Tl sequestration in the middle part of the Tl–Sb–Au Allchar deposit, North Macedonia

Djordjevic, Tamara and Kolitsch, Uwe and Drahota, Petr and Peresta, Magdalena and Majzlan, Juraj and Tasev, Goran and Serafimovski, Todor and Boev, Ivan and Boev, Blazo (2021) Tl sequestration in the middle part of the Tl–Sb–Au Allchar deposit, North Macedonia. In: Goldschmidt2021 • Virtual, 4-9 July 2021, Switzerland.

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Abstract

In the geogenic Tl-extreme environments, such as Tl-rich sulphide deposits, secondary Tl-minerals play a crucial role in the mobility and fate of this toxic element.
In the middle part of Allchar, there is a prevalence of Sb-mineralization accompanied with As, followed by minor Tl, Ba, Hg and Au. We used PXRD, SEM-EDS, Raman spectroscopy, pore-water analysis and chemical extractions to determine the distribution and speciation of Tl in the As- and Sb-rich waste dumps and soils (As: 3.8-17.7 g/kg; Sb: 0.9-16.4 g/kg and Tl: 127-837 mg/kg).
Soil samples and waste dump material are composed mostly of dolomite, quartz, gypsum, pyrite, marcasite, stibnite, realgar and barite, followed by muscovite, kaolinite-group minerals and various Sb-oxides. Tl-sulfosalts fangite, Tl3AsS4, lorándite, TlAsS2 and pierrotite, Tl(Sb,As)10S12 are the primary Tl-sources and are mostly hosted in realgar. Tl dissolved during weathering under cicumneutral conditions is precipitated as As-beraing avicennite (0.55-6 at% of As), Tl2O3, crystallizing in massive aggregates up to 200 µm in length and tiny, fibrous Tl-bearing todorokite- or birnessite-type Mn-oxides (up to 8.5 at% of Tl) intregrown with avicennite and dolomite. Furthermore, sperulitic crystals of tiny (up to 3µm) Tl-Sb-oxides (Tl:Sb  3:1) (unknown mineral species) have been found intergrown with quartz, muscovite and minor dolomite. Thallium dissolved during weathering under acidic conditions (pH 2.8-3.1) didn’t precipitate at all. In these samples jarosite-group minerals, scorodite, tripuhyite and oxycalcioroméite have been formed.
The pore water (pH: 2.8-7.8) contained large aqueous concentrations of Sb (up to 14 mg/l), As (up to 8.5 mg/l) and Tl (up to 464 µg/l). Mild extractions (ammonium nitrate and phosphate) mobilized up to xx% of the total Tl, xx% of the total Sb and xx% of the total As, indicating that large fraction of Tl is weakly bound and could be easily mobilized into the surrounding ecosystems.
The identification of avicennite, Tl-Mn-oxides and Tl-Sb-oxides in near-neutral soils points to their stability at near-neutral soil pH and indicates their potential for the storage and preservation of toxic Tl in mine wastes and contaminated environments.
Financial support of the Austrian Science Fund (FWF) (P 30900-N28) is gratefully acknowledged.

Item Type:	Conference or Workshop Item (Poster)
Subjects:	Natural sciences > Earth and related environmental sciences
Divisions:	Faculty of Natural and Technical Sciences
Depositing User:	Ivan Boev
Date Deposited:	22 Nov 2021 12:00
Last Modified:	22 Nov 2021 12:00
URI:	https://eprints.ugd.edu.mk/id/eprint/28788

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