DOIUrl":"https://doi.org/10.3749/canmin.2000034","url":null,"abstract":"\u0000 Fulbrightite (IMA2019–032), Ca(VO)2(AsO4)2·4H2O, is a new mineral from the Packrat mine, near Gateway, Mesa County, Colorado, USA, and from the Rovnost mine, Jáchymov, Czech Republic. It is a low-temperature secondary phase. The mineral most typically occurs in shades of light green and forms rosettes of roughly square (pseudotetragonal) plates. The streak is colorless to pale green and the luster is vitreous to pearly. The Mohs hardness is about 2½. Crystals are brittle, but slightly flexible in thin plates. Cleavages are (001) perfect, (100) and (010) excellent, (110) and fair. Fracture is stepped, irregular, and curved. The measured density is 3.12(2) g/cm3. The mineral is optically biaxial (–), α = 1.675(3), β = 1.718(3), and γ = 1.718(3) (white light); 2V ≈ 5°; orientation: X ≈ c; pleochroism: X colorless, Y and Z pale green (X < Y = Z). Electron-microprobe analyses gave the empirical formulae Ca0.99(V4+1.00O)2[(As5+0.98V5+0.02)O4]2·4(H2.005O) (Packrat mine) and (Ca1.02Fe0.01Ba0.01)Σ1.04(V4+O)1.96[(As5+0.99P0.01)O4]2·4.04H2O (Rovnost mine). X-ray powder diffraction (coupled with the chemical analyses) showed fulbrightite to be the arsenate analog of sincosite. The mineral is triclinic, space group P1, with cell parameters a = 6.434(8), b = 6.480(8), c = 6.718(8) Å, α = 107.90(6), β = 94.06(4), γ = 90.06(3)°, V = 265.8(6) Å3, and Z = 1. The Raman and infrared spectra of fulbrightite and sincosite are consistent with them being arsenate and phosphate analogs, respectively.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"663-671"},"PeriodicalIF":0.9,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41840175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The concept of metamorphic facies has been used as a tool in the interpretation of metamorphic rocks for almost 100 years. The preferred definition is a set of mineral assemblages which are repeatedly associated in space and time. Equilibrium or physical conditions (pressure-temperature) should not be part of the definition. The emphasis has always been on identification of the minerals with the petrographic microscope. Chemical analyses of the minerals using the electron microprobe is not necessary. The original definition of metamorphic facies used the metamorphic mineralogy of metabasic rocks. This bulk composition is not useful for the definition of all metamorphic facies. Several critical minerals in metabasic rocks cannot be readily identified with a petrographic microscope (albite versus oligoclase and actinolite versus hornblende). A revised set of metamorphic facies is proposed and mineral assemblages in both metabasic and pelitic rocks are outlined to provide definitions of the individual facies. Metamorphic facies should not be used to give quantitative estimates of P-T conditions. Only relative P-T can be estimated. The interpretation of “equilibrium” in metamorphic facies can be modeled using the Gibbs phase rule and simple assumptions about phases and components. This leads to an interpretation that metamorphic facies could represent divariant or higher variance equilibrium.
