Abstract

VIDAL ROMANI, J. R.; SANJURJO SANCHEZ, J.; VAQUEIRO, M.  and  FERNANDEZ MOSQUERA, D.. Speleothems of Granite Caves. Comunicações Geológicas [online]. 2010, n.97, pp.71-80. ISSN 1647-581X.

The run-off infiltration through the discontinuities of the granitic rocky massifs causes the alteration of the rock and the associated formation of deposits which are considered speleothems due to the environment and genetic process where they are formed. Speleothems are formed by minerals (opal-A, pigotite, struvite, evansite-bolivarite, taranakite, goethite, etc.) whose constituent elements come from the rock weathering by the water strengthened by the biological activity that is developed in the fissural system and that modifies the geochemical properties of the water increa­sing its corrosivity. The fabric of these speleothems is highly porous and allows the development of microorganisms either in the voids or on the surface of the speleothem. There have been identified colonies of bacteria, cells, fungi hyphae, spores, algae, diatoms, polychetes, mites, etc., organisms that at least develop part of their vital cycle in the speleothem and that have an active role in the construction of speleothems when acting as deposition nuclei or sedimentary trap of the mobilized materials. The development of speleothems is intermittent and associated with water circulation episodes normally coupled with rain events.

Keywords : Granite cave; biospeleothem; opal-A; pigotite; struvite; evansite.

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