Genthelvite Overgrowths On Danalite Cores From A Pegmatite Miarolitic Cavity In Cheyenne Canyon, El Paso County, Colorado

Zito, Gary; Hanson, Sarah L.

doi:10.3749/canmin.1600066

Cited by 16 publications

(9 citation statements)

References 18 publications

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“…Crystallization of large portions of tourmaline resulted in enrichment of the ongoing melt in Mn, which facilitated the formation of helvite to Mn-rich danalite. Despite this, the chemical composition of primary helvite-group minerals differs from most granitic pegmatites where Fe-poor helvite (e.g., Barton and Young 2002;Černý 2002) and locally Zn-rich to genthelvite (Glass and Adams 1953;Zito and Hanson 2017;Larsen 1988) are typical.…”

Section: Chemical Composition Of Be-mineralsmentioning

confidence: 99%

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

Zachař¹,

Novák²,

Škoda³

2020

Jour. Geosci.

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Mineral assemblages of primary and secondary Be-minerals were examined in intraplutonic euxenite-type NYF pegmatites of the Třebíč Pluton, Moldanubian Zone occurring between Třebíč and Vladislav south of the Třebíč fault. Primary magmatic Be-minerals crystallized mainly in massive pegmatite (paragenetic type I) including common beryl I, helvite-danalite I, and a rare phenakite I. Rare primary hydrothermal beryl II and phenakite II occur in miarolitic pockets (paragenetic type II). Secondary hydrothermal Be-minerals replaced primary precursors or filled fractures and secondary cavities, or they are associated with ,,adularia" and quartz (paragenetic type III). They include minerals of bohseite-bavenite series, less abundant beryl III, bazzite III, helvite-danalite III, milarite-agakhanovite-(Y) III, phenakite III, and datolite-hingganite-(Y) III. Chemical composition of the individual minerals is characterized by elevated contents of Na, Cs, Mg, Fe, Sc in beryl I and II; Na, Ca, Mg, Fe, Al in bazzite III; REE in milarite-agakhanovite-(Y) III; variations in Fe/Mn in helvite-danalite and high variation of Al in bohseite-bavenite series. Replacement reactions of primary Be-minerals are commonly complex and the sequence of crystallization of secondary Be-minerals is not defined; minerals of bohseite-bavenite series are mostly the latest. Beryl usually occurs in pegmatites with rare tourmaline, whereas helvite-danalite bearing pegmatites are tourmaline-rich. Abundant tourmaline in pegmatites with helvite-danalite and its scarcity in beryl-bearing pegmatites indicate that early tourmaline crystallization affected activity of Al in the parental medium and thus may have controlled formation of primary Be-minerals (beryl-higher Al, helvite-danalite-lower Al) which crystallized later. Secondary Be-minerals with dominant minerals of bohseite-bavenite series and milarite suggest high activity of Ca in fluids. Variations in chemical composition (Al contents) of bohseite-bavenite series were controlled by the chemical composition of the precursor. High variability of primary magmatic Be-minerals within a single pegmatite district is exceptional and it is constrained by variable activities of Si and mainly Al, divalent cations-Ca, Mn, Fe, Zn and Mg, trivalent cations-REEs, Sc, and B, S, and f O2 in the individual pegmatites.

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Section: Chemical Composition Of Be-mineralsmentioning

confidence: 99%

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

Zachař¹,

Novák²,

Škoda³

2020

Jour. Geosci.

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“…Uranium concentrations have not been reported in genthelvite from other localities, but in Pitinga it occurs in all genthelvite samples with 0.13 to 0.25 wt.% UO 2 . Additionally, the genthelvite samples have high contents of REE (maximum 0.40 wt.% REE 2 O 3 ) relative to that from Cheyenne Canyon (USA, 4.1 ppm REE 2 O 3 ; Zito and Hanson, 2017) and other helvine-group minerals such as the Mn–Zn-rich danalite from Sucuri (Brazil, maximum 363 ppm REE 2 O 3 ; Raimbault and Bilal, 1993) and the Zn–Fe-rich helvine from Dajishan (China, maximum 13 ppm REE 2 O 3 ; Raimbault and Bilal, 1993). The average concentration of light rare earth elements (LREE) (723 ppm) is slightly higher than that of HREE (565 ppm) in genthelvite from Pitinga.…”

Section: Resultsmentioning

confidence: 98%

“…The helvine-group minerals can be represented by the general formula A 2+ 8 Be 6 Si 6 O 24 S 2 . Structural formulae calculated on the basis of 26 O and S atoms and Be = 6 atoms per formula unit (apfu) (Zito and Hanson, 2017) show cations systematically in deficit on the A site and in excess on the Si site. Therefore, in this study calculations were performed with the following assumptions: the crystal structure is charge balanced; the anion site is fully occupied (i.e.…”

Section: Resultsmentioning

confidence: 99%

Mn–Fe-rich genthelvite from pegmatites associated with the Madeira Sn–Nb–Ta deposit, Pitinga, Brazil: new constraints on the magmatic-hydrothermal transition in the albite-enriched granite system

