Metallogenesis of Zn-Pb carbonate-hosted mineralization in the southeastern region of the Picos de Europa (central northern Spain) province: Geologic, fluid inclusion, and stable isotope studies

The Zn-Pb deposits of the southeastern area of the Picos de Europa province display an epigenetic hydrothermal mineralization of moderate temperature hosted by intensely dolomitized limestones of Carboniferous age. They are s tructurally and lithologically controlled since the three phenomena of frac turing, dolomitization, and mineralization are interrelated. Two types of m ineralization have been found: type I, granular dark brown-colored sphaleri te, galena, and dolomite, and type II, toffee-colored sphalerite, galena, a nd calcite. Type II mineralization is later than type I. The Aliva and Andara deposits are the two largest in the Picos de Europa ar ea, and both contain type I and type II styles of mineralization. Fluid inc lusion studies indicate that the mineralizing solutions for both stages wer e similar and had trapping temperatures between 170 degrees and 200 degrees C and salinities around 15 wt percent NaCl equiv. However; microthermometr ic data from sphalerite (I and II), dolomite I, calcite II, and fluorite sa mples show various stages of circulation and trapping of brines with spatia l and temporal variations in salinity and temperature. Calcite and dolomite from the mineralization have delta(13)C(PDB) values be tween 1 and 2.9 per mil (delta(13)C Sigma(CO2) = -0.8-1.1 parts per thousan d), and delta(18)O(SMOW) values between 11.5 and 16.2 per mil (delta(18)O(H 2O) varied from 0.7-1.9 parts per thousand). Sulfides show delta(34)S value s between 12.9 and -16.8 per mil (delta(34)S(fluid) for the Aliva deposit r anged between 13.4 and -2.5 parts per thousand). The combined stable isotop e data indicate evolved marine waters. Isotope evidence suggests that the m ineralizing fluids were probably formation waters of the Palentine zone and the Picos de Europa province sediments. During the Permian, possibly durin g extensional tectonic phases, these brines moved toward and through the Pi cos de Europa province along late Hercynian fractures giving rise to the Zn -Pb mineralization.