Oxide minerals in the granitic cupola of the Jálama Batholith, Salamanca, Spain. Part II: Sn, W and Ti minerals in intra-granitic quartz veins

Abstract

*Corresponding author The mineralized quartz veins hosted by the distal granitic facies of the Jalama Batholith were generated by successive processes of the fractures opening and filling by hydrothermal fluids enriched in volatiles. Cassiterite I, wolframite I and rutile I crystallized during an early stage, followed – after a ductile deformation – by a main Fe–Zn sulphide deposition, composed initially by subordinate cassiterite II and wolframite II. Later during this main sulphide deposition, ixiolite and Nb–Ta-rich rutile II filled fractures. Finally, the late open spaces and cavities were sealed by quartz and carbonates. The crystallization of wolframite II indicates enrichment in Mn of the fluid, compared with wolframite I, suggesting a normal evolutionary trend from the early Sn–W deposition to the first stage of the main Fe–Zn sulphide precipitation in the quartz veins. The scarcity of Sn during the latest stages of the ore deposition prevented the crystallization of cassiterite, favoring instead the incorporation of this element into the ixiolite and rutile II structure. This hydrothermal evolution from the crystallization of wolframite II to ixiolite and rutile II responded to enrichment in Ti and Fe of the late fluid, thus favoring a partially reversed trend in the Nb–Ta–Ti oxides composition. The late enrichment in Ti and Fe of the hydrothermal fluid could be explained by contamination by external metamorphic and/or meteoric fluids en riched in these elements. The incorporation of Ti, Nb and Ta into the ixiolite and rutile structure was favored by high F concentrations in the hydrothermal fluids, inherited from the residual melts of the Jalama Batholith.