Secondary Fe–As–Tl mineralization in soils near Buus in the Swiss Jura Mountains

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Marco E. Ciriotti
Messaggi: 24284
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Secondary Fe–As–Tl mineralization in soils near Buus in the Swiss Jura Mountains

Messaggio da Marco E. Ciriotti » ven 25 mag, 2018 18:13

Prossima pubblicazione.

Referenza:
▪ Herrmann, J., Voegelin, A., Palatinus, L., Mangold, S., Majzlan, J. (2018): Secondary Fe–As–Tl mineralization in soils near Buus in the Swiss Jura Mountains. European Journal of Mineralogy, 30, (in press).

Abstract:
Soils at the locality Erzmatt near the village of Buus in the Swiss Jura Mountains are part of the oxidation zone of a small hydrothermal Fe–As–Tl ore occurrence in dolomite rock. The soils are characterized mostly by near-neutral pH values, buffered by the dolomite and limestone bedrock. The concentrations of As and Tl in the soil profiles increase with depth and attain maximum values of ∼20 000 mg/kg for As and ∼10 000 mg/kg for Tl. Using a combination of mineralogical, geochemical, and spectroscopic techniques, we investigated soil samples from the Erzmatt with respect to the characterization of As- and Tl-bearing secondary minerals using total digestions, powder X-ray diffraction, X-ray absorption spectroscopy (XAS), polarized light microscopy, electron microprobe analysis (EMPA), scanning and transmission electron microscopy (SEM, TEM). Arsenic K edge XAS data reveal little variation in bulk soil As speciation and suggest that most As is arsenate bound to iron oxides. Samples with As contents exceeding ∼1 wt% As2O5 contain abundant crystals of bariopharmacosiderite [Ba0.5Fe4(OH)4(AsO4)3·nH2O] in the voids in the soil matrix. Less commonly, Ca–Fe arsenates (arseniosiderite) were identified. An earlier study also identified Tl(I)-containing jarosite and avicennite (Tl2O3) as secondary Tl-bearing minerals. The EMP analyses reveal the degree of jarosite–dorallcharite [(K,Tl)Fe3(SO4)2(OH)6] solid solution formation, and indicate the presence of Tl2O3 with variable contents of As and P. Using electron diffraction, Tl2O3 with low As content was positively identified as avicennite. The platy morphology of the Tl2O3 aggregates is not compatible with the cubic morphology of avicennite, indicating that they may be pseudomorphs after an unknown primary mineral, possibly carlinite, Tl2S. The identification of bariopharmacosiderite, jarosite and avicennite in near-neutral soils points to their stability at near-neutral soil pH (in contrast to scorodite) and indicates their potential for the storage and retention of toxic As and Tl in mine wastes and contaminated environments. The mineralization on the Erzmatt could be an example of a geochemical anomaly similar to the famous Lengenbach deposit (Switzerland) before the metamorphic overprint at Lengenbach.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24284
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: Secondary Fe–As–Tl mineralization in soils near Buus in the Swiss Jura Mountains

Messaggio da Marco E. Ciriotti » ven 25 mag, 2018 18:17

Penso di ben ricordare che una presentazione su questa speciale località è stata presentata da Nicolas Meisser al Susy - Sulfosalts Symposium tenutosi a Tavagnasco l'anno scorso.

Gli autori del precedente messaggio anticipano buona parte di quanto Nicolas Meisser intendeva pubblicare?
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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