Speleothems of the granite Gobholo Cave in Eswatini

0532062 - GLÚ 2021 RIV GB eng J - Článek v odborném periodiku
Filippi, Michal - Bruthans, J. - Skála, Roman - Mészárosová, Noemi
Speleothems of the granite Gobholo Cave in Eswatini.
Journal of African Earth Sciences. Roč. 172, December (2020), č. článku 103986. ISSN 1464-343X. E-ISSN 1879-1956
Grant CEP: GA ČR(CZ) GA16-19459S; GA ČR(CZ) GA19-14082S
Institucionální podpora: RVO:67985831
Klíčová slova: Corestone weathering * Speleothems * Gibbsite * Allophane * Pigotite
Obor OECD: Geology
Impakt faktor: 2.046, rok: 2020
Způsob publikování: Omezený přístup
https://www.sciencedirect.com/science/article/pii/S1464343X20302375

The Gobholo Cave is one of the ten worldʼs largest granite caves (and the longest on the African continent),
abound with relatively rich speleothem deposits. For the first time, a set of instrumental techniques (XRD, SEM/
EDS, Raman micro-spectroscopy) was used to characterize the speleothems and also waters (ICP-OES) from
which these speleothems have been deposited. Several types of speleothems (and sedimentary fill) were
distinguished and studied: “muddy” flowstone, coralloids, black coatings. The results show that the mass of all
studied speleothems is amorphous with a variable chemical composition. Therefore, the speleothems are rather
natural substances than mineral species. Four main groups of substances were distinguished, based on their
general chemistry: i) Al-rich substances close to gibbsite composition, ii) Al + Si-rich substances close to allophane
composition, iii) Si-rich substances close to opal-A composition, and iv) Mn-rich substances (unspecified
Mn oxyhydroxides). Although the samples are nearly amorphous, poorly crystalline gibbsite and birnessite were
found to be possibly present. Based on Raman spectroscopy, strongly altered kerogen was detected in some Al +
Si-rich samples. Raman data indicate that the growth of Gobholo speleothems is most probably tightly related to
the activity of microorganisms. Based on collected instrumental data, the problematic issue of “mineral” pigotite
(a substance commonly referred to from granite caves but only vaguely defined) is critically discussed in the
paper.
Trvalý link: http://hdl.handle.net/11104/0314824