{"title":"Metamorphic facies: A review and some suggestions for changes","authors":"E. Ghent","doi":"10.3749/canmin.1900078","DOIUrl":"https://doi.org/10.3749/canmin.1900078","url":null,"abstract":"\u0000 The concept of metamorphic facies has been used as a tool in the interpretation of metamorphic rocks for almost 100 years. The preferred definition is a set of mineral assemblages which are repeatedly associated in space and time. Equilibrium or physical conditions (pressure-temperature) should not be part of the definition. The emphasis has always been on identification of the minerals with the petrographic microscope. Chemical analyses of the minerals using the electron microprobe is not necessary. The original definition of metamorphic facies used the metamorphic mineralogy of metabasic rocks. This bulk composition is not useful for the definition of all metamorphic facies. Several critical minerals in metabasic rocks cannot be readily identified with a petrographic microscope (albite versus oligoclase and actinolite versus hornblende). A revised set of metamorphic facies is proposed and mineral assemblages in both metabasic and pelitic rocks are outlined to provide definitions of the individual facies. Metamorphic facies should not be used to give quantitative estimates of P-T conditions. Only relative P-T can be estimated. The interpretation of “equilibrium” in metamorphic facies can be modeled using the Gibbs phase rule and simple assumptions about phases and components. This leads to an interpretation that metamorphic facies could represent divariant or higher variance equilibrium.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"437-444"},"PeriodicalIF":0.9,"publicationDate":"2020-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3749/canmin.1900078","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45269308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work we present the results of experimental interaction of gabbro-syenite melt, corresponding to the average composition of Northern Timan rocks, with a complex hydrogen-containing fluid. The composition of the magmatic fluid was controlled to be close to natural conditions using a special cell in a high gas-pressure vessel. Under superliquidus conditions, the initial melt exsolves into melts of different composition, forming contrast, cryptic, and rhythmic melt stratifications. The experimental results agree with natural data in the petrochemical diagram. It follows from our experimental data that fluid-saturated melts in magmatic chambers are completely differentiated in the liquid state. In the absence of temperature gradients in the magma, gravitational migration of nanoclusters of different densities forms flotation, sedimentation, and rhythmic types of melt stratification. Transmission electron microscopy of the glasses formed in the cell was used to study the formation of nanoclusters in a fluid-saturated superliquidus anorthosite-granite model melt. Clusters with a size of 6 nm consist of a pseudo-crystalline anorthite core surrounded by fluid-saturated shells of the melt. The migration of fluid and fluid-enriched clusters to the upper part of the magmatic chamber results in the activation, from bottom to top, of the processes of crystallization in the magma.
{"title":"Experimental study of the differentiation of gabbro-syenite melt under superliquidus conditions","authors":"N. Bezmen, P. Gorbachev, R. Seltmann","doi":"10.3749/canmin.1900057","DOIUrl":"https://doi.org/10.3749/canmin.1900057","url":null,"abstract":"In this work we present the results of experimental interaction of gabbro-syenite melt, corresponding to the average composition of Northern Timan rocks, with a complex hydrogen-containing fluid. The composition of the magmatic fluid was controlled to be close to natural conditions using a special cell in a high gas-pressure vessel. Under superliquidus conditions, the initial melt exsolves into melts of different composition, forming contrast, cryptic, and rhythmic melt stratifications. The experimental results agree with natural data in the petrochemical diagram. It follows from our experimental data that fluid-saturated melts in magmatic chambers are completely differentiated in the liquid state. In the absence of temperature gradients in the magma, gravitational migration of nanoclusters of different densities forms flotation, sedimentation, and rhythmic types of melt stratification. Transmission electron microscopy of the glasses formed in the cell was used to study the formation of nanoclusters in a fluid-saturated superliquidus anorthosite-granite model melt. Clusters with a size of 6 nm consist of a pseudo-crystalline anorthite core surrounded by fluid-saturated shells of the melt. The migration of fluid and fluid-enriched clusters to the upper part of the magmatic chamber results in the activation, from bottom to top, of the processes of crystallization in the magma.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"445-460"},"PeriodicalIF":0.9,"publicationDate":"2020-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3749/canmin.1900057","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44850191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Northstarite, Pb6(Te4+O3)5(S2O3), is a new mineral from the North Star mine, Tintic district, Juab County, Utah, USA. It is an oxidation-zone mineral occuring in a vug in massive quartz-baryte-enargite-pyrite in association with anglesite, azurite, chrysocolla, fluorapatite, plumbogummite, tellurite, zincospiroffite, and the new mineral adanite. Crystals are beige short prisms with pyramidal terminations, up to about 1 mm in length. The mineral is transparent to translucent with adamantine luster, white streak, Mohs hardness 2, brittle tenacity, irregular fracture, and no cleavage. The calculated density is 6.888 g/cm3. Northstarite is uniaxial (–) and nonpleochroic. The Raman spectrum is consistent with the presence of tellurite and thiosulfate groups and the absence of OH and H2O. Electron-microprobe analyses gave the empirical formula Pb5.80Sb3+0.05Te4+5.04S6+1.02S2–1.02O18. The mineral is hexagonal, space group P63, with a = 10.2495(5), c = 11.6677(8) Å, V = 1061.50(13) Å3, and Z = 2. The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 3.098(100)(113), 2.957(88)(300), 2.140(42)(223), 1.7335(41)(413), and 1.6256(31)(306). The structure (R1 = 0.033 for 1476 I > 2σI reflections) is a framework constructed of short (strong) Pb–O and Te–O bonds with channels along the 63 axes. The thiosulfate groups at the centers of the channels are only weakly bonded to the framework.
