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Native silver in the eastern part of the Karkonosze granitoid pluton, Lower Silesia, Poland

Kozłowski Andrzej, Matyszczak Witold

Acta Geologica Polonica

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2023

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Vol. 73, no. 2

223--245

EN

This article describes silver specimens of the size of tenths to a few millimetres, found in small pegmatites and quartz veinlets of the porphyritic granitoid area in 22 sites in the eastern part of the Variscan granitoid Karkonosze pluton, from 20 of which native silver occurrences were previously not known. The sites are scattered on the whole surface of the granitoid. The native silver occurred in wire, rod, platy, dendritic, anhedral granular and euhedral cubic and octahedral habits; in some specimens twins and fenster faces were also found. Associated with native silver small amounts of acanthite crystallized commonly, sometimes apparently formed by sulphur diffusion into silver. Inclusions of native gold, electrum, galena, chalcopyrite and pyrite occurred in the native silver. The parent fluids of the specimens were epithermal, because the homogenization temperature (Th) of inclusions in quartz, calcite and cleavelandite that were the host minerals of the native silver was generally 91–165ºC and for individual samples the Th range was 4–11ºC. The total salinity of the fluid was 2.4–7.2 wt. % with Na and Ca (hydro)carbonates as the main dissolved components and admixtures of K, Mg, Fe, Al, S, Cl and F. The parent granitoid contains Ag in trace amounts (0.034–0.056 ppm) and was probably the source of this element for the crystals of native silver. Migration of Ag was made easier by the presence of fluoride ions in fluids.

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Silver compounds as minerals in the eastern Karkonosze granitoid pluton, Sudetes, Poland

Kozłowski Andrzej, Matyszczak Witold

Acta Geologica Polonica

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2022

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Vol. 72, no. 4

443--468

EN

Twenty silver minerals of the sulphide, arsenide, selenide, telluride, sulphosalt and chloride groups were found in 13 locations in the Variscan Karkonosze granitoid pluton. Previously only one of these minerals was known from this area. The findings include species characterized in publications as rare or exceptionally rare, e.g., muthmannite and tsnigriite. They occur in pegmatites and quartz veins; their parageneses are described. The studies include determination of chemical compositions, formulae calculations and recording of XRD patterns. Inclusion studies in paragenetic quartz indicate that they crystallized from epithermal fluids with a common but low component of CO2. The results suggest that the minerals formed from trace elements (Ag included) in the Karkonosze granitoid due to very local degrees of recrystallization of the host granitoid.

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Kozłowski Andrzej, Matyszczak Witold

Acta Geologica Polonica

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2022

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Vol. 72, no. 1

9--31

EN

Fluorite mineralization was studied in the Variscan granitoid Karkonosze pluton in the northern part of the Bohemian massif (Lower Silesia, Poland). Fluid inclusions in fluorite and quartz were investigated by the following methods: heating and freezing on an immersion microscope stage, spectrophotometric and electron probe analysis, calcination and water leachate. The parent fluids of fluorite were of the Na-Ca-Cl type with a low CO₂ content. The fluoride ions had sources in the pluton and in its host rocks. Fluid inclusion observations provide evidence of various post-formation alteration. such as refilling, partition, cracking, migration, expulsion or vacuole modification from irregular to cubic habit. A final model of fluorite origin and parent fluid evolution is presented.