The Absolute Age and Origin of the Giant Gypsum Geode of Pulpí (Almería, SE Spain)
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Author/sGázquez Sánchez, Fernando; Monteserín, Ana; Obert, Christina; Fernández Cortés, Ángel; Calaforra Chordi, José María
Subaqueous gypsum (CaSO4·2H2O) crystals are relatively common in epithermal systems where sulfide ore deposits are present. The Giant Geode of Pulpí (Almería, SE Spain) hosts some of the largest (up to 2 m in length) subaqueous gypsum crystals discovered to date. Here, we present the first U-series ages of its crystals and reconstruct the oxygen and hydrogen isotopic composition (δ18O and δ2H) of the Pulpí paleo-aquifer from which the crystals formed by using stable isotopes of gypsum hydration water. We successfully dated the onset of gypsum precipitation in the Geode at 164 ± 15 ka. However, the extremely low U concentration (<11 ppb) and relatively high detrital Th content (230Th/232Th < 3.2) hinder accurate dating other gypsum samples. The δ18O and δD values of the paleo-aquifer during the growth of the crystals aligned with the local meteoric water line, suggesting that the sulfate-enriched mother solution consisted of meteoric water that recharged the aquifer during that period. ...
gypsum hydration water