Trace Element Composition of Sphalerite from the Raibl Pb-Zn mine

Research output: ThesisMaster's Thesis

Abstract

Raibl (Cave del Predil) in the North-East of Italy is a low-temperature carbonate-hosted lead-zinc deposit in the Southern Alps. The lead-zinc mineralization consisting mainly of sphalerite, galena and pyrite is hosted in the Ladinian Upper Schlern Dolomite. Since the 19th century sphalerite from Raibl is known to contain significant amounts of trace elements. Sphalerite from Raibl was investigated by microscopy, photography under UVlight, Raman spectroscopy, SEM and LA-ICP-MS. The results provide new data that link textural and color varieties of sphalerites to trace element compositions. For the first time a tubular ore sample was investigated by LA-ICP-MS. Significantly high contents of iron (median = 267 µg/g, max = 6973µg/g), germanium (median = 168 µg/g; maximum = 1524 µg/g), arsenic (median = 779 µg/g; maximum = 10618 µg/g), cadmium (median = 1593 µg/g; maximum = 7640 µg/g), thallium (median = 132 µg/g; maximum = 2324 µg/g) and lead (median = 2477 µg/g; maximum = 39955 µg/g) were found in sphalerite from Raibl. Arsenic, thallium, germanium, lead, manganese and iron exhibit significant positive correlation. Cadmium is negatively correlated to arsenic, thallium, germanium, lead and manganese. Additionally, some sphalerite samples show notably elevated contents of copper, gallium, tin, antimony and mercury. The sphalerite exhibits insignificant amounts of vanadium, chromium, manganese, cobalt, nickel, selenium, molybdenum, silver, indium, tellurium, gold and bismuth. Sphalerite from Raibl can be classified according to color (brown, red, grey, yellow and green sphalerite) or texture (colloform, agglomerated (type A and B), tubular, fern and layered sphalerite). Tubular sphalerite is part of tubes formed by primary ore. Such samples have also been found in other Alpine-type lead-zinc deposits. Fern sphalerite consists of clusters of grains resembling leaves. Based on texture, color and chemical composition, colloform, agglomerated sphalerite type B, fern and tubular sphalerite can be grouped together, whereas layered sphalerite and agglomerated sphalerite type A should be considered separately. Colloform sphalerite and agglomerated sphalerite type B show varying trace element contents depending on place of origin in the mine. Samples from the north are richer in germanium, thallium and arsenic, while samples from the south are richer in cadmium. Considering petrography, chemical composition and temperature calculations, similar formation processes for colloform, agglomerated type B, fern and tubular sphalerite are postulated. Although several hypotheses have been proposed, the formation of tubular ore remains unknown. Fern sphalerite is an altered variation of colloform sphalerite. In contrast, layered sphalerite and agglomerated sphalerite type A likely were formed by different processes and are not linked to the other textural varieties of sphalerite. The GGIMFis geothermometer yields an overall formation temperature of sphalerite of 88 ± 6 °C. This temperature fits well with the classification of Raibl as a low-temperature carbonate hosted Alpine type lead-zinc deposit. Layered sphalerite shows a lower formation temperature compared to the other textural varieties of sphalerite.

Details

Translated title of the contributionSpurenelementzusammensetzung von Sphalerit aus dem Blei-Zink-Bergbau Raibl
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
Supervisors/Advisors
Award date31 Mar 2023
DOIs
Publication statusPublished - 2023