The mineral alabandite, cubic MnS with variable amounts of FeS, occurs in a number of mineral assemblages in manganiferous metasedimentary rocks, some of which are mined as manganese ore. One of them is Morro da Mina, Mina Gerais, Brazil, where alabandite is a minor component of “queluzite”, a manganese-silicate–carbonate rock. The Morro da Mina alabandite contains 7.3 ± 1.4 mol% FeS and makes up aggregates with graphite and molybdenite. A comparison of alabandite occurrences worldwide indicates four main types of mineral assemblages: (1) alabandite + graphite; (2) alabandite + graphite + molybdenite; (3) alabandite + rhodochrosite + molybdenite; (4) and alabandite + rhodochrosite. The different assemblages suggest that manganese sulfide formed in a range of marine palaeoenvironments, from highly reducing and sulfidic – i.e., euxinic – settings to manganese-oxide-precipitating conditions. Morro da Mina represents assemblage (2), which is characteristic of a euxinic water column in a stratified ocean. In general, our comparison of alabandite-bearing mineral assemblages indicates that palaeoenvironmental information can be retrieved from sedimentary rocks that experienced variable degrees of metamorphic overprint.
Alabandite (MnS) in metamorphosed manganiferous rocks at Morro da Mina, Brazil: palaeoenvironmental significance
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Alexandre Raphael Cabral, Armin Zeh, Nívea Cristina da Silva Viana, Marco Paulo de Castro, František Laufek, Bernd Lehmann, Gláucia Queiroga; Alabandite (MnS) in metamorphosed manganiferous rocks at Morro da Mina, Brazil: palaeoenvironmental significance. European Journal of Mineralogy doi: https://doi.org/10.1127/ejm/2019/0031-2879
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