Origin, ore forming fluid evolution and timing of the Logrosán Sn-(W) ore deposits (Central Iberian Zone, Spain)

Abstract

© 2015 Elsevier B.V. The Logrosán Sn-(W) ore deposits in the metallogenic Sn-W province of the European Variscan Belt consist of endo- and exogranitic greisen-type and quartz-cassiterite veins associated with a S-type granite. Mineral characterization, fluid inclusion study, isotope geochemistry and Ar-Ar geochronology have been combined in order to reconstruct the conditions for Sn-(W) mineralization. The endo- and exogranitic mineralization must have been developed in a relatively long-lived system (~308-303Ma), during or soon after the emplacement of the Logrosán related-granite (at ca. 308Ma). The mineralizing fluids are characterized by complex aqueous and volatile (H2O-N2-CO2-CH4-NaCl) fluid inclusions. Microthermometry and Raman analyses indicate that fluid composition evolved from N2-CH4 to N2-rich, followed by CO2-rich fluids, with varying amounts of H2O. The presence of N2 and CH4 suggests the interaction with fluids derived from the nearby metasedimentary host rocks. A model of host-rock interaction, assimilation, and mixing of metamorphic and magmatic fluids, resulting in change of the redox conditions, is proposed for tin deposition. Later sulfide minerals were precipitated as a result of pressure and temperature release.