Hadlich,

Bastos Neto,

Pereira

et al. 2024

MinMag

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Genthelvite from pegmatite veins hosted by the albite-enriched granite (ca.1.8 Ga) corresponding to the Sn–Nb–Ta (F, REE, Li, Zr, U, Th) Madeira deposit, Amazonas, Brazil was studied. Genthelvite, the exclusive Be-bearing mineral within the deposit, occurs as massive crystals of up to 4.7 cm in size. Compositions are homogeneous within individual crystals, although there is moderate variation in the overall composition reflecting relatively limited substitutions within the helvine–genthelvite–danalite solid-solution series, with relatively high Zn contents (36.96 to 49.45 wt.% ZnO), lower Mn contents (0.61 to 3.03 wt.% MnO), and variable Fe contents (2.10 to 10.94 wt.% FeO), completing an existing compositional gap in this system. Genthelvite formed in an alkaline and subaluminous environment, under stable conditions within the late-evolved fluids, at relatively high temperature (>400°C), in a reducing environment. The extremely high concentration of fluorine in the magma and the crystallisation of magmatic galena resulted in an effective reduction of H2S fugacity. This resulted in the stabilisation of genthelvite during the transition from the late magmatic to early hydrothermal stages of the albite-enriched granite evolution. The variability in Fe content within genthelvite is associated primarily with localised variations in the mineral assemblage (e.g. the presence of riebeckite and polylithionite). Genthelvite was altered by low-temperature aqueous fluids rich in F which resulted in the incorporation of Fe, Mn, Mg, Pb, Ba, Na, K, U and REE into the Zn2+ structural site and the allocation of excess Si, Al, Ti and P in the IVSi and IVBe structural sites. The substantial content of U and REE substituting for Zn, together with Si substituting for Be, is charge balanced by the presence of vacancies at the A site.

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“…По элементам-примесям гельвин из Шахдаринской жилы гораздо богаче берилла, на котором он часто нарастает, и заметно обогащен Sc, Sn, Li, Y и HREE. Повышенные содержания лития (37.4 ppm), олова (20.8 ppm) и скандия (625 ppm) отмечались также для даналита из миароловых пегматитов Cheyenne Canyon, El Paso Co., Колорадо, США (Zito, Hanson, 2017). Распределение редкоземельных элементов в гельвине из Шахдаринской жилы на Юго-Западном Памире (рис.…”

Section: описание гельвинаunclassified

“…7) характеризуется обогащением тяжелыми HREE по сравнению с легкими LREE с проявленными тетрад-эффектами Mтипа (T1 = 1.14, T3 = 1.71, T4 = 1.38, T1-4 = 1.39). График нормированных к хондриту C1 (Sun, McDonough, 1989) содержаний редкоземельных элементов в гельвине из миаролового гранитного пегматита на Юго-Западном Памире имеет ярко выраженный Eu-минимум и значительно отличается от аналогичных графиков для минералов группы гельвина из миароловых пегматитов Коло-радо (Zito, Hanson, 2017), альбититов Sucuri в Бразилии и особенно из W-содержащих кварцевых жил Dajishan в Китае (Raimbault, Bilal, 1993). Вероятно, обогащенность гельвина тяжелыми редкоземельными элементами связана не столько с составом минералообразующей среды, сколько с кристаллохимическими особенностями (большей близостью ионных радиусов HREE по сравнению с LREE к размерам ионов Mn +2 , Fe +2 и Zn +2 в 8-ной координации) и кристаллизацией его из нейтральных и слабощелочных растворов, в пользу чего свидетельствует и тетраэдрическая форма кристаллов гельвина, о которой говорилось выше.…”

Section: описание гельвинаunclassified

Фосфорсодержащий Гельвин Шахдаринской Пегматитовой Жилы (Юго-Западный Памир, Таджикистан)

Pautov¹,

Мираков²,

Шодибеков³

et al. 2020

Новые Данные О Минералах

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В миароловой пегматитовой жиле Шахдаринская, расположенной на юго-западном склоне Шугнанского хребта на Юго-Западном Памире (ГБАО, Таджикистан), диагностирован гельвин. Минерал обнаружен в виде тетраэдрических кристаллов (0.2–1 мм) и зернистых агрегатов в миароловых полостях в ассоциации с кварцем, щелочным бериллом, литиевыми слюдами, эльбаитом, кальцитом. Цвет гельвина от лимонножелтого до желто-коричневого. Микротвердость VHN = 762. Показатель преломления n = 1.733(2). Плотность 3.22(3) г/см3. Параметр кубической элементарной ячейки a = 8.2705(8) Å, V = 565.7(2) Å3. Приведена рентгеновская дифрактограмма. ИК-спектр близок к опубликованным данным для гельвина, но содержит дополнительные полосы поглощения 1095 и 1048 см–1, возможно, принадлежащие колебаниям PO4- тетраэдров. Химический состав гельвина изучен электронно-зондовым методом и LA-ICP-MS. Среднее по 7 анализам (мас.%): SiO2 32.08, Al2O3 0.25, SnO2 0.04, FeO 11.47, MnO 37.64, ZnO 1.63, CaO 0.07, BeO 13.4, Li2O 0.06, P2O5 0.54, S 5.59, – S = O 2.80, сумма 99.96. Эмпирическая формула (расчет на сумму катионов 10): (Mn2.95Fe0.89Zn0.11Li0.02Ca0.01)3.98(Be2.98Al0.03)3.01(Si2.97P0.04)3.01O12.07S0.97. Гельвин обогащен элементамипримесями (ppm): Sc 297, Li 260, Sn 327, Y 32, HREE 11. Фосфор (P2O5 от 0.1 до 1.1 мас.%), по косвенным данным, входит в гельвин как изоморфная примесь.

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Genthelvite Overgrowths On Danalite Cores From A Pegmatite Miarolitic Cavity In Cheyenne Canyon, El Paso County, Colorado

Cited by 16 publications

References 18 publications

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

Mn–Fe-rich genthelvite from pegmatites associated with the Madeira Sn–Nb–Ta deposit, Pitinga, Brazil: new constraints on the magmatic-hydrothermal transition in the albite-enriched granite system

Фосфорсодержащий Гельвин Шахдаринской Пегматитовой Жилы (Юго-Западный Памир, Таджикистан)

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