Barren and Li–Sn–Ta Mineralized Pegmatites from NW Spain (Central Galicia): A Comparative Study of Their Mineralogy, Geochemistry, and Wallrock Metasomatism

Abstract

In Central Galicia, there are occurrences of barren and Li–Sn–Ta-bearing pegmatites hosted by metasedimentary rocks. A number of common and contrasting features between Panceiros pegmatites (barren) and Li–Sn–Ta mineralized Presqueira pegmatite are established in this study. K-feldspar and muscovite have the same trace elements (Rb, Cs, P, Zn, and Ba), but the mineralized one has the highest Rb and Cs and the lowest P contents. The barren bodies show fluorapatite and eosphorite–childrenite replacing early silicates. The mineralized body has primary phosphates (fluorapatite and montebrasite), a metasomatic paragenesis (fluorapatite and goyazite) replacing early silicates, and a late hydrothermal assemblage (vivianite and messelite). Ta–Nb oxides from the Presqueira body show a trend from columbite-(Fe) to tantalite-(Fe) and tapiolite-(Fe). In this body, the Li-aluminosilicate textures support primary crystallization of petalite that was partially transformed into Spodumene + Quartz (SQI) during cooling, and into myrmekite during a Na-metasomatism stage. As a result of both processes, spodumene formed. The geochemical study supports magmatic differentiation increasing from the neighboring granites to the Li–Sn–Ta mineralized pegmatite. In both barren and mineralized bodies, the pegmatite-derived fluids that migrated into the wallrock were enriched in B, F, Li, Rb, and Cs and, moreover, in Sn, Zn, and As.

Alpine eclogite-facies modification of Li-Cs-Ta pegmatite from the Wolfsberg lithium deposit, Austria

“…Despite its textural variability, columbite compositions follow a relatively consistent trend of increasing X Ta with negligible X Mn change (Fig. 9) that is observed in other lithium pegmatite regions, such as Namibia (Fuchsloch et al 2019), Spain (Llera et al 2019) and Zimbabwe (Shaw et al 2022). This trend is suggested to be controlled by the fluorine activity of the melt, with low F activity promoting Mn-poor columbite compositions while X Ta continues to increase with fractionation (Černý et al 1986;Wise et al 2012).…”

“…The same authors obtained tourmaline fluid entrapment conditions of 4.5-5.5 kbar at 650-750 ˚C, which were interpreted as minimum pegmatite crystallization conditions, consistent with crystallization within the During the magmatic-hydrothermal stage, in addition to Na, concentrations of Li, Cs, Sn, Ta and Nb are expected to increase within the system. Fluids exsolved from Na-rich melts during late pegmatite crystallization have also been associated with replacement of Nb-rich columbite by Taricher compositions (Llera et al 2019;Shaw et al 2022). This could explain the observed columbite zoning trends of increasing X Ta , either as normal zoning to more Ta-rich compositions (Fig.…”

Rare Element Enrichment in Lithium Pegmatite Exomorphic Halos and Implications for Exploration: Evidence from the Leinster Albite-Spodumene Pegmatite Belt, Southeast Ireland

“…The metasomatism of wall rocks has been well studied around a variety of types of granitic intrusions and related ore deposits (e.g., [38][39][40]). Chemical changes and often recognizable mineral assemblages are developed, mostly following an alkalic to argillic sequence that represents the increasing activity of H + ions in the system as it evolves to lower temperatures and pressures [6].…”

Editorial for the Special Issue “Development of W-Sn and Rare-Metal Metallogenic Systems in an Orogenic Belt”

“…Roza Liera et al [10] develop an interesting mineralogical and geochemical comparison of barren (Panceiros) and Li-Sn-Ta-bearing pegmatites (Presqueira) from central Galicia for application in exploration. Mineralized pegmatites are characterized by higher Rb, Cs, and Li contents in muscovite and crystallization of montebrasite, but they have surprisingly lower P contents, contrarily to what is usually observed in Li-Nb-Ta-rich highly peraluminous pegmatite or granite occurrences [11,12].…”