Composition of Nb-Ta-Ti-Sn-W oxide minerals: indicators of magmatic to hydrothermal evolution of the Cínovec granite intrusion and Sn-W deposit (Czech Republic)

• Autorzy: Chladek S. , Breiter K. , Uher P.

Identyfikatory

DOI

10.7494/geol.2016.42.1.61

• Konferencja: XVIIth International Conference of Young Geologists Herl'any 2016
• Języki publikacji: EN

Abstrakty

EN

The Cínovec (Zinnwald) Sn-W ore deposit is genetically linked to intrusion of late Variscan, highly fractionated granite which expresses the latest evolutionary stage of a volcano-plutonic system of the Teplice caldera. Whole intrusion is relatively highly fractionated and from bottom ( ~ 1500 m) to top part of cupola-shaped deposit is obviously following succession from biotite (annite) granodiorite-granite-zinnwaldite granite, with the partly greisenized uppermost part at 300–500 m depth (Štemprok 1965, 1971). In 1961−63 the Czechoslovakian Geological Survey (CGS) drilled a 1596 m deep borehole in the Sn-W-mineralized Cínovec granite cupola (Štemprok 1965, Štemprok & Šulcek 1969). All studied rock types include W- and Sn-bearing minerals (wolframite series, scheelite and cassiterite) and disseminated accessory Nb-Ta-Ti-W- Sn minerals (Štemprok & Šulcek 1969, Štemprok 1989, Johan and Johan 1994) which were obtained from the collection of CGS in Prague and studied by BSE and electron microprobe. They crystallized in following succession: rutile + columbite + cassiterite (biotite granodiorite) → rutile + columbite + W-rich ixiolite + cassiterite + scheelite in zinnwaldite granite. Textural relationships of these Nb- Ta-Ti-Sn-W minerals indicate predominantly their magmatic origin and part of them (e.g., cassiterite and columbite) show minor post-magmatic alteration phenomena like distinctly inhomogeneous mixtures of secondary pyrochlore-group minerals (“oxykenopyrochlore” and oxycalciopyrochlore). Nb/Ta and Fe/Mn fractionation trends led to characteristic Mn and Ta enrichment from bottom (biotite granite) to uppermost zinnwaldite granite, especially in columbite-group minerals. While Nb/ Ta fractionation is limitedly applied, effective Fe/ Mn fractionation led to significant Mn – enrichment of late-magmatic phases [columbite-(Mn) and W-rich ixiolite]. Post-magmatic to hydrothermal metasomatic fluids caused partial greisenization of the granites and this stage is represented by latest columbite + scheelite + cassiterite + wolframite assemblage. The last two minerals were objects of extensive mining in the past. Although the hydrothermal system was enriched in F and Li (presence of topaz and zinnwaldite), there are only relatively limited Nb/Ta and Fe/Mn fractionations in post-magmatic columbite. Similarly to primary fractionation, both Nb/Ta and Fe/Mn ones take place and overlap characteristic primary Mn-enrichment. Effective Mn-redistribution is predominantly controlled by crystallization of Mn-dominant wolframite like hübnerite in the hydrothermal stage. Scandium is typical rare element in primary (magmatic) and secondary (hydrothermal) mineral assemblage. While primary Sc-fractionation continues the ongoing Sc-enrichment mostly in columbite to uppermost parts of intrusion, the hydrothermal Sc-redistribution is controlled by crystallization of main ore mineral – wolframite, which consumed a major part of scandium. Main substitution mechanisms in rutile-cassiterite-wolframite-columbite assemblage include following heterovalent substitutions: (i) Ti 3 (Fe,Mn) 2+ −1 (Nb,Ta) −2 , (ii) Ti 2 Fe 3+ −1 (Nb,Ta) −1 , (iii) (Nb,Ta) 4 Fe 2+ −1 W −3 . Moreover, a part of minor cations can enter via: (iv) (Fe,Mn) 2+ 1 W 1 (Fe,Sc) 3+ −1 (Nb,Ta) −1 into wolframite lattice, (v) W 1 (Ti,Sn) 1 (Nb,Ta) −2 , (vi) (Sc,Fe) 3+ 3 (Fe,Mn) 2+ −2 (Nb,Ta) −1 , and (vii) W 2 Sc 3+ 1 (Nb,Ta) −3 into columbite lattice. Calculated Fe 3+ can be introduced into rutile lattice predominantly via mechanism (ii), while via (iv) into wolframite lattice and together with Sc 3+ via (vi) into columbite lattice. The last mechanism results in charge imbalance of A and B positions of columbite lattice entering R 3+ cations to. The distinctly varying calculated Fe 3+ values can refer to changing f O 2 during columbite, rutile, W-rich ixiolite and wolframite crystallization. Therefore, the textural and crystallo-chemical features of studied Nb-Ta-Ti-Sn-W oxide minerals in the Cínovec granite cupola reflect a complex geochemical development of this granite system and ore mineralization from primary magmatic stage, through late-magmatic to subsolidus conditions, and ending in distinct hydrothermally – metasomatic overprint of pre-existing phases.

Słowa kluczowe

EN

late Variscan; intrusion; caldera

• Wydawca: Wydawnictwa AGH
• Czasopismo: Geology, Geophysics and Environment
• Rocznik: 2016
• Tom: Vol. 42, no. 1
• Strony: 61--62
• Opis fizyczny: Bibliogr. 5 poz.

Twórcy

autor

Chladek S.

• Comenius University, Department. of Mineralogy and Petrology; Ilkovičova 6, 842 15 Bratislava, Slovakia

autor

Breiter K.

• Institute of Geology of the CAS; Rozvojová 269, 165 00 Praha, Czech Republic

autor

Uher P.

• Comenius University, Department. of Mineralogy and Petrology; Ilkovičova 6, 842 15 Bratislava, Slovakia

Bibliografia

• Johan V. & Johan Z., 1994. Accessory minerals of the Cínovec (Zinnwald) granite cupola, Czech Republic. Part 1: Nb-, Ta- and Ti-bearing oxides. Mineralogy and Petrology, 51, 323−343.
• Štemprok M., 1965. Petrografie a vertikální rozsah mineralizace v cínovecké žulové klenbě. Sborník geologických věd. Řada LG: Ložisková geologie, 5, 7−106.
• Štemprok M., 1971. Petrochemical features of tin-bearing granites in the Krusne Hory Mts., Czechoslovakia. Society of Mining Geologists of Japan, Special Issue, 2, 112−118.
• Štemprok M., 1989. Rare earths elements in the rocks of the Cínovec granite cupola (Czechoslovakia). Věstník Ústředního ústavu geologického, 64, 1, 1−15.
• Štemprok M. &, Šulcek Z., 1969. Geochemical profile through an ore-bearing lithium granite. Economic Geology, 64, 4, 392−404.

Uwagi

PL

Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę.