Large celestine orebodies formed by early-diagenetic replacement of gypsified stromatolites (Upper Miocene, Montevive–Escúzar deposit, Granada Basin, Spain)
Ore Geology Reviews, 2015
Abstract The Montevive and the Escuzar stratabound celestine orebodies in the Upper Miocene evapo... more Abstract The Montevive and the Escuzar stratabound celestine orebodies in the Upper Miocene evaporite succession of the intramontane Granada Basin (Spain) constitute one of the largest strontium deposits in the world. Celestine occurs within a gypsum/anhydrite–halite evaporite sequence where it replaces gypsum and gypsified stromatolites preserving carbonate peloids. 87 Sr/ 86 Sr and δ 34 S values in the Montevive celestine deposit are close to those reported for the saline unit (Chimeneas Halite; marine to nonmarine) but higher than those of the overlying gypsum unit (Agron Gypsum; nonmarine). 87 Sr/ 86 Sr and δ 34 S isotope values in the Escuzar celestine deposit match the nonmarine values recorded in the upper part of the Agron Gypsum. The similarity in isotope values between celestine and the corresponding gypsum host in the Escuzar deposit points to early-diagenetic mineralization. According to that, both orebodies are diachronous. Gypsum pseudomorphs and molds, intraformational breccias and karst structures in these celestine deposits point to dissolved gypsum as the main sulfate source. Diagenetic–hydrothermal CaCl 2 brines are interpreted to be the main strontium source. The spatial relationship between gypsified stromatolites and the ore deposits suggests the existence of coeval thermal springs related to fractures, bordering the saline lake. The proposed model envisages gypsum dissolution by SO 4 2 − -poor and Sr 2 + -rich, CaCl 2 diagenetic–hydrothermal water discharging in coastal ponds at times of dry periods and low meteoric water inflow. The increase in SO 4 2 − concentration by gypsum dissolution and the low solubility of SrSO 4 would lead to celestine precipitation replacing gypsum and gypsified stromatolites.
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