Northstarite (Pb6(Te4+O3)5(S2O3))是美国犹他州Juab县Tintic地区North Star矿的一种新矿物。它是一种氧化带矿物，赋存于块状石英-重晶石-辉石-黄铁矿中的孔洞中，伴生有菱镁石、蓝铜矿、黄铜矿、氟磷灰石、铅铅矿、碲矿、锌榴辉石和新矿物阿铁长石。晶体是米色的短棱镜，末端呈锥体状，长度可达1毫米左右。该矿物透明至半透明，具有金刚光泽，白色条纹，莫氏硬度2，脆韧性，不规则断裂，无解理。计算密度为6.888 g/cm3。北星岩是单轴(-)和非多时性的。拉曼光谱与碲和硫代硫酸盐基团的存在一致，没有OH和H2O。电子探针分析得到经验式Pb5.80Sb3+0.05Te4+5.04S6+ 1.02S2-1.02O18。矿物为六边形，空间群为P63, a = 10.2495(5)， c = 11.6677(8) Å， V = 1061.50(13) Å3, Z = 2。5条最强的x射线粉末衍射线为[dobs Å(I)(hkl)]: 3.098(100)(113)、2.957(88)(300)、2.140(42)(223)、1.7335(41)(413)和1.6256(31)(306)。该结构是由短(强)Pb-O和Te-O键组成的框架，沿63轴有通道。通道中心的硫代硫酸盐基团仅与骨架弱结合。
{"title":"Northstarite, a new lead-tellurite-thiosulfate mineral from the North Star mine, Tintic, Utah, USA","authors":"A. Kampf, R. Housley, G. Rossman","doi":"10.3749/canmin.1900105","DOIUrl":"https://doi.org/10.3749/canmin.1900105","url":null,"abstract":"Northstarite, Pb6(Te4+O3)5(S2O3), is a new mineral from the North Star mine, Tintic district, Juab County, Utah, USA. It is an oxidation-zone mineral occuring in a vug in massive quartz-baryte-enargite-pyrite in association with anglesite, azurite, chrysocolla, fluorapatite, plumbogummite, tellurite, zincospiroffite, and the new mineral adanite. Crystals are beige short prisms with pyramidal terminations, up to about 1 mm in length. The mineral is transparent to translucent with adamantine luster, white streak, Mohs hardness 2, brittle tenacity, irregular fracture, and no cleavage. The calculated density is 6.888 g/cm3. Northstarite is uniaxial (–) and nonpleochroic. The Raman spectrum is consistent with the presence of tellurite and thiosulfate groups and the absence of OH and H2O. Electron-microprobe analyses gave the empirical formula Pb5.80Sb3+0.05Te4+5.04S6+1.02S2–1.02O18. The mineral is hexagonal, space group P63, with a = 10.2495(5), c = 11.6677(8) Å, V = 1061.50(13) Å3, and Z = 2. The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 3.098(100)(113), 2.957(88)(300), 2.140(42)(223), 1.7335(41)(413), and 1.6256(31)(306). The structure (R1 = 0.033 for 1476 I > 2σI reflections) is a framework constructed of short (strong) Pb–O and Te–O bonds with channels along the 63 axes. The thiosulfate groups at the centers of the channels are only weakly bonded to the framework.","PeriodicalId":9455,"journal":{"name":"Canadian Mineralogist","volume":"58 1","pages":"533-542"},"PeriodicalIF":0.9,"publicationDate":"2020-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3749/canmin.1900105","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42395193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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