Fe-Mn phosphate associations as indicators of the magmatic-hydrothermal and supergene evolution of the Jálama batholith in the Navasfrías Sn-W District, Salamanca, Spain

Abstract

The residual melts that remained after the consolidation of the Jálama batholith crystallized to form a group of intra-granitic pegmatite dykes, which are hosted by its outermost facies (the External Unit), and the most evolved residual melts migrated through fractures to form the Cruz del Rayo field of pegmatite dykes, which are hosted by pre-Ordovician low-grade metasedimentary rocks. The increasing activity of phosphorus as magmatic differentiation took place led to the crystallization of primary phosphates, including members of the tripliteÀzwieselite and the amblygoniteÀmontebrasite series. A strong albitization of the granitic and pegmatite rocks led to the replacement of the primary assemblage by other phosphates such as alluaudite. The influx of post-magmatic hydrothermal fluids, produced quartz veins, gave rise to the crystallization of ore minerals and triplite, and altered the granites, aplites and pegmatites, replacing some of the phosphate minerals and feldspars and depositing goyazite, montebrasite and childreniteÀeosphorite. The interaction of the residual hydrothermal fluids with those from the surrounding metamorphic rocks during later alteration events resulted in the influx of large quantities of Ca and Mg, and produced phosphate assemblages enriched in those elements. Finally, late goyazite, hydroxylapatite and an unidentified Fe-rich phosphate were formed as a result of supergene alteration by percolating meteoric waters, which added Ca, Sr and other elements into the system, and increased fO 2 .

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

“…This is evident from the early ore deposition, where cassiterite I crystallized with high contents in Ti and was associated with Mg-and Ca-bearing phosphates, such as triplite (Llorens and Moro 2012a).…”

“…Consequently, in a fluid enriched in F and Ti, the crystallization of F-bearing minerals will induce the increase in Ti activity and the crystallization of rutile (Rapp et al 2010). In the mineralized quartz veins of the Jálama Batholith, the presence of F in the ore fluid led to the crystallization of fluorapatite, which is present at nearly all the depositional stages in these quartz veins, and of isokite, which crystallized during the same deposition stage as rutile II and ixiolite (Llorens and Moro 2012a). Both these phosphate minerals contain high amounts of F.…”

“…This influx of external fluids would not only contribute Ti, but also elements such as Mg, Ca, Sr and Ba (Llorens and Moro 2012a). Bearing in mind that these elements are commonly compatible, and thus preferentially incorporated into minerals during the magmatic stage, their presence in the later depositional events may point to a contamination by fluid expelled from the host metamorphic rocks.…”

“…Finally, the quartz veins striking preferentially from N90ºE to 100ºE contain an interesting phosphate assemblage. This consists mainly of triplite and its alteration products, such as isokite, bermanite, phosphosiderite and fluorapatite Llorens and Moro 2012a).…”

“…Recent contributions showed the broad mineralogical and chemical variability of these deposits, which is not restricted to the Sn and W ores. For example, abundant Fe-, Mn-, Sr-, Li-, Ca-and Mg-bearing phosphates have been documented from the granites, the pegmatite dikes and the mineralized quartz veins (Llorens and Moro 2007, 2008, 2012aMoro and Llorens 2008). These phosphates have been useful for determining the magmatic, hydrothermal and supergene evolution of the Jálama Batholith.…”