%0 Journal Article
%T Gypsum-carbonate speleothems from Cueva de las Espadas (Naica mine, Mexico): mineralogy and palaeohydrogeological implications
%A G¨˘zquez Fernando
%A Calaforra Jos¨¦ Maria
%A Forti Paolo
%A Rull Fernando
%J International Journal of Speleology
%D 2012
%I Societ¨¤ Speleologica Italiana
%X Some of the most outstanding hypogenic gypsum speleothems worldwide have been recently discovered in the Naica mines. The Cueva de las Espadas (Swords Cave), which lies at 120 m depth, hosts a rare type of speleothem called ˇ°espadaˇ± (ˇ°swordˇ±). This study contributes to the understanding of the mineralogical composition of these singular speleothems, by means of their examination using micro-Raman spectroscopy, FT-IR spectroscopy and EDX microprobe. Our data revealed a complex mineralogy comprising a high-purity selenite core covered by several layers of calcite, aragonite and gypsum. Solid inclusions of polymetallic oxides (Mn-Pb-Zn) and graphite were also detected. The position of the water table during the genesis of the ˇ°espadaˇ± speleothems (over the past 60 kyr) was deduced from their mineralogy. Water level fluctuations at around -120 m depth led to environmental changes within the Cueva de las Espadas. The selenite core and gypsum layers were precipitated under biphasic (water-rock) conditions when the cave was submerged under hydrothermal water. The aragonite precipitation required triphasic (air-water-rock) conditions and occurred when the water table intercepted the cave, allowing the CO2 exchange necessary for carbonate precipitation. Solid inclusions were trapped in an aerobic environment when the gypsum-aragonite boundary condition occurred. A thin calcite layer was precipitated under vadose conditions after the water table definitively moved out of the cave.
%K gypsum speleothems
%K hydrothermal aquifer
%K water table oscillation
%K Naica caves
%U http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1076&context=